Root hairs are single cells specializedin the absorption of water andnutrients from the soil. Growing roothairs require intensive cell-wall changesto accommodate cell expansion at theapical end by a process known as tipor polarized growth. We have recentlyshown that cell wall glycoproteins suchas extensins (EXTs) are essential componentsof the cell wall during polarizedgrowth. Proline hydroxylation, anearly posttranslational modification ofcell wall EXTs that is catalyzed by prolyl4-hydroxylases (P4Hs), defines the subsequentO-glycosylation sites in EXTs.Biochemical inhibition or genetic disruptionof specific P4Hs resulted in theblockage of polarized growth in roothairs. Our results demonstrate thatcorrect hydroxylation and also furtherO-glycosylation on EXTs are essentialfor cell-wall self-assembly and, hence,root hair elongation. The changes thatO-glycosylated cell-wall proteins likeEXTs undergo during cell growth representa starting point to unravel the entirebiochemical pathway involved in plantdevelopment.
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