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Plant Transporter Papers in The Last Three Months

Updated on 6/29/2008

1: Trends Biotechnol. 2008 Jun 23. [Epub ahead of print] Related Articles, Links: Raising the bar for biofortification: enhanced levels of bioavailable calcium in carrots.

Connolly EL.

Department of Biological Sciences, University of South Carolina, 715 Sumter St., Columbia, SC 29208, USA.

Recent efforts to increase the levels of Ca in the edible portions of plants have used a modified calcium/proton antiporter [known as short cation exchanger 1 (sCAX1)] to increase Ca transport into vacuoles. New work has shown that consumption of Ca-fortified carrots results in enhanced Ca absorption. These studies highlight the potential of increasing plant nutrient content through expression of a high-capacity transporter and illustrate the importance of demonstrating that the fortified nutrient is bioavailable.

PMID: 18579243 [PubMed - as supplied by publisher]

2: FEBS Lett. 2008 Jun 17. [Epub ahead of print] Related Articles, Links: Molecular determinants of ammonia and urea conductance in plant aquaporin homologs.

Dynowski M, Mayer M, Moran O, Ludewig U.

Zentrum für Molekularbiologie der Pflanzen (ZMBP), Pflanzenphysiologie, Universität Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany.

Aquaporins and/or aquaglyceroporins regulate the permeability of plant membranes to water and small, uncharged molecules. Using molecular simulations with a plant plasma membrane aquaporin tetramer, the residues in the channel constriction region were identified as the crucial determinants of ammonia and urea conductance. The impact of these residues was experimentally verified using AtPIP2;1 pore mutants. Several, but not all, mutants with a NIP-like selectivity filter promoted yeast growth on urea or ammonia as sole sources of nitrogen. TIP-like mutants conducted urea but not NH(3), and a residue without direct contact to the pore lumen was critical for conduction in the mutants.

PMID: 18565332 [PubMed - as supplied by publisher]

3: Cell Mol Life Sci. 2008 Jun 14. [Epub ahead of print] Related Articles, Links: Functions and transport of silicon in plants.

Ma JF, Yamaji N.

Research Institute for Bioresources, Okayama University, Chuo 2-20-1, Kurashiki, Japan, maj@rib.okayama-u.ac.jp.

Silicon exerts beneficial effects on plant growth and production by alleviating both biotic and abiotic stresses including diseases, pests, lodging, drought, and nutrient imbalance. Recently, two genes (Lsi1 and Lsi2) encoding Si transporters have been identified from rice. Lsi1 (low silicon 1) belongs to a Nod26-like major intrinsic protein subfamily in aquaporin, while Lsi2 encodes a putative anion transporter. Lsi1 is localized on the distal side of both exodermis and endodermis in rice roots, while Lsi2 is localized on the proximal side of the same cells. Lsi1 shows influx transport activity for Si, while Lsi2 shows efflux transport activity. Therefore, Lsi1 is responsible for transport of Si from the external solution to the root cells, whereas Lsi2 is an efflux transporter responsible for the transport of Si from the root cells to the apoplast. Coupling of Lsi1 with Lsi2 is required for efficient uptake of Si in rice.

PMID: 18560761 [PubMed - as supplied by publisher]

4: Plant Cell. 2008 Jun 13. [Epub ahead of print] Related Articles, Links: Channelrhodopsin-1 Initiates Phototaxis and Photophobic Responses in Chlamydomonas by Immediate Light-Induced Depolarization.

Berthold P, Tsunoda SP, Ernst OP, Mages W, Gradmann D, Hegemann P.

Institute for Biology, Experimental Biophysics, Humboldt-Universität, 10115 Berlin, Germany.

Channelrhodopsins (CHR1 and CHR2) are light-gated ion channels acting as sensory photoreceptors in Chlamydomonas reinhardtii. In neuroscience, they are used to trigger action potentials by light in neuronal cells, tissues, or living animals. Here, we demonstrate that Chlamydomonas cells with low CHR2 content exhibit photophobic and phototactic responses that strictly depend on the availability of CHR1. Since CHR1 was described as a H(+)-channel, the ion specificity of CHR1 was reinvestigated in Xenopus laevis oocytes. Our experiments show that, in addition to H(+), CHR1 also conducts Na(+), K(+), and Ca(2+). The kinetic selectivity analysis demonstrates that H(+) selectivity is not due to specific translocation but due to selective ion binding. Purified recombinant CHR1 consists of two isoforms with different absorption maxima, CHR1505 and CHR1463, that are in pH-dependent equilibrium. Thus, CHR1 is a photochromic and protochromic sensory photoreceptor that functions as a light-activated cation channel mediating phototactic and photophobic responses via depolarizing currents in a wide range of ionic conditions.

PMID: 18552201 [PubMed - as supplied by publisher]

5: Proc Natl Acad Sci U S A. 2008 Jun 17;105(24):8476-81. Epub 2008 Jun 9. Related Articles, Links

Abscisic acid regulation of guard-cell K+ and anion channels in Gbeta- and RGS-deficient Arabidopsis lines.

Fan LM, Zhang W, Chen JG, Taylor JP, Jones AM, Assmann SM.

Biology Department, Penn State University, University Park, PA 16802-5301.

