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Plant Transporter Papers in The Last Three Months

Updated on 10/25/2009

1: J Exp Bot. 2009 Oct 16. [Epub ahead of print] Related Articles, Links: Gene expression analysis in cadmium-stressed roots of a low cadmium-accumulating solanaceous plant, Solanum torvum.

Yamaguchi H, Fukuoka H, Arao T, Ohyama A, Nunome T, Miyatake K, Negoro S.

Molecular Genetics and Physiology Research Team, National Institute of Vegetable and Tea Science, 360 Kusawa, Ano-cho, Tsu, Mie, 514-2392, Japan.

Solanum torvum Sw. cv. Torubamubiga (TB) is a low cadmium (Cd)-accumulating plant. To elucidate the molecular mechanisms of the Cd acclimation process in TB roots, transcriptional regulation was analysed in response to mild Cd treatment: 0.1 muM CdCl(2) in hydroponic solution. A unigene set consisting of 6296 unigene sequences was constructed from 18 816 TB cDNAs. The distribution of functional categories was similar to tomato, while 330 unigenes were suggested to be TB specific. For expression profiling, the SuperSAGE method was adapted for use with Illumina sequencing technology. Expression tag libraries were constructed from Cd-treated (for 3 h, 1 d, and 3 d) and untreated roots, and 34 269 species of independent tags were collected. Moreover, 6237 tags were ascribed to the TB or eggplant (aubergine) unigene sequences. Time-course changes were examined, and 2049 up- and 2022 down-regulated tags were identified. Although no tags annotated to metal transporter genes were significantly regulated, a tag annotated to AtFRD3, a xylem-loading citrate transporter, was down-regulated. In addition to induction of heavy metal chaperone proteins, antioxidative and sulphur-assimilating enzymes were induced, confirming that oxidative stress developed even using a mild Cd concentration. Rapid repression of dehydration-related transcription factors and aquaporin isoforms suggests that dehydration stress is a potential constituent of Cd-induced biochemical impediments. These transcriptional changes were also confirmed by real-time reverse transcription-PCR. Further additions of TB unigene sequences and functional analysis of the regulated tags will reveal the molecular basis of the Cd acclimation process, including the low Cd-accumulating characteristics of TB.

PMID: 19837731 [PubMed - as supplied by publisher]

2: Ann Bot (Lond). 2009 Oct 13. [Epub ahead of print] Related Articles, Links: Polyamines: ubiquitous polycations with unique roles in growth and stress responses.

Takahashi T, Kakehi JI.

Graduate School of Natural Science and Technology, Okayama University, 700-8530 Okayama, Japan.

Background Polyamines are small polycationic molecules found ubiquitously in all organisms and function in a wide variety of biological processes. In the past decade, molecular and genetic studies using mutants and transgenic plants with an altered activity of enzymes involved in polyamine biosynthesis have contributed much to a better understanding of the biological functions of polyamines in plants. Possible roles Spermidine is essential for survival of Arabidopsis embryos. One of the reasons may lie in the fact that spermidine serves as a substrate for the lysine --> hypusine post-translational modification of the eukaryotic translation initiation factor 5A, which is essential in all eukaryotic cells. Spermine is not essential but plays a role in stress responses, probably through the modulation of cation channel activities, and as a source of hydrogen peroxide during pathogen infection. Thermospermine, an isomer of spermine, is involved in stem elongation, possibly by acting on the regulation of upstream open reading frame-mediated translation. Conclusions The mechanisms of action of polyamines differ greatly from those of plant hormones. There remain numerous unanswered questions regarding polyamines in plants, such as transport systems and polyamine-responsive genes. Further studies on the action of polyamines will undoubtedly provide a new understanding of plant growth regulation and stress responses.

PMID: 19828463 [PubMed - as supplied by publisher]

3: Plant Signal Behav. 2009 Oct 17;4(10). [Epub ahead of print] Related Articles, Links: Roles of SCaBP8 in salt stress response.

Xie CG, Lin H, Deng XW, Guo Y.

College of Life Sciences, Peking University, Beijing, China.

The tissue-preferential distributed calcium sensors, SOS3 and SCaBP8, play important roles in SOS pathway to cope with saline conditions. Both SOS3 and SCaBP8 interact with and activate SOS2. However the regulatory mechanism for SOS2 activation and membrane recruitment by SCaBP8 differs from SOS3. SCaBP8 is phosphorylated by SOS2 at plasma membrane (PM) under salt stress. This phosphorylation anchors the SCaBP8-SOS2 complex on plasma membrane and activates PM Na(+)/H(+) antiporter, such as SOS1. Here, we describe that SOS2 has high binding affinity and catalytic efficiency to SCaBP8, suggesting that phosphorylation of SCaBP8 by SOS2 perhaps occurs rapidly in salt condition. SCaBP8 is also phosphorylated by PKS5 (SOS2-like Protein Kinase5) which negatively regulates PM H(+)-ATPase activity and functions in plant alkaline tolerance, providing a clue to roles of SCaBP8 in both salt and alkaline tolerance. SOS2 interacts with SOS3 and SCaBP8 with its FISL motif at C-terminus. However, luciferase activity complement assay indicates that SOS2 N-terminal is also essential for interacting with these proteins in plant.

PMID: 19826238 [PubMed - as supplied by publisher]

4: Plant Signal Behav. 2009 Aug;4(8):718-26. Epub 2009 Aug 9. Related Articles, Links: Regulation by salt of vacuolar H(+)-ATPase and H(+)-pyrophosphatase activities and Na(+)/H(+) exchange.

Silva P, Gerós H.

Centro de Investigação e de Tecnologias Agro-Ambientais e Biológicas (CITAB), Portugal; Departamento de Biologia, Universidade do Minho, Braga, Portugal.

Over the last decades several efforts have been carried out to determine the mechanisms of salt homeostasis in plants and, more recently, to identify genes implicated in salt tolerance, with some plants being successfully genetically engineered to improve resistance to salt. It is well established that the efficient exclusion of Na(+) excess from the cytoplasm and vacuolar Na(+) accumulation are the most important steps towards the maintenance of ion homeostasis inside the cell. Therefore, the vacuole of plant cells plays a pivotal role in the storage of salt. After the identification of the vacuolar Na(+)/H(+) antiporter Nhx1 in Saccharomyces cerevisiae, the first plant Na(+)/H(+) antiporter, AtNHX1, was isolated from Arabidopsis and its overexpression resulted in plants exhibiting increased salt tolerance. Also, the identification of the plasma membrane Na(+)/H(+) exchanger SOS1 and how it is regulated by a protein kinase SOS2 and a calcium binding protein SOS3 were great achievements in the understanding of plant salt resistance. Both tonoplast and plasma membrane antiporters exclude Na+ from the cytosol driven by the proton-motive force generated by the plasma membrane H(+)-ATPase and by the vacuolar membrane H(+)-ATPase and H(+)-pyrophosphatase and it has been shown that the activity of these proteins responds to salinity. In this review we focus on the transcriptional and post-transcriptional regulation by salt of tonoplast proton pumps and Na(+)/H(+) exchangers and on the signalling pathways involved in salt sensing.

PMID: 19820346 [PubMed - in process]

5: Plant Cell. 2009 Sep 30. [Epub ahead of print] Related Articles, Links: The ABC Transporter PXA1 and Peroxisomal {beta}-Oxidation Are Vital for Metabolism in Mature Leaves of Arabidopsis during Extended Darkness.

Kunz HH, Scharnewski M, Feussner K, Feussner I, Flügge UI, Fulda M, Gierth M.

Department of Botany II, University of Cologne, 50931 Koeln, Germany.

Fatty acid beta-oxidation is essential for seedling establishment of oilseed plants, but little is known about its role in leaf metabolism of adult plants. Arabidopsis thaliana plants with loss-of-function mutations in the peroxisomal ABC-transporter1 (PXA1) or the core beta-oxidation enzyme keto-acyl-thiolase 2 (KAT2) have impaired peroxisomal beta-oxidation. pxa1 and kat2 plants developed severe leaf necrosis, bleached rapidly when returned to light, and died after extended dark treatment, whereas the wild type was unaffected. Dark-treated pxa1 plants showed a decrease in photosystem II efficiency early on and accumulation of free fatty acids, mostly alpha-linolenic acid [18:3(n-3)] and pheophorbide a, a phototoxic chlorophyll catabolite causing the rapid bleaching. Isolated wild-type and pxa1 chloroplasts challenged with comparable alpha-linolenic acid concentrations both showed an 80% reduction in photosynthetic electron transport, whereas intact pxa1 plants were more susceptible to the toxic effects of alpha-linolenic acid than the wild type. Furthermore, starch-free mutants with impaired PXA1 function showed the phenotype more quickly, indicating a link between energy metabolism and beta-oxidation. We conclude that the accumulation of free polyunsaturated fatty acids causes membrane damage in pxa1 and kat2 plants and propose a model in which fatty acid respiration via peroxisomal beta-oxidation plays a major role in dark-treated plants after depletion of starch reserves.

PMID: 19794119 [PubMed - as supplied by publisher]

6: Plant Cell. 2009 Sep 30. [Epub ahead of print] Related Articles, Links: A Tripartite SNARE-K+ Channel Complex Mediates in Channel-Dependent K+ Nutrition in Arabidopsis.

