Séminaire IBIP
Les séminaires ont lieu sur le Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)

Jeudi 7 mai 2026 à 14h, Amphi 208

Stijn Dames
Université de Leuven, Belgique

Crassulacean acid metabolism (CAM) is an evolutionary photosynthetic adaptation that enables plants to conserve substantial amounts of water and thrive in arid environments. Unlike C3 and C4 plants, CAM species open their stomata at night, fixing atmospheric CO2 and storing it as malic acid in their vacuoles. This process is accompanied by proton transport into the vacuole, lowering its pH to ~3.5. The next day, malate is remobilised and decarboxylated behind closed stomata to supply CO2 for Rubisco assimilation, thereby minimising transpirational water loss. Concurrently, protons are exported back to the cytosol, which, given its relatively small volume (0.5-1% of the total cell volume), is especially prone to over-acidification. However, maintaining cytosolic pH homeostasis is crucial to preserve its functionality as an important transit compartment for many solutes and as a medium to accommodate important biochemical pathways including gluconeogenesis and sucrose biosynthesis.
How CAM plants secure diurnal cytosolic proton homeostasis, and how malate remobilisation is regulated by light intensity and photoperiod remains unclear. Therefore, I developed a novel metabolic flux balance analysis (FBA) model that captures diel CAM biochemistry at a 2-h resolution, depicting all intracellular proton-involving reactions in a mesophyll cell. By integrating this computational model with plant physiological, biochemical, and molecular methods, we uncovered how diurnal proton homeostasis is secured in CAM plants. Our modelling work revealed that the mitochondrial phosphate carrier (PiC), which co-transports inorganic phosphate (Pi) and protons into the mitochondrial matrix, acts as a major consumer of cytosolic protons. These protons are subsequently consumed in the respiratory electron transport chain and ATP synthesis. Furthermore, we identified pyruvate orthophosphate dikinase (PPDK) as the most strictly light-regulated (intensity and photoperiod) player at the transcript, protein abundance, and enzyme activity levels, closely matching malate dynamics. This suggests PPDK as a key regulator of diurnal deacidification in CAM leaves.

Contact : Alexis De Angeli