The Arabidopsis pop2-1 mutant reveals the involvement of GABA transaminase in salt stress tolerance

<p>Abstract</p> <p>Background</p> <p>GABA (γ-aminobutyric acid) is a non protein amino acid that has been reported to accumulate in a number of plant species when subjected to high salinity and many other environmental constraints. However, no experimental data are to date available on the molecular function of GABA and the involvement of its metabolism in salt stress tolerance in higher plants. Here, we investigated the regulation of GABA metabolism in <it>Arabidopsis thaliana </it>at the metabolite, enzymatic activity and gene transcription levels upon NaCl stress.</p> <p>Results</p> <p>We identified the GABA transaminase (GABA-T), the first step of GABA catabolism, as the most responsive to NaCl. We further performed a functional analysis of the corresponding gene <it>POP2 </it>and demonstrated that the previously isolated loss-of-function <it>pop2-1 </it>mutant was oversensitive to ionic stress but not to osmotic stress suggesting a specific role in salt tolerance. NaCl oversensitivity was not associated with overaccumulation of Na⁺and Cl^-but mutant showed a slight decrease in K⁺. To bring insights into <it>POP2 </it>function, a promoter-reporter gene strategy was used and showed that <it>POP2 </it>was mainly expressed in roots under control conditions and was induced in primary root apex and aerial parts of plants in response to NaCl. Additionally, GC-MS- and UPLC-based metabolite profiling revealed major changes in roots of <it>pop2-1 </it>mutant upon NaCl stress including accumulation of amino acids and decrease in carbohydrates content.</p> <p>Conclusions</p> <p>GABA metabolism was overall up-regulated in response to NaCl in <it>Arabidopsis</it>. Particularly, GABA-T was found to play a pivotal function and impairment of this step was responsible for a decrease in salt tolerance indicating that GABA catabolism was a determinant of <it>Arabidopsis </it>salt tolerance. GABA-T would act in salt responses in linking N and C metabolisms in roots.</p

Génomique fonctionnelle du métabolisme du GABA chez Arabidopsis thaliana (contribution à l étude des réponses au stress salin)

L acide g-aminobutyrique (GABA) est un acide aminé présent dans la plupart des organismes vivants. Cette ubiquité a laissé entendre qu il pouvait revêtir des fonctions prépondérantes et conservées au sein des organismes. Alors que chez les animaux les fonctions du GABA sont clairement établies, en particulier dans la transduction du signal nerveux, peu de données en contraste sont disponibles sur ses rôles chez les plantes. Il est néanmoins connu que le GABA s accumule chez les plantes en réponse à une gamme très large de contraintes environnementales suggérant son intervention dans la tolérance aux stress. Dans ce cadre, nous avons choisi d étudier la contribution du métabolisme du GABA dans la réponse au stress salin en utilisant la plante-modèle Arabidopsis thaliana qui autorise l adoption d une démarche de génomique fonctionnelle. Couplant des analyses systématiques du transcriptome à des approches moléculaires, biochimiques, cellulaires et génétiques, nous avons mis en évidence que le métabolisme du GABA était globalement activé en réponse au stress salin et fonctionnellement impliqué dans la tolérance à cette contrainte. En addition d un rôle métabolique, il est apparu que le GABA était également capable d altérer le développement de la plante en l absence de stress en jouant sur la voie de sécrétion. Cette propriété a également été mise en évidence au cours du stress salin et a été rapprochée d un impact sur l activité du réticulum endoplasmique révélant des fonctions insoupçonnées et inédites pour le GABA dans l activité cellulaire.The g-aminobutyric acid (GABA) is an amino acid found in almost all living organisms. This ubiquity has led to postulate it could have prominent and conserved functions in organisms. While the functions of GABA in animals are well-documented, especially in nervous signal transduction, little information is available in contrast about its roles in plants. However, GABA is known to accumulate in response to a wide range of environmental constraints suggesting that it could participate to stress tolerance. In this context, we decided to study the involvement of GABA metabolism in salt stress responses using the model-plant Arabidopsis thaliana allowing adoption of a functional genomic approach. Through systematic analysis of the transcriptome coupled to molecular, biochemical, cellular and genetic approaches, we demonstrated that GABA metabolism was overall up-regulated in response to salt stress and was functionally involved in salt tolerance. In addition to a metabolic function, GABA was shown to alter plant development under non-stress conditions by acting on secretory pathway. This property was also observed under salt stress conditions and was linked to an impact on endoplasmic reticulum activity revealing unexpected and fundamental functions for GABA in cellular activity.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Réponses des plantes aquatiques à une augmentation de température

National audienc

Réponses des plantes aquatiques à une augmentation de température

National audienc

Growth, regeneration and colonisation of Egeria densa fragments: the effect of autumn temperature increases