Honsbein A, Sokolovski S, Grefen C, Campanoni P, Pratelli R, Paneque M, Chen Z, Johansson I, Blatt MR.

Laboratory of Plant Physiology and Biophysics, Faculty of Biomedical and Life Sciences-Plant Sciences, University of Glasgow, G12 8QQ United Kingdom.

A few membrane vesicle trafficking (SNARE) proteins in plants are associated with signaling and transmembrane ion transport, including control of plasma membrane ion channels. Vesicle traffic contributes to the population of ion channels at the plasma membrane. Nonetheless, it is unclear whether these SNAREs also interact directly to affect channel gating and, if so, what functional impact this might have on the plant. Here, we report that the Arabidopsis thaliana SNARE SYP121 binds to KC1, a regulatory K(+) channel subunit that assembles with different inward-rectifying K(+) channels to affect their activities. We demonstrate that SYP121 interacts preferentially with KC1 over other Kv-like K(+) channel subunits and that KC1 interacts specifically with SYP121 but not with its closest structural and functional homolog SYP122 nor with another related SNARE SYP111. SYP121 promoted gating of the inward-rectifying K(+) channel AKT1 but only when heterologously coexpressed with KC1. Mutation in any one of the three genes, SYP121, KC1, and AKT1, selectively suppressed the inward-rectifying K(+) current in Arabidopsis root epidermal protoplasts as well as K(+) acquisition and growth in seedlings when channel-mediated K(+) uptake was limiting. That SYP121 should be important for gating of a K(+) channel and its role in inorganic mineral nutrition demonstrates an unexpected role for SNARE-ion channel interactions, apparently divorced from signaling and vesicle traffic. Instead, it suggests a role in regulating K(+) uptake coordinately with membrane expansion for cell growth.

PMID: 19794113 [PubMed - as supplied by publisher]

7: Ann Bot. 2009 Nov;104(6):1121-8. Epub 2009 Sep 29. Related Articles, Links: Arabidopsis plants harbouring a mutation in AtSUC2, encoding the predominant sucrose/proton symporter necessary for efficient phloem transport, are able to complete their life cycle and produce viable seed.

Srivastava AC, Dasgupta K, Ajieren E, Costilla G, McGarry RC, Ayre BG.

University of North Texas, Department of Biological Sciences, 1155 Union Circle #305220, Denton TX 76203-5017, USA.

Background and Aims AtSUC2 encodes a sucrose/proton symporter that localizes throughout the collection and transport phloem and is necessary for efficient transport of sucrose from source to sink tissues in Arabidopsis thaliana. Plants harbouring homozygous AtSUC2 null alleles accumulate sugar, starch, and anthocyanin in mature leaves, have severely delayed development and stunted growth and, in previous studies, failed to complete their life cycle by producing viable seed. Methods An AtSUC2 allele with a T-DNA insertion in the second intron was analysed. Full-length transcript from this allele is not produced, and a truncated protein translated from sequences upstream of the insertion site did not catalyse sucrose uptake into yeast, supporting the contention that this is a null allele. Mutant plants were grown in a growth chamber with a diurnal light/dark cycle, and growth patterns recorded. Key Results This allele (SALK_038124, designated AtSUC2-4) has the hallmarks of previously described null alleles but, despite compromised carbon partitioning and growth, produces viable seeds. The onset of flowering was chronologically delayed but occurred at the same point in the plastochron index as wild type. Conclusions AtSUC2 is important for phloem loading and is therefore fundamental to phloem transport and plant productivity, but plants can complete their life cycle and produce viable seed in its absence. Arabidopsis appears to have mechanisms for mobilizing reduced carbon from the phloem into developing seeds independent of AtSUC2.

PMID: 19789176 [PubMed - in process]

8: Biochem J. 2009 Sep 28. [Epub ahead of print] Related Articles, Links: Threonine at position 306 of the KAT1 potassium channel is essential for channel activity and is a target site for ABA-activated SnRK2/OST1/SnRK2.6 protein kinase.

Sato A, Sato Y, Fukao Y, Fujiwara M, Umezawa T, Shinozaki K, Hibi T, Taniguchi M, Miyake H, Goto DB, Uozumi N.

The Arabidopsis thaliana K+ channel KAT1 has been suggested to have a key role in mediating the aperture of stomata pores on the surface of plant leaves. Although activity of KAT1 is thought to be regulated by phosphorylation, the endogenous pathway and the primary target site for this modification remained unknown. In this study, we have demonstrated that the carboxyl-terminus region of KAT1 acts as a phosphorylation target for the Arabidopsis calcium-independent, ABA-activated protein kinase SnRK2.6. This was confirmed by LC-MS/MS analysis, which showed that KAT1 Thr306 and Thr308 residues were modified by phosphorylation. The role of these specific residues was examined by single point mutation and measurement of KAT1 channel activities in Xenopus oocyte and yeast systems. Modification of Thr308 had minimal effect on KAT1 activity. On the other hand, modification of Thr306 reduced K+ transport uptake activity of KAT1 in both systems, indicating that Thr306 is responsible for the functional regulation of KAT1. This data suggests that negative regulation of KAT1 activity required for stomatal closure likely occurs by phosphorylation of KAT1 Thr306 by the stress-activated endogenous SnRK2.6 protein kinase.

PMID: 19785574 [PubMed - as supplied by publisher]

9: Curr Opin Plant Biol. 2009 Sep 25. [Epub ahead of print] Related Articles, Links: The cellular dynamics of plant aquaporin expression and functions.

Maurel C, Santoni V, Luu DT, Wudick MM, Verdoucq L.

Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, F-34060 Montpellier Cedex 1, France.

Aquaporins are channel proteins that facilitate the transport of water and small neutral molecules, including gases, across cell membranes of most of the living organisms. Integrative studies have stressed the role of aquaporins in maintaining the whole plant water and nutrient status. Cellular aspects of plant aquaporin functions and regulations are also extensively investigated. The present review provides a glance at recent progresses in this area. One first direction concerns the mechanisms that determine aquaporin targeting to specific subcellular membranes and a dynamic and stimulus-dependent control of their density in these membranes. The regulation of aquaporin opening and closing and its links to cell signalling cascades are also discussed. Multiple cellular functions are now attributed to plant aquaporins. They include the dynamic equilibration and subcellular partitioning of their various substrates and a contribution to cell expansion and possibly cell division.

PMID: 19783200 [PubMed - as supplied by publisher]

10: Cell. 2009 Sep 18;138(6):1184-94.
Related Articles, Links

Comment in:

Cell. 2009 Sep 18;138(6):1064-6.

CHL1 functions as a nitrate sensor in plants.

Ho CH, Lin SH, Hu HC, Tsay YF.

Molecular Cell Biology, Institute of Molecular Biology, Academia Sinica, and Taipei, Taiwan.

Ions serve as essential nutrients in higher plants and can also act as signaling molecules. Little is known about how plants sense changes in soil nutrient concentrations. Previous studies showed that T101-phosphorylated CHL1 is a high-affinity nitrate transporter, whereas T101-dephosphorylated CHL1 is a low-affinity transporter. In this study, analysis of an uptake- and sensing-decoupled mutant showed that the nitrate transporter CHL1 functions as a nitrate sensor. Primary nitrate responses in CHL1T101D and CHLT101A transgenic plants showed that phosphorylated and dephosphorylated CHL1 lead to a low- and high-level response, respectively. In vitro and in vivo studies showed that, in response to low nitrate concentrations, protein kinase CIPK23 can phosphorylate T101 of CHL1 to maintain a low-level primary response. Thus, CHL1 uses dual-affinity binding and a phosphorylation switch to sense a wide range of nitrate concentrations in the soil, thereby functioning as an ion sensor in higher plants. For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.

Publication Types:

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

PMID: 19766570 [PubMed - indexed for MEDLINE]

11: Cell. 2009 Sep 18;138(6):1064-6.
Related Articles, Links

Comment on:

Cell. 2009 Sep 18;138(6):1184-94.

A toggle switch in plant nitrate uptake.

Vert G, Chory J.

BPMP, CNRS UMR 5004, 34060 Montpellier Cedex 1, France. gregory.vert@supagro.inra.fr

In plants, the uptake of nitrate from the soil is a critical process controlled by complex regulatory networks that target nitrate transporters in the roots. In this issue, Ho et al. (2009) show that phosphorylation of the CHL1 nitrate transporter allows the plant root to sense and respond to different nitrate concentrations in the soil.

Publication Types:

PMID: 19766561 [PubMed - indexed for MEDLINE]

12: Mol Biosyst. 2009 Aug 3. [Epub ahead of print]
Related Articles, Links: Systems analyses of circadian networks.

Hubbard KE, Robertson FC, Dalchau N, Webb AA.

Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, UK CB2 3EA.

The circadian clock is a 24 hour timing device that co-ordinates biological activity with day/night cycles. The long history of systems analysis of circadian biology extends back to the first half of the last century when theoretical studies based on physiological experiments predicted the essential network properties, architecture and performance of circadian oscillators long before the first genetic components were isolated in the second half of the century. Systems approaches have continued to be important in analysing the circadian network in the model plant Arabidopsis thaliana and in mammals. We describe how systems analyses of transcriptional changes have led to formal mathematical models of circadian oscillators. Predictions within these mathematical models have been used to identify potential new components of circadian systems. Cross-referencing circadian regulation of transcript abundance with transcriptomic responses to abiotic and biotic signals has increased understanding of the nature of circadian clocks and their significance in regulating the daily life of plants and animals. We also highlight the need for systems analyses of the circadian regulation of proteins, metabolites and other physiological activities such as ion channel regulation.

