Release of SOS2 kinase from sequestration with GIGANTEA determines salt tolerance in Arabidopsis

Kim, Woe-Yeon et al.--Environmental challenges to plants typically entail retardation of vegetative growth and delay or cessation of flowering. Here we report a link between the flowering time regulator, GIGANTEA (GI), and adaptation to salt stress that is mechanistically based on GI degradation under saline conditions, thus retarding flowering. GI, a switch in photoperiodicity and circadian clock control, and the SNF1-related protein kinase SOS2 functionally interact. In the absence of stress, the GI:SOS2 complex prevents SOS2- based activation of SOS1, the major plant Na+/H+-antiporter mediating adaptation to salinity. GI over-expressing, rapidly flowering, plants show enhanced salt sensitivity, whereas gi mutants exhibit enhanced salt tolerance and delayed flowering. Salt-induced degradation of GI confers salt tolerance by the release of the SOS2 kinase. The GISOS2 interaction introduces a higher order regulatory circuit that can explain in molecular terms, the long observed connection between floral transition and adaptive environmental stress tolerance in Arabidopsis.This research was supported by the Next-Generation BioGreen 21 Program (Systems and Synthetic Agrobiotech Center, no. PJ008025), a Cooperative Research Program for Agriculture Science & Technology Development (Project No. PJ007850), and the Ministry of Education, Science and Technology for the World Class University (WCU) program (R32-10148) from the Rural Development Administration, Republic of Korea, and by grant BIO2009-08641 financed by the Spanish Ministry of Science and Innovation and the FEDER program.Peer reviewe

Transcriptional activity of transposable elements in maize

<p>Abstract</p> <p>Background</p> <p>Mobile genetic elements represent a high proportion of the Eukaryote genomes. In maize, 85% of genome is composed by transposable elements of several families. First step in transposable element life cycle is the synthesis of an RNA, but few is known about the regulation of transcription for most of the maize transposable element families. Maize is the plant from which more ESTs have been sequenced (more than two million) and the third species in total only after human and mice. This allowed us to analyze the transcriptional activity of the maize transposable elements based on EST databases.</p> <p>Results</p> <p>We have investigated the transcriptional activity of 56 families of transposable elements in different maize organs based on the systematic search of more than two million expressed sequence tags. At least 1.5% maize ESTs show sequence similarity with transposable elements. According to these data, the patterns of expression of each transposable element family is variable, even within the same class of elements. In general, transcriptional activity of the <it>gypsy</it>-like retrotransposons is higher compared to other classes. Transcriptional activity of several transposable elements is specially high in shoot apical meristem and sperm cells. Sequence comparisons between genomic and transcribed sequences suggest that only a few copies are transcriptionally active.</p> <p>Conclusions</p> <p>The use of powerful high-throughput sequencing methodologies allowed us to elucidate the extent and character of repetitive element transcription in maize cells. The finding that some families of transposable elements have a considerable transcriptional activity in some tissues suggests that, either transposition is more frequent than previously expected, or cells can control transposition at a post-transcriptional level.</p

Vacuolar dynamics in guard cells and stomatal movements depend on postassium uptake at the tonoplast

