Thèse Régulation du Transport des Acides Organiques dans les Stomates et les Tissus Photosynthétiques Impact sur la Croissance des Plantes et leur Adaptation à l'Environnement H/F - Doctorat.Gouv.Fr

Établissement : Université de Montpellier École doctorale : GAIA - Biodiversité, Agriculture, Alimentation, Environnement, Terre, Eau Laboratoire de recherche : IPSiM - Institut des Sciences des Plantes de Montpellier Direction de la thèse : Alexis DE ANGELI ORCID 0000000330727932 Début de la thèse : 2026-10-01 Date limite de candidature : 2026-05-07T23:59:59 Malgré leur importance, le rôle de l'accumulation vacuolaire de malate et fumarate dans le métabolisme et la croissance des plantes C3 reste mal compris. Les systèmes de transport qui assurent le flux de ces acides organiques à travers les membranes cellulaires sont des régulateurs de cette accumulation, et des progrès significatifs ont été réalisés dans leur identification au niveau des membranes vacuolaires et plasmiques. Notamment les membres de la famille ALMT (Aluminum-Activated Malate Transporter) sont parmi les plus importants. Des découvertes récentes montrent que la suppression des canaux ALMT vacuolaires chez Arabidopsis entraîne des défauts de croissance majeu, avec une réduction de la biomasse pouvant atteindre 85 %. Ces canaux, en particulier ALMT4, ALMT5 et ALMT9, interviennent dans le transport du malate et du fumarate dans les vacuoles, ce qui montre que l'accumulation d'acides organiques dans les vacuoles est essentielle, même chez les plantes C3. Il est important de noter que ces transporteurs sont exprimés à la fois dans les cellules du mésophylle et dans les cellules de garde. Ces duex tyoes cellulaires jouent des rôles distincts mais complémentaires dans la photosynthèse : les cellules du mésophylle fixent le CO via la photosynthèse, tandis que les cellules de garde régulent l'entrée du CO dans les feuilles via le contrôle de l'ouverture stomatique. Le projet de thèse vise à comprendre comment les canaux ALMT fonctionnent et sont régulés dans différents types de cellules, comment ils s'intègrent dans le métabolisme du carbone et comment ils influencent la croissance des plantes dans différentes conditions environnementales. La compréhension de ces mécanismes pourrait révéler de nouvelles stratégies pour améliorer la production de biomasse et l'adaptation des plantes. In land plants, a significant part of the C fixed by photosynthesis is stored as starch, sugars and organic acids (Gibon et al., 2009). The main organic acids produced and accumulated are malate, citrate, and, in some plants, including Arabidopsis, fumarate. These three organic acids are key metabolites at the crossroad of several metabolic pathways. Interestingly, at the shoot level, these organic ions play important physiological roles in photosynthetic cells (i.e., mesophyll cells) and in guard cells. In all cell types, the compartmentalisation of these organic acids is a keystone for their biological function. Indeed, malate, fumarate, and citrate are present in different subcellular compartments where they are produced, consumed, or stored. For example, these organic acids are part of the TCA cycle in the mitochondria, they are involved in the redox status in the cytosol, in the amino acids production, and pH homeostasis in the vacuole, where they are also transiently stored for metabolic and, in guard cells, osmotic regulation. Notably, in C3 plants, the function of vacuolar malate and fumarate loading /unloading in the regulation of the metabolism, and how it influences plant growth is still unclear. In this context, the transport systems mediating the fluxes of these organic acids across the cellular membranes are essential actors. The molecular identity of many of ion transport systems for malate and fumarate in the vacuolar and plasma membranes was disclosed, and the host team significantly contributed to these findings (Doireau et al. 2024; De Angeli et al. 2013; Eisenach et al. 2017; Jaslan et al. 2022; Lee et al. 2025). Nonetheless, several key questions are still open on the role of these ion transporters and their role in plant adaptation to the environment and growth.
The present proposal is based on recent findings of the host team showing that, in Arabidopsis thaliana, multiple knockouts targeting vacuolar ion channels of the ALMT (Aluminum Activated Malate Transporters) family show dramatic growth defect, up to 85% decrease. These ion channels mediate the transport of malate and fumarate, thus the observed biomass decrease is associated to the impairment of the vacuolar transport of fumarate and malate. These data demonstrate that also in C3 plants, the vacuolar accumulation of organic acids is crucial and we could show that the vacuolar loading of these species is integrated in the regulation of the carbon metabolism. Interestingly, the vacuolar transporter we have identified (ALMT4, ALMT5 and ALMT9) are expressed, in the shoots, in different cell types including the mesophyll cells and in guard cells. Interestingly, these two cell types are both involved in the photosynthetic processes, although they play different roles. Indeed, in mesophyll cells most of the fixation of CO2 into organic molecules takes place, while guard-cells regulate CO2 entry in the leaf to feed photosynthetic reactions. In mesophyll, cells the vacuolar transport of organic acid is linked to the specialised metabolism of these cells, while in guard cells it is linked to osmotic pressure regulation to open and close stomata. Therefore, what is the role of these ion channels in the different cell types? How they are regulated? how they affect plant growth and biomass production under different environmental conditions? These are still open question that could potentially lead to the identification of new possibilities to act on the control of biomass production under different environmental conditions.
The main objective of the thesis will be disentangle the functions and regulations of the vacuolar ion channels of the ALMT family at a cell specific level, namely mesophyll cells and guard cells, and how they contribute to plant growth and adaptation to the environment. To develop the present thesis the candidate will use:
- Molecular biology approaches (cloning, PCR, qPCR, electrophoresis...)
- Biochemistry (Western blots, protein extraction, mass spectrometry..)
- Imaging (confocal and wide field fluorescence microscopy)
- Plant physiology (stomata aperture, leaf transpiration, drought assays...)
- Electrophysiology (quantify ion transport across cell membranes)

Master en Biologie végétale ou Biologie

Connaissances niveau master:
Biologie végétale
biologie moléculaires (PCR, gel electrophorèse, qPCR...)
biochimie (western blot)
imagerie (microscopie plain champ et confocale)