PMID: 19763342 [PubMed - as supplied by publisher]

13: Microbiology. 2009 Sep 17. [Epub ahead of print]
Related Articles, Links: Deletion of Mid1, a putative stretch-activated calcium channel in Claviceps purpurea, affects vegetative growth, cell wall synthesis and virulence.

Bormann J, Tudzynski P.

Institut fuer Botanik, Westf.Wilhelms Universitaet Muenster, Germany;

The putative Claviceps purpurea homologue of the Saccharomyces cerevisiae stretch-activated calcium ion channel Mid1 was investigated for its role in vegetative growth, differentiation and pathogenicity on Secale cereale. Gene replacement mutants of C. purpurea mid1 were not affected in polar growth and branching in axenic culture but showed a significantly reduced growth rate. The growth defect could not be complemented by Ca2+ supplementation, in contrast to mid1 mutants in yeast, but altered sensitivity of the mutants towards changes in external and internal Ca2+-concentrations indicate some role of Mid1 in Ca2+ homoeostasis. The major effect of mid1 deletion, however, was the complete loss of virulence: infected rye plants show no disease symptoms at all. Detailed analyses of in vitro infected rye ovaries demonstrate that the mid1 mutants show multiple apical branches and are unable to infect the host tissue, suggesting that Mid1 is essential for generating the necessary mechanical force for penetration. This is the first report on an essential role of a Mid1 homologue in virulence of a plant pathogenic fungus.

PMID: 19762439 [PubMed - as supplied by publisher]

14: Physiol Plant. 2009 Oct;137(2):155-65.
Related Articles, Links

Na(+)/H(+) antiporter activity of the SOS1 gene: lifetime imaging analysis and electrophysiological studies on Arabidopsis seedlings.

Guo KM, Babourina O, Rengel Z.

School of Earth and Geographical Sciences, University of Western Australia, Crawley WA, Australia.

Based on sequence analysis, the salt overly sensitive (SOS1) gene has been suggested to function as a Na(+)/H(+) antiporter located at the plasma membrane of plant cells, being expressed mostly in the meristem zone of the root and in the parenchyma cells surrounding the vascular tissue of the stem. In this study, we compared net H(+) and Ca(2+) fluxes and intracellular pH and [Ca(2+)](cyt) in the root meristem zone of Arabidopsis wild-type (WT) and sos mutants before and after salt stress. In addition, we studied the effect of pretreatment with amiloride (an inhibitor of Na(+)/H(+) antiporters) on net ion fluxes, intracellular pH and intracellular Ca(2+) activity ([Ca(2+)](cyt)) in WT plants and sos1 mutants before and after salt stress. Net ion fluxes were measured using microelectrode ion flux estimation (MIFE) and intracellular pH and [Ca(2+)](cyt) using fluorescence lifetime imaging microscopy (FLIM) techniques. During the first 15 min after NaCl application, sos1 mutants showed net H(+) efflux and intracellular alkalinization in the meristem zone, whereas sos2 and sos3 mutants and WT showed net H(+) influx and slight intracellular acidification in the meristem zone. Treatment with amiloride led to intracellular acidification and lower net H(+) flux in WT plants and to a decrease in intracellular Ca(2+) in WT and sos1 plants. WT plants pretreated with amiloride did not show positive net H(+) flux and intracellular acidification. After NaCl application, internal pH shifted to higher values in WT and sos1 plants. However, absolute values of H(+) fluxes were higher and internal pH values were lower in WT plants pretreated with amiloride compared with sos1 mutants. Therefore, the SOS1 transporter is involved in H(+) influx into the meristem zone of Arabidopsis roots, or it may function as a Na(+)/H(+) antiporter. Amiloride affects SOS1 and other Na(+)/H(+) antiporters in plant cells because of its ability to decrease the H(+) gradient across the plasma membrane.

Publication Types:

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

PMID: 19758408 [PubMed - indexed for MEDLINE]

15: Plant Physiol. 2009 Sep 9. [Epub ahead of print]
Related Articles, Links: Vascular function in grape berries across development and its relevance to apparent hydraulic isolation.

Choat B, Gambetta GA, Shackel KA, Matthews MA.

Department of Viticulture and Enology, University of California, Davis, CA, 95616, USA.

During the latter stages of development in fleshy fruit, water flow through the xylem declines markedly and the requirements of transpiration and further expansion are fulfilled primarily by the phloem. We evaluated the hypothesis that cessation of water transport through the xylem results from disruption or occlusion of pedicel and berry xylem conduits (hydraulic isolation). Xylem hydraulic resistance (R h) was measured in developing fruit of Vitis vinifera cv Chardonnay 20 - 100 days after anthesis (DAA) and compared with observations of xylem anatomy by light and cryo-scanning electron microscopy and expression of six aquaporin genes (VvPIP1;1, VvPIP1;2, VvPIP1;3, VvPIP2;1, VvPIP2;2, VvPIP2;3). There was a significant increase in whole berry R h and receptacle R h in the latter stages of ripening (80 - 100 DAA), which was associated with deposition of gels or solutes in many receptacle xylem conduits. Peaks in the expression of some aquaporin isoforms corresponded to lower whole berry R h 60 - 80 DAA and the increase in R h beginning at 80 DAA correlated with decreases in the expression of the two most predominantly expressed PIP genes. Although significant, the increase in berry R h was not great enough, and occurred too late in development, to explain the decline in xylem flow which occurs at 60-75 DAA. The evidence suggests that the fruit is not hydraulically isolated from the parent plant by xylem occlusion, but rather, is "hydraulically buffered" by water delivered via the phloem.

PMID: 19741048 [PubMed - as supplied by publisher]

16: Biochem J. 2009 Sep 9. [Epub ahead of print]
Related Articles, Links: A large-conductance calcium-activated potassium channel in potato tuber mitochondria.

Koszela-Piotrowska I, Matkovic K, Szewczyk A, Jarmuszkiewicz W.

In the present study, we describe the existence of a novel potassium channel in the plant (potato tuber) mitochondrial inner membrane. We found that substances known to modulate large-conductance calcium-activated potassium channel activity influenced the bioenergetics of potato tuber mitochondria. In isolated mitochondria, Ca2+ and NS1619 (a potassium channel opener) were found to depolarize the mitochondrial membrane potential and to stimulate resting respiration. These effects were blocked by iberiotoxin (a potassium channel inhibitor) in a potassium-dependent manner. Additionally, the electrophysiological properties of the large-conductance potassium channel present in the potato tuber inner mitochondrial membrane are described in a reconstituted system, using planar lipid bilayers. After incorporation in 50/450 mM KCl gradient solutions, we recorded large-conductance potassium channel activity with conductance from 502 +/- 15 to 615 +/- 12 pS. The probability of channel opening was increased by Ca2+ and reduced by iberiotoxin. Immunological analysis with antibodies raised against the mammalian plasma membrane large-conductance Ca2+-dependent K+ channel identified a pore-forming alpha subunit and an auxiliary beta2 subunit of the channel in potato tuber mitochondrial inner membrane. These results suggest that a large-conductance calcium-activated potassium channel similar to that of mammalian mitochondria is present in potato tuber mitochondria.

PMID: 19740073 [PubMed - as supplied by publisher]

17: J Plant Physiol. 2009 Aug 29. [Epub ahead of print]
Related Articles, Links: Interactions between salinity and boron toxicity in tomato plants involve apoplastic calcium.

Bastías E, Alcaraz-López C, Bonilla I, Martínez-Ballesta MC, Bolaños L, Carvajal M.

Departamento de Producción Agrícola, Facultad de Ciencias Agronómicas, Universidad de Tarapacá, Casilla 6-D, Arica, Chile.

The lack of consensus about the mutual relations between salinity and boron (B) toxicity with respect to the physiological response of plants necessitates investigation of the interactions of soluble B with salinity. In this investigation, the effect of B was compared with Ca in order to elucidate whether the two nutrients have similar effects and/or to elucidate a relationship under salinity. Following addition of B or Ca, salinity was applied to tomato plants and the cell wall and plasma membrane permeability, measured as water permeability and electrolyte leakage, in relation to amino acid and ion cell wall composition, were determined. As the relationship between B and salinity was complex, several hypotheses are established. The increase of aquaporin functionality due to the presence of B and Ca compared with NaCl-treated plants could be the most feasible, whereas there is currently no satisfactory explanation for the results for the cell wall amino acid composition. In addition, the elemental composition results revealed that, in addition the known interactions between B and Ca with respect to cell wall stability, Mg and Mn were also increased in NaCl+B and NaCl+Ca treatments, suggesting their possible involvement in the cell wall function necessary for plant growth.

PMID: 19720429 [PubMed - as supplied by publisher]

18: Physiol Plant. 2009 Oct;137(2):188-99. Epub 2009 Jul 21.
Related Articles, Links: Drought stress effects on photosystem I content and photosystem II thermotolerance analyzed using Chl a fluorescence kinetics in barley varieties differing in their drought tolerance.

Oukarroum A, Schansker G, Strasser RJ.

