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Plant Transporter Papers in The Last Three Months

Updated on 6/28/2009

1: J Pharm Sci. 2009 Jun 18. [Epub ahead of print] Related Articles, Links: Modulation of the activity of ABC transporters (P-glycoprotein, MRP2, BCRP) by flavonoids and drug response.

Alvarez AI, Real R, Pérez M, Mendoza G, Prieto JG, Merino G.

Area de Fisiología, Departamento de Ciencias Biomédicas, Facultad de Veterinaria, Universidad de León, Campus de Vegazana, 24071 León, Spain.

The present article aims to review the up-to-date information on the most recent studies of the interaction of flavonoids with ABC transporters, in particular the drug pharmacokinetic consequences of such a relationship. In addition, the modulation of the expression of the ABC transporters by flavonoids is also illustrated. Flavonoids are a large group of plant polyphenols present extensively in our daily diets and herbal products. High intake of isoflavones has been associated with a variety of beneficial effects on several common diseases. These polyphenols interact with ABC drug transporters involved in drug resistance and drug absorption, distribution and excretion. A number of studies have demonstrated inhibition of drug transporters by flavonoids. This flavonoid-ABC-transporter interaction could be beneficial for poorly absorbed drugs but could also result in severe drug intoxication, especially drugs with a narrow therapeutic window. On the other hand, flavonoids are themselves substrates of ABC transporters. These proteins can affect the oral availability and tissue distribution of these compounds, modifying their beneficial effects. The challenge is to find a suitable way to predict harmful drug-flavonoid interactions mediated by these transporters. (c) 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci.

PMID: 19544374 [PubMed - as supplied by publisher]

2: Plant Physiol. 2009 Jun 19. [Epub ahead of print] Related Articles, Links: The rice aquaporin Lsi1 mediates uptake of methylated arsenic species.

Li RY, Ago Y, Liu WJ, Mitani N, Feldmann J, McGrath SP, Ma JF, Zhao FJ.

Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK; Research Institute for Bioresources, Okayama University, Chuo 2-20-1, Kurashiki 710-0046 Japan; Department of Chemistry, University of Aberdeen, Meston Building, Meston Walk, Aberdeen, AB24 3UE, UK.

Pentavalent methylated arsenic species such as monomethylarsonic acid (MMA(V)) and dimethylarsinic acid (DMA(V)) are used as herbicides or pesticides, and can also be synthesized by soil microorganisms or algae through As methylation. The mechanism of MMA(V) and DMA(V) uptake remains unknown. Recent studies have shown that arsenite is taken up by rice (Oryza sativa) roots through two Si transporters, Lsi1 (the aquaporin NIP2;1) and Lsi2 (an efflux carrier). Here we investigated whether these two transporters also mediate the uptake of MMA(V) and DMA(V). MMA(V) was partly reduced to trivalent MMA(III) in rice roots, but only MMA(V) was translocated to shoots. DMA(V) was stable in plants. The rice lsi1 mutant lost about 80% and 50% of the uptake capacity for MMA(V) and DMA(V), respectively, compared with the wild-type rice, whereas Lsi2 mutation had little effect. The short-term uptake kinetics of MMA(V) can be described by a Michaelis-Menten plus linear model, with the wild-type having 3.5-fold higher V max than the lsi1 mutant. The uptake kinetics of DMA(V) were linear with the slope being 2.8-fold higher in the wild-type than the lsi1 mutant. Heterologous expression of Lsi1 in Xenopus laevis oocytes significantly increased the uptake of MMA(V) but not DMA(V), possibly because of a very limited uptake of the latter. Uptake of MMA(V) and DMA(V) by wild-type rice was increased as the pH of the medium decreased, consistent with an increasing proportion of the undissociated species. The results demonstrate that Lsi1 mediates the uptake of undissociated methylated As in rice roots.

PMID: 19542298 [PubMed - as supplied by publisher]

3: Plant J. 2009 Jun 5. [Epub ahead of print] Related Articles, Links: Auxin Transport into Cotyledons and Cotyledon Growth Depend Similarly on the ABCB19 Multidrug Resistance-like Transporter.

Lewis DR, Wu G, Ljung K, Spalding EP.

Department of Botany University of Wisconsin 430 Lincoln Drive Madison, WI 53706.

ABCB19 of Arabidopsis thaliana (formerly known as MDR1 and PGP19) belongs to the Multidrug Resistance-like (MDR) or B group of the ATP-binding cassette (ABC) transporter super family and mediates polar auxin transport in stems and roots. The present study investigated the role of ABCB19 and auxin distribution in cotyledon development. During embryogenesis, confocal microscopy showed ABCB19 protein to be present in cotyledons during their main growth phase, though not later. Analysis of ProDR5:GFP expression patterns showed a significantly diminished and restricted auxin-distribution pattern in abcb19 cotyledons. Nonetheless, abcb19 embryonic cotyledons developed very similar to the wild type. Post-germination, ABCB19 was present in the plasma membrane of cotyledon epidermal, mesophyll, and petiole cells during blade expansion. Post-germination cotyledon blade expansion in abcb19 was 65% slower than wild-type, though epidermal cell area was reduced by only 17%. The growth rate reduction quantitatively correlated with reduced auxin levels rather than auxin sensitivity as indicated by quantitative ProDR5:GUS assays and direct auxin measurements, and could be explained by a 50% reduction in the import of auxin through the petioles of abcb19 cotyledons during the time of their maximum expansion. Taken together, these data indicate that cotyledon expansion during the establishment of photoautotrophic growth depends on ABCB19-mediated auxin import.

PMID: 19508431 [PubMed - as supplied by publisher]

4: Microb Ecol. 2009 Jun 4. [Epub ahead of print] Related Articles, Links: Differential Effects of Pseudomonas mendocina and Glomus intraradices on Lettuce Plants Physiological Response and Aquaporin PIP2 Gene Expression Under Elevated Atmospheric CO(2) and Drought.

Alguacil MD, Kohler J, Caravaca F, Roldán A.

Department of Soil and Water Conservation, CSIC-Centro de Edafología y Biología Aplicada del Segura, P.O. Box 164, Campus de Espinardo, 30100, Murcia, Spain, mmalguacil@cebas.csic.es.

Arbuscular mycorrhizal (AM) symbiosis and plant-growth-promoting rhizobacterium (PGPR) can alleviate the effects of water stress in plants, but it is unknown whether these benefits can be maintained at elevated CO(2). Therefore, we carried out a study where seedlings of Lactuca sativa were inoculated with the AM fungus (AMF) Glomus intraradices N.C. Schenk & G.S. Sm. or the PGPR Pseudomonas mendocina Palleroni and subjected to two levels of watering and two levels of atmospheric CO(2) to ascertain their effects on plant physiological parameters and gene expression of one PIP aquaporin in roots. The inoculation with PGPR produced the greatest growth in lettuce plants under all assayed treatments as well as the highest foliar potassium concentration and leaf relative water content under elevated [CO(2)] and drought. However, under such conditions, the PIP2 gene expression remained almost unchanged. G. intraradices increased significantly the AMF colonization, foliar phosphorus concentration and leaf relative water content in plants grown under drought and elevated [CO(2)]. Under drought and elevated [CO(2)], the plants inoculated with G. intraradices showed enhanced expression of the PIP2 gene as compared to P. mendocina or control plants. Our results suggest that both microbial inoculation treatments could help to alleviate drought at elevated [CO(2)]. However, the PIP2 gene expression was increased only by the AMF but not by the PGPR under these conditions.

PMID: 19495853 [PubMed - as supplied by publisher]

5: Plant Biotechnol J. 2009 Jun;7(5):391-400. Related Articles, Links

Transgenic barley (Hordeum vulgare L.) expressing the wheat aluminium resistance gene (TaALMT1) shows enhanced phosphorus nutrition and grain production when grown on an acid soil.

Delhaize E, Taylor P, Hocking PJ, Simpson RJ, Ryan PR, Richardson AE.

CSIRO Plant Industry, Canberra, ACT 2601, Australia.

Barley (Hordeum vulgare L.), genetically modified with the Al(3+) resistance gene of wheat (TaALMT1), was compared with a non-transformed sibling line when grown on an acidic and highly phosphate-fixing ferrosol supplied with a range of phosphorus concentrations. In short-term pot trials (26 days), transgenic barley expressing TaALMT1 (GP-ALMT1) was more efficient than a non-transformed sibling line (GP) at taking up phosphorus on acid soil, but the genotypes did not differ when the soil was limed. Differences in phosphorus uptake efficiency on acid soil could be attributed not only to the differential effects of aluminium toxicity on root growth between the genotypes, but also to differences in phosphorus uptake per unit root length. Although GP-ALMT1 out-performed GP on acid soil, it was still not as efficient at taking up phosphorus as plants grown on limed soil. GP-ALMT1 plants grown in acid soil possessed substantially smaller rhizosheaths than those grown in limed soil, suggesting that root hairs were shorter. This is a probable reason for the lower phosphorus uptake efficiency. When grown to maturity in large pots, GP-ALMT1 plants produced more than twice the grain as GP plants grown on acid soil and 80% of the grain produced by limed controls. Expression of TaALMT1 in barley was not associated with a penalty in either total shoot or grain production in the absence of Al(3+), with both genotypes showing equivalent yields in limed soil. These findings demonstrate that an important crop species can be genetically engineered to successfully increase grain production on an acid soil.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19490502 [PubMed - indexed for MEDLINE]

6: Environ Pollut. 2009 May 19. [Epub ahead of print] Related Articles, Links: Ectopic expression of Arabidopsis ABC transporter MRP7 modifies cadmium root-to-shoot transport and accumulation.

Wojas S, Hennig J, Plaza S, Geisler M, Siemianowski O, Skłodowska A, Ruszczyńska A, Bulska E, Antosiewicz DM.

Faculty of Biology, University of Warsaw, Miecznikowa str. 1, 02-096 Warszawa, Poland.