In mammals, basal currents through G protein-coupled inwardly rectifying K(+) (GIRK) channels are repressed by Galpha(i/o)GDP, and the channels are activated by direct binding of free Gbetagamma subunits released upon stimulation of Galpha(i/o)-coupled receptors. However, essentially all information on G protein regulation of GIRK electrophysiology has been gained on the basis of coexpression studies in heterologous systems. A major advantage of the model organism, Arabidopsis thaliana, is the ease with which knockout mutants can be obtained. We evaluated plants harboring mutations in the sole Arabidopsis Galpha (AtGPA1), Gbeta (AGB1), and Regulator of G protein Signaling (AtRGS1) genes for impacts on ion channel regulation. In guard cells, where K(+) fluxes are integral to cellular regulation of stomatal apertures, inhibition of inward K(+) (K(in)) currents and stomatal opening by the phytohormone abscisic acid (ABA) was equally impaired in Atgpa1 and agb1 single mutants and the Atgpa1 agb1 double mutant. AGB1 overexpressing lines maintained a wild-type phenotype. The Atrgs1 mutation did not affect K(in) current magnitude or ABA sensitivity, but K(in) voltage-activation kinetics were altered. Thus, Arabidopsis cells differ from mammalian cells in that they uniquely use the Galpha subunit or regulation of the heterotrimer to mediate K(in) channel modulation after ligand perception. In contrast, outwardly rectifying (K(out)) currents were unaltered in the mutants, and ABA activation of slow anion currents was conditionally disrupted in conjunction with cytosolic pH clamp. Our studies highlight unique aspects of ion channel regulation by heterotrimeric G proteins and relate these aspects to stomatal aperture control, a key determinant of plant biomass acquisition and drought tolerance.

Publication Types:

PMID: 18541915 [PubMed - in process]

6: CNS Neurol Disord Drug Targets. 2008 Apr;7(2):159-71. Related Articles, Links

Transient receptor potential vanilloid 1 and xenobiotics.

Cuypers E, Dabrowski M, Horoszok L, Terp GE, Tytgat J.

Lab of Toxicology, Campus Gasthuisberg, O&N2, Herestraat 49, Leuven, Belgium. eva.cuypers@pharm.kuleuven.be

Over the last couple of years, transient receptor potential vanilloid 1(TRPV1) channels have been a hot topic in ion channel research. Since this research field is still rather new, there is not much known about the working mechanism of TRPV1 and its ligands. Nevertheless, the important physiological role and therapeutic potential are promising. Therefore, extensive research is going on and a lot of natural as well as synthetic compounds are already described. In this review, we briefly give an overview of capsaicin's history and the current knowledge of its working mechanism and physiological role. We discuss the best known plant molecules acting on TRPV1 and highlight the latest discovery in TRPV1 research: animal venoms and toxins acting on TRPV1 channels. In an effort to give the complete image of TRPV1 ligands known today, the most promising synthetic compounds are presented. Finally, we present a novel pharmacophore model describing putative ligand binding domains.

Publication Types:

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

PMID: 18537644 [PubMed - in process]

7: Mycol Res. 2008 Jun;112(Pt 6):737-46. Epub 2008 Feb 3. Related Articles, Links: Cloning and functional characterization of BcatrA, a gene encoding an ABC transporter of the plant pathogenic fungus Botryotinia fuckeliana (Botrytis cinerea).

Del Sorbo G, Ruocco M, Schoonbeek HJ, Scala F, Pane C, Vinale F, De Waard MA.

Department Ar.Bo.Pa.Ve. - Section of Plant Pathology, University of Naples "Federico II", Via Università 100, 80055 Portici (Naples), Italy.

BcatrA was cloned from the plant pathogenic fungus Botryotinia fuckeliana (Botrytis cinerea) and sequenced. Sequence analysis revealed that BcatrA encodes a protein composed of 1562 amino acid residues displaying high similarity with various fungal ATP-binding cassette (ABC) transporters having the (NBF-TM(6))(2) topology. Expression of BcatrA is barely detectable during normal vegetative growth in liquid substrates. Transcript levels of BcatrA are enhanced in a dose- and time-dependent manner after treatment with cycloheximide or catechol, but not by a number of other drugs or fungicides, including fludioxonil, fenarimol, imazalil, and the plant defense compounds pisatin and resveratrol. Quantitative analysis of BcatrA during the synchronized infection of bean leaves revealed an overaccumulation of the gene transcript at 6, 12 and 24h post-inoculation, suggesting an involvement of the gene in the first steps of pathogenesis. Functional analysis of BcatrA was performed by targeted gene replacement in a wild-type strain of the fungus, and by overexpression in a mutant of Saccharomyces cerevisiae carrying multiple non-functional multidrug-resistance genes. BcatrA replacement mutants did not show any significant increase in sensitivity to drugs, including inducers of BcatrA transcription, and displayed an unaltered virulence on several common host plants of B. cinerea. However, when expressed in the heterologous system, BcatrA reduced sensitivity to cycloheximide and catechol, thus indicating the ability of the BcatrA product to function as a multidrug transporter.

PMID: 18515055 [PubMed - in process]

8: Plant Cell Physiol. 2008 May 29. [Epub ahead of print] Related Articles, Links: Plant Inner Membrane Anion Channel (PIMAC) function in plant mitochondria.

Laus MN, Soccio M, Trono D, Cattivelli L, Pastore D.

Dipartimento di Scienze Agro-ambientali, Chimica e Difesa Vegetale, Facoltà di Agraria, Università degli Studi di Foggia, Via Napoli, 25 - 71100 Foggia, Italy.

To date, the existence of the Plant Inner Membrane Anion Channel (PIMAC) has been shown only in potato mitochondria, but its physiological role remains unclear. In this paper, by means of swelling experiments in K(+) and ammonium salts, we characterize a PIMAC-like anion-conducting pathway in mitochondria from durum wheat (DWM), a monocotyledonous species phylogenetically far from potato. DWM were investigated since they possess a very active potassium channel (PmitoK(ATP)), so implying a well active matching anion uniport pathway and, possibly, a coordinated function. As in potato mitochondria, the electrophoretic uptake of chloride and succinate resulted inhibited by matrix [H(+)], propranolol, tributyltin, and insensitive to Mg(2+), N,N'-dicyclohexylcarbodiimide (DCCD) and mercurials, thus showing PIMAC existence in DWM. PIMAC actively transports dicarboxylates, oxodicarboxylates, tricarboxylates and Pi. Interestingly, a novel mechanism of swelling in ammonium salts of isolated plant mitochondria is reported, based on electrophoretic anion uptake via PIMAC and ammonium uniport via PmitoK(ATP). PIMAC is inhibited by physiological compounds, such as ATP and free fatty acids, by high electrical membrane potential (triangle upPsi), but not by acyl-CoAs or reactive oxygen species. PIMAC was found to cooperate with dicarboxylate carrier by allowing succinate uptake that triggers succinate/malate exchange in isolated DWM. Similar results were obtained using mitochondria from the dicotyledonous species topinambur, so suggesting generalization of results. We propose that PIMAC is normally inactive in vivo due to ATP and triangle upPsi inhibition, but activation may occur in mitochondria de-energized by PmitoK(ATP) (or other dissipative systems) to replace or integrate the operation of classical anion carriers.