International audienceThe present study analysed the influence of higher temperatures on the growth, regeneration and colonisation abilities of apical shoot fragments from three naturalised and one cultivated population of Egeria densa. Our hypotheses were that (1) increased temperatures would favour the growth, regeneration and colonisation of E. densa shoots and (2) fragments from naturalised populations would have higher establishment success than fragments from cultivated plants. We tested the effect of average minimal autumn temperature (9 °C), average maximal autumn temperature (16 °C) and an increase of 3 °C above these values, on apical shoots of these four populations of E. densa under controlled conditions in two growth chambers. Our results showed that temperature and the origin of the population had an effect on the growth rate of E. densa fragments, on their regeneration and colonisation abilities at the maximal autumn temperature. An increase of 3 °C stimulated the growth rate of E. densa at low temperatures but had no effect on the plant colonisation and regeneration abilities. The responses of populations to low temperatures (9–12 °C) were more similar than expected. In contrast, at higher temperatures (16–19 °C) the cultivated population showed lower apical growth, higher regeneration and similar colonisation abilities to the naturalised populations. At these higher temperatures, the responses also differed among the naturalised populations. These results suggest that global warming has implications for the invasiveness of E. dens

Modulation of ethylene biosynthesis by ACC and AIB reveals a structural and functional relationship between the (KNO3)-N-15 uptake rate and root absorbing surfaces

International audienceThe modification of root traits in relation to nitrate uptake represents a source for improvement of nitrogen uptake efficiency. Because ethylene signalling modulates growth of exploratory and root hair systems more rapidly (minutes to hours) than nitrate signalling (days to weeks), a pharmacological approach was used to decipher the relationships between root elongation and N uptake. Rape seedlings were grown on agar plates supplied with 1mM (KNO3)-N-15 and treated with different concentrations of either the ethylene precursor, ACC (0.1, 1, and 10 M) or an inhibitor of ethylene biosynthesis, AIB (0.5 and 1 M). The results showed that rapid modulation of root elongation (up to 8-fold) is more dependent on the ethylene than the nitrate signal. Indeed, ACC treatment induced a partial compensatory increase in N-15 uptake associated with overexpression of the BnNRT2.1 and BnNRT1.1 genes. Likewise, daily root elongation between treatments was not associated with daily nitrate uptake but was correlated with N status. This suggested that a part of the daily root response was modulated by cross talks between ethylene signalling and N and C metabolisms. This was confirmed by the reduction in C allocation to the roots induced by ACC treatment and the correlations of changes in the root length and shoot surface area with the aspartate content. The observed effects of ethylene signalling in the root elongation and NRT gene expression are discussed in the context of the putative role of NRT2.1 and NRT1.1 transporters as nitrate sensors

Present and future distribution of three aquatic plants taxa across the world: decrease in native and increase in invasive ranges

International audienceInland aquatic ecosystems are vulnerable to both climate change and biological invasion at broad spatial scales. The aim of this study was to establish the current and future potential distribution of three invasive plant taxa, Egeria densa, Myriophyllum aquaticum and Ludwigia spp., in their native and exotic ranges. We used species distribution models (SDMs), with nine different algorithms and three global circulation models, and we restricted the suitability maps to cells containing aquatic ecosystems. The current bioclimatic range of the taxa was predicted to represent 6.6-12.3% of their suitable habitats at global scale, with a lot of variations between continents. In Europe and North America, their invasive ranges are predicted to increase up to two fold by 2070 with the highest gas emission scenario. Suitable new areas will mainly be located to the north of their current range. In other continents where they are exotic and in their native range (South America), the surface areas of suitable locations are predicted to decrease with climate change, especially for Ludwigia spp. in South America (down to -55% by 2070 with RCP 8.5 scenario). This study allows to identify areas vulnerable to ongoing invasions by aquatic plant species and thus could help the prioritisation of monitoring and management, as well as contribute to the public awareness regarding biological invasions

The lysine-ketoglutarate reductase-saccharopine dehydrogenase is involved in the osmo-induced synthesis of pipecolic acid in rapeseed leaf tissus

International audienceHigher plant responses to abiotic stresses are associated with physiological and biochemical changes triggering a number of metabolic adjustments. We focused on l-lysine catabolism, and have previously demonstrated that degradation of this amino acid is osmo-regulated at the level of lysine-ketoglutarate reductase (LKR, EC 1.5.1.8) and saccharopine dehydrogenase (SDH, EC 1.5.1.9) in Brassica napus. LKR and SDH activities are enhanced by decreasing osmotic potential and decrease when the upshock osmotic treatment is followed by a downshock osmotic one. Moreover we have shown that the B. napus LKR/SDH gene is up-regulated in osmotically-stressed tissues. The LKR/SDH activity produces alpha-aminoadipate semialdehyde which could be further converted into alpha-aminoadipate and acetyl CoA. Alternatively alpha-aminoadipate could behave as a precursor for pipecolic acid. Pipecolic acid is described as an osmoprotectant in bacteria and is co-accumulated with proline in halophytic plants. We suggest that osmo-induction of the LKR/SDH activity could be partly responsible for pipecolic acid accumulation. This proposal has been assessed in this study through pipecolic acid amounts determination in rape leaf discs subjected to various upshift and downshift osmotic treatments. Changes in pipecolic acid level actually behave as those observed for LKR and SDH activities, since it increases or decreases in rape leaf discs treated under hyper- or hypo-osmotic conditions, respectively. In addition we show that pipecolic acid level is positively correlated with the external osmotic potential as well as with the duration of the applied treatment. On the other hand pipecolic acid level is related to the availability of l-lysine and not to that of d-lysine. Collectively the results obtained demonstrate that lysine catabolism through LKR/SDH activity is involved in osmo-induced synthesis of pipecolic aci