Arabidopsis MRPs/ABCCs have been shown to remove various organic and inorganic substrates from the cytosol to other subcellular compartments. Here we first demonstrate that heterologous expression of AtMRP7 in tobacco (Nicotiana tabacum var. Xanthi) modifies cadmium accumulation, distribution and tolerance. Arabidopsis MRP7 was localized both in the tonoplast and in the plasma membrane when expressed in tobacco. Its overexpression increased tobacco Cd-tolerance and resulted in enhanced cadmium concentration in leaf vacuoles, indicating more efficient detoxification by means of vacuolar storage. Heterologous AtMRP7 expression also led to more efficient retention of Cd in roots, suggesting a contribution to the control of cadmium root-to-shoot translocation. The results underscore the use of AtMRP7 in plant genetic engineering to modify the heavy-metal accumulation pattern for a broad range of applications.

PMID: 19467746 [PubMed - as supplied by publisher]

7: Microbiology. 2009 May 21. [Epub ahead of print] Related Articles, Links: pH-dependent regulation of the multi-subunit cation/proton antiporter Pha1 system from Sinorhizobium meliloti.

Yamaguchi T, Tsutsumi F, Putnoky P, Fukuhara M, Nakamura T.

Niigata University of Pharmacy and Applied Life Sciences;

The pha1 gene cluster (pha1A'-G) of Sinorhizobium meliloti had been characterized as a necessary component for proper invasion into plant root tissue. It has been suggested to encode a multi-subunit K(+)/H(+) antiporter, since mutations in the pha1 region rendered S. meliloti cells K(+) and alkaline sensitive, and because there is high amino acid sequence similarity to previously characterized multi-subunit cation/H(+) antiporters (Mrp antiporters). However, the detailed transport properties of the Pha1 system are yet to be determined. Interestingly, most of the Mrp antiporters are highly selective to Na(+), unlike the Pha1 system. Here, we report the functional expression of the Pha1 system in Escherichia coli and the measurement of cation/H(+) antiport activity. We showed that the Pha1 system is indeed a K(+)/H(+) antiporter with a pH optimum at mildly alkaline conditions. Moreover, we found that the Pha1 system can transport Na(+); this was unexpected based on previous phenotypical analyses of pha1 mutants. Furthermore, we demonstrated that the cation selectivity of the Pha1 system was altered when the pH was lowered from its optimum pH. The down-regulation of Na(+)/H(+) and K(+)/H(+) antiport activities upon acidic shift appeared to occur via different processes, which might indicate the presence of distinct mechanisms for the regulation of the K(+)/H(+) and Na(+)/H(+) antiport activities on the Pha1 system.

PMID: 19460820 [PubMed - as supplied by publisher]

8: J Exp Bot. 2009;60(9):2589-99. Epub 2009 May 19. Related Articles, Links

Comment in:

J Exp Bot. 2009;60(9):2451-3.

Comparing induction at an early and late step in signal transduction mediating indirect defence in Brassica oleracea.

Bruinsma M, Pang B, Mumm R, van Loon JJ, Dicke M.

Laboratory of Entomology, Wageningen University, PO Box 8031, 6700 EH Wageningen, The Netherlands.

The induction of plant defences involves a sequence of steps along a signal transduction pathway, varying in time course. In this study, the effects of induction of an early and a later step in plant defence signal transduction on plant volatile emission and parasitoid attraction are compared. Ion channel-forming peptides represent a class of inducers that induce an early step in signal transduction. Alamethicin (ALA) is an ion channel-forming peptide mixture from the fungus Trichoderma viride that can induce volatile emission and increase endogenous levels of jasmonic acid (JA) and salicylic acid in plants. ALA was used to induce an early step in the defence response in Brussels sprouts plants, Brassica oleracea var. gemmifera, and to study the effect on volatile emission and on the behavioural response of parasitoids to volatile emission. The parasitoid Cotesia glomerata was attracted to ALA-treated plants in a dose-dependent manner. JA, produced through the octadecanoid pathway, activates a later step in induced plant defence signal transduction, and JA also induces volatiles that are attractive to parasitoids. Treatment with ALA and JA resulted in distinct volatile blends, and both blends differed from the volatile blends emitted by control plants. Even though JA treatment of Brussels sprouts plants resulted in higher levels of volatile emission, ALA-treated plants were as attractive to C. glomerata as JA-treated plants. This demonstrates that on a molar basis, ALA is a 20 times more potent inducer of indirect plant defence than JA, although this hormone has more commonly been used as a chemical inducer of plant defence.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19454598 [PubMed - in process]

PMCID: PMC2692015

9: Plant Physiol. 2009 May 15. [Epub ahead of print] Related Articles, Links: Microbial siderophores exert a subtle role in Arabidopsis during infection by manipulating the immune response and the iron status.

Dellagi A, Segond D, Rigault M, Fagard M, Simon C, Saindrenan P, Expert D.

Laboratoire des Interactions Plantes-Pathogenes UMR217 INRA/AgroParisTech/UPMC, 16 rue Claude Bernard 75231 Paris cedex 05 France; Institut de Biotechnologie des Plantes UMR8618 Centre National de la Recherche Scientifique-Universite Paris-Sud 91405 Orsay cedex France.

Siderophores (ferric ion chelators) are secreted by organisms in response to iron deficiency. The pathogenic enterobacterium Erwinia chrysanthemi produces two siderophores, achromobactin and chrysobactin (CB), which are required for systemic dissemination in host plants. Previous studies have shown that CB is produced in planta and can trigger the upregulation of the plant ferritin gene AtFER1. To further investigate the function of CB during pathogenesis, we analyzed its effect in Arabidopsis plants following leaf infiltration. CB activates the salicylic acid (SA) mediated signaling pathway, while the CB ferric complex is ineffective, suggesting that the elicitor activity of this siderophore is due to its iron-binding property. We confirmed this hypothesis by testing the effect of siderophores structurally unrelated to CB including deferrioxamine. There was no activation of SA dependent defense in plants grown under iron deficiency before CB treatment. Transcriptional analysis of the genes encoding the root ferrous ion transporter (IRT1) and ferric chelate reductase (FRO2), and determination of activity of this enzyme in response to CB or deferrioxamine showed that these compounds induce a leaf to root iron deficiency signal. This root response as well as ferritin gene upregulation in the leaf were not compromised in a SA-deficient mutant line. Using the A. thaliana-E. chrysanthemi pathosystem, we have shown that CB promotes bacterial growth in planta, and can modulate plant defenses through an antagonistic mechanism between SA and JA signaling cascades. Collectively, the data reveal a new link between two processes mediated by SA and Fe in response to microbial siderophores.

PMID: 19448037 [PubMed - as supplied by publisher]

10: Plant Cell Environ. 2009 Apr 22. [Epub ahead of print]
Related Articles, Links: Dynamics of vacuoles and actin filaments in guard cells and their roles in stomatal movement.

Gao XQ, Wang XL, Ren F, Chen J, Wang XC.

State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Taian 271018, China.

ABSTRACT Vacuoles and actin filaments are important cytoarchitectures involved in guard cell function. The changes in the morphology and number of vacuoles and the regulation of ion channel activity in tonoplast of guard cells are essential for stomatal movement. A number of studies have investigated the regulation of ion channels in animal and plant cells; however, little is known about the regulating mechanism for vacuolar dynamics in stomatal movement. Actin filaments of guard cells are remodelling with the changes in the stomatal aperture; however, the dynamic functions of actin filaments in stomatal movement remain elusive. In this paper, we summarize the recent developments in the understanding of the dynamics of actin filaments and vacuoles of guard cells during stomatal movement. All relevant studies suggest that actin filaments might be involved in stomatal movement by regulating vacuolar dynamics and the ion channels in tonoplast. The future study could be focused on the linker protein mediating the interaction between actin filaments and tonoplast, which will provide insights into the interactive function of actin and vacuole in stomatal movement regulation.

PMID: 19422610 [PubMed - as supplied by publisher]

11: New Phytol. 2009 Apr 27. [Epub ahead of print]
Related Articles, Links: pH regulation in an acidophilic green alga - a quantitative analysis.

Bethmann B, Schönknecht G.

Julius-von-Sachs-lnstitut für Biowissenschaften der Universität Würzburg, Lehrstuhl für Botanik I, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany.

* Short-term cytosolic pH regulation has three components: H(+) binding by buffering groups; H(+) transport out of the cytosol; and H(+) transport into the vacuole. To understand the large differences plants show in their tolerance to acidic environments, these three components were quantified in the acidophilic unicellular green alga Eremosphaera viridis. * Intracellular pH was recorded using ion-selective microelectrodes, whereas constant doses of weak acid were applied over different time intervals. A mathematical model was developed that describes the recorded cytosolic pH changes. Recordings of cytosolic K(+) and Na(+) activities, and application of anion channel inhibitors, revealed which ion fluxes electrically compensate H(+) transport. * The cytosolic buffer capacity was beta = 30 mM. Acidification resulted in a substantial and constant H(+) efflux that was probably driven by the plasmalemma H(+)-ATPase, and a proportional pH regulation caused by H(+) pumped into the vacuole. Under severe cytosolic acidification (>/= 1 pH) more than 50% of the ATP synthesized was used for H(+) pumping. While H(+) influx into the vacuole was compensated by cation release, H(+) efflux out of the cell was compensated by anion efflux. * The data presented here give a complete and quantitative picture of the ion fluxes during acid loading in an acidophilic green plant cell.

PMID: 19413688 [PubMed - as supplied by publisher]

12: Plant Mol Biol. 2009 Jul;70(5):565-79. Epub 2009 Apr 29.
Related Articles, Links

Exogenous ABA accentuates the differences in root hydraulic properties between mycorrhizal and non mycorrhizal maize plants through regulation of PIP aquaporins.

Ruiz-Lozano JM, del Mar Alguacil M, Bárzana G, Vernieri P, Aroca R.

Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Profesor Albareda no.1, Granada, Spain. juanmanuel.ruiz@eez.csic.es

The arbuscular mycorrhizal (AM) symbiosis has been shown to modulate the same physiological processes as the phytohormone abscisic acid (ABA) and to improve plant tolerance to water deficit. The aim of the present research was to evaluate the combined influence of AM symbiosis and exogenous ABA application on plant root hydraulic properties and on plasma-membrane intrinsic proteins (PIP) aquaporin gene expression and protein accumulation after both a drought and a recovery period. Results obtained showed that the application of exogenous ABA enhanced osmotic root hydraulic conductivity (L) in all plants, regardless of water conditions, and that AM plants showed lower L values than nonAM plants, a difference that was especially accentuated when plants were supplied with exogenous ABA. This effect was clearly correlated with the accumulation pattern of the different PIPs analyzed, since most showed reduced expression and protein levels in AM plants fed with ABA as compared to their nonAM counterparts. The possible involvement of plant PIP aquaporins in the differential regulation of L by ABA in AM and nonAM plants is further discussed.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19404751 [PubMed - in process]

13: New Phytol. 2009;183(1):88-94. Epub 2009 Apr 23.
Related Articles, Links

Two anion transporters AtClCa and AtClCe fulfil interconnecting but not redundant roles in nitrate assimilation pathways.

Monachello D, Allot M, Oliva S, Krapp A, Daniel-Vedele F, Barbier-Brygoo H, Ephritikhine G.

Institut des Sciences du Végétal, Centre National de la Recherche Scientifique (CNRS-UPR 2355), Gif sur Yvette, France.

* In plants, the knowledge of the molecular identity and functions of anion channels are still very limited, and are almost restricted to the large ChLoride Channel (CLC) family. In Arabidopsis thaliana, some genetic evidence has suggested a role for certain AtCLC protein members in the control of plant nitrate levels. In this context, AtClCa has been demonstrated to be involved in nitrate transport into the vacuole, thereby participating in cell nitrate homeostasis. * In this study, analyses of T-DNA insertion mutants within the AtClCa and AtClCe genes revealed common phenotypic traits: a lower endogenous nitrate content; a higher nitrite content; a reduced nitrate influx into the root; and a decreased expression of several genes encoding nitrate transporters. * This set of nitrate-related phenotypes, displayed by clca and clce mutant plants, showed interconnecting roles of AtClCa and AtClCe in nitrate homeostasis involving two different endocellular membranes. * In addition, it revealed cross-talk between two nitrate transporter families participating in nitrate assimilation pathways. The contribution to nitrate homeostasis at the cellular level of members of these different families is discussed.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19402883 [PubMed - in process]

14: Gene. 2009 Aug 1;442(1-2):26-36. Epub 2009 Apr 22.
Related Articles, Links: Fruitlet abscission: A cDNA-AFLP approach to study genes differentially expressed during shedding of immature fruits reveals the involvement of a putative auxin hydrogen symporter in apple (Malus domestica L. Borkh).

Dal Cin V, Barbaro E, Danesin M, Murayama H, Velasco R, Ramina A.

Department of Environmental Agronomy and Crop Science, University of Padova, Italy. vdalcin@ufl.edu

Apple Malus X domestica fruitlet abscission is preceded by a stimulation of ethylene biosynthesis and a gain in sensitivity to the hormone. This phase was studied by a differential screening carried out by cDNA-AFLP in abscising (AF) and non-abscising (NAF) fruitlet populations. Fifty-three primer combinations allowed for the isolation of 131, 66 and 30 differentially expressed bands from cortex, peduncle and seed, respectively. All sequences were then classified as up- or down-regulated by comparing the profile in AFs and NAFs. Almost all of these sequences showed significant homology to genes encoding proteins with known or putative function. The gene ontology analysis of the TDFs isolated indicated a deep change in metabolism, plastid and hormonal status, especially auxin. Furthermore, some common elements between abscission and senescence were identified. The isolation of the full length of one of these TDFs allowed for the identification of a gene encoding an auxin hydrogen symporter (MdAHS). Bioinformatic analysis indicated that the deduced protein shares some features with other auxin efflux carriers, which include PINs. Nevertheless the 3D structure pointed out substantial differences and a conformation largely dissimilar from canonical ion transporters. The expression analysis demonstrated that this gene is regulated by light and development but not affected by ethylene or auxin.

PMID: 19393302 [PubMed - indexed for MEDLINE]

15: Proteomics. 2009 May;9(10):2668-77.
Related Articles, Links

Quantitative detection of changes in the leaf-mesophyll tonoplast proteome in dependency of a cadmium exposure of barley (Hordeum vulgare L.) plants.

Schneider T, Schellenberg M, Meyer S, Keller F, Gehrig P, Riedel K, Lee Y, Eberl L, Martinoia E.

Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, Zurich, Switzerland. Thomas.Schneider@botinst.uzh.ch

Although the vacuole is the most important final store for toxic heavy metals like cadmium (Cd(2+)), our knowledge on how they are transported into the vacuole is still insufficient. It has been suggested that Cd(2+) can be transported as phytochelatin-Cd(2+) by an unknown ABC transporter or in exchange with protons by cation/proton exchanger (CAX) transporters. To unravel the contribution of vacuolar transporters to Cd(2+) detoxification, a quantitative proteomics approach was performed. Highly purified vacuoles were isolated from barley plants grown under minus, low (20 microM), and high (200 microM) Cd(2+ )conditions and protein levels of the obtained tonoplast samples were analyzed using isobaric tag for relative and absolute quantitation (iTRAQ). Although 56 vacuolar transporter proteins were identified, only a few were differentially expressed. Under low-Cd(2+) conditions, an inorganic pyrophosphatase and a gamma-tonoplast intrinsic protein (gamma-TIP) were up-regulated, indicating changes in energization and water fluxes. In addition, the protein ratio of a CAX1a and a natural resistance-associated macrophage protein (NRAMP), responsible for vacuolar Fe(2+) export was increased. CAX1a might play a role in vacuolar Cd(2+) transport. An increase in NRAMP activity leads to a higher cytosolic Fe(2+) concentration, which may prevent the exchange of Fe(2+) by toxic Cd(2+). Additionally, an ABC transporter homolog to AtMRP3 showed up-regulation. Under high Cd(2+) conditions, the plant response was more specific. Only a protein homologous to AtMRP3 that showed already a response under low Cd(2+) conditions, was up-regulated. Interestingly, AtMRP3 is able to partially rescue a Cd(2+)-sensitive yeast mutant. The identified transporters are good candidates for further investigation of their roles in Cd(2+) detoxification.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19391183 [PubMed - in process]

16: Biochem Biophys Res Commun. 2009 Jun 12;383(4):392-6. Epub 2009 Apr 18.
Related Articles, Links

Characterization of a PutCAX1 gene from Puccinellia tenuiflora that confers Ca2+ and Ba2+ tolerance in yeast.

Liu H, Zhang X, Takano T, Liu S.

Alkali Soil Natural Environmental Science Center (ASNESC), Stress Molecular Biology Laboratory, Northeast Forestry University, Harbin, Heilongjiang Province 150040, PR China.

The gene for a novel cation/H+ antiporter from Puccinellia tenuiflora, PutCAX1, was cloned from a cDNA library. The PutCAX protein was localized in the vacuolar membrane using a GFP marker. Several yeast transformants were created using full-length and truncated form of PutCAX1 and their growths in the presence of various cations (Mg2+, Ca2+, Mn2+, Ni2+, Cu2+, Zn2+, Se2+, and Ba2+) were analyzed. PutCAX1 expression was found to affect the response to Ca2+ and Ba2+ in yeast. The PutCAX1 and C-terminally truncated PutCAX1 (DeltaCPutCAX1) transformants grew in the presence of 70 mM Ca2+ as well as in the presence of 8 mM Ba2+. However, the DeltaCPutCAX1 transformant was able to grow in the presence of 20 mM Ba2+ while the PutCAX1 transformant could not. On the other hand, expression of the N-terminally truncated form and the N- and C-terminally truncated form failed to suppress the Ca2+ or Ba2+ sensitivity of yeast. These results suggest that PutCAX1 can complement the active Ca2+ transporters at some level and confer yeast Ba2+ tolerance, and that the N- and C-terminal regions of PutCAX1 play important roles in increasing the Ca2+ or Ba2+ tolerance of yeast.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19379714 [PubMed - indexed for MEDLINE]

17: Gene. 2009 May 15;437(1-2):45-53.
Related Articles, Links

Genotype-specific regulation of cold-responsive genes in cypress (Cupressus sempervirens L.).

Pedron L, Baldi P, Hietala AM, La Porta N.

IASMA Research Centre, Via E. Mach, 1-38010-San Michele all'Adige, Italy. luca.pedron@iasma.it

Cold acclimation in plants involves a very complex molecular response, with the regulation of many different genes and metabolic pathways. In this work fifteen cypress (Cupressus sempervirens) genes putatively regulated during cold exposure were isolated and their expression was studied in five cypress genotypes, along 15 days of treatment at 3 degrees C. Treated samples of shoots were collected from four year old cypress seedlings and a subtractive hybridization approach (PCR-Select) was performed after mRNA extraction. Fifteen genes were selected according to sequence similarities after a GenBank search and their expression was studied using Real-time PCR. Among these genes, five (ELIP, aquaporin, dehydrin and two cold-induced proteins) and four (oleosin, chlorophyll a/b-binding protein, oxidoreductase and rubisco activase) resulted respectively up- and down-regulated by the treatment in all tested genotypes. Finally, three genes (metal-binding protein, nodulin-like protein and beta-amylase) showed remarkable different pattern among genotypes. A consistent relationship was found between the cold regulation of the genes studied and their putative function, suggesting the existence of different cold response pathways in cypress. The possible roles of the low temperature-regulated sequences and of the individual expression differences during cypress cold acclimation are proposed and discussed.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19374025 [PubMed - indexed for MEDLINE]

18: Plant Physiol. 2009 Jun;150(2):1093-104. Epub 2009 Apr 15.
Related Articles, Links: Aquaporin-Mediated Reduction in Maize Root Hydraulic Conductivity Impacts Cell Turgor and Leaf Elongation Even without Changing Transpiration.

Ehlert C, Maurel C, Tardieu F, Simonneau T.

Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, UMR759 INRA/Montpellier SupAgro, 34060 Montpellier, France.

