Séminaire Interne
Jeudi 2 février à 14h00 Salle Bibliothèque

Roxane Doireau:
Supervisor: Alexis DeAngeli
Team: INFLUX, IPSIM

The transport of organic anions (malate2-, fumarate2- and citrate3-) is crucial in plant physiology. Indeed, they are a source of carbon skeletons necessary for metabolism, they can participate to the osmotic load of the cells and play a role in the maintenance of cellular. Among them, malate appears to be a central metabolite. In fact, vacuolar malate fluctuates relatively rapidly, whereas cytosolic malate is kept at a rather constant level allowing optimal metabolism. Fumarate is present in Arabidopsis in quite high quantity. It is a transient storage form of fixed carbon in plants and is directly synthetized in the cytosol from malate. In order to fulfil their functions organic anions are mobile within the plant and within the cells. In Arabidopsis thaliana, organic anions transport is made possible by numerous channels and transporters, including the AtALMT channel family. Among the latter, two anion channels, AtALMT9 and AtALMT5 are located in the tonoplast of the mesophyll and guard cells, where they allow the transport of malate2- and fumarate2- into the vacuole. almt5 and almt9 are involved in stomatal aperture process by generating ion influx into the guard cells vacuoles. Moreover, almt9 and almt5almt9 loss-of-function plants display a growth phenotype with a lower biomass than wild-type plants. Notably, the leaves of these mutants display a modified malate2- and fumarate2- content. My work aims to characterize these two channels and identify the causes of the visible phenotype of our loss-of-function lines.

Omar Hdedeh
Supervisor: Enric ZELAZNY
Team: AQUA, IPSIM

Role of the membrane nanodomain protein HIR2 in the regulation of PIP2 aquaporins in Arabidopsis thaliana

The plasma membrane (PM) is involved in the cellular communication, the transduction of environmental signals and the transport of water and ions. The PM is a heterogeneous structure comprising a multitude of different nanodomains containing specific lipids and proteins. Hypersensitive Induced Reaction (HIR) proteins are specific to plants and only localize in membrane nanodomains. So far, the function of HIR remains mysterious. Interestingly, some HIR proteins, including HIR2 isoform, were identified in the interactome of aquaporins from the Plasma membrane Intrinsic Proteins (PIP) sub-family that facilitate the movement of water across the PM and are essential to maintain plant water status. Whether HIR proteins regulate PIP to modulate water transport remains to be determined. The aim of my thesis is to investigate the significance of the interaction between HIR2 and PIP proteins at the cellular level and its physiological outcome. First, I confirmed the interaction between HIR2 and PIP2 proteins by co-immunopurification and split-ubiquitin approaches. Secondly, I showed that the root hydraulic conductivity (Lpr) is decreased in plants where HIR2 and multiple HIR genes were mutated by the CRISPR/Cas9 technic, suggesting that HIR behave as positive regulators of aquaporins. One hypothesis is that HIR2 may act as a scaffolding protein allowing the recruitment of PIP in specific PM nanodomains to regulate their activity. Different approaches combining microscopy and biochemistry are now carried out to investigate how HIR2 can regulate PIP proteins.