PMID: 18511459 [PubMed - as supplied by publisher]

9: Plant J. 2008 May 20. [Epub ahead of print] Related Articles, Links: Increasing amino acid supply in pea embryos reveals specific interactions of N and C metabolism and highlights the importance of mitochondrial metabolism.

Weigelt K, Küster H, Radchuk R, Müller M, Weichert H, Fait A, Fernie AR, Saalbach I, Weber H.

Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), D-06466 Gatersleben, Germany.

Nitrogen application to legumes regulates seed metabolism and composition. We recently showed that seed-specific overexpression of amino acid permease VfAAP1, increases amino acid supply, seed N and protein. Two consecutive field trials using Pisum sativum-AAP1-lines confirmed increases in seed N and globulin content, however, compensatory changes of sucrose/starch and individual seed weight were observed. We present a comprehensive analysis of AAP1-seeds using combinatorial transcript and metabolite profiling to monitor effects of nitrogen supply on seed metabolism. AAP1-seeds have increased amino acids and stimulated gene expression associated to storage protein synthesis, maturation, deposition and vesicle trafficking. Transcript/metabolite changes reveal channelling of surplus N into transient storage pools asparagine and arginine, indicating that asparagine-synthase is transcriptionally activated by high N status and/or C limitation. Increased C-acceptor demand for amino acid synthesis due to elevated seed N initiates sucrose mobilisation and sucrose dependent pathways via sucrose synthase, glycolysis and the TCA-cycle. AAP1-seeds display C-limitation, leading to catabolism of arginine, glutamic acid and methionine to putrescine, beta-alanine and succinate. Mitochondria are involved in the coordination of C/N metabolism with branched-chain amino acid catabolism and gamma-amino-butyric acid-shunt. AAP1-seeds contain higher abscisic acid, possibly involved in storage-associated gene expression and N-dependent stimulation of sucrose mobilisation indicating a signalling network of C, N and ABA operating during seed maturation. These results demonstrate that legume seeds have high capacity to regulate N to C ratios and highlight the importance of mitochondria in the control of N to C balance and amino acid homeostasis.

PMID: 18494854 [PubMed - as supplied by publisher]

10: Biochem Biophys Res Commun. 2008 Jul 11;371(4):883-8. Epub 2008 May 9.
Related Articles, Links

Proteomic analysis of phosphoproteins regulated by abscisic acid in rice leaves.

He H, Li J.

Department of Biochemistry and Molecular Biology, Mississippi State University, 32 Creelman Street, Mississippi State, MS 39762, USA.

Abscisic acid (ABA) is a hormone that regulates plant development and adaptation to environmental stresses. Protein phosphorylation has been recognized as an important mechanism for ABA signaling. However, the target phosphoproteins regulated by ABA are still largely unknown. Here, we report the identification of ABA-regulated phosphoproteins in rice using proteomic approaches. Six ABA-regulated phosphoproteins were identified as G protein beta subunit-like protein, ascorbate peroxidase, manganese superoxide dismutase, triosephosphate isomerase, putative Ca(2+)/H(+) antiporter regulator protein, and glyoxysomal malate dehydrogenase. These results provide new insight into the regulatory mechanism for some ABA signaling proteins and implicate several previously unrecognized proteins in ABA action.

Publication Types:

PMID: 18468508 [PubMed - indexed for MEDLINE]

11: Int J Biol Sci. 2008 Apr 26;4(2):116-25.
Related Articles, Links

Relationship between calcium decoding elements and plant abiotic-stress resistance.

Song WY, Zhang ZB, Shao HB, Guo XL, Cao HX, Zhao HB, Fu ZY, Hu XJ.

Center for Agricultural Resources Research, Institute of Genetic &Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, 050021, China.

Serving as an important second messenger, calcium ion has unique properties and universal ability to transmit diverse signals that trigger primary physiological actions in cells in response to hormones, pathogens, light, gravity, and stress factors. Being a second messenger of paramount significance, calcium is required at almost all stages of plant growth and development, playing a fundamental role in regulating polar growth of cells and tissues and participating in plant adaptation to various stress factors. Many researches showed that calcium signals decoding elements are involved in ABA-induced stomatal closure and plant adaptation to drought, cold, salt and other abiotic stresses. Calcium channel proteins like AtTPC1 and TaTPC1 can regulate stomatal closure. Recently some new studies show that Ca(2+) is dissolved in water in the apoplast and transported primarily from root to shoot through the transpiration stream. The oscillating amplitudes of [Ca(2+)](o) and [Ca(2+)](i) are controlled by soil Ca(2+) concentrations and transpiration rates. Because leaf water use efficiency (WUE) is determined by stomatal closure and transpiration rate, so there may be a close relationship between Ca(2+) transporters and stomatal closure as well as WUE, which needs to be studied. The selection of varieties with better drought resistance and high WUE plays an increasing role in bio-watersaving in arid and semi-arid areas on the globe. The current paper reviews the relationship between calcium signals decoding elements and plant drought resistance as well as other abiotic stresses for further study.

Publication Types:

PMID: 18463716 [PubMed - indexed for MEDLINE]

PMCID: PMC2359902

12: Biochem J. 2008 May 8. [Epub ahead of print]
Related Articles, Links: Plant plasma membrane water channels conduct the signaling molecule H2O2.

