PROLINE HYDROXYLATION ON HYDROXYPROLINE RICH-GLYCOPROTEINS (HRGPS) MEDIATED BY P4HS IS CRUCIAL FOR POLARIZED GROWTH IN ARABIDOPSIS ROOT HAIRS

SILVIA M. VELASQUEZ; MARTINIANO M. RICARDI; JAVIER GLOAZZO DOROSZ; NORBERTO D. IUSEM; JOSE M. ESTEVEZ

La Plata

Congreso; XXVIII Reunión Argentina de Fisiología Vegetal.; 2010

Sociedad Argentina de Fisiología Vegetal.

Precise biological roles for posttranslational modifications on plant O-glycoproteins have been elusive. Prolyl 4-hydroxylases from Arabidopsis (AtP4