Bioenergetics and Microbiology laboratory, University of Geneva, Jussy-Geneva, Switzerland. oukarro1@etu.unige.ch

Drought stress has multiple effects on the photosynthetic system. Here, we show that a decrease of the relative contribution of the I-P phase, DeltaV(IP) = -V(I) = (F(M)-F(I))/(F(M)- F(o)), to the fluorescence transient OJIP is observed in 10 drought-stressed barley and 9 chickpea varieties. The extent of the I-P loss in the barley varieties depended on their drought tolerance. The relative loss of the I-P phase seems to be related to a loss of photosystem (PS) I reaction centers as determined by 820-nm transmission measurements. In the second part of this study, the interaction of drought and heat stress in two barley varieties (the drought tolerant variety Aït Baha and the drought sensitive variety Lannaceur) was studied using a new approach. Heat stress was induced by exposing the plant leaves to temperatures of 25-45 degrees C and the inactivation of the O(2)-evolving complex (OEC) was followed measuring chlorophyll a (Chl a) fluorescence using a protocol consisting of two 5-ms pulses spaced 2.3 ms apart. In active reaction centers, the dark interval is long enough to allow the OEC to recover from the first pulse; whereas in heat-inactivated reaction centers it is not. In the latter category of reaction centers, no further fluorescence rise is induced by the second pulse. Lannaceur, under well-watered conditions, was more heat tolerant than Aït Baha. However, this difference was lost following drought stress. Drought stress considerably increased the thermostability of PS II of both varieties.

PMID: 19719481 [PubMed - indexed for MEDLINE]

19: Planta. 2009 Oct;230(5):1071-9.
Related Articles, Links

Protein phosphatase activity and sucrose-mediated induction of fructan synthesis in wheat.

Martínez-Noël GM, Tognetti JA, Salerno GL, Wiemken A, Pontis HG.

Centro de Investigaciones Biológicas, Fundación para Investigaciones Biológicas Aplicadas, Vieytes 3103, 7600 Mar del Plata, Argentina. giselle.martinez@imdea.org

In this work, we analyze protein phosphatase (PP) involvement in the sucrose-mediated induction of fructan metabolism in wheat (Triticum aestivum). The addition of okadaic acid (OA), a PP-inhibitor, to sucrose-fed leaves reduced fructosylsucrose-synthesizing activity (FSS) induction in a dose-dependent manner. The expression of the two enzymes that contribute to FSS activity, 1-SST (1-sucrose:sucrose fructosyltransferase, E.C. 2.4.1.99) and 6-SFT (6-sucrose:fructan fructosyltransferase, E.C. 2.4.1.10), was blocked by 1 microM OA. These results suggest the involvement of a PP type 2A in sucrose signaling leading to fructan synthesis. OA addition to the feeding medium impaired both sucrose accumulation in leaves and the expression of sucrose-H+ symporter (SUT1). It is known that sucrose concentration must exceed a threshold for the induction of fructan metabolism; hence PP2A inhibition may result in lower sucrose levels than required for this induction. OA also induced the vacuolar acid invertase (acid INV) transcript levels suggesting that PP activity might play a role in carbon partitioning. Total extractable PP2A activity decreased during 24 h of treatment with sucrose, in parallel with declining sugar uptake into leaf tissues. In conclusion, our results suggest that PP2A is involved in sucrose-induction of fructan metabolism and may play a role in regulating sucrose uptake, but do not rule out that further steps in sucrose signaling pathway may be affected.

Publication Types:

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

PMID: 19714360 [PubMed - in process]

20: Plant J. 2009 Aug 26. [Epub ahead of print]
Related Articles, Links: Identification of novel proteins in isolated polyphosphate vacuoles in the primitive red alga Cyanidioschyzon merolae.

Yagisawa F, Nishida K, Yoshida M, Ohnuma M, Shimada T, Fujiwara T, Yoshida Y, Misumi O, Kuroiwa H, Kuroiwa T.

Research Information Center for Extremophiles, Rikkyo (St Paul's) University, Nishi-Ikebukuro, Tokyo 171-8501, Japan.

Summary Plant vacuoles are organelles bound by a single membrane, and involved in various functions such as intracellular digestion, metabolite storage, and secretion. To understand their evolution and fundamental mechanisms, characterization of vacuoles in primitive plants would be invaluable. Algal cells often contain polyphosphate-rich compartments, which are thought to be the counterparts of seed plant vacuoles. Here, we developed a method for isolating these vacuoles from Cyanidioschyzon merolae, and identified their proteins by MALDI TOF-MS. The vacuoles were of unexpectedly high density, and were highly enriched at the boundary between 62 and 80% w/v iodixanol by density-gradient ultracentrifugation. The vacuole-containing fraction was subjected to SDS-PAGE, and a total of 46 proteins were identified, including six lytic enzymes, 13 transporters, six proteins for membrane fusion or vesicle trafficking, five non-lytic enzymes, 13 proteins of unknown function, and three miscellaneous proteins. Fourteen proteins were homologous to known vacuolar or lysosomal proteins from seed plants, yeasts or mammals, suggesting functional and evolutionary relationships between C. merolae vacuoles and these compartments. The vacuolar localization of four novel proteins, namely CMP249C (metallopeptidase), CMJ260C (prenylated Rab receptor), CMS401C (ABC transporter) and CMT369C (o-methyltransferase), was confirmed by labeling with specific antibodies or transient expression of hemagglutinin-tagged proteins. The results presented here provide insights into the proteome of C. merolae vacuoles and shed light on their functions, as well as indicating new features.

PMID: 19709388 [PubMed - as supplied by publisher]

21: J Genet Genomics. 2009 Aug;36(8):455-66.
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Characterization of the promoter of phosphate transporter TaPHT1.2 differentially expressed in wheat varieties.

Miao J, Sun J, Liu D, Li B, Zhang A, Li Z, Tong Y.

The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.

TaPHT1.2 is a functional, root predominantly expressed and low phosphate (Pi) inducible high-affinity Pi transporter in wheat, which is more abundant in the roots of P-efficient wheat genotypes (e.g., Xiaoyan 54) than in P-inefficient genotypes (e.g., Jing 411) under both Pi-deficient and Pi-sufficient conditions. To characterize TaPHT1.2 further, we genetically mapped a TaPHT1.2 transporter, TaPHT1.2-D1, on the long arm of chromosome 4D using a recombinant inbred line population derived from Xiaoyan 54 and Jing 411, and isolated a1,302 bp fragment of the TaPHT1.2-D1 promoter (PrTaPHT1.2-D1) from Xiaoyan 54. TaPHT1.2-D1 shows collinearity with OsPHT1.2 that has previously been reported to mediate the translocation of Pi from roots to shoots. PrTaPHT1.2-D contains a number of Pi-starvation responsive elements, including P1BS, WRKY-binding W-box, and helix-loop-helix-binding elements. PrTaPHT1.2-D1 was then used to drive expression of beta-glucuronidase (GUS) reporter gene in Arabidopsis through Agrobacterium-mediated transformation. Histochemical analysis of transgenic Arabidopsis plants showed that the reporter gene was specifically induced by Pi-starvation and predominantly expressed in the roots. As there is only one SNP between the TaPHT1.2-D1 promoters of Xiaoyan 54 and Jing 411, and this SNP does not exist within the Pi-starvation responsive elements, the differential expression of TaPHT1.2 in Xiaoyan 54 and Jing 411 may not be caused by this SNP.

Publication Types:

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

PMID: 19683668 [PubMed - indexed for MEDLINE]

22: Physiol Plant. 2009 Oct;137(2):166-74. Epub 2009 Jul 14.
Related Articles, Links

Molecular characterization of putative vacuolar NHX-type Na(+)/H(+) exchanger genes from the salt-resistant tree Populus euphratica.

Ye CY, Zhang HC, Chen JH, Xia XL, Yin WL.

National Engineering Laboratory for Tree Breeding, Beijing Forestry University, Beijing, China.

The vacuolar NHX-type Na(+)/H(+) exchangers play a key role in salt tolerance in plants. However, little is known about the Na(+)/H(+) exchangers in the salt-resistant tree, Populus euphratica. In this study, we identified six putative vacuolar Na(+)/H(+) exchanger genes from P. euphratica, designated as PeNHX1-6. Real-time polymerase chain reaction indicated that the PeNHX1/3/6 transcripts were abundant compared with the other three PeNHX genes in the three tissues (roots, stems and leaves) examined. After NaCl treatment for 6 h, the transcript levels of PeNHX1-6 were upregulated in the roots. To address the function of PeNHX1-6, complementation studies were performed with the salt-sensitive yeast mutant strain R100, which lacks activity of the endosomal Na(+)/H(+) antiporter NHX1. The results showed that PeNHX1-6 compensates, at least in part, for the function of yeast NHX1. Moreover, PeNHX3 was targeted to the tonoplast when transiently expressed in onion. Together, these results suggest that PeNHX1-6 function as vacuolar Na(+)/H(+) exchangers and that PeNHX products play an important role in the salt resistance of P. euphratica.

Publication Types:

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

PMID: 19678897 [PubMed - indexed for MEDLINE]

23: New Phytol. 2009 Oct;184(2):289-302. Epub 2009 Aug 11.
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A look inside: localization patterns and functions of intracellular plant aquaporins.