Dynowski M, Schaaf G, Loque D, Moran O, Ludewig U.

Hydrogen peroxide (H2O2) is a relatively long-lived reactive oxygen species that signals between cells and organisms. H2O2 signaling in plants is essential for response to stress, defense against pathogens, and the regulation of programmed cell death. Although H2O2 diffusion across membranes is often considered as a passive property of lipid bilayers, native membranes represent significant barriers for hydrogen peroxide. We addressed the question of whether channels might facilitate H2O2 transport across plasma membranes. The expression of several plant plasma membrane aquaporins in yeast, including PIP2;1 from Arabidopsis, enhanced the toxicity of H2O2 and increased the fluorescence of dye-loaded yeast when exposed to H2O2. The sensitivity of aquaporin-expressing yeast to hydrogen peroxide was altered by mutations that alter gating and the selectivity of the aquaporins. The transport of water, H2O2 and urea was compared, using molecular dynamics simulations based on the crystal structure of SoPIP2;1 from spinach. The calculations identify differences in the conduction between the substrates and reveal channel residues critically involved in H2O2 conduction. The results of the calculations on tetramers and monomers are in agreement with the biochemical data. Taken together, the data strongly postulate that plasma membrane aquaporin pores determine the efficiency of H2O2-signaling between cells. Aquaporins are present in most species and their capacity to facilitate the diffusion of H2O2 may be of physiological significance in many organisms and particularly in communication between different species.

PMID: 18462192 [PubMed - as supplied by publisher]

13: IUBMB Life. 2008 May 5. [Epub ahead of print]
Related Articles, Links: Novel families of vacuolar amino acid transporters.

Sekito T, Fujiki Y, Ohsumi Y, Kakinuma Y.

Department of Applied Bioscience, Faculty of Agriculture, Tarumi 3‐5‐7, Ehime University, Matsuyama, Ehime, Japan.

Amino acids are compartmentalized in the vacuoles of microorganisms and plants. In Saccharomyces cerevisiae, basic amino acids accumulate preferentially into vacuoles but acidic amino acids are almost excluded from them. This indicates that selective machineries operate at the vacuolar membrane. The members of the amino acid/auxin permease family and the major facilitator superfamily involved in the vacuolar compartmentalization of amino acids have been recently identified in studies using S. cerevisiae. Homologous genes for these transporters are also found in plant and mammalian genomes. The physiological significance in response to nitrogen starvation can now be discussed. (c) 2008 IUBMB IUBMB Life, 2008.

PMID: 18459165 [PubMed - as supplied by publisher]

14: Eukaryot Cell. 2008 May 2. [Epub ahead of print]
Related Articles, Links: Functional characterization of cgCTR2, a putative vacuole copper transporter that is involved in germination and pathogenicity in Colletotrichum gloeosporioides.

Barhoom S, Kupiec M, Zhao X, Xu JR, Sharon A.

Department of Plant Sciences, Tel Aviv University, Tel Aviv 69978, Israel; Department of Microbiology and Biotechnology, Tel Aviv University, Tel Aviv 69978, Israel; Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907.

Copper is a cofactor and transition metal involved in redox reactions that are essential in all eukaryotes. Here we report that a vacuolar copper transporter that is highly expressed in resting spores is involved in germination and pathogenicity in the plant pathogen Colletotrichum gloeosporioides. A screen of C. gloeosporioides transformants obtained by transforming with a promoter-less GFP construct led to the identification of transformant N159 in which GFP signal was observed in spores. The transforming vector was inserted 70 bp upstream of a putative gene with homology to the Saccharomyces cerevisiae vacuolar copper transporter gene CTR2. The CgCTR2 gene fully complemented growth defects of yeast ctr2Delta mutants, and a CgCTR2-CFP fusion protein localized in vacuole membranes confirming the function of the protein as a vacuolar copper transporter. Expression analysis indicated that CgCTR2 transcript is abundant in resting conidia and during germination in rich medium and down-regulated during "pathogenic" germination and early stages of plant infection. CgCTR2 overexpression and silencing mutants were generated and characterized. The cgctr-2 mutants had markedly reduced Cu SOD activity, suggesting that CgCTR-2 is important in providing cupper to copper-dependent cytosolic activities. The cgctr2 silenced mutants had increased sensitivity to H2O2 and reduced germination rates. The mutants were also less virulent to plants, but they did not display any defects in appressoria formation and penetration efficiency. External copper supply compensated for the hypersensitivity to H2O2 but not for the germination and pathogenicity defects of the mutants. Similarly, overexpression of CgCTR2 enhanced resistance to H2O2 but had no effect on germination or pathogenicity. The vacuolar copper transporter CgCTR2 is probably involved in this process, possibly by exporting copper from the vacuole to the cytoplasm, thereby providing the copper to cytosolic enzymes such as SOD.

PMID: 18456860 [PubMed - as supplied by publisher]

15: Nat Cell Biol. 2008 May;10(5):509-11.
Related Articles, Links

Coming closer to a stoma ion channel.

Serna L.

Publication Types:

News

PMID: 18454130 [PubMed - indexed for MEDLINE]

16: Plant J. 2008 Apr 30. [Epub ahead of print]
Related Articles, Links: Silencing of NtMPK4 impairs CO(2)-induced stomatal closure, activation of anion channels and cytosolic Ca(2+)-signals in Nicotiana tabacum guard cells.

Marten H, Hyun T, Gomi K, Seo S, Hedrich R, Roelfsema MR.

Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Biosciences, Biocenter, Würzburg University, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany.