Root hydraulic conductivity in plants (Lp(r)) exhibits large variations in response to abiotic stimuli. In this study, we investigated the impact of dynamic, aquaporin-mediated changes of Lp(r) on leaf growth, water potential, and water flux throughout the plant. For this, we manipulated Lp(r) by subjecting roots to four independent treatments, with aquaporin inhibitors applied either to transpiring maize (Zea mays) plants grown in hydroponics or to detopped root systems for estimation of Lp(r). The treatments were acid load at pH 6.0 and 5.0 and hydrogen peroxide and anoxia applied for 1 to 2 h and subsequently reversed. First, we established that acid load affected cell hydraulic conductivity in maize root cortex. Lp(r) was reduced by all treatments by 31% to 63%, with half-times of about 15 min, and partly recovered when treatments were reversed. Cell turgor measured in the elongating zone of leaves decreased synchronously with Lp(r), and leaf elongation rate closely followed these changes across all treatments in a dose-dependent manner. Leaf and xylem water potentials also followed changes in Lp(r). Stomatal conductance and rates of transpiration and water uptake were not affected by Lp(r) reduction under low evaporative demand. Increased evaporative demand, when combined with acid load at pH 6.0, induced stomatal closure and amplified all other responses without altering their synchrony. Root pressurization reversed the impact of acid load or anoxia on leaf elongation rate and water potential, further indicating that changes in turgor mediated the response of leaf growth to reductions in Lp(r).

PMID: 19369594 [PubMed - in process]
PMCID: PMC2689965 [Available on 2010/06/01]

19: Plant J. 2009 Apr 1. [Epub ahead of print]
Related Articles, Links: A vacuolar iron transporter in tulip, TgVit1, is responsible for blue coloration in petal cells through iron accumulation.

Momonoi K, Yoshida K, Mano S, Takahashi H, Nakamori C, Shoji K, Nitta A, Nishimura M.

Graduate School of Information Science, Nagoya University, Nagoya 464-8601, Japan.

Blue color in flowers is due mainly to anthocyanins, and a considerable part of blue coloration can be attributed to metal-complexed anthocyanins. However, the mechanism of metal ion transport into vacuoles and subsequent flower color development has yet to be fully explored. Previously, we studied the mechanism of blue color development specifically at the bottom of the inner perianth in purple tulip petals of Tulipa gesneriana cv. Murasakizuisho. We found that differences in iron content were associated with the development of blue- and purple-colored cells. Here, we identify a vacuolar iron transporter in T. gesneriana (TgVit1), and characterize the localization and function of this transporter protein in tulip petals. The amino acid sequence of TgVit1 is 85% similar that of the Arabidopsis thaliana vacuolar iron transporter AtVIT1, and also showed similarity to the AtVIT1 homolog in yeast, Ca(2+)-sensitive cross-complementer 1 (CCC1). The gene TgVit1 was expressed exclusively in blue-colored epidermal cells, and protein levels increased with increasing mRNA expression and blue coloration. Transient expression experiments revealed that TgVit1 localizes to the vacuolar membrane, and is responsible for the development of the blue color in purple cells. Expression of TgVit1 in yeast rescued the growth defect of ccc1 mutant cells in the presence of high concentrations of FeSO(4). Our results indicate that TgVit1 plays an essential role in blue coloration as a vacuolar iron transporter in tulip petals. These results suggest a new role for involvement of a vacuolar iron transporter in blue flower color development.

PMID: 19366427 [PubMed - as supplied by publisher]

20: BMC Genomics. 2009 Apr 6;10:147.
Related Articles, Links

Early iron-deficiency-induced transcriptional changes in Arabidopsis roots as revealed by microarray analyses.

Buckhout TJ, Yang TJ, Schmidt W.

Institute of Plant and Microbial Biology, Academia Sinica, 115 Taipei, Taiwan. thomas.buckhout@cms.hu-berlin.de

BACKGROUND: Iron (Fe) is an essential nutrient in plants and animals, and Fe deficiency results in decreased vitality and performance. Due to limited bio-availability of Fe, plants have evolved sophisticated adaptive alterations in development, biochemistry and metabolism that are mainly regulated at the transcriptional level. We have investigated the early transcriptional response to Fe deficiency in roots of the model plant Arabidopsis, using a hydroponic system that permitted removal of Fe from the nutrient solution within seconds and transferring large numbers of plants with little or no mechanical damage to the root systems. We feel that this experimental approach offers significant advantages over previous and recent DNA microarray investigations of the Fe-deficiency response by increasing the resolution of the temporal response and by decreasing non-Fe deficiency-induced transcriptional changes, which are common in microarray analyses. RESULTS: The expression of sixty genes were changed after 6 h of Fe deficiency and 65% of these were found to overlap with a group of seventy-nine genes that were altered after 24 h. A disproportionally high number of transcripts encoding ion transport proteins were found, which function to increase the Fe concentration and decrease the zinc (Zn) concentration in the cytosol. Analysis of global changes in gene expression revealed that changes in Fe availability were associated with the differential expression of genes that encode transporters with presumed function in uptake and distribution of transition metals other than Fe. It appeared that under conditions of Fe deficiency, the capacity for Zn uptake increased, most probably the result of low specificity of the Fe transporter IRT1 that was induced upon Fe deficiency. The transcriptional regulation of several Zn transports under Fe deficiency led presumably to the homeostatic regulation of the cytosolic concentration of Zn and of other transition metal ions such as Mn to avoid toxicity. CONCLUSION: The genomic information obtained from this study gives insights into the rapid transcriptional responses to Fe shortage in plants, and is important for understanding how changes in nutrient availability are translated into responses that help to avoid imbalances in ion distribution. We further identified rapidly induced or repressed genes with potential roles in perception and signaling during Fe deficiency which may aid in the elucidation of these processes.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19348669 [PubMed - in process]

PMCID: PMC2676303

21: Mol Plant Microbe Interact. 2009 May;22(5):529-37.
Related Articles, Links: Different regulation and roles of lactonases AiiB and AttM in Agrobacterium tumefaciens C58.

Haudecoeur E, Tannières M, Cirou A, Raffoux A, Dessaux Y, Faure D.

Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.

The phytopathogen Agrobacterium tumefaciens C58 expresses two lactonases, AttM and AiiB. We showed that expression of the aiiB gene was controlled by agrocinopines A and B and required the agrocinopine-ABC transporter Acc, but was not affected by the level of quorum-sensing (QS) signal 3-oxo-octanoylhomoserine lactone (OC8-HSL). In the presence of agrocinopines, a constructed aiiB mutant accumulated OC8-HSL at a level 10-fold higher than that of the wild-type strain, and showed an exacerbated expression of a key QS-regulated function, conjugation of Ti plasmid (in vitro and in planta), as well as an increase of the number of emerging tumors on the host plant. The expression and acyl-HSL-degrading activity of AttM were evident in the presence of wounded tissues; however, in unwounded plant tumors, the QS-regulated functions were weakly affected in an attM mutant. By contrast, we observed that attM conferred a selective advantage in the course of colonization of plant tumors. Finally, polymerase chain reaction survey of genes attM and aiiB showed that they were not strictly conserved in the genus Agrobacterium. This work proved that the lactonases AttM and AiiB are regulated by different plant signals and are implicated in different functions in the course of the A. tumefaciens C58-host interaction.

PMID: 19348571 [PubMed - in process]

22: Trends Cell Biol. 2009 May;19(5):228-35. Epub 2009 Apr 1.
Related Articles, Links

Feeling green: mechanosensing in plants.

Monshausen GB, Gilroy S.

Department of Botany, University of Wisconsin, Birge Hall, 430 Lincoln Drive, Madison, WI 53706, USA.

Owing to the sessile nature of their lifestyle, plants have to respond to a wide range of signals, such as the force of the wind or the impedance of the soil, to entrain their development to prevailing environmental conditions. Indeed, mechanically responsive growth has been documented in plants for many years but new work on lateral root formation strongly supports the idea that biophysical forces can elicit complete de novo developmental programs. In addition, only recently have molecular candidates for plant mechanosensors emerged. Such advances in understanding plant mechanoresponsive development have relied heavily on comparison with mechanosensors characterized in organisms such as Saccharomyces cerevisiae and Escherichia coli, but key questions remain about the cellular basis of the plant mechanosensory system.

Publication Types:

PMID: 19342240 [PubMed - indexed for MEDLINE]

23: Fungal Genet Biol. 2009 Jun-Jul;46(6-7):461-72. Epub 2009 Mar 24.
Related Articles, Links

Reactive oxygen species and autophagy play a role in survival and differentiation of the phytopathogen Moniliophthora perniciosa.

Pungartnik C, Melo SC, Basso TS, Macena WG, Cascardo JC, Brendel M.

Laboratório de Biologia de Fungos, Centro de Biotecnologia e Genética, Universidade Estadual de Santa Cruz (UESC), Rodovia Ilhéus-Itabuna, CEP, Brazil.

The hemibiotrophic basidiomycete Moniliophthora perniciosa causes "witches' broom disease" in cacao (Theobroma cacao). During plant infection, M. perniciosa changes from mono to dikaryotic life form, an event which could be triggered by changes in plant nutritional offer and plant defense molecules, i.e., from high to low content of glycerol and hydrogen peroxide. We have recently shown that in vitro glycerol induces oxidative stress resistance in dikaryotic M. perniciosa. In order to understand under which conditions in parasite-plant interaction M. perniciosa changes from intercellular monokaryotic to intracellular dikaryotic growth phase we studied the role of glycerol on mutagen-induced oxidative stress resistance of basidiospores and monokaryotic hyphae; we also studied the role of H(2)O(2) as a signaling molecule for in vitro dikaryotization and whether changes in nutritional offer by the plant could be compensated by inducible fungal autophagy. Mono-/dikaryotic glycerol or glucose-grown cells and basidiospores were exposed to the oxidative stress-inducing mutagens H(2)O(2) and Paraquat as well as to pre-dominantly DNA damaging 4-nitroquinoline-1-oxide and UVC irradiation. Basidiospores showed highest resistance to all treatments and glycerol-grown monokaryotic hyphae were more resistant than dikaryotic hyphae. Monokaryotic cells exposed to 1microM of H(2)O(2) in glycerol-media induced formation of clamp connections within 2 days while 1mM H(2)O(2) did not within a week in the same medium; no clamp connections were formed in H(2)O(2)-containing glucose media within a week. Lower concentrations of H(2)O(2) and glycerol, when occurring in parallel, are shown to be two signals for dikaryotization in vitro and may be also during the course of infection. Q-PCR studies of glycerol-grown dikaryotic cells exposed to oxidative stress (10mM H(2)O(2)) showed high expression of MpSOD2 and transient induction of ABC cytoplasmic membrane transporter gene MpYOR1 and autophagy-related gene MpATG8. Expression of a second ABC transporter gene MpSNQ2 was 14-fold induced after H(2)O(2) exposure in glucose as compared to glycerol-grown hyphae while MpYOR1 did not show strong variation of expression under similar conditions. Glucose-grown dikaryotic cells showed elevated expression of MpATG8, especially after exposure to H(2)O(2) and 4-nitroquinoline-1-oxide. During different stages preceding basidiocarp formation MpATG8 and the two catalase-encoding genes MpCTA1 and MpCTT1 were expressed continuously. We have compiled our results and literature data in a model graph, which compares the in vitro and in planta development and differentiation of M. perniciosa with the help of physiological and morphological landmarks.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19324099 [PubMed - indexed for MEDLINE]

24: J Phys Chem B. 2009 Apr 16;113(15):5239-44.
Related Articles, Links

To gate or not to gate: using molecular dynamics simulations to morph gated plant aquaporins into constitutively open conformations.

