Filling the Gaps to Solve the Extensin Puzzle

MARZOL, ELIANA; BORASSI, CECILIA; BRINGAS, MAURO; SEDE, ANA; RODRÍGUEZ GARCIA, DIANA ROSA; CAPECE, LUCIANA; ESTEVEZ, JOSE M.

MOLECULAR PLANT

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2018

1674-2052

Extensins (EXTs) are highly repetitive plant O-glycoproteins that require several post-translational modifications (PTMs) to become functional in plant cell walls. First, they are hydroxylated on contiguous proline residues; then, they are O-glycosylated on hydroxyproline (Hyp) and serine. After secretion into the apoplast, O-glycosylated EXTs form a tridimensional network organized by inter- and intra-Tyr linkages. Recent studies have made significant progress in the identification of the enzymatic machinery required to process EXTs, which includes prolyl 4-hydroxylases (P4Hs), glycosyltransferases (GTs), papain-type cysteine-endopeptidases (CEPs), and peroxidases (PERs). EXTs are abundant components of plant tissues, and are particularly important in rapidly expanding root hairs and pollen tubes, which grow in a polar manner. Small changes in EXT PTMs affect fast-growing cells, although the molecular mechanisms underlying this regulation are unknown. In this review, we highlight recent advances in our understanding of EXT modifications  throughout the secretory pathway, EXT assembly in the cell walls, and possible sensing  mechanisms triggered by the Catharanthus roseus cell surface sensor receptor-like kinases (CrRLK1Ls) located at the interface between the apoplast and the cytoplasmic side of the plasma membrane.