Wudick MM, Luu DT, Maurel C.

Biochimie et physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, F-34060 Montpellier Cedex 2, France.

Aquaporins form a superfamily of intrinsic channel proteins in the plasma and intracellular membranes of plant cells. While a lot of research effort has substantiated the importance of plasma membrane aquaporins for the regulation of plant water homeostasis, comparably little is known about the function of intracellular aquaporins. Yet, various low-molecular-weight compounds, in addition to water, were recently shown to permeate some of these aquaporins. In this review, we examine the diversity of transport properties and localization patterns of intracellular aquaporins. The discussed profiles include, for example, water and ammonia transport across the tonoplast or CO2 transport through the chloroplast envelope. Furthermore, we try to assess to what extent the diverse aquaporin distribution patterns, in relation to the high degree of compartmentation of plant cells, can be linked to a wide range of cellular functions.

Publication Types:

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

PMID: 19674338 [PubMed - in process]

24: Plant Physiol. 2009 Oct;151(2):843-56. Epub 2009 Aug 5.
Related Articles, Links: Involvement of HbPIP2;1 and HbTIP1;1 Aquaporins in Ethylene Stimulation of Latex Yield through Regulation of Water Exchanges between Inner Liber and Latex Cells in Hevea brasiliensis.

Tungngoen K, Kongsawadworakul P, Viboonjun U, Katsuhara M, Brunel N, Sakr S, Narangajavana J, Chrestin H.

Department of Biotechnology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.

Natural rubber is synthesized in specialized articulated cells (laticifers) located in the inner liber of Hevea brasiliensis. Upon bark tapping, the laticifer cytoplasm (latex) is expelled due to liber tissue turgor pressure. In mature virgin (untapped) trees, short-term kinetic studies confirmed that ethylene, the rubber yield stimulant used worldwide, increased latex yield, with a concomitant decrease in latex total solid content, probably through water influx in the laticifers. As the mature laticifers are devoid of plasmodesmata, the rapid water exchanges with surrounding liber cells probably occur via the aquaporin pathway. Two full-length aquaporin cDNAs (HbPIP2;1 and HbTIP1;1, for plasma membrane intrinsic protein and tonoplast intrinsic protein, respectively) were cloned and characterized. The higher efficiency of HbPIP2;1 than HbTIP1;1 in increasing plasmalemma water conductance was verified in Xenopus laevis oocytes. HbPIP2;1 was insensitive to HgCl(2). In situ hybridization demonstrated that HbPIP2;1 was expressed in all liber tissues in the young stem, including the laticifers. HbPIP2;1 was up-regulated in both liber tissues and laticifers, whereas HbTIP1;1 was down-regulated in liber tissues but up-regulated in laticifers in response to bark Ethrel treatment. Ethylene-induced HbPIP2;1 up-regulation was confirmed by western-blot analysis. The promoter sequences of both genes were cloned and found to harbor, among many others, ethylene-responsive and other chemical-responsive (auxin, copper, and sulfur) elements known to increase latex yield. Increase in latex yield in response to ethylene was emphasized to be linked with water circulation between the laticifers and their surrounding tissues as well as with the probable maintenance of liber tissue turgor, which together favor prolongation of latex flow.

PMID: 19656906 [PubMed - in process]
PMCID: PMC2754619 [Available on 2010/10/01]

25: Mol Plant Microbe Interact. 2009 Sep;22(9):1169-78.
Related Articles, Links

Expression analysis of the first arbuscular mycorrhizal fungi aquaporin described reveals concerted gene expression between salt-stressed and nonstressed mycelium.

Aroca R, Bago A, Sutka M, Paz JA, Cano C, Amodeo G, Ruiz-Lozano JM.

Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Granada Spain. raroca@eez.csic.es

Roots of most plants in nature are colonized by arbuscular mycorrhizal (AM) fungi. Among the beneficial effects of this symbiosis to the host plant is the transport of water by the AM mycelium from inaccessible soil water resources to host roots. Here, an aquaporin (water channel) gene from an AM fungus (Glomus intraradices), which was named GintAQP1, is reported for the first time. From experiments in different colonized host roots growing under several environmental conditions, it seems that GintAQP1 gene expression is regulated in a compensatory way regarding host root aquaporin expression. At the same time, from in vitro experiments, it was shown that a signaling communication between NaCl-treated mycelium and untreated mycelium took place in order to regulate gene expression of both GintAQP1 and host root aquaporins. This communication could be involved in the transport of water from osmotically favorable growing mycelium or host roots to salt-stressed tissues.

Publication Types:

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

PMID: 19656051 [PubMed - indexed for MEDLINE]

26: J Exp Bot. 2009;60(14):4063-75. Epub 2009 Aug 3.
Related Articles, Links

Aquaporin gene expression and apoplastic water flow in bur oak (Quercus macrocarpa) leaves in relation to the light response of leaf hydraulic conductance.

Voicu MC, Cooke JE, Zwiazek JJ.

Department of Renewable Resources, University of Alberta, 4-42 Earth Sciences Bldg., Edmonton, Alberta, Canada T6G 2E3.

It has previously been shown that hydraulic conductance in bur oak leaves (Quercus macrocarpa Michx.), measured with the high pressure flow meter technique (HPFM), can significantly increase within 30 min following exposure to high irradiance. The present study investigated whether this increase could be explained by an increase in the cell-to-cell pathway and whether the response is linked to changes in the transcript level corresponding to aquaporin genes. Four cDNA sequences showing high similarity to members of the aquaporin gene family from other plant species were characterized from bur oak leaves and the expression levels of these cDNA sequences were examined in leaves by quantitative real-time PCR (QRT-PCR). No change was found in the relative transcript abundance corresponding to these four putative aquaporin genes in leaves with light-induced high hydraulic conductance (exposed to high irradiance) compared to leaves with low hydraulic conductance (exposed to low irradiance). However, in sun leaves that were exposed to different light levels prior to leaf collection (full sunlight, shade, and covered with aluminium foil for 16 h), the relative transcript levels of two of the putative aquaporin genes increased several-fold in shaded leaves compared to the sun-exposed or covered leaves. When the leaves were pressure-infiltrated with the apoplastic tracer dye trisodium 3-hydroxy-5,8,10-pyrenetrisulphonate (PTS(3), 0.02%), there was no change in the PTS(3) concentration of leaf exudates collected in ambient light or in high irradiance, but there was a small apoplastic acidification. There was also no change in PTS(3) concentration between the leaves infiltrated under high irradiance with 0.02% PTS(3) or with 0.1 mM HgCl(2) in 0.02% PTS(3). The results suggest that the putative aquaporin genes that were identified in the present study probably do not play a role in the light responses of hydraulic conductance at the transcript level, but they may function in regulating water homeostasis in leaves adapted to different light conditions. In addition, it is shown that high irradiance induced changes in the pH of the apoplast and that there does not appear to be a significant shift to the cell-to-cell mediated water transport in bur oak leaves exposed to high irradiance as measured by the apoplastic tracer dye.

Publication Types:

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

PMID: 19651684 [PubMed - in process]

PMCID: PMC2755026

27: J Biol Chem. 2009 Sep 25;284(39):26526-32. Epub 2009 Jul 27.
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ATP binding to the C terminus of the Arabidopsis thaliana nitrate/proton antiporter, AtCLCa, regulates nitrate transport into plant vacuoles.

De Angeli A, Moran O, Wege S, Filleur S, Ephritikhine G, Thomine S, Barbier-Brygoo H, Gambale F.

Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy.

Nitrate, one of the major nitrogen sources for plants, is stored in the vacuole. Nitrate accumulation within the vacuole is primarily mediated by the NO(3)(-)/H(+) exchanger AtCLCa, which belongs to the chloride channel (CLC) family. Crystallography analysis of hCLC5 suggested that the C-terminal domain, composed by two cystathionine beta-synthetase motifs in all eukaryotic members of the CLC family is able to interact with ATP. However, interaction of nucleotides with a functional CLC protein has not been unambiguously demonstrated. Here we show that ATP reversibly inhibits AtCLCa by interacting with the C-terminal domain. Applying the patch clamp technique to isolated Arabidopsis thaliana vacuoles, we demonstrate that ATP reduces AtCLCa activity with a maximum inhibition of 60%. ATP inhibition of nitrate influx into the vacuole at cytosolic physiological nitrate concentrations suggests that ATP modulation is physiologically relevant. ADP and AMP do not decrease the AtCLCa transport activity; nonetheless, AMP (but not ADP) competes with ATP, preventing inhibition. A molecular model of the C terminus of AtCLCa was built by homology to hCLC5 C terminus. The model predicted the effects of mutations of the ATP binding site on the interaction energy between ATP and AtCLCa that were further confirmed by functional expression of site-directed mutated AtCLCa.

Publication Types:

PMID: 19636075 [PubMed - in process]

28: Plant Cell Physiol. 2009 Sep;50(9):1579-86. Epub 2009 Jul 24.
Related Articles, Links

Arabidopsis bile acid:sodium symporter family protein 5 is involved in methionine-derived glucosinolate biosynthesis.

Sawada Y, Toyooka K, Kuwahara A, Sakata A, Nagano M, Saito K, Hirai MY.

RIKEN Plant Science Center, Yokohama, Kanagawa, Japan.