Khandelia H, Jensen MØ, Mouritsen OG.

MEMPHYS-Center for Biomembrane Physics, Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark. hkhandel@memphys.sdu.dk

The spinach plant aquaporin SoPIP2;1 is a gated water channel, which switches between open and closed states depending on the conformation of a 20-residue cytoplasmic loop, the D-loop. Using fully atomistic molecular dynamics simulations, we have investigated the possibility of driving the conformational equilibrium of the protein toward a constitutively open state. We introduce two separate mutations in the D-loop, while being in the closed conformation. We show that the single channel permeability of both mutants is comparable to that of the open conformation. This Article provides new molecular insight into the gating mechanism of SoPIP2;1. It is proposed that residues Arg190, Asp191, and Ser36 might play important roles in the gating of the protein.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19320451 [PubMed - indexed for MEDLINE]

25: J Biol Chem. 2009 May 22;284(21):14276-85. Epub 2009 Mar 23.
Related Articles, Links

Mutants of the Arabidopsis thaliana cation/H+ antiporter AtNHX1 conferring increased salt tolerance in yeast: the endosome/prevacuolar compartment is a target for salt toxicity.

Hernández A, Jiang X, Cubero B, Nieto PM, Bressan RA, Hasegawa PM, Pardo JM.

Instituto de Recursos Naturales y Agrobiología, Consejo Superior de Investigaciones Científicas (IRNASE-CSIC), Avda. Reina Mercedes 10, Seville 41012, Spain.

Mutants of the plant cation/H(+) antiporter AtNHX1 that confer greater halotolerance were generated by random mutagenesis and selected in yeast by phenotypic complementation. The amino acid substitutions that were selected were conservative and occurred in the second half of the membrane-associated N terminus. AtNHX1 complemented the lack of endogenous ScNHX1 in endosomal protein trafficking assays. Growth enhancement on hygromycin B and vanadate media agreed with a generally improved endosomal/prevacuolar function of the mutated proteins. In vivo measurements by (31)P NMR revealed that wild-type and mutant AtNHX1 transporters did not affect cytosolic or vacuolar pH. Surprisingly, when yeast cells were challenged with lithium, a tracer for sodium, the main effect of the mutations in AtNHX1 was a reduction in the amount of compartmentalized lithium. When purified and reconstituted into proteoliposomes or assayed in intact vacuoles isolated from yeast cells, a representative mutant transporter (V318I) showed a greater cation discrimination favoring potassium transport over that of sodium or lithium. Together, our data suggest that the endosome/prevacuolar compartment is a target for salt toxicity. Poisoning by toxic cations in the endosome/prevacuolar compartment is detrimental for cell functions, but it can be alleviated by improving the discrimination of transported alkali cations by the resident cation/H(+) antiporter.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19307188 [PubMed - in process]

PMCID: PMC2682876 [Available on 2010/05/22]

26: Biochem Biophys Res Commun. 2009 May 8;382(3):637-41. Epub 2009 Mar 21.
Related Articles, Links

Knock-out of Arabidopsis AtNHX4 gene enhances tolerance to salt stress.

Li HT, Liu H, Gao XS, Zhang H.

Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai 200032, China.

AtNHX4 belongs to the monovalent cation:proton antiporter-1 (CPA1) family in Arabidopsis. Several members of this family have been shown to be critical for plant responses to abiotic stress, but little is known on the biological functions of AtNHX4. Here, we provide the evidence that AtNHX4 plays important roles in Arabidopsis responses to salt stress. Expression of AtNHX4 was responsive to salt stress and abscisic acid. Experiments with CFP-AtNHX4 fusion protein indicated that AtNHX4 is vacuolar localized. The nhx4 mutant showed enhanced tolerance to salt stress, and lower Na(+) content under high NaCl stress compared with wild-type plants. Furthermore, heterologous expression of AtNHX4 in Escherichia coli BL21 rendered the transformants hypersensitive to NaCl. Deletion of the hydrophilic C-terminus of AtNHX4 dramatically increased the hypersensitivity of transformants, indicating that AtNHX4 may function in Na(+) homeostasis in plant cell, and its C-terminus plays a role in regulating the AtNHX4 activity.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19306843 [PubMed - indexed for MEDLINE]

27: C R Biol. 2009 Apr;332(4):351-62. Epub 2009 Jan 31.
Related Articles, Links

The dynamic changing of Ca2+ cellular localization in maize leaflets under drought stress.

Ma YY, Song WY, Liu ZH, Zhang HM, Guo XL, Shao HB, Ni FT.

The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.

Maize cultivar zhengdan958 was selected as materials. The sub-cellular distribution of soluble calcium at different phases was shown by the potassium-pyroantinonate-precipitation method and transmission electron microscopy. The results showed that the deposits of calcium antimonate as the indicator for Ca(2+) localization were mainly concentrated within the vacuoles and intercellular spaces without PEG treatment. Firstly, when the leaf was treated with PEG, the Ca(2+) level increased remarkably in the cytoplasm, but considerably decreased in vacuoles and intercellular gaps. Meanwhile, the level of Ca(2+) also increased in chloroplast and nucleus. When the treatment continued, the level of Ca(2+) in chloroplasts and nucleus continued to increase and some cells and chloroplasts finally disintegrated, showing that there is a relationship between the distribution of Ca(2+) and the super-microstructure of cells. Ca(2+) plays a role in the plant drought resistance. The changes of cytosolic Ca(2+) localization in cells treated by ABA, EGTA, Verapamil and TFP were investigated too. The increase of cytosolic calcium induced by ABA was mainly caused by calcium influx. Calmodulin participated in ABA signal transduction, which was indicated by the variation of cytosolic Ca(2+)/CaM concentration change induced by ABA. The above results provided a direct evidence for calcium ion as an important signal at the experimental cellular level.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19304265 [PubMed - indexed for MEDLINE]

28: J Mol Biol. 2009 Apr 3;387(3):653-68. Epub 2009 Feb 4.
Related Articles, Links

Structural and functional analysis of SoPIP2;1 mutants adds insight into plant aquaporin gating.

Nyblom M, Frick A, Wang Y, Ekvall M, Hallgren K, Hedfalk K, Neutze R, Tajkhorshid E, Törnroth-Horsefield S.

Department of Chemical and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden.

Plant plasma membrane aquaporins facilitate water flux into and out of plant cells, thus coupling their cellular function to basic aspects of plant physiology. Posttranslational modifications of conserved phosphorylation sites, changes in cytoplasmic pH and the binding of Ca(2+) can regulate water transport activity by gating the plasma membrane aquaporins. A structural mechanism unifying these diverse biochemical signals has emerged for the spinach aquaporin SoPIP2;1, although several questions concerning the opening mechanism remain. Here, we describe the X-ray structures of the S115E and S274E single SoPIP2;1 mutants and the corresponding double mutant. Phosphorylation of these serines is believed to increase water transport activity of SoPIP2;1 by opening the channel. However, all mutants crystallised in a closed conformation, as confirmed by water transport assays, implying that neither substitution fully mimics the phosphorylated state. Nevertheless, a half-turn extension of transmembrane helix 1 occurs upon the substitution of Ser115, which draws the C(alpha) atom of Glu31 10 A away from its wild-type conformation, thereby disrupting the divalent cation binding site involved in the gating mechanism. Mutation of Ser274 disorders the C-terminus but no other significant conformational changes are observed. Inspection of the hydrogen-bond interactions within loop D suggested that the phosphorylation of Ser188 may also produce an open channel, and this was supported by an increased water transport activity for the S188E mutant and molecular dynamics simulations. These findings add additional insight into the general mechanism of plant aquaporin gating.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19302796 [PubMed - indexed for MEDLINE]

29: Planta. 2009 May;229(6):1171-9. Epub 2009 Feb 28.
Related Articles, Links

Arabidopsis IRT2 cooperates with the high-affinity iron uptake system to maintain iron homeostasis in root epidermal cells.

Vert G, Barberon M, Zelazny E, Séguéla M, Briat JF, Curie C.

Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, CNRS UMR 5004, 2 place Viala, 34060, Montpellier Cedex 1, France.

Iron is an essential nutrient for all organisms but toxic when present in excess. Consequently, plants carefully regulate their iron uptake, dependent on the FRO2 ferric reductase and the IRT1 transporter, to control its homeostasis. Arabidopsis IRT2 gene, whose expression is induced in root epidermis upon iron deprivation, was shown to encode a functional iron/zinc transporter in yeast, and proposed to function in iron acquisition from the soil. In this study, we demonstrate that, unlike its close homolog IRT1, IRT2 is not involved in iron absorption from the soil since overexpression of IRT2 does not rescue the iron uptake defect of irt1-1 mutant and since a null irt2 mutant shows no chlorosis in low iron. Consistently, an IRT2-green fluorescent fusion protein, transiently expressed in culture cells, localizes to intracellular vesicles. However, IRT2 appears strictly co-regulated with FRO2 and IRT1, supporting the view that IRT2 is an integral component of the root response to iron deficiency in root epidermal cells. We propose a model where IRT2 likely prevents toxicity from IRT1-dependent iron fluxes in epidermal cells, through compartmentalization.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19252923 [PubMed - in process]

30: Mycol Res. 2009 Jun-Jul;113(Pt 6-7):737-45. Epub 2009 Feb 26.
Related Articles, Links: Phylogenetic analysis of heavy-metal ATPases in fungi and characterization of the copper-transporting ATPase of Cochliobolus heterostrophus.

