Doctorate thesis of University of Montpellier

Wednesday, November 29, 2017

 

Functional characterisation of proteins interacting with the aquaporin PIP2;1

Chloé Champeyroux
BPMP, “Aquaporins” team

 

Jury :
François CHAUMONT, Professor, Institute of Life Sciences and Earth, Louvain University, Rapporteur
Laurent NUSSAUME, Research Director, Biosciences et Biotechnology Institut, CEA-CNRS-Aix Marseille University , Rapporteur
Marie BARBERON, Researcher Associate, Department Vegetable Molecular Biology, Lausanne University , Reviewer
Alain GOJON, Research Director, UMR Biochemistry and Plant Molecular Physiology, INRA Montpellier, Reviewer
Véronique SANTONI, Research Director, UMR Biochemistry and Plant Molecular Physiology, INRA Montpellier, Thesis Director

 

Abstract :
The root hydraulic conductivity (Lpr) reflects the water transport capacity of the root. During its transfer from the soil to the xylem, water can diffuse in the apoplasm or through the cells (cell-to-cell pathway). At the endodermis, the apoplastic diffusion of water is blocked by the Casparian Strip and suberin lamellae. The cell-to-cell pathway mainly relies on aquaporin activity which can be regulated by protein interactions. This study aims at characterizing new interactants of the root aquaporin PIP2;1: the receptor kinase RKL1 and 4 proteins of unknown function belonging to the Casparian Strip membrane domain Protein Like 1 sub-family (CASPL1-B1/B2/D1/D2). RKL1 is expressed in the endodermis, can physically interact with PIP2;1 and stimulates its water transport function in vitro. However a loss-of-function of RKL1 does not affect the Lpr., independently of a putative functional redundancy with its closest homolog RLK902. Concerning CASPL, D1 is expressed in every tissue of the root whereas B1, B2 and D2 appear to be specifically expressed in suberized tissues. This suggests a putative role of these isoforms in aquaporin regulation and suberisation. At the molecular level, D2 does not modulate PIP2;1 water transport activity despite a physical interaction between the two partners. By contrast, B1 interacts with PIP2;1 preferentially in its phosphorylated form and enhances the water transport activity of the aquaporin. At the plant level, disrupting one or two CASPL genes neither impact the Lpr nor affect the suberisation. However, the loss of function of both PIP2;1 and PIP2;2 reveals a negative effect of these aquaporins on suberisation. In conclusion, this study, uncovered novel regulation mechanisms of aquaporins. It also raises the question of the existence of a putative relationship between water transport by the apoplastic pathway and by aquaporins.