Glucosinolates (GSLs) are a group of plant secondary metabolites that have repellent activity against herbivore insects and pathogens, and anti-carcinogenic activity in humans. They are produced in plants of the Brassicaceae and other related families. Biosynthesis of GSLs from precursor amino acids takes place in two subcellular compartments; amino acid biosynthesis and side chain elongation occur mainly in the chloroplast, whereas the following core structure synthesis takes place in the cytosol. Although the genes encoding biosynthetic enzymes of GSLs are well known in Arabidopsis thaliana, the transporter genes responsible for translocation of biosynthetic intermediates between the chloroplast and cytosol are as yet unidentified. In this study, we identified the bile acid:sodium symporter family protein 5 (BASS5) gene in Arabidopsis as a candidate transporter gene involved in methionine-derived GSL (Met-GSL) biosynthesis by means of transcriptome co-expression analysis. Knocking out BASS5 resulted in a decrease of Met-GSLs and concomitant increase of methionine. A transient assay using fluorescence fusion proteins indicated a chloroplastic localization of BASS5. These results supported the idea that BASS5 plays a role in translocation across the chloroplast membranes of the biosynthetic intermediates of Met-GSLs.

Publication Types:

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

PMID: 19633020 [PubMed - indexed for MEDLINE]

PMCID: PMC2739670 [Available on 2010/09/01]

29: FEBS J. 2009 Aug;276(16):4381-94. Epub 2009 Jul 15.
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The proximity between C-termini of dimeric vacuolar H+-pyrophosphatase determined using atomic force microscopy and a gold nanoparticle technique.

Liu TH, Hsu SH, Huang YT, Lin SM, Huang TW, Chuang TH, Fan SK, Fu CC, Tseng FG, Pan RL.

Department of Life Sciences and Institute of Bioinformatics and Structural Biology, College of Life Sciences, National Tsing Hua University, Hsin Chu, Taiwan, ROC.

Vacuolar H(+)-translocating inorganic pyrophosphatase [vacuolar H(+)-pyrophosphatase (V-PPase); EC 3.6.1.1] is a homodimeric proton translocase; it plays a pivotal role in electrogenic translocation of protons from the cytosol to the vacuolar lumen, at the expense of PP(i) hydrolysis, for the storage of ions, sugars, and other metabolites. Dimerization of V-PPase is necessary for full proton translocation function, although the structural details of V-PPase within the vacuolar membrane remain uncertain. The C-terminus presumably plays a crucial role in sustaining enzymatic and proton-translocating reactions. We used atomic force microscopy to visualize V-PPases embedded in an artificial lipid bilayer under physiological conditions. V-PPases were randomly distributed in reconstituted lipid bilayers; approximately 43.3% of the V-PPase protrusions faced the cytosol, and 56.7% faced the vacuolar lumen. The mean height and width of the cytosolic V-PPase protrusions were 2.8 +/- 0.3 nm and 26.3 +/- 4.7 nm, whereas those of the luminal protrusions were 1.2 +/- 0.1 nm and 21.7 +/- 3.6 nm, respectively. Moreover, both C-termini of dimeric subunits of V-PPase are on the same side of the membrane, and they are close to each other, as visualized with antibody and gold nanoparticles against 6xHis tags on C-terminal ends of the enzyme. The distance between the V-PPase C-terminal ends was determined to be approximately 2.2 +/- 1.4 nm. Thus, our study is the first to provide structural details of a membrane-bound V-PPase dimer, revealing its adjacent C-termini.

Publication Types:

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

PMID: 19614743 [PubMed - indexed for MEDLINE]

30: Plant Physiol. 2009 Sep;151(1):210-22. Epub 2009 Jul 1.
Related Articles, Links

Loss of halophytism by interference with SOS1 expression.

Oh DH, Leidi E, Zhang Q, Hwang SM, Li Y, Quintero FJ, Jiang X, D'Urzo MP, Lee SY, Zhao Y, Bahk JD, Bressan RA, Yun DJ, Pardo JM, Bohnert HJ.

Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

The contribution of SOS1 (for Salt Overly Sensitive 1), encoding a sodium/proton antiporter, to plant salinity tolerance was analyzed in wild-type and RNA interference (RNAi) lines of the halophytic Arabidopsis (Arabidopsis thaliana)-relative Thellungiella salsuginea. Under all conditions, SOS1 mRNA abundance was higher in Thellungiella than in Arabidopsis. Ectopic expression of the Thellungiella homolog ThSOS1 suppressed the salt-sensitive phenotype of a Saccharomyces cerevisiae strain lacking sodium ion (Na(+)) efflux transporters and increased salt tolerance of wild-type Arabidopsis. thsos1-RNAi lines of Thellungiella were highly salt sensitive. A representative line, thsos1-4, showed faster Na(+) accumulation, more severe water loss in shoots under salt stress, and slower removal of Na(+) from the root after removal of stress compared with the wild type. thsos1-4 showed drastically higher sodium-specific fluorescence visualized by CoroNa-Green, a sodium-specific fluorophore, than the wild type, inhibition of endocytosis in root tip cells, and cell death in the adjacent elongation zone. After prolonged stress, Na(+) accumulated inside the pericycle in thsos1-4, while sodium was confined in vacuoles of epidermis and cortex cells in the wild type. RNAi-based interference of SOS1 caused cell death in the root elongation zone, accompanied by fragmentation of vacuoles, inhibition of endocytosis, and apoplastic sodium influx into the stele and hence the shoot. Reduction in SOS1 expression changed Thellungiella that normally can grow in seawater-strength sodium chloride solutions into a plant as sensitive to Na(+) as Arabidopsis.

Publication Types:

PMID: 19571313 [PubMed - in process]

PMCID: PMC2735974

31: Cell Mol Life Sci. 2009 Oct;66(19):3161-75. Epub 2009 Jun 30.
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Plant aquaporin selectivity: where transport assays, computer simulations and physiology meet.

Ludewig U, Dynowski M.

Institute of Botany, Darmstadt University of Technology, Schnittspahnstr. 10, 64287, Darmstadt, Germany. ludewig@bio.tu-darmstadt.de

Plants contain a large number of aquaporins with different selectivity. These channels generally conduct water, but some additionally conduct NH(3), CO(2) and/or H(2)O(2). The experimental evidence and molecular basis for the transport of a given solute, the validation with molecular dynamics simulations and the physiological impact of the selectivity are reviewed here. The aromatic/arginine (ar/R) constriction is most important for solute selection, but the exact pore requirements for efficient conduction of small solutes remain difficult to predict. Yeast growth assays are valuable for screening substrate selectivity and are explicitly shown for hydrogen peroxide and methylamine, a transport analog of ammonia. Independent assays need to address the relevance of different substrates for each channel in its physiological context. This is emphasized by the fact that several plant NIP channels, which conduct several solutes, are specifically involved in the transport of metalloids, such as silicic acid, arsenite, or boric acid in planta.

Publication Types:

PMID: 19565186 [PubMed - indexed for MEDLINE]

32: Plant Cell Environ. 2009 Oct;32(10):1357-65. Epub 2009 Jun 10.
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The involvement of aquaglyceroporins in transport of boron in barley roots.

Fitzpatrick KL, Reid RJ.

School of Earth and Environmental Sciences, University of Adelaide, Adelaide, Australia. kate.fitzpatrick@adelaide.edu.au

Boron (B) enters cells as the uncharged boric acid, a small neutral molecule with sufficient lipid solubility to cross cell membranes without the aid of transport proteins. The extent to which the observed uptake rates for B in plants can be explained by this simple physical process was examined by applying treatments expected to inhibit the membrane transporters most likely to be involved in B transport. These experiments established that at least 50% of B uptake could be facilitated by transporters. The B transport characteristics of two barley aquaglyceroporins, HvPIP1;3 and HvPIP1;4, were investigated using yeast complementation assays. Expression of both genes in yeast resulted in increased B sensitivity. Transport assays in yeast confirmed that HvPIP1;3 and HvPIP1;4 are both capable of transporting B. The physiological role of these HvPIP1 genes in B transport is uncertain since their expression was not responsive to B nutritional status, and they continued to be expressed under toxicity conditions.

Publication Types:

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

PMID: 19552667 [PubMed - indexed for MEDLINE]

33: Biochem J. 2009 Aug 13;422(2):217-28.
Related Articles, Links

The NRAMP6 metal transporter contributes to cadmium toxicity.

Cailliatte R, Lapeyre B, Briat JF, Mari S, Curie C.

Laboratoire de Biochimie et Physiologie Moléculaire des Plantes CNRS UMR5004, Institut de Biologie Intégrative des Plantes, F-34060 Montpellier, France.

