O-Glycosylated Cell Wall Proteins are Essential in Root Hair Growth

VELASQUEZ SM; SALGADO SALTER J; GLOAZZO DOROSZ J; ESTEVEZ JM

Providence, Rhode Island

Congreso; Plant Biology 2013; 2013

American Society of Plant Biologists

Growing root hairs undergo intensive cell-wall changes to accommodate cell expansion at the apical end by a process known as tip growth. However, during plant growth these cells increase 200 times their original size by addition of sugars and proteins. To achieve this growth, changes in wall constituents and wall networks orchestrated by various enzymes and genes would be taking place. To address this issue, our group focused on root hairs as a model since they constitute a single cell system. One of the cell wall components is hydroxyproline-rich glycoproteins (HRGPs) that include extensins (EXTs) among other proteins. The posttranslational modifications undergone by EXTs is known as O-Glycosylation and it starts with the addition of an hydroxyl group on proline residues, carried out by Prolyl 4-hydroxylases (P4Hs) and secondly, the addition of arabinoses and/or galactoses, done by glycosyltransferases, finally these modified proteins form a covalent network at the cell wall. P4Hs define the O-glycosylation sites in EXTs. We explored the biological function of P4Hs, arabinosyltransferases (AraTs), and EXTs in root hair cell growth. Biochemical inhibition or genetic disruption of P4Hs, AraTs or EXTs resulted in the blockage of polarized growth in root hairs and reduced arabinosylation of EXTs. On the other hand, over-expression of P4Hs doubles the length of root hairs. AraTs and EXTs T-DNA mutants also resulted in a short root hair phenotype. Our results demonstrate that correct O-glycosylation on EXTs is essential for cell-wall self-assembly and, hence, root hair elongation. The changes that O-glycosylated cell-wall proteins undergo during growth represent a starting point to unravel the entire biochemical pathway involved in plant growth and development.