Résumé
HIR are plant-specific proteins belonging to the superfamily of SPFH domain- containing proteins that are proposed to play scaffolding functions in membranes. HIR2 isoform organizes into plasma membrane (PM) nanodomains that correspond to nanoscale structures enriched in specific lipids and proteins, acting as signaling/regulation platforms. Using state-of-the-art microscopy techniques, we investigated the mechanisms governing the trafficking and the organization into nanodomains of Arabidopsis HIR2 protein. Our findings demonstrated that the S- acylations of two N-terminally located cysteines act redundantly to target HIR2 to the PM, although they are not essential for HIR2 nanoclustering. Moreover, we provided evidence that the lipid composition of the PM in sterols and very long-chain fatty acids influences HIR2 nanodomain organization. Importantly, we showed that HIR2 oligomerization via its C-terminal region was essential for its organization into nanodomains and for maintaining HIR2 lateral stability in the PM.So far, the molecular functions of HIR proteins remain largely unknown. Interestingly, HIR proteins were identified in the interactome of Arabidopsis aquaporins from the PIP subfamily that facilitate the transport of water and H2O2 across the PM. We investigated a putative role of HIR2 in the regulation of PIP proteins and showed using co-immunopurifications and the split-ubiquitin method that HIR2 forms a complex with PIP proteins. Additionally, HIR influence the radial transport of water in the root, which is largely insured by PIP proteins, as attested by a strong reduction of the root hydraulic conductivity (Lpr) in Arabidopsis hir mutants. Interestingly, co-expression of HIR2 with PIP2;1 protein in yeast enhances the PIP2;1-mediated transport of H2O2, suggesting a positive regulatory role of HIR2 on PIP. Ongoing research aims to decipher the role of HIR2 in PIP regulation by exploring a putative impact of HIR2 on PIP dynamics in PM nanodomains and/or on the modulation of PIP activity by phosphorylation.