NRAMP (natural resistance-associated macrophage protein) homologues are evolutionarily conserved bivalent metal transporters. In Arabidopsis, AtNRAMP3 and AtNRAMP4 play a key role in iron nutrition of the germinating plantlet by remobilizing vacuolar iron stores. In the present paper we describe the molecular and physiological characterization of AtNRAMP6. AtNRAMP6 is predominantly expressed in the dry seed embryo and to a lesser extent in aerial parts. Its promoter activity is found diffusely distributed in cotyledons and hypocotyl, as well as in the vascular tissue region of leaf and flower. We show that the AtNRAMP6 transcript coexists with a partially spliced isoform in all shoot cell types tested. When expressed in yeast, AtNRAMP6, but not its misspliced derivative, increased sensitivity to cadmium without affecting cadmium content in the cell. Likewise, Arabidopsis transgenic plants overexpressing AtNRAMP6 were hypersensitive to cadmium, although plant cadmium content remained unchanged. Consistently, a null allele of AtNRAMP6, named nramp6-1, was more tolerant to cadmium toxicity, a phenotype that was reverted by expressing AtNRAMP6 in the mutant background. We used an AtNRAMP6::HA (where HA is haemagglutinin) fusion, shown to be functional in yeast, to demonstrate through immunoblot analysis of membrane fractions and immunofluorescence localization that, in yeast cells, AtNRAMP6 is targeted to a vesicular-shaped endomembrane compartment distinct from the vacuole or mitochondria. We therefore propose that AtNRAMP6 functions as an intracellular metal transporter, whose presence, when modified, is likely to affect distribution/availability of cadmium within the cell.

Publication Types:

PMID: 19545236 [PubMed - indexed for MEDLINE]

34: Plant Cell Rep. 2009 Aug;28(8):1253-64. Epub 2009 Jun 18.
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Analysis of the tip-to-base gradient of CaM in pollen tube pulsant growth using in vivo CaM-GFP system.

Shi YY, Tao WJ, Liang SP, Lü Y, Zhang L.

Key Lab of MOE for Plant Developmental Biology, Wuhan University, 430072, Wuhan, People's Republic of China.

Ca(2+)-CaM signaling is involved in pollen tube development. However, the distribution and function of CaM and the downstream components of Ca(2+)-CaM signal in pollen tube development still need more exploration. Here we obtained the CaM-GFP fusion protein transgenic line of Nicotiana tobacum SRI, which allowed us to monitor CaM distribution pattern in vivo and provided a useful tool to observe CaM response to various exogenous stimulations and afforded solid evidences of the essential functions of CaM in pollen tube growth. CaM-GFP fusion gene was constructed under the control of Lat52-7 pollen-specific promoter and transformed into Nicotiana tobacum SRI. High level of CaM-GFP fluorescence was detected at the germinal pores and the tip-to-base gradient of fluorescence was observed in developing pollen tubes. The distribution of CaM at apical dome had close relationship with the pulsant growth mode of pollen tubes: when CaM aggregated at the apical dome, pollen tubes stepped into growth state; When CaM showed non-polarized distribution, pollen tubes stopped growing. In addition, after affording exogenous Ca(2+), calmidazolium (antagonism of CaM) or Brefeldin A (an inhibitor of membrane trafficking), CaM turned to a uniform distribution at the apical dome and pollen tube growth was held back. Taken together, our results showed that CaM played a vital role in pollen tube elongation and growth rate, and the oscillation of tip-to-base gradient of CaM was required for the normal pulsant growth of pollen tube.

Publication Types:

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

PMID: 19536549 [PubMed - indexed for MEDLINE]

35: Plant Mol Biol. 2009 Sep;71(1-2):157-71. Epub 2009 Jun 17.
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Silencing of a single gene in tomato plants resistant to Tomato yellow leaf curl virus renders them susceptible to the virus.

Eybishtz A, Peretz Y, Sade D, Akad F, Czosnek H.

The Otto Warburg Minerva Center for Agricultural Biotechnology and the Robert H. Smith Institute of Plant Science and Genetics in Agriculture, Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.

A reverse-genetics approach was applied to identify genes involved in Tomato yellow leaf curl virus (TYLCV) resistance, taking advantage of two tomato inbred lines from the same breeding program-one susceptible (S), one resistant (R-that used Solanum habrochaites as the source of resistance. cDNA libraries from inoculated and non-inoculated R and S plants were compared, postulating that genes preferentially expressed in the R line may be part of the network sustaining resistance to TYLCV. Further, we assumed that silencing genes located at important nodes of the network would lead to collapse of resistance. Approximately 70 different cDNAs representing genes preferentially expressed in R plants were isolated and their genes identified by comparison with public databases. A Permease I-like protein gene encoding a transmembranal transporter was further studied: it was preferentially expressed in R plants and its expression was enhanced several-fold following TYLCV inoculation. Silencing of the Permease gene of R plants using Tobacco rattle virus-induced gene silencing led to loss of resistance, expressed as development of disease symptoms typical of infected susceptible plants and accumulation of large amounts of virus. Silencing of another membrane protein gene preferentially expressed in R plants, Pectin methylesterase, previously shown to be involved in Tobacco mosaic virus translocation, did not lead to collapse of resistance of R plants. Thus, silencing of a single gene can lead to collapse of resistance, but not every gene preferentially expressed in the R line has the same effect, upon silencing, on resistance.

Publication Types:

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

PMID: 19533378 [PubMed - indexed for MEDLINE]

36: J Biol Chem. 2009 Aug 7;284(32):21288-95. Epub 2009 Jun 9.
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Heteromeric AtKC1{middle dot}AKT1 channels in Arabidopsis roots facilitate growth under K+-limiting conditions.

Geiger D, Becker D, Vosloh D, Gambale F, Palme K, Rehers M, Anschuetz U, Dreyer I, Kudla J, Hedrich R.

Julius-von-Sachs-Institute, Molecular Plant Physiology and Biophysics, University of Wuerzburg, Julius-von-Sachs-Platz 2, D-97082 Wuerzburg, Germany.

Plant growth and development is driven by osmotic processes. Potassium represents the major osmotically active cation in plants cells. The uptake of this inorganic osmolyte from the soil in Arabidopsis involves a root K(+) uptake module consisting of the two K(+) channel alpha-subunits, AKT1 and AtKC1. AKT1-mediated potassium absorption from K(+)-depleted soil was shown to depend on the calcium-sensing proteins CBL1/9 and their interacting kinase CIPK23. Here we show that upon activation by the CBL.CIPK complex in low external potassium homomeric AKT1 channels open at voltages positive of E(K), a condition resulting in cellular K(+) leakage. Although at submillimolar external potassium an intrinsic K(+) sensor reduces AKT1 channel cord conductance, loss of cytosolic potassium is not completely abolished under these conditions. Depending on channel activity and the actual potassium gradients, this channel-mediated K(+) loss results in impaired plant growth in the atkc1 mutant. Incorporation of the AtKC1 subunit into the channel complex, however, modulates the properties of the K(+) uptake module to prevent K(+) loss. Upon assembly of AKT1 and AtKC1, the activation threshold of the root inward rectifier voltage gate is shifted negative by approximately -70 mV. Additionally, the channel conductance gains a hypersensitive K(+) dependence. Together, these two processes appear to represent a safety strategy preventing K(+) loss through the uptake channels under physiological conditions. Similar growth retardation phenotypes of akt1 and atkc1 loss-of-function mutants in response to limiting K(+) supply further support such functional interdependence of AKT1 and AtKC1. Taken together, these findings suggest an essential role of AtKC1-like subunits for root K(+) uptake and K(+) homeostasis when plants experience conditions of K(+) limitation.

Publication Types:

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

PMID: 19509299 [PubMed - indexed for MEDLINE]

PMCID: PMC2755853 [Available on 2010/08/07]

37: Plant J. 2009 Oct;60(1):91-101. Epub 2009 Jun 5.
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, Madison, WI 53706, USA.

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 superfamily, and mediates polar auxin transport in stems and roots. Here we have 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, but not later. Analysis of ProDR5:GFP expression patterns showed a significantly diminished and restricted auxin distribution pattern in abcb19 cotyledons. Nonetheless, development of abcb19 embryonic cotyledons was very similar to that of 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 in wild-type, although the 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 may be explained by the 50% reduction in the import of auxin through the petioles of abcb19 cotyledons during the period of maximum expansion. Taken together, these data indicate that cotyledon expansion during the establishment of photoautotrophic growth depends on ABCB19-mediated auxin import.

Publication Types:

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

PMID: 19508431 [PubMed - in process]

38: Plant Cell Rep. 2009 Aug;28(8):1235-42. Epub 2009 Jun 4.
Related Articles, Links

The cation-efflux transporter BjCET2 mediates zinc and cadmium accumulation in Brassica juncea L. leaves.

Xu J, Chai T, Zhang Y, Lang M, Han L.

College of Life Science, Graduate University of Chinese Academy of Sciences, Yuquan Rd 19, 100049, Beijing, China.

Brassica juncea L. is a Zn/Cd accumulator. To determine the physiological basis of its metal accumulation phenotype, the functional properties and role of the metal efflux transporter BjCET2 were investigated using transgenic technology. Heterologous expression of BjCET2 in the double mutant yeast strain Deltazrc1Deltacot1 enhanced the metal tolerance of the yeast strain and led to decrease in Zn or Cd accumulation. Detection of green fluorescence from green fluorescent protein (GFP) in the root tip of transgenic tobacco further revealed that BjCET2::GFP is localized at the plasma membrane. Semi-quantitative RT-PCR analysis showed that BjCET2 was most abundant in the root and was weakly expressed in the stem and leaves. The expression of BjCET2 was up-regulated by heavy metals. However, exposure to low temperature, salt and drought did not affect the expression of BjCET2. Overexpression of BjCET2 in transgenic B. juncea plants conferred heavy metal tolerance and increased Cd/Zn accumulation in the leaves. BjCET2-deficient B. juncea mediated by antisense RNA resulted in hypersensitivity to heavy metals and decreased Zn/Cd accumulation in the plants. These results suggest that the heavy metal efflux of BjCET2 plays important roles in the metal tolerance of B. juncea and in Zn/Cd accumulation in B. juncea.