Resumen de la comunicación orial presentada en Environment Workshop 2013: Genomic, Physiological and Breeding Approaches for Enhancing Drought Resistance in Crops. Baeza (Spain), 23-25 September (2013)The rapid uptake and loss of K+ and of other osmolytes by guard cells, mostly in the vacuolar compartment, controls the opening and closing of stomata, and thereby gas exchange and transpiration of plants. Despite the established role of osmolyte transport accross the plasma membrane of guard cell in stomata function, osmolyte uptake into the cytosol represents only a transient step to the vacuole since more than 90% of the solutes accumulate into the vacuoles. The question addressed here is: How is K+ taken into the vacuoles of guard cells to sustain stomatal opening? We show that tonoplast-localized K+/H+ antiporters in guard cells mediate the vacuolar accumulation of K+ and that these transporters are not only required for stomatal openning but, unexpectedly, for stomatal closure as well. Arabidopsis mutants deficient in genes the two major forms of K+/H+ antiporters that are highly expressed in guard cells, NHX1 and NHX2, were used. Double mutant lines of genotype nhx1 nhx2 presented stomata with aberrant morphologies and a vacuolar K+ pool in guard cells that was only half the size of the wild type. These results imply that K+ transport by NHX proteins represents the main pathway for the K+ uptake into the vacuoles of guard cells. Infrared thermography on whole plants revealed altered transpiration rates in the mutant. In stomatal bioassays with epidermal strips, a hypomorphic mutant exhibited impaired stomata opening and delayed closure, whereas the double knockout line was defective in both processes. These results establish that the large uptake flux of K+ into vacuoles is not only a physicochemical requisite for stomatal opening, but also a critical component of the K+ homeostasis that is needed for stomatal closure. Abrogation of K+ accumulation by guard cells correlated with more acidic vacuoles in the mutant and the disappearance of the highly dynamic changes in vacuolar structure associated to stomatal movements. By using guard cell imaging, we show that K+ transport is a critical component of the guard cell vacuole remodeling and the control of vacuolar pH that together sustain stomatal movements. Sodium supplementation partly restored stomatal opening, vacuolar dynamics and lumenal pH control. Delayed responses of stomata in the null mutant in daily cycles led to the counterintuitive finding that mutant plants survived longer under water deprivation because the plants were not only smaller but they also transpired less per leaf area unit during the day, thus consuming less soil water. Water loss at night in the mutant was greater compared to the wild type, but this was apparently compensated by diurnal water savings. In summary, this work uncovers the essential role that the active accumulation of K+ in the vacuoles of guard cells plays in guard cell dynamics and stomatal functionPeer reviewe

Control of vacuolar dynamics and regulation of stomatal aperture by tonoplast potassium uptake

Zaida Andrés... [et al].-- 10 páginas.-- 8 figuras.-- 54 referencias.-- En Información suplementaria: 9 páginas.- 9S figuras.-- 1S tabla.-- http://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1320421111/-/DCSupplemental .-- En el archivo de acceso abierto de este Item aparecen juntos el texto y archivo suplementario.Stomatal movements rely on alterations in guard cell turgor. This requires massive K+ bidirectional fluxes across the plasma and tonoplast membranes. Surprisingly, given their physiological importance, the transporters mediating the energetically uphill transport of K+ into the vacuole remain to be identified. Here, we report that, in Arabidopsis guard cells, the tonoplast-localized K+/H+ exchangers NHX1 and NHX2 are pivotal in the vacuolar accumulation of K+ and that nhx1 nhx2 mutant lines are dysfunctional in stomatal regulation. Hypomorphic and complete-loss-of-function double mutants exhibited significantly impaired stomatal opening and closure responses. Disruption of K+ accumulation in guard cells correlated with more acidic vacuoles and the disappearance of the highly dynamic remodelling of vacuolar structure associated with stomatal movements. Our results show that guard cell vacuolar accumulation of K+ is a requirement for stomatal opening and a critical component in the overall K+ homeostasis essential for stomatal closure, and suggest that vacuolar K+ fluxes are also of decisive importance in the regulation of vacuolar dynamics and luminal pH that underlie stomatal movements.This work was supported by Ministerio de Economia y Competitividad Grants BIO2009-08641 and BFU2012-35060, cofinanced by the European Regional Development Fund (to J.M.P.); Deutsche Forschungsgemeinschaft Grants Ku931/7-1 (to J.K.), SFB629 (to J.K.), FOR964 (to J.K.), and FOR1061 (to K.S.); Biotechnology and Biological Sciences Research Council of the United Kingdom (A.M.H.); and Junta de Ampliacion de Estudios Fellowship Program of Consejo Superior de Investigaciones Cientificas (to Z.A.).Peer reviewe

Vacuolar dynamics in guard cells and stomatal movements depend on postassium uptake at the tonoplast