Saitoh Y, Izumitsu K, Tanaka C.

Laboratory of Environmental Mycoscience, Graduate School of Agriculture, Kyoto University, Kitashirakawa oiwakecho 1, Sakyo-ku, Kyoto 606-8502, Japan.

We performed a phylogenetic analysis of heavy-metal ATPases (HMAs) in fungi and found that HMAs can be divided into three groups, A, B, and C. Group A is predicted to deliver copper ions to copper-containing proteins, while Groups B and C are thought to function as cell-membrane copper-efflux pumps. Furthermore, Groups B and C consist of fungal-specific HMAs, while Group A consists of fungal orthologues that have been well conserved in eukaryotes. We also cloned and characterized a Group A-type HMA gene (i.e., ChCcc2) of the filamentous plant pathogen, Cochliobolus heterostrophus. Mutation of ChCcc2 severely affected growth, pigmentation, conidiation, and colonial morphology. Activity of the copper-containing protein, laccase, was also lost in ChCcc2 mutants, suggesting that ChCCC2 plays an important role in growth and morphology by activating various copper-containing proteins in C. heterostrophus.

PMID: 19249363 [PubMed - indexed for MEDLINE]

31: Gene. 2009 May 1;436(1-2):45-55. Epub 2009 Feb 25.
Related Articles, Links

The Arabidopsis basic leucine zipper transcription factor AtbZIP24 regulates complex transcriptional networks involved in abiotic stress resistance.

Yang O, Popova OV, Süthoff U, Lüking I, Dietz KJ, Golldack D.

Department of Biochemistry and Physiology of Plants, Faculty of Biology, Bielefeld University, Bielefeld, Germany.

Soil salinity severely affects plant growth and agricultural productivity. AtbZIP24 encodes a bZIP transcription factor that is induced by salt stress in Arabidopsis thaliana but suppressed in the salt-tolerant relative Lobularia maritima. Transcriptional repression of AtbZIP24 using RNA interference improved salt tolerance in A. thaliana. Under non-stress growth conditions, transgenic A. thaliana lines with decreased AtbZIP24 expression activated the expression of stress-inducible genes involved in cytoplasmic ion homeostasis and osmotic adjustment: the Na(+) transporter AtHKT1, the Na(+)/H(+) antiporter AtSOS1, the aquaporin AtPIP2.1, and a glutamine synthetase. In addition, candidate target genes of AtbZIP24 with functions in plant growth and development were identified such as an argonaute (AGO1)-related protein and cyclophilin AtCYP19. The salt tolerance in transgenic plants correlated with reduced Na(+) accumulation in leaves. In vivo interaction of AtbZIP24 as a homodimer was shown using fluorescence energy transfer (FRET) with cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP) as fused FRET pairs. Translational fusion of AtbZIP24 with GFP showed subcellular localization of the protein in nucleus and cytoplasm in plants grown under control conditions whereas in response to salt stress AtbZIP24 was preferentially targeted to the nucleus. It is concluded that AtbZIP24 is an important regulator of salt stress response in plants. The modification of transcriptional control by regulatory transcription factors provides a useful strategy for improving salt tolerance in plants.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19248824 [PubMed - indexed for MEDLINE]

32: Plant Mol Biol. 2009 May;70(1-2):193-209. Epub 2009 Feb 20.
Related Articles, Links

Life with and without AtTIP1;1, an Arabidopsis aquaporin preferentially localized in the apposing tonoplasts of adjacent vacuoles.

Beebo A, Thomas D, Der C, Sanchez L, Leborgne-Castel N, Marty F, Schoefs B, Bouhidel K.

UMR INRA 1088/CNRS 5184/Université de Bourgogne, Plante-Microbe-Environnement, BP 86510, 21065, Dijon, France. azeez.beebo@u-bourgogne.fr

The Arabidopsis thaliana Tonoplast Intrinsic Protein 1;1 (AtTIP1;1) is a member of the tonoplast aquaporin family. The tissue-specific expression pattern and intracellular localization of AtTIP1;1 were characterized using GUS and GFP fusion genes. Results indicate that AtTIP1;1 is expressed in almost all cell types with the notable exception of meristematic cells. The highest level of AtTIP1;1 expression was detected in vessel-flanking cells in vascular bundles. AtTIP1;1-GFP fusion protein labelled the tonoplast of the central vacuole and other smaller peripheral vacuoles. The fusion protein was not found evenly distributed along the tonoplast continuum but concentrated in contact zones of tonoplasts from adjacent vacuoles and in invaginations of the central vacuole. Such invaginations may result from partially engulfed small vacuoles. A knockout mutant was isolated and characterized to gain insight into AtTIP1;1 function. No phenotypic alteration was found under optimal growth conditions indicating that AtTIP1;1 function is not essential to the plant and that some members of the TIP family may act redundantly to facilitate water flow across the tonoplast. However, a conditional root phenotype was observed when mutant plants were grown on a glycerol-containing medium.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19229639 [PubMed - indexed for MEDLINE]

33: Acta Physiol (Oxf). 2009 Apr;195(4):415-47. Epub 2009 Feb 12.
Related Articles, Links

Evolutionary origins of the purinergic signalling system.

Burnstock G, Verkhratsky A.

Autonomic Neuroscience Centre, Royal Free and University College Medical School, London, UK. g.burnstock@ucl.ac.uk

Purines appear to be the most primitive and widespread chemical messengers in the animal and plant kingdoms. The evidence for purinergic signalling in plants, invertebrates and lower vertebrates is reviewed. Much is based on pharmacological studies, but important recent studies have utilized the techniques of molecular biology and receptors have been cloned and characterized in primitive invertebrates, including the social amoeba Dictyostelium and the platyhelminth Schistosoma, as well as the green algae Ostreococcus, which resemble P2X receptors identified in mammals. This suggests that contrary to earlier speculations, P2X ion channel receptors appeared early in evolution, while G protein-coupled P1 and P2Y receptors were introduced either at the same time or perhaps even later. The absence of gene coding for P2X receptors in some animal groups [e.g. in some insects, roundworms (Caenorhabditis elegans) and the plant Arabidopsis] in contrast to the potent pharmacological actions of nucleotides in the same species, suggests that novel receptors are still to be discovered.

Publication Types:

PMID: 19222398 [PubMed - in process]

34: Plant Physiol. 2009 Apr;149(4):2000-12. Epub 2009 Feb 11.
Related Articles, Links

Drought and abscisic acid effects on aquaporin content translate into changes in hydraulic conductivity and leaf growth rate: a trans-scale approach.

Parent B, Hachez C, Redondo E, Simonneau T, Chaumont F, Tardieu F.

INRA, UMR 759 Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, F-34060 Montpellier, France.

The effects of abscisic acid (ABA) on aquaporin content, root hydraulic conductivity (Lpr), whole plant hydraulic conductance, and leaf growth are controversial. We addressed these effects via a combination of experiments at different scales of plant organization and tested their consistency via a model. We analyzed under moderate water deficit a series of transformed maize (Zea mays) lines, one sense and three antisense, affected in NCED (for 9-cis-epoxycarotenoid dioxygenase) gene expression and that differed in the concentration of ABA in the xylem sap. In roots, the mRNA expression of most aquaporin PIP (for plasma membrane intrinsic protein) genes was increased in sense plants and decreased in antisense plants. The same pattern was observed for the protein contents of four PIPs. This resulted in more than 6-fold differences between lines in Lpr under both hydrostatic and osmotic gradients of water potential. This effect was probably due to differences in aquaporin activity, because it was nearly abolished by a hydrogen peroxide treatment, which blocks the water channel activity of aquaporins. The hydraulic conductance of intact whole plants was affected in the same way when measured either in steady-state conditions or via the rate of recovery of leaf water potential after rewatering. The recoveries of leaf water potential and elongation upon rehydration differed between lines and were accounted for by the experimentally measured Lpr in a model of water transfer. Overall, these results suggest that ABA has long-lasting effects on plant hydraulic properties via aquaporin activity, which contributes to the maintenance of a favorable plant water status.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19211703 [PubMed - indexed for MEDLINE]

PMCID: PMC2663730

35: Physiol Plant. 2009 Apr;135(4):426-35. Epub 2009 Feb 5.
Related Articles, Links

Isolation and functional characterization of the Arabidopsis salt-tolerance 32 (AtSAT32) gene associated with salt tolerance and ABA signaling.

Park MY, Chung MS, Koh HS, Lee DJ, Ahn SJ, Kim CS.

Department of Plant Biotechnology and Agricultural Plant Stress Research Center, Chonnam National University, Gwangju, Korea.

Recently, we have isolated salt-tolerance genes (SATs) on the basis of the overexpression screening of yeast with a maize cDNA library from kernels. One of the selected genes [salt-tolerance 32 (SAT32)] appears to be a key determinant for salt stress tolerance in yeast cells. Maize SAT32 cDNA encodes for a 49-kDa protein, which is 41% identity with the Arabidopsis salt-tolerance 32 (AtSAT32) unknown gene. Arabidopsis Transfer-DNA (T-DNA) knockout AtSAT32 (atsat32) altered root elongation, including reduced silique length and reduced seed number. In an effort to further assess salinity tolerance in Arabidopsis, we have functionally characterized the AtSAT32 gene and determined that salinity and the plant hormone ABA induced the expression of AtSAT32. The atsat32 mutant was more sensitive to salinity than the wild-type plant. On the contrary, Arabidopsis overexpressing AtSAT32 (35S::AtSAT32) showed enhanced salt tolerance and increased activity of vacuolar H(+)-pyrophosphatase (V-PPase, EC 3.6.1.1) under high-salt conditions. Consistent with these observations, 35S::AtSAT32 plants exhibited increased expression of salt-responsive and ABA-responsive genes, including the Rd29A, Erd15, Rd29B, Rd22 and RAB18 genes. Therefore, our results indicate that AtSAT32 is involved in both salinity tolerance and ABA signaling as a positive regulator in Arabidopsis.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19210750 [PubMed - indexed for MEDLINE]

36: Plant Cell Environ. 2009 May;32(5):585-91. Epub 2009 Feb 2.
Related Articles, Links

Plant mitochondria electron partitioning is independent of short-term temperature changes.