Light-induced stomatal opening in C3- and C4-plants is mediated by two signalling pathways. One pathway is specific for blue light and involves phototropins, while the second pathway depends on Photosynthetic Active Radiation (PAR). Here, the role of NtMPK4 on light-induced stomatal opening was studied, since silencing of this MAP kinase stimulates stomatal opening. Stomata of NtMPK4-silenced plants do not close in elevated atmospheric CO(2) and show a reduced response to PAR. However, stomatal closure can still be induced by ABA. Measurements with multi-barrelled intracellular micro electrodes showed that CO(2) activates plasma membrane anion channels in wild type Nicotiana tabacum guard cells, but not in NtMPK4-silenced cells. Anion channels also were activated after switching off PAR in wild type guard cells. In approximately half of these cells, the activation of anion channels was accompanied by a rise of the cytosolic free Ca(2+) concentration. The activity of anion channels was higher in cells displaying a parallel rise in cytosolic Ca(2+), than in those with steady Ca(2+) levels. Both the darkness-induced anion channel activation and Ca(2+)-signals were repressed in NtMPK4-silenced guard cells. These data show that CO(2) and darkness can activate anion channels in a Ca(2+)-independent manner, but the anion channel activity is enhanced by parallel rises of the cytosolic Ca(2+) concentration. NtMPK4 plays an essential role in CO(2)- and darkness-induced activation of guard cell anion channels, through Ca(2+)-independent as well as Ca(2+)-dependent signalling pathways.

PMID: 18452588 [PubMed - as supplied by publisher]

17: PLoS ONE. 2008 Apr 30;3(4):e2033.
Related Articles, Links

In silico and biochemical analysis of Physcomitrella patens photosynthetic antenna: identification of subunits which evolved upon land adaptation.

Alboresi A, Caffarri S, Nogue F, Bassi R, Morosinotto T.

Laboratoire de Génétique et Biophysique des Plantes-UMR 6191 CEA-CNRS-Université de la Méditerranée, Marseille, France.

BACKGROUND: In eukaryotes the photosynthetic antenna system is composed of subunits encoded by the light harvesting complex (Lhc) multigene family. These proteins play a key role in photosynthesis and are involved in both light harvesting and photoprotection. The moss Physcomitrella patens is a member of a lineage that diverged from seed plants early after land colonization and therefore by studying this organism, we may gain insight into adaptations to the aerial environment. PRINCIPAL FINDINGS: In this study, we characterized the antenna protein multigene family in Physcomitrella patens, by sequence analysis as well as biochemical and functional investigations. Sequence identification and analysis showed that some antenna polypeptides, such as Lhcb3 and Lhcb6, are present only in land organisms, suggesting they play a role in adaptation to the sub-aerial environment. Our functional analysis which showed that photo-protective mechanisms in Physcomitrella patens are very similar to those in seed plants fits with this hypothesis. In particular, Physcomitrella patens also activates Non Photochemical Quenching upon illumination, consistent with the detection of an ortholog of the PsbS protein. As a further adaptation to terrestrial conditions, the content of Photosystem I low energy absorbing chlorophylls also increased, as demonstrated by differences in Lhca3 and Lhca4 polypeptide sequences, in vitro reconstitution experiments and low temperature fluorescence spectra. CONCLUSIONS: This study highlights the role of Lhc family members in environmental adaptation and allowed proteins associated with mechanisms of stress resistance to be identified within this large family.

Publication Types:

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

PMID: 18446222 [PubMed - indexed for MEDLINE]

PMCID: PMC2323573

18: BMC Plant Biol. 2008 Apr 28;8:49.
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The SNF1-type serine-threonine protein kinase SAPK4 regulates stress-responsive gene expression in rice.

Diédhiou CJ, Popova OV, Dietz KJ, Golldack D.

Department of Physiology and Biochemistry of Plants, Faculty of Biology, University of Bielefeld, 33615 Bielefeld, Germany. calliste.diedhiou@uni-bielefeld.de

BACKGROUND: Plants respond to extracellularly perceived abiotic stresses such as low temperature, drought, and salinity by activation of complex intracellular signaling cascades that regulate acclimatory biochemical and physiological changes. Protein kinases are major signal transduction factors that have a central role in mediating acclimation to environmental changes in eukaryotic organisms. In this study, we characterized the function of the sucrose nonfermenting 1-related protein kinase2 (SnRK2) SAPK4 in the salt stress response of rice. RESULTS: Translational fusion of SAPK4 with the green fluorescent protein (GFP) showed subcellular localization in cytoplasm and nucleus. To examine the role of SAPK4 in salt tolerance we generated transgenic rice plants with over-expression of rice SAPK4 under control of the CaMV-35S promoter. Induced expression of SAPK4 resulted in improved germination, growth and development under salt stress both in seedlings and mature plants. In response to salt stress, the SAPK4-overexpressing rice accumulated less Na+ and Cl- and showed improved photosynthesis. SAPK4-regulated genes with functions in ion homeostasis and oxidative stress response were identified: the vacuolar H+-ATPase, the Na+/H+ antiporter NHX1, the Cl- channel OsCLC1 and a catalase. CONCLUSION: Our results show that SAPK4 regulates ion homeostasis and growth and development under salinity and suggest function of SAPK4 as a regulatory factor in plant salt stress acclimation. Identification of signaling elements involved in stress adaptation in plants presents a powerful approach to identify transcriptional activators of adaptive mechanisms to environmental changes that have the potential to improve tolerance in crop plants.

Publication Types:

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

PMID: 18442365 [PubMed - in process]

PMCID: PMC2386468

19: Plant Cell. 2008 Apr;20(4):1073-87. Epub 2008 Apr 25.
Related Articles, Links

Functional and physiological characterization of Arabidopsis INOSITOL TRANSPORTER1, a novel tonoplast-localized transporter for myo-inositol.

Schneider S, Beyhl D, Hedrich R, Sauer N.

Molekulare Pflanzenphysiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany.

