Résumé
Aquaporins of the Plasma membrane Intrinsic Protein (PIP) subfamily mediate multiple controls of plant tissue hydraulics. New insights into the mechanisms and hormonal and environmental cues at work in these regulations will be presented. A quantitative proteomic approach in Arabidopsis roots revealed a general role of PIP phosphorylation in regulation of root hydraulic conductivity in response to various abiotic, oxidative and nutritional stimuli. A strong regulation of aquaporins in lateral root primordia, based on auxin-dependent inhibition, was also uncovered. We show that auxin can thereby promote lateral root emergence by regulating the spatial and temporal distribution of root tissue water transport. In leaves, three PIP isoforms, including AtPIP2;1, contribute to water transport in inner tissues. Light-dependent changes in phosphorylation of AtPIP2;1 and expression in transgenic plants of aquaporin phosphorylation mutants showed that C-terminal diphosphorylation of this single isoform is necessary for light-dependent regulation of leaf hydraulics. Based on functional assays in epidermal peels, AtPIP2;1 was also found to play a role in stomatal closure, specifically in response to abscisic acid (ABA). Recent data indicate that AtPIP2;1 acts on guard cell water permeability, with ABA-dependent phosphorylation of the aquaporin at a specific site. The protein kinase and signaling intermediates involved will be discussed.