Macfarlane C, Hansen LD, Florez-Sarasa I, Ribas-Carbo M.

CSIRO Forest Biosciences, Centre for Environment and Life Sciences, Private Bag No. 5, Wembley, Australia.

We tested the hypotheses that relative activity of the less efficient alternative oxidase (AOX) path changes with diurnal temperature changes, and thus changes carbon use efficiency with temperature. The activities of the alternative and cytochrome oxidase (COX) paths in plant tissues of three species were determined by measuring 18O/16O discrimination and total respiration from 17 to 36 degrees C. A new, more accurate method for calculating oxygen uptake rate from the mass spectrometry data was developed. Total carbon use efficiency was calculated from the ratio of respiratory heat and CO2 rates measured from 10 to 35 degrees C. Oxygen isotope discrimination (22.9 +/- 0.4 per thousand) and AOX participation were invariant with temperature in leaf tissue of Cucurbita pepo, Nicotiana sativa and Vicia faba, thus falsifying the first part of the hypothesis. Stress responses of respiration at the temperature extremes limited the range for which carbon use efficiency could be accurately measured to 15-30 degrees C in N. sativa, to 10-25 degrees C in C. pepo and to 20-30 degrees C in V. faba. Carbon-use efficiency was invariant at these temperatures in these species, demonstrating that changes in other pathways that would vary carbon-use efficiency were also invariant with temperature.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19210639 [PubMed - indexed for MEDLINE]

37: Brain Res Rev. 2009 Apr;60(1):2-23. Epub 2008 Dec 31.
Related Articles, Links

Roles of transient receptor potential channels in pain.

Stucky CL, Dubin AE, Jeske NA, Malin SA, McKemy DD, Story GM.

Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. cstucky@mcw.edu

Pain perception begins with the activation of primary sensory nociceptors. Over the past decade, flourishing research has revealed that members of the Transient Receptor Potential (TRP) ion channel family are fundamental molecules that detect noxious stimuli and transduce a diverse range of physical and chemical energy into action potentials in somatosensory nociceptors. Here we highlight the roles of TRP vanilloid 1 (TRPV1), TRP melastatin 8 (TRPM8) and TRP ankyrin 1 (TRPA1) in the activation of nociceptors by heat and cold environmental stimuli, mechanical force, and by chemicals including exogenous plant and environmental compounds as well as endogenous inflammatory molecules. The contribution of these channels to pain and somatosensation is discussed at levels ranging from whole animal behavior to molecular modulation by intracellular signaling proteins. An emerging theme is that TRP channels are not simple ion channel transducers of one or two stimuli, but instead serve multidimensional roles in signaling sensory stimuli that are exceptionally diverse in modality and in their environmental milieu.

Publication Types:

Research Support, N.I.H., Extramural

PMID: 19203589 [PubMed - in process]

PMCID: PMC2683630

38: Planta. 2009 Apr;229(5):1047-56. Epub 2009 Feb 8.
Related Articles, Links: BAT1, a bidirectional amino acid transporter in Arabidopsis.

Dündar E, Bush DR.

Biyoloji Bölümü, Fen Edebiyat Fakültesi, Balikesir Universitesi, Balikesir, Turkey. ekremdundar@yahoo.com

The Arabidopsis thaliana At2g01170 gene is annotated as a putative gamma amino butyric acid (GABA) permease based on its sequence similarity to a yeast GABA transporting gene (UGA4). A cDNA of At2g01170 was expressed in yeast and analyzed for amino acid transport activity. Both direct measurement of amino acid transport and yeast growth experiments demonstrated that the At2g01170 encoded-protein exhibits transport activity for alanine, arginine, glutamate and lysine, but not for GABA or proline. Significantly, unlike other amino acid transporters described in plants to date, At2g01170 displayed both export and import activity. Based on that observation, it was named bidirectional amino acid transporter 1 (BAT1). Sequence comparisons show BAT1 is not a member of any previously defined amino acid transporter family. It does share, however, several conserved protein domains found in a variety of prokaryotic and eukaryotic amino acid transporters, suggesting membership in an ancient family of transporters. BAT1 is a single copy gene in the Arabidopsis genome, and its mRNA is ubiquitously expressed in all organs. A transposon--GUS gene-trap insert in the BAT1 gene displays GUS localization in the vascular tissues (Dundar in Ann Appl Biol, 2009) suggesting BAT1 may function in amino acid export from the phloem into sink tissues.

PMID: 19199104 [PubMed - in process]

39: Plant Cell Environ. 2009 Apr;32(4):408-16. Epub 2009 Jan 14.
Related Articles, Links

Over-expression of OsIRT1 leads to increased iron and zinc accumulations in rice.

Lee S, An G.

Department of Life Science and Functional Genomic Center, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.

Uptake and translocation of micronutrients are essential for plant growth. These micronutrients are also important food components. We generated transgenic rice plants over-expressing OsIRT1 to evaluate its functional roles in metal homeostasis. Those plants showed enhanced tolerance to iron deficiency at the seedling stage. In paddy fields, this over-expression caused plant architecture to be altered. In addition, those plants were sensitive to excess Zn and Cd, indicating that OsIRT1 also transports those metals. As expected, iron and zinc contents were elevated in the shoots, roots and mature seeds of over-expressing plants. This demonstrates that OsIRT1 can be used for enhancing micronutrient levels in rice grains.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19183299 [PubMed - indexed for MEDLINE]

40: Plant Cell Environ. 2009 May;32(5):465-75. Epub 2009 Jan 14.
Related Articles, Links

Plasma membrane H-ATPase-dependent citrate exudation from cluster roots of phosphate-deficient white lupin.

Tomasi N, Kretzschmar T, Espen L, Weisskopf L, Fuglsang AT, Palmgren MG, Neumann G, Varanini Z, Pinton R, Martinoia E, Cesco S.

Dipartimento di Scienze Agrarie e Ambientali, University of Udine, Via delle Scienze 208, I-33100 Udine, Italy. nicola.tomasi@uniud.it

White lupin (Lupinus albus L.) is able to grow on soils with sparingly available phosphate (P) by producing specialized structures called cluster roots. To mobilize sparingly soluble P forms in soils, cluster roots release substantial amounts of carboxylates and concomitantly acidify the rhizosphere. The relationship between acidification and carboxylate exudation is still largely unknown. In the present work, we studied the linkage between organic acids (malate and citrate) and proton exudations in cluster roots of P-deficient white lupin. After the illumination started, citrate exudation increased transiently and reached a maximum after 5 h. This effect was accompanied by a strong acidification of the external medium and alkalinization of the cytosol, as evidenced by in vivo nuclear magnetic resonance (NMR) analysis. Fusicoccin, an activator of the plasma membrane (PM) H+-ATPase, stimulated citrate exudation, whereas vanadate, an inhibitor of the H+-ATPase, reduced citrate exudation. The burst of citrate exudation was associated with an increase in expression of the LHA1 PM H+-ATPase gene, an increased amount of H+-ATPase protein, a shift in pH optimum of the enzyme and post-translational modification of an H+-ATPase protein involving binding of activating 14-3-3 protein. Taken together, our results indicate a close link in cluster roots of P-deficient white lupin between the burst of citrate exudation and PM H+-ATPase-catalysed proton efflux.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19183296 [PubMed - indexed for MEDLINE]

41: Eur Biophys J. 2009 Apr;38(4):495-501. Epub 2009 Jan 23.
Related Articles, Links

Response to cytosolic nickel of Slow Vacuolar channels in the hyperaccumulator plant Alyssum bertolonii.

Corem S, Carpaneto A, Soliani P, Cornara L, Gambale F, Scholz-Starke J.

Institute of Biophysics, National Research Council, Via De Marini 6, 16149, Genoa, Italy.

We applied the patch-clamp technique to investigate the transport properties of the Slow Vacuolar (SV) channel identified in leaf vacuoles of Alyssum bertolonii Desv., a nickel hyperaccumulator plant growing in serpentine soil of the northern Apennines (Italy). SV currents recorded in vacuoles from adult plants collected in their natural habitat showed high sensitivity towards cytosolic nickel. Dose-response analyses indicated half-maximal current inhibition at submicromolar concentrations, i.e. up to three orders of magnitude lower than previously reported values from other plant species. The voltage-dependent increase of residual currents at saturating nickel concentrations could be interpreted as relief of channel block by nickel permeation at high positive membrane potentials. Including young plants of A. bertolonii into the study, we found that SV channels from these plants did not display elevated nickel sensitivity. This difference may be related to age-dependent changes in nickel hyperaccumulation of A. bertolonii leaf cells.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19165480 [PubMed - indexed for MEDLINE]

42: Plant J. 2009 May;58(3):499-510. Epub 2008 Jan 18.
Related Articles, Links

The ABC transporter BcatrB from Botrytis cinerea exports camalexin and is a virulence factor on Arabidopsis thaliana.

Stefanato FL, Abou-Mansour E, Buchala A, Kretschmer M, Mosbach A, Hahn M, Bochet CG, Métraux JP, Schoonbeek HJ.

Department of Biology, University of Fribourg, Chemin du Musée 8, CH-1700 Fribourg, Switzerland.

Arabidopsis thaliana is known to produce the phytoalexin camalexin in response to abiotic and biotic stress. Here we studied the mechanisms of tolerance to camalexin in the fungus Botrytis cinerea, a necrotrophic pathogen of A. thaliana. Exposure of B. cinerea to camalexin induces expression of BcatrB, an ABC transporter that functions in the efflux of fungitoxic compounds. B. cinerea inoculated on wild-type A. thaliana plants yields smaller lesions than on camalexin-deficient A. thaliana mutants. A B. cinerea strain lacking functional BcatrB is more sensitive to camalexin in vitro and less virulent on wild-type plants, but is still fully virulent on camalexin-deficient mutants. Pre-treatment of A. thaliana with UV-C leads to increased camalexin accumulation and substantial resistance to B. cinerea. UV-C-induced resistance was not seen in the camalexin-deficient mutants cyp79B2/B3, cyp71A13, pad3 or pad2, and was strongly reduced in ups1. Here we demonstrate that an ABC transporter is a virulence factor that increases tolerance of the pathogen towards a phytoalexin, and the complete restoration of virulence on host plants lacking this phytoalexin.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19154205 [PubMed - indexed for MEDLINE]

43: Plant J. 2009 May;58(3):437-49. Epub 2009 Jan 8.
Related Articles, Links

De-regulated expression of the plant glutamate receptor homolog AtGLR3.1 impairs long-term Ca2+-programmed stomatal closure.

