Thèse de Doctorat de l’Université de Montpellier

Jeudi 12 décembre 2024 à 14h

The vacuolar malate and fumarate channels of the ALMT family participate to the Arabidopsis carbon metabolism

Nathalie LEONHARDT, Directrice de Recherche, CEA Cadarache
Martine DIEUAIDE – NOUBHANI, Professeure, Université de Bordeaux
Bertrand MULLER, Directeur de Recherche, INRAE Montpellier
Sylvie DINANT, Directrice de Recherche, INRAE Versailles
Alexis DE ANGELI, Directeur de recherche, CNRS Montpellier

Résumé:

In plants, organic acids (malate, fumarate) constitute a significant part of the carbon fixed by photosynthesis. These organic acids are part of the primary metabolic pathways, being intermediates of the tricarboxylic acid (TCA) cycle, playing an essential role in regulating cellular pH, and involved in stomatal movement. In Arabidopsis thaliana, the vacuole is an important transient store of malate and fumarate, allowing to keep the cytosolic pools in a physiological range. While the role of the vacuole as a stock of organic acids is well known in C4 and CAM plants, in C3 plants it is still to be understood. This is raising the question if and how the vacuolar transport of organic acids regulates photosynthetic metabolism. My study focuses on the channel family ALMT (Aluminium Activated Malate transporter), which are present only in plants. First, the characterisation of AtALMT5, until now unknown, revealed its vacuolar localisation as well as its capacity to mediate fumarate influx during the photoperiod. This revealed the importance of AtALMT channels in the carbon metabolism. The study of multiple knock-out mutants for vacuolar AtALMT4, AtALMT5 and AtALMT9 channels enabled us to reveal the importance of these channels in the storage of organic acids in the vacuole. Furthermore, mutants showing a reduction in vacuolar malate and fumarate accumulation also show a modified carbon stock composition. These mutants accumulate more carbon in the form of soluble sugars. In addition, TCA cycle activity is increased during photoperiod, resulting in greater amino acid accumulation. These metabolic changes lead to a rosette growth defect with an early senescence of the oldest leaves. Moreover, the last part of this study decipher the functions of the AtALMT channels in the guard cells, separately from the mesophyll cells. We complemented multiple knock-out mutants only in the guard cells using the guard cell 1 (GC1) promoter. This enabled to reveal that several AtALMT with similar expression pattern could have different functions in different plants organs. Altogether, my study identify key molecular actors at the tonoplast able to influence the carbon metabolism in plants.