PRX1, PRX44, and PRX73 are Class-III extensin-related peroxidases that modulates root hair growth in Arabidopsis thaliana

Root hair cells acts at the root surface as important sensors of soil conditions. Root hairs are able to expand several hundred times their original size in a couple of hours to reach and uptake water-soluble nutrients. This fast and oscillating growth requires a continuous remodelling of the cell wall to allow for the root hair to expand in a tightly controlled manner. Root hair cell walls contain polysaccharides and hydroxyproline-rich glycoproteins (HRGPs) including extensins (EXTs). Class-III peroxidases (PRXs) are secreted into the apoplastic space and are thought to trigger either cell wall loosening mediated by oxygen radical species, or polymerization of cell wall components including the Tyr-mediated assembly of an EXT network (EXT-PRXs). The precise role of each of these EXT-PRXs remains to be discovered. By using genetic, biochemical and modeling approaches we have identified and characterized three root hair specific EXT-PRXs, PRX01, PRX44, and PRX73. The triple mutant prx01,44,73 as well as the overexpressors for PRX44 and PRX73 showed opposite effect on root hair growth, peroxidase activity, ROS-production, cell wall thickness, and Tyr-crosslinks in EXTs. These results suggest a key role of these three EXT-PRXs in the control of root hair growth linked to cell wall properties during polar cell expansion. Finally, modeling and docking calculations have suggested these three EXT-PRXs might be able to interact with non-O-glycosylated sections of EXT peptides that reduced Tyr-to-Tyr intra-chain distances in EXT aggregates and might enhance Tyr-crosslinks.