Cho D, Kim SA, Murata Y, Lee S, Jae SK, Nam HG, Kwak JM.

Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.

Cytosolic Ca(2+) ([Ca(2+)](cyt)) mediates diverse cellular responses in both animal and plant cells in response to various stimuli. Calcium oscillation amplitude and frequency control gene expression. In stomatal guard cells, [Ca(2+)](cyt) has been shown to regulate stomatal movements, and a defined window of Ca(2+) oscillation kinetic parameters encodes necessary information for long-term stomatal movements. However, it remains unknown how the encrypted information in the cytosolic Ca(2+) signature is decoded to maintain stomatal closure. Here we report that the Arabidopsis glutamate receptor homolog AtGLR3.1 is preferentially expressed in guard cells compared to mesophyll cells. Furthermore, over-expression of AtGLR3.1 using a viral promoter resulted in impaired external Ca(2+)-induced stomatal closure. Cytosolic Ca(2+) activation of S-type anion channels, which play a central role in Ca(2+)-reactive stomatal closure, was normal in the AtGLR3.1 over-expressing plants. Interestingly, AtGLR3.1 over-expression did not affect Ca(2+)-induced Ca(2+) oscillation kinetics, but resulted in a failure to maintain long-term 'Ca(2+)-programmed' stomatal closure when Ca(2+) oscillations containing information for maintaining stomatal closure were imposed. By contrast, prompt short-term Ca(2+)-reactive closure was not affected in AtGLR3.1 over-expressing plants. In wild-type plants, the translational inhibitor cyclohexamide partially inhibited Ca(2+)-programmed stomatal closure induced by experimentally imposed Ca(2+) oscillations without affecting short-term Ca(2+)-reactive closure, mimicking the guard cell behavior of the AtGLR3.1 over-expressing plants. Our results suggest that over-expression of AtGLR3.1 impairs Ca(2+) oscillation-regulated stomatal movements, and that de novo protein synthesis contributes to the maintenance of long-term Ca(2+)-programmed stomatal closure.

Publication Types:

PMID: 19143998 [PubMed - indexed for MEDLINE]

44: Mol Genet Genomics. 2009 Apr;281(4):375-90. Epub 2009 Jan 8.
Related Articles, Links

Identification of proteins that interact with catalytically active calcium-dependent protein kinases from Arabidopsis.

Uno Y, Rodriguez Milla MA, Maher E, Cushman JC.

Department of Biochemistry and Molecular Biology, University of Nevada, Reno, NV 89557-0200, USA.

Calcium-dependent protein kinases (CDPKs) are essential sensor-transducers of calcium signaling pathways in plants. Functional characterization of CDPKs is of great interest because they play important roles during growth, development, and in response to a wide range of environmental stimuli. The Arabidopsis genome encodes 34 CDPKs, but very few substrates of these enzymes have been identified. In this study, we exploited the unique characteristics of CDPKs to develop an efficient approach for the discovery of CDPK-interacting proteins. High-throughput, semi-automated yeast two-hybrid interaction screens with two different cDNA libraries each containing 18 million prey clones were performed using catalytically impaired and constitutively active AtCPK4 and AtCPK11 variants as baits. The use of the constitutively active versions of the CPK baits improved the recovery of positive interacting proteins relative to the wild type kinase. Titration of interaction strength by growth under increasing concentrations of 3-aminotriazole (3-AT), a histidine analog and competitive inhibitor of the His3 gene product, confirmed these results. Possible mechanisms for this observed improvement are discussed. The reproducibility of this approach was assessed by the overlap of several interacting proteins of AtCPK4 and AtCPK11 and the recovery of several putative substrates and indicated that yeast two-hybrid screens using constitutively active and/or catalytically impaired forms of CDPK provides a useful tool to identify potential substrates of the CDPK family and potentially the entire protein kinase superfamily.

Publication Types:

PMID: 19130088 [PubMed - indexed for MEDLINE]

45: J Plant Physiol. 2009 May 1;166(7):697-711. Epub 2008 Dec 21.
Related Articles, Links

Transcript profiling of the salt-tolerant Festuca rubra ssp. litoralis reveals a regulatory network controlling salt acclimatization.

Diédhiou CJ, Popova OV, Golldack D.

Department of Physiology and Biochemistry of Plants, Faculty of Biology, University of Bielefeld, 33615 Bielefeld, Germany.

We report an analysis of salt-stress responses in the monocotyledonous halophyte Festuca rubra ssp. litoralis. Salt-dependent expression of transcripts encoding a PIP2;1 aquaporin, V-ATPase subunit B, and the Na+/H+ antiporter NHX was characterized. Transcription of FrPIP2;1, FrVHA-B, and FrNHX1 was induced in root tissue of F. rubra ssp. litoralis by salt treatment, and during salt-stress F. rubra ssp. litoralis accumulated sodium in leaves and roots. Cell specificity of FrPIP2;1, FrVHA-B, and FrNHX1 transcription was analyzed by in situ PCR in roots of F. rubra ssp. litoralis. Expression of the genes was localized to the root epidermis, cortex cells, endodermis, and the vascular tissue. In plants treated with 500 mM NaCl, transcripts were repressed in the epidermis and the outer cortex cells, whereas endodermis and vasculature showed strong signals. These data demonstrate that transcriptional regulation of the aquaporin PIP2;1, V-ATPase, and the Na+/H+ antiporter NHX is correlated with salt tolerance in F. rubra ssp. litoralis and suggests coordinated control of ion homeostasis and water status at high salinity in plants. Salt-induced transcript accumulation in F. rubra ssp. litoralis was further monitored by cDNA-arrays with expressed sequence tags derived from a cDNA subtraction library. The salt-regulated transcripts included those involved in the control of gene expression and signal transduction elements such as a serine/threonine protein kinase, an SNF1-related protein kinase, and a WRKY-type transcription factor. Other ESTs with salt-dependent regulation included transcripts encoding proteins that function in metabolism, general stress responses, and defense and transport proteins.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19106017 [PubMed - indexed for MEDLINE]

46: Biochim Biophys Acta. 2009 May;1787(5):320-7. Epub 2008 Nov 12.
Related Articles, Links: Developing a genetic approach to investigate the mechanism of mitochondrial competence for DNA import.

Weber-Lotfi F, Ibrahim N, Boesch P, Cosset A, Konstantinov Y, Lightowlers RN, Dietrich A.

Institut de Biologie Moléculaire des Plantes, CNRS and Université Louis Pasteur, 12 rue du Général Zimmer, 67084 Strasbourg, France.

Mitochondrial gene products are essential for the viability of eukaryote obligate aerobes. Consequently, mutations of the mitochondrial genome cause severe diseases in man and generate traits widely used in plant breeding. Pathogenic mutations can often be identified but direct genetic rescue remains impossible because mitochondrial transformation is still to be achieved in higher eukaryotes. Along this line, it has been shown that isolated plant and mammalian mitochondria are naturally competent for importing linear DNA. However, it has proven difficult to understand how such large polyanions cross the mitochondrial membranes. The genetic tractability of Saccharomyces cerevisae could be a powerful tool to unravel this molecular mechanism. Here we show that isolated S. cerevisiae mitochondria can import linear DNA in a process sharing similar characteristics to plant and mammalian mitochondria. Based on biochemical data, translocation through the outer membrane is believed to be mediated by voltage-dependent anion channel (VDAC) isoforms in higher eukaryotes. Both confirming this hypothesis and validating the yeast model, we illustrate that mitochondria from S. cerevisiae strains deleted for the VDAC-1 or VDAC-2 gene are severely compromised in DNA import. The prospect is now open to screen further mutant yeast strains to identify the elusive inner membrane DNA transporter.

PMID: 19056337 [PubMed - in process]

47: Plant Cell Environ. 2009 Apr;32(4):319-26. Epub 2008 Nov 25.
Related Articles, Links

Heat-induced electrical signals affect cytoplasmic and apoplastic pH as well as photosynthesis during propagation through the maize leaf.

Grams TE, Lautner S, Felle HH, Matyssek R, Fromm J.

Ecophysiology of Plants, Department of Ecology and Ecosystem Sciences, Technische Universität München, Am Hochanger 13, Freising, Germany.

Combining measurements of electric potential and pH with such of chlorophyll fluorescence and leaf gas exchange showed heat stimulation to evoke an electrical signal (propagation speed: 3-5 mm s(-1)) that travelled through the leaf while reducing the net CO(2) uptake rate and the photochemical quantum yield of both photosystems (PS). Two-dimensional imaging analysis of the chlorophyll fluorescence signal of PS II revealed that the yield reduction spread basipetally via the veins through the leaf at a speed of 1.6 +/- 0.3 mm s(-1) while the propagation speed in the intervein region was c. 50 times slower. Propagation of the signal through the veins was confirmed because PS I, which is present in the bundle sheath cells around the leaf vessels, was affected first. Hence, spreading of the signal along the veins represents a path with higher travelling speed than within the intervein region of the leaf lamina. Upon the electrical signal, cytoplasmic pH decreased transiently from 7.0 to 6.4, while apoplastic pH increased transiently from 4.5 to 5.2. Moreover, photochemical quantum yield of isolated chloroplasts was strongly affected by pH changes in the surrounding medium, indicating a putative direct influence of electrical signalling via changes of cytosolic pH on leaf photosynthesis.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 19054346 [PubMed - indexed for MEDLINE]

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A distributed project investigating gene networks that control uptake and accumulation of plant nutrients and toxic metals. Funded by the plant genome program of the National Science Foundation (DBI-0077378). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

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