Prolyl 4-Hydroxylase 5 that defines the subsequent O-glycosylation sites in extensins controls polarized growth in plant cells

VELÁSQUEZ SM; RICARDI MM; ESTEVEZ JM

Paris

Congreso; The 26th International Conference on Arabidopsis Research; 2015

ICAR

Root hairs are single cells that develop by tip growth and are specialized in the absorption of nutrients. Structural cell walls imposed constraints prompt utilization of new molecules to accomplish tip growth in plants. Their cell walls are composed of polysaccharides and hydroxyproline-rich glycoproteins (HRGPs) that include extensins (EXTs). Proline hydroxylation, an early post-translational modification (MPT) of HRGPs that is catalyzed by prolyl 4-hydroxylases (P4Hs), defines the subsequent O-glycosylation sites in EXTs, which are mainly arabinosylated. Here, we explored the biological function of P4Hs in root hair cell growth. Biochemical inhibition or genetic disruption of P4Hs resulted in the blockage of polarized growth in root hairs and reduced arabinosylation of EXTs. Secondly, we demonstrate that prolyl-4 hydroxylase 5 (P4H5), and to a lower extent P4H2 and P4H13, are pivotal for EXT-mediated root hair tip-growth. These three P4Hs are targeted to the secretory pathway, most specifically to the ER and Golgi compartments, where P4H5 forms dimers with P4H2 and P4H13 suggesting the existence of P4Hs protein complexes. Thirdly, we explored the subcellular localization and substrate specificity of the P4H5, as well as the resulting cell wall architecture in the p4h5 mutant. We also addressed the physiological significance of the MPTs of EXTs. In particular, mutants who were deficient in Hyp-O-arabinosylation or in Ser-O-galactosylation showed shorter root hairs, due to both slower kinetics and premature growth termination. Our results demonstrate that correct O-glycosylation on EXTs is essential for cell wall self-assembly and hence root hair elongation in Arabidopsis thaliana.