Arabidopsis thaliana INOSITOL TRANSPORTER1 (INT1) is a member of a small gene family with only three more genes (INT2 to INT4). INT2 and INT4 were shown to encode plasma membrane-localized transporters for different inositol epimers, and INT3 was characterized as a pseudogene. Here, we present the functional and physiological characterization of the INT1 protein, analyses of the tissue-specific expression of the INT1 gene, and analyses of phenotypic differences observed between wild-type plants and mutant lines carrying the int1.1 and int1.2 alleles. INT1 is a ubiquitously expressed gene, and Arabidopsis lines with T-DNA insertions in INT1 showed increased intracellular myo-inositol concentrations and reduced root growth. In Arabidopsis, tobacco (Nicotiana tabacum), and Saccharomyces cerevisiae, fusions of the green fluorescent protein to the C terminus of INT1 were targeted to the tonoplast membranes. Finally, patch-clamp analyses were performed on vacuoles from wild-type plants and from both int1 mutant lines to study the transport properties of INT1 at the tonoplast. In summary, the presented molecular, physiological, and functional studies demonstrate that INT1 is a tonoplast-localized H(+)/inositol symporter that mediates the efflux of inositol that is generated during the degradation of inositol-containing compounds in the vacuolar lumen.

Publication Types:

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

PMID: 18441213 [PubMed - in process]

PMCID: PMC2390729 [Available on 04/01/09]

20: New Phytol. 2008 Apr 22. [Epub ahead of print]
Related Articles, Links: Overexpression of the tomato K(+)/H(+) antiporter LeNHX2 confers salt tolerance by improving potassium compartmentalization.

Rodríguez-Rosales MP, Jiang X, Gálvez FJ, Aranda MN, Cubero B, Venema K.

Department of Biochemistry and Molecular and Cell Biology of Plants, Estación Experimental del Zaidín, CSIC, 18008 Granada, Spain.

* Here, the function of the tomato (Solanum lycopersicon) K(+)/H(+) antiporter LeNHX2 was studied using 35S-driven gene overexpression of a histagged LeNHX2 protein in Arabidopsis thaliana and LeNHX2 gene silencing in tomato. * Transgenic A. thaliana plants expressed the histagged LeNHX2 both in shoots and in roots, as assayed by western blotting. Transitory expression of a green fluorescent protein (GFP) tagged protein showed that the antiporter is present in small vesicles. Internal membrane vesicles from transgenic plants displayed enhanced K(+)/H(+) exchange activity, confirming the K(+)/H(+) antiporter function of this enzyme. Transgenic A. thaliana plants overexpressing the histagged tomato antiporter LeNHX2 exhibited inhibited growth in the absence of K(+) in the growth medium, but were more tolerant to high concentrations of Na(+) than untransformed controls. When grown in the presence of NaCl, transgenic plants contained lower concentrations of intracellular Na(+), but more K(+), as compared with untransformed controls. * Silencing of LeNHX2 in S. lycopersicon plants produced significant inhibition of plant growth and fruit and seed production as well as increased sensitivity to NaCl. * The data indicate that regulation of K(+) homeostasis by LeNHX2 is essential for normal plant growth and development, and plays an important role in the response to salt stress by improving K(+) accumulation.

PMID: 18433429 [PubMed - as supplied by publisher]

21: Mol Membr Biol. 2008 Apr;25(3):179-91.
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Advances in functional regulation mechanisms of plant aquaporins: their diversity, gene expression, localization, structure and roles in plant soil-water relations (Review).

Shao HB, Chu LY, Shao MA, Zhao CX.

Institute of Soil and Water Conservation, Chinese Academy of Sciences, Northwest A&F University, Yangling, China. shaohongbo@qust.edu.cn

Aquaporins are important molecules that control the moisture level of cells and water flow in plants. Plant aquaporins are present in various tissues, and play roles in water transport, cell differentiation and cell enlargement involved in plant growth and water relations. The insights into aquaporins' diversity, structure, expression, post-translational modification, permeability properties, subcellular location, etc., from considerable studies, can lead to an understanding of basic features of the water transport mechanism and increased illumination into plant water relations. Recent important advances in determining the structure and activity of different aquaporins give further details on the mechanism of functional regulation. Therefore, the current paper mainly focuses on aquaporin structure-function relationships, in order to understand the function and regulation of aquaporins at the cellular level and in the whole plant subjected to various environmental conditions. As a result, the straightforward view is that most aquaporins in plants are to regulate water flow mainly at cellular scale, which is the most widespread general interpretation of the physiological and functional assays in plants.

Publication Types:

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

PMID: 18428034 [PubMed - in process]

22: Plant J. 2008 Apr 4. [Epub ahead of print]
Related Articles, Links: Cytokinins Negatively Regulate the Root Iron Uptake Machinery in Arabidopsis through a growth-dependent pathway.

Séguéla M, Briat JF, Vert G, Curie C.

Biochimie et Physiologie Moléculaire des Plantes UMR 5004 CNRS/INRA/UM2/SupAgro, Institut de Biologie Intégrative des Plantes, 2 Place Viala 34060 Montpellier CEDEX 1 France.

Plants display a number of biochemical and developmental responses to low iron availability to increase iron uptake from the soil. The ferric-chelate reductase FRO2 and the ferrous iron transporter IRT1 control iron entry from the soil into root epidermis. In Arabidopsis, expression of IRT1 and FRO2 is tightly controlled to maintain iron homeostasis and involves local and long-distance signals, as well as transcriptional and post-transcriptional events. FIT encodes a putative bHLH transcription factor that regulates iron uptake responses in Arabidopsis. Here we uncover a new regulation of the root iron uptake genes. We show that IRT1, FRO2 and FIT are repressed by exogenous addition of cytokinins (CKs), and that this repression acts at the level of transcript accumulation and depends on the AHK3 and CRE1 CK receptors. The CKs and iron-deficiency signals act through distinct pathways to regulate the soil iron uptake genes since (i) CK repression is independent of the iron status, (ii) IRT1 and FRO2 down-regulation is unchanged in a fit loss-of-function mutant, indicating that FIT does not mediate CK repression, and (iii) the iron-regulated genes AtNRAMP3 and AtNRAMP4 are not down-regulated by CKs. We show that root growth-inhibitory conditions such as abiotic stresses (mannitol, NaCl) and hormonal treatments (auxin, abscissic acid) repress the iron starvation response genes. We propose that CKs control the root iron uptake machinery through a root growth dependent pathway in order to adapt nutrient uptake to the plant demand.