Resumen de la comunicación orial presentada en Environment Workshop 2013: Genomic, Physiological and Breeding Approaches for Enhancing Drought Resistance in Crops. Baeza (Spain), 23-25 September (2013)The rapid uptake and loss of K+ and of other osmolytes by guard cells, mostly in the vacuolar compartment, controls the opening and closing of stomata, and thereby gas exchange and transpiration of plants. Despite the established role of osmolyte transport accross the plasma membrane of guard cell in stomata function, osmolyte uptake into the cytosol represents only a transient step to the vacuole since more than 90% of the solutes accumulate into the vacuoles. The question addressed here is: How is K+ taken into the vacuoles of guard cells to sustain stomatal opening? We show that tonoplast-localized K+/H+ antiporters in guard cells mediate the vacuolar accumulation of K+ and that these transporters are not only required for stomatal openning but, unexpectedly, for stomatal closure as well. Arabidopsis mutants deficient in genes the two major forms of K+/H+ antiporters that are highly expressed in guard cells, NHX1 and NHX2, were used. Double mutant lines of genotype nhx1 nhx2 presented stomata with aberrant morphologies and a vacuolar K+ pool in guard cells that was only half the size of the wild type. These results imply that K+ transport by NHX proteins represents the main pathway for the K+ uptake into the vacuoles of guard cells. Infrared thermography on whole plants revealed altered transpiration rates in the mutant. In stomatal bioassays with epidermal strips, a hypomorphic mutant exhibited impaired stomata opening and delayed closure, whereas the double knockout line was defective in both processes. These results establish that the large uptake flux of K+ into vacuoles is not only a physicochemical requisite for stomatal opening, but also a critical component of the K+ homeostasis that is needed for stomatal closure. Abrogation of K+ accumulation by guard cells correlated with more acidic vacuoles in the mutant and the disappearance of the highly dynamic changes in vacuolar structure associated to stomatal movements. By using guard cell imaging, we show that K+ transport is a critical component of the guard cell vacuole remodeling and the control of vacuolar pH that together sustain stomatal movements. Sodium supplementation partly restored stomatal opening, vacuolar dynamics and lumenal pH control. Delayed responses of stomata in the null mutant in daily cycles led to the counterintuitive finding that mutant plants survived longer under water deprivation because the plants were not only smaller but they also transpired less per leaf area unit during the day, thus consuming less soil water. Water loss at night in the mutant was greater compared to the wild type, but this was apparently compensated by diurnal water savings. In summary, this work uncovers the essential role that the active accumulation of K+ in the vacuoles of guard cells plays in guard cell dynamics and stomatal functionPeer reviewe

MYB36 controls root cell elongation by modulating auxin response

Póster presentado en la 29th International Conference on Arabidopsis Research (2018) ICAR 2018 25-29 June 2018, Turku, FinlandWe and others [1,2] have studied the role of MYB36, an Arabidopsis R2R3-MYB class transcription factor as a master regulator of the differentiation of the endodermis during root development. We present here our results confirming that MYB36 promotes the development of the Casparian band in root endodermal cells by the transcriptional regulation of genes involved in localized lignin assembly and deposition. Moreover, the transcriptional and developmental outcome from MYB36 overexpression support the idea that MYB36 is also involved in the coordinated arrest of cell elongation in the differentiation zone by modulating auxin signalling/perception in the root. Arabidopsis transgenic lines overexpressing MYB36 have pleiotropic phenotypes in auxin-related growth and development, reduced sensitivity to exogenous auxin, and altered gene expression in response to auxin. Both the initiation and lateral root emergence were impaired when MYB36 was overexpressed, but the lateral root phenotype was partially rescued by auxin treatments. However the expression of DR5:GUS and LAX3:YFP marker genes were not properly induced by auxin in the roots confirming that MYB36 function affects auxin responses. The transcriptomic landscape of the MYB36 conditional overexpressing line reveals a strong down-regulation of auxin signallling in shoots 24 hours after induction. These results would explain the drastic effect on cell elongation/expansion when MYB36 is expressed ectopically in Arabidopsis supporting endodermal differentiation as a developmental shift for auxin regulation in the primary root. Kamiya, T, et al. (2015) Proc Natl Acad Sci USA 112(33):10533–10538. Liberman, LM, et al. (2015) Proc Natl Acad Sci USA 112(39):12099-104.Peer reviewe

MYB36 regulates root cell elongation by modulating auxin response in Arabidopsis thaliana