Publication Types:

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

PMID: 19495770 [PubMed - indexed for MEDLINE]

39: Biochim Biophys Acta. 2009 Oct;1787(10):1230-7. Epub 2009 May 30.
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Comparison of the electron transport properties of the psbo1 and psbo2 mutants of Arabidopsis thaliana.

Allahverdiyeva Y, Mamedov F, Holmström M, Nurmi M, Lundin B, Styring S, Spetea C, Aro EM.

Department of Biology, Plant Physiology and Molecular Biology, University of Turku, Turku, Finland.

Genome sequence of Arabidopsis thaliana (Arabidopsis) revealed two psbO genes (At5g66570 and At3g50820) which encode two distinct PsbO isoforms: PsbO1 and PsbO2, respectively. To get insights into the function of the PsbO1 and PsbO2 isoforms in Arabidopsis we have performed systematic and comprehensive investigations of the whole photosynthetic electron transfer chain in the T-DNA insertion mutant lines, psbo1 and psbo2. The absence of the PsbO1 isoform and presence of only the PsbO2 isoform in the psbo1 mutant results in (i) malfunction of both the donor and acceptor sides of Photosystem (PS) II and (ii) high sensitivity of PSII centers to photodamage, thus implying the importance of the PsbO1 isoform for proper structure and function of PSII. The presence of only the PsbO2 isoform in the PSII centers has consequences not only to the function of PSII but also to the PSI/PSII ratio in thylakoids. These results in modification of the whole electron transfer chain with higher rate of cyclic electron transfer around PSI, faster induction of NPQ and a larger size of the PQ-pool compared to WT, being in line with apparently increased chlororespiration in the psbo1 mutant plants. The presence of only the PsbO1 isoform in the psbo2 mutant did not induce any significant differences in the performance of PSII under standard growth conditions as compared to WT. Nevertheless, under high light illumination, it seems that the presence of also the PsbO2 isoform becomes favourable for efficient repair of the PSII complex.

Publication Types:

PMID: 19486880 [PubMed - indexed for MEDLINE]

40: Environ Pollut. 2009 Oct;157(10):2781-9. Epub 2009 May 20.
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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.

Publication Types:

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

PMID: 19467746 [PubMed - in process]

41: Plant Cell Environ. 2009 Oct;32(10):1334-45. Epub 2009 May 15.
Related Articles, Links

Membrane water permeability and aquaporin expression increase during growth of maize suspension cultured cells.

Moshelion M, Hachez C, Ye Q, Cavez D, Bajji M, Jung R, Chaumont F.

Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.

Aquaporins (AQPs) are water channels that allow cells to rapidly alter their membrane water permeability. A convenient model for studying AQP expression and activity regulation is Black Mexican Sweet (BMS) maize cultured cells. In an attempt to correlate membrane osmotic water permeability coefficient (P(f)) with AQP gene expression, we first examined the expression pattern of 33 AQP genes using macro-array hybridization. We detected the expression of 18 different isoforms representing the four AQP subfamilies, i.e. eight plasma membrane (PIP), five tonoplast (TIP), three small basic (SIP) and two NOD26-like (NIP) AQPs. While the expression of most of these genes was constant throughout all growth phases, mRNA levels of ZmPIP1;3, ZmPIP2;1, ZmPIP2;2, ZmPIP2;4 and ZmPIP2;6 increased significantly during the logarithmic growth phase and the beginning of the stationary phase. The use of specific anti-ZmPIP antisera showed that the protein expression pattern correlated well with mRNA levels. Cell pressure probe and protoplast swelling measurements were then performed to determine the P(f). Interestingly, we found that the P(f) were significantly increased at the end of the logarithmic growth phase and during the steady-state phase compared to the lag phase, demonstrating a positive correlation between AQP abundance in the plasma membrane and the cell P(f).

Publication Types:

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

PMID: 19453479 [PubMed - indexed for MEDLINE]

42: Oecologia. 2009 Aug;161(1):15-24. Epub 2009 May 16.
Related Articles, Links

The importance of nutritional regulation of plant water flux.

Cramer MD, Hawkins HJ, Verboom GA.

Department of Botany, University of Cape Town, Rondebosch, South Africa. michael.cramer@uct.ac.za

Transpiration is generally considered a wasteful but unavoidable consequence of photosynthesis, occurring because water is lost when stomata open for CO(2) uptake. Additionally, transpiration has been ascribed the functions of cooling leaves, driving root to shoot xylem transport and mass flow of nutrients through the soil to the rhizosphere. As a consequence of the link between nutrient mass flow and transpiration, nutrient availability, particularly that of NO(3)(-), partially regulates plant water flux. Nutrient regulation of transpiration may function through the concerted regulation of: (1) root hydraulic conductance through control of aquaporins by NO(3)(-), (2) shoot stomatal conductance (g(s)) through NO production, and (3) pH and phytohormone regulation of g(s). These mechanisms result in biphasic responses of water flux to NO(3)(-) availability. The consequent trade-off between water and nutrient flux has important implications for understanding plant distributions, for production of water use-efficient crops and for understanding the consequences of global-change-linked CO(2) suppression of transpiration for plant nutrient acquisition.

Publication Types:

PMID: 19449035 [PubMed - indexed for MEDLINE]

43: Plant Mol Biol. 2009 Aug;70(6):647-61. Epub 2009 May 13.
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Hydrogen peroxide effects on root hydraulic properties and plasma membrane aquaporin regulation in Phaseolus vulgaris.

Benabdellah K, Ruiz-Lozano JM, Aroca R.

Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín (CSIC), Profesor Albareda 1, 18008 Granada, Spain.

In the last few years, the role of reactive oxygen species as signaling molecules has emerged, and not only as damage-related roles. Here, we analyzed how root hydraulic properties were modified by different hydrogen peroxide (H2O2) concentrations applied exogenously to the root medium. Two different experimental setups were employed: Phaseolus vulgaris plants growing in hydroponic or in potted soils. In both experimental setups, we found an increase of root hydraulic conductance (L) in response to H2O2 application for the first time. Twenty millimolar was the threshold concentration of H2O2 for observing an effect on L in the soil experiment, while in the hydroponic experiment, a positive effect on L was observed at 0.25 mM H2O2. In the hydroponic experiment, a correlation between increased L and plasma membrane aquaporin amount and their root localization was observed. These findings provide new insights to study how several environmental factors modify L.

Publication Types:

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

PMID: 19437122 [PubMed - indexed for MEDLINE]

44: Plant Mol Biol. 2009 Aug;70(6):663-8. Epub 2009 May 3.
Related Articles, Links

RNA processing in plant mitochondria is independent of transcription.

Hinrichsen I, Bolle N, Paun L, Kempken F.

Abteilung Botanische Genetik und Molekularbiologie, Botanisches Institut und Botanischer Garten, Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, 24098 Kiel, Germany.

We analyzed the ability of plant mitochondria to process introduced RNA. Arabidopsis thaliana cox2 transcripts were synthesized in vitro. The in vitro transcribed mRNA was electroporated into maize and cauliflower mitochondria and incubated in organello. RNA was isolated and RT-PCR was carried out to analyze RNA processing. Our data indicate that cox2 transcripts introduced into isolated plant mitochondria are processed completely. This is the first report of in organello editing of introduced transcripts. We also found that none of the transcription, translation, or respiration inhibitors we used influenced RNA splicing or RNA editing of the cox2 transcript. Thus, our data also demonstrate that plant mitochondrial RNA processing may be independent of both transcription and respiratory regulation.

Publication Types:

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

PMID: 19412686 [PubMed - indexed for MEDLINE]

45: 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]

46: Plant J. 2009 Aug;59(3):437-47. Epub 2009 Apr 2.
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, 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.

Publication Types:

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

PMID: 19366427 [PubMed - indexed for MEDLINE]

47: Biol Trace Elem Res. 2009 Aug;130(2):141-51. Epub 2009 Feb 17.
Related Articles, Links

Physico-chemical property of rare earths-effects on the energy regulation of photosystem II in Arabidopsis thaliana.

Xiaoqing L, Hao H, Chao L, Min Z, Fashui H.

Medical College of Soochow University, Suzhou, People's Republic of China.

Photosystem II (PSII) from Arabidopsis thaliana treated by lanthanum (La(3+)), cerium (Ce(3+)), and neodymium (Nd(3+)) were isolated to investigate the effects of 4f electron characteristics and alternation valence of rare earth elements (REEs) on PSII function regulation comparatively. Results showed that REE treatment could induce the generous expression of LhcII b in A. thaliana and increase the content of light-harvesting complex II and its trimer on the thylakoid membrane significantly. Meanwhile, the light absorption in the red and blue region and fluorescence quantum yield near 683 nm were obviously increased; oxygen evolution rate was greatly improved too, suggesting that REEs could enhance the efficiency of light absorption, regulate excitation energy distribution from photosystem I (PSI) to PSII, and thus increase the activity of photochemical reaction and oxygen evolution accordingly. The efficiency order of the four treatments was Ce(3+) > Nd(3+) > La(3+) > control.

Publication Types:

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

PMID: 19221699 [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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