PMID: 18397377 [PubMed - as supplied by publisher]

23: J Exp Bot. 2008;59(6):1375-81. Epub 2008 Apr 4.
Related Articles, Links

Expression of the nuclear gene TaF(A)d is under mitochondrial retrograde regulation in anthers of male sterile wheat plants with timopheevii cytoplasm.

Xu P, Yang Y, Zhang Z, Chen W, Zhang C, Zhang L, Zou S, Ma Z.

The Applied Plant Genomics Laboratory, Crop Genomics and Bioinformatics Center & National Key Lab of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Jiangsu 210095, China.

Alterations of mitochondrial-encoded subunits of the F(o)F(1)-ATP synthase are frequently associated with cytoplasmic male sterility (CMS) in plants; however, little is known about the relationship of the nuclear encoded subunits of this enzyme with CMS. In the present study, the full cDNA of the gene TaF(A)d that encodes the putative F(A)d subunit of the F(o)F(1)-ATP synthase was isolated from the wheat (Triticum aestivum) fertility restorer '2114' for timopheevii cytoplasm-based CMS. The deduced 238 amino acid polypeptide is highly similar to its counterparts in dicots and other monocots but has low homology to its mammalian equivalents. TaF(A)d is a single copy gene in wheat and maps to the short arm of the group 6 chromosomes. Transient expression of the TaF(A)d-GFP fusion in onion epidermal cells demonstrated TaF(A)d's mitochondrial location. TaF(A)d was expressed abundantly in stem, leaf, anther, and ovary tissues of 2114. Nevertheless, its expression was repressed in anthers of CMS plants with timopheevii cytoplasm. Genic male sterility did not affect its expression in anthers. The expression of the nuclear gene encoding the 20 kDa subunit of F(o) was down-regulated in a manner similar to TaF(A)d in the T-CMS anthers while that of genes encoding the 6 kDa subunit of F(o) and the gamma subunit of F(1) was unaffected. These observations implied that TaF(A)d is under mitochondrial retrograde regulation in the anthers of CMS plants with timopheevii cytoplasm.

Publication Types:

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

PMID: 18390847 [PubMed - indexed for MEDLINE]

24: Photochem Photobiol Sci. 2008 Apr;7(4):498-502. Epub 2008 Feb 15.
Related Articles, Links

Chlorophyll fluorescence emission spectrum inside a leaf.

Pedrós R, Moya I, Goulas Y, Jacquemoud S.

Solar Radiation Group, Department of Earth Physics and Thermodynamics, University of Valencia, Spain.

Chlorophyll a fluorescence can be used as an early stress indicator. Fluorescence is also connected to photosynthesis so it can be proposed for global monitoring of vegetation status from a satellite platform. Nevertheless, the correct interpretation of fluorescence requires accurate physical models. The spectral shape of the leaf fluorescence free of any re-absorption effect plays a key role in the models and is difficult to measure. We present a vegetation fluorescence emission spectrum free of re-absorption based on a combination of measurements and modelling. The suggested spectrum takes into account the photosystem I and II spectra and their relative contribution to fluorescence. This emission spectrum is applicable to describe vegetation fluorescence in biospectroscopy and remote sensing.

Publication Types:

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

PMID: 18385895 [PubMed - indexed for MEDLINE]

25: Photochem Photobiol Sci. 2008 Apr;7(4):485-91. Epub 2008 Feb 19.
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Heat-induced changes in photosystem I activity as measured with different electron donors in isolated spinach thylakoid membranes.

Tiwari A, Jajoo A, Bharti S.

School of Life Sciences, Life Science Annexe Building, Devi Ahilya University, Khandwa Road, Indore 452017, MP, India.

Heat-induced changes in photosystem I (PSI) have been studied in terms of rates of oxygen consumption using various donors (DCPIPH2, TMPDred and DADred), formation of photo-oxidized P700 and changes in Chl a fluorescence emission at 77 K. Linear heating of thylakoid membranes from 35 degrees C to 70 degrees C caused an enhancement in PSI-mediated electron transfer rates (DCPIPH2-->MV) up to 55 degrees C. However, no change was observed in PSI rates when other electron donors were used (TMPDred and DADred). Similarly, Chl a fluorescence emission spectra at 77 K of heat-treated thylakoid membranes did not show any increase in peak at 735 nm, however, a significant decrease was observed as a function of temperature in the peaks at 685 and 694 nm. In DCMU-treated control thylakoid membranes maximum photo-oxidized P700 was generated at g = 2.0025. In heat-treated thylakoid membranes maximum intensity of photo-oxidized P700 signal was observed at approximately 50-55 degrees C without DCMU treatment. The steady-state signal of the photo-oxidized P700 was studied in the presence of DCPIPH2 and TMPDred as electron donors in DCMU-treated control and in 50 degrees C treated thylakoid membranes. We present here the first of such comparative study of PSI activity in terms of the rates of oxygen consumption and re-reduction kinetics of photo-oxidized P700 in the presence of different electron donors. It appears that the formation of the P700+ signal in heat-treated thylakoid membranes is due to an inhibited electron supply from PSII and not due to spillover or antenna migration.

Publication Types:

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

PMID: 18385893 [PubMed - indexed for MEDLINE]

26: Plant Cell Physiol. 2008 May;49(5):801-13. Epub 2008 Apr 1.
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Drought stress alters water relations and expression of PIP-type aquaporin genes in Nicotiana tabacum plants.