We and others [1,2] have studied the role of MYB36, an Arabidopsis R2R3-MYB class transcription factor (TF), as a master regulator of the differentiation of the endodermis during root development. Our results support that MYB36 regulates a developmental switch from proliferative to differentiated state that promotes the development of the Casparian band, in part by regulation of the expression of genes involved in the very localized lignin assembly and deposition in cells from root endodermis. The genetic and molecular mechanisms controlling the cell size in the root elongation zone and the regulators driving the coordinated arrest of cell elongation in the transition from elongation to differentiation zone, are still poorly understood. Here, we present the transcriptional and developmental outcome from MYB36 overexpression, which supports the idea that MYB36 is involved in this process by modulating auxin signalling/perception in the root. Arabidopsis transgenic lines overexpressing MYB36 have pleiotropic phenotypes in auxin-related growth and development, reduced sensitivity to exogenous auxin, and altered gene expression in response to auxin. Both the initiation and lateral root emergence were impaired when MYB36 was overexpressed, but the lateral root phenotype was partially rescued by auxin treatments. However the expression of DR5:GUS and LAX3pro:YFP auxin-marker genes were not properly induced by auxin in the overexpressing line confirming that MYB36 function affects auxin responses. Moreover the transcriptome analysis of a line MYB36 conditionally overexpressing MYB36 revealed a strong down-regulation of auxin signalling in shoots 24 hours after induction. These results would explain the drastic effect on cell elongation/expansion when MYB36 is expressed ectopically in Arabidopsis 1 Kamiya, T, el al. (2015). Proc Natl Acad Sci USA 112(33):10533-10538. 2 Liberman, LM, el al. (2015). Proc Nall Acad Sci USA 112(39):12099-104.Peer Reviewe

Unraveling of the main physiological processes affected by the Na+, K+ transporters NHX1 and NHX2 of Arabidopsis thaliana

The Arabidopsis thaliana NHX1 and NHX2 are the two major tonoplast-localized isoforms of Na+,K+/H+ antiporters. NHX1 and NHX2 have similar expression patterns and identical biochemical activity, and together they account for a significant amount of the Na+,K+/H+ antiport activity in tonoplast vesicles. Double mutants nhx1 nhx2 have reduced ability to create the vacuolar K+ pool, show high K+ retention in the cytosol, impaired osmoregulation, and compromised turgor generation for cell expansion. Moreover NHX1 and NHX2 exchangers are pivotal in the vacuolar accumulation of K+ of guard cells as the nhx1 nhx2 mutant lines are dysfunctional in stomatal regulation, showing impaired stomatal opening and closure due to the abrogation of K+ accumulation in the guard cells. Other phenotypic traits of the double mutant are poor growth, hypersensitivity to osmotic stress and very low fertility. Some of these phenotypic traits can be suppressed by the addition of moderate amounts of NaCl in the substrate. To determine what is the precise physiological function critically affected by nhx1 nhx2 that accounts for most of the mutant phenotype, we have analyzed the root and aerial part functions of NHX proteins by reciprocal micrografting of wild-type and mutant roots and shoots, and by guard cell specific expression of NHX1 and NHX2 proteins in a double mutant genetic background. We have evaluated the growth, fertility and stomatal function of these chimaeric plants. The results indicate that defective osmotic regulation is the main cause of the pleiotropic phenotype of mutants impaired in NHX function.Peer Reviewe

New insights on the critical role of vacuolar potassium uptake in stomatal function.

Peer Reviewe

Vacuolar NHX antiporters: understanding structure-function relationships and regulation

Potassium (K) is an essential nutrient for plants and the most abundant cation in plant cells, comprising up to 10% of plant dry weight. While cytosolic K is kept at homeostatic concentrations close to 100 mM, surplus K is stored in vacuoles. The tonoplast-localized K+,Na+/H+ exchangers NHX1 and NHX2 proteins of Arabidopsis mediate this K+ accumulation in the vacuole, thereby increasing the osmotic potential, water uptake and the turgor pressure necessary for cell expansion and growth. Vacuolar remodeling during stomatal movements also depends on these proteins. Structural domains and essential amino acid residues putatively involved in ion transport, cation coordination and pH sensing, have been identified by phylogenetic analysis and computational modeling of the NHX1 protein. To determine the relevance of these residues in the biochemical activity of NHX1, and its pH dependence, point-mutation alleles have been generated. Mutant NHX1 proteins have been functionally tested in yeasts nhx1 mutants and in vitro ion transport assays. The presence of a calmodulin-binding domain comprising amphipathic ¿-helices at the C-termini of NHX1 and NHX2 have also been detected by computational and biochemical analyses. The importance of the putative calmodulin-binding domain for NHX1 activity has been demonstrated by functional analyses in yeast, whereas the interaction of NHX1 and NHX2 with CalModulin-Like18 (CML18) has been analyzed by BiFC and Y2H assays. Our results evidence the fine-tuning of NHX1 and NHX2 activity in response to developmental and environmental cues. In addition, we expect to unravel the biochemical mechanisms for pH sensing and regulation of these critical K transporters of Arabidopsis.Peer Reviewe