Mahdieh M, Mostajeran A, Horie T, Katsuhara M.

Department of Biology, The University of Isfahan, Isfahan, 81746-73441, Iran.

Plasma membrane intrinsic proteins (PIPs), a type of aquaporins, mediate water transport in many plant species. In this study, we investigated the relationship between the functions of PIP-type water channels and water relations of tobacco plants (Nicotiana tabacum cv. Samsun) under drought stress. Drought stress treatments have led to reductions in the stomatal conductance, transpiration, water potential and turgor pressure in leaves, and also the sap flow rate and osmotic hydraulic conductance in roots. In contrast, leaf osmotic pressure was increased in response to drought stress. Interestingly, the accumulation of NtPIP1;1 and NtPIP2;1 transcripts was significantly decreased, but only that of the NtAQP1 transcript was increased under drought stress. Functional analysis using Xenopus laevis oocytes revealed that NtPIP2;1 shows marked water transport activity, but the activities of NtAQP1 and NtPIP1;1 are weak or almost negligible, respectively, when expressed alone. However, co-expression of NtPIP1;1 with NtPIP2;1 significantly enhanced water transport activity compared with that of NtPIP1;1- or NtPIP2;1-expressing oocytes, suggesting that these two aquaporins may function as a water channel, forming a heterotetramer. Heteromerization of NtPIP1;1 and NtPIP2;1 was also suggested by co-expression analyses of NtPIP1;1-GFP (green fluorescent protein) and NtPIP2;1 in Xenopus oocytes. Re-watering treatments recovered water relation parameters and the accumulation of the three NtPIP transcripts to levels similar to control conditions. These results suggest that NtPIP1;1 and NtPIP2;1 play an important role in water transport in roots, and that expression of NtPIP1;1 and NtPIP2;1 is down-regulated in order to reduce osmotic hydraulic conductance in the roots of tobacco plants under drought stress.

Publication Types:

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

PMID: 18385163 [PubMed - in process]

27: FEMS Microbiol Lett. 2008 May;282(2):174-81. Epub 2008 Mar 26.
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Inhibitory effects of 7-epiclusianone on glucan synthesis, acidogenicity and biofilm formation by Streptococcus mutans.

Murata RM, Branco de Almeida LS, Yatsuda R, Dos Santos MH, Nagem TJ, Rosalen PL, Koo H.

Department of Physiological Sciences, State University of Campinas, SP, Brazil.

The aim of this study was to examine the effects of 7-epiclusianone, a new prenylated benzophenone isolated from the plant Rheedia gardneriana, on some of the virulence properties of Streptococcus mutans associated with biofilm development and acidogenicity. The synthesis of glucans by glucosyltransferases B (GTF B) and C (GTF C) was markedly reduced by 7-epiclusianone showing more than 80% inhibition of enzymatic activity at a concentration of 100 microg mL(-1). Double-reciprocal analysis (Lineweaver-Burk plots) revealed that the inhibition of GTF B activity was noncompetitive (mixed) while GTF C was inhibited uncompetitively. The glycolytic pH drop by S. mutans cells was also disrupted by 7-epiclusianone without affecting the bacterial viability, an effect that can be attributed, in part, to inhibition of F-ATPase activity (61.1+/-3.0% inhibition at 100 microg mL(-1)). Furthermore, topical applications (1-min exposure, twice daily) of 7-epiclusianone (at 250 microg mL(-1)) disrupted biofilm formation and physiology. The biomass (dry-weight), extracellular insoluble polysaccharide concentration and acidogenicity of the biofilms were significantly reduced by the test agent (P<0.05). The data show that 7-epiclusianone disrupts the extracellular and intracellular sugar metabolism of S. mutans, and holds promise as a novel, naturally occurring compound to prevent biofilm-related oral diseases.

Publication Types:

PMID: 18371068 [PubMed - in process]

28: Proc Natl Acad Sci U S A. 2008 Apr 1;105(13):5271-6. Epub 2008 Mar 26.
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Plant adaptation to fluctuating environment and biomass production are strongly dependent on guard cell potassium channels.

Lebaudy A, Vavasseur A, Hosy E, Dreyer I, Leonhardt N, Thibaud JB, Véry AA, Simonneau T, Sentenac H.

Biochimie et Physiologie Moléculaire des Plantes, Unité Mixte de Recherche 5004, Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique (U.386)/Montpellier SupAgro/Université Montpellier 2, Montpellier, France.

At least four genes encoding plasma membrane inward K+ channels (K(in) channels) are expressed in Arabidopsis guard cells. A double mutant plant was engineered by disruption of a major K(in) channel gene and expression of a dominant negative channel construct. Using the patch-clamp technique revealed that this mutant was totally deprived of guard cell K(in) channel (GCK(in)) activity, providing a model to investigate the roles of this activity in the plant. GCK(in) activity was found to be an essential effector of stomatal opening triggered by membrane hyperpolarization and thereby of blue light-induced stomatal opening at dawn. It improved stomatal reactivity to external or internal signals (light, CO2 availability, and evaporative demand). It protected stomatal function against detrimental effects of Na+ when plants were grown in the presence of physiological concentrations of this cation, probably by enabling guard cells to selectively and rapidly take up K+ instead of Na+ during stomatal opening, thereby preventing deleterious effects of Na+ on stomatal closure. It was also shown to be a key component of the mechanisms that underlie the circadian rhythm of stomatal opening, which is known to gate stomatal responses to extracellular and intracellular signals. Finally, in a meteorological scenario with higher light intensity during the first hours of the photophase, GCK(in) activity was found to allow a strong increase (35%) in plant biomass production. Thus, a large diversity of approaches indicates that GCK(in) activity plays pleiotropic roles that crucially contribute to plant adaptation to fluctuating and stressing natural environments.

Publication Types:

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

PMID: 18367672 [PubMed - indexed for MEDLINE]

PMCID: PMC2278230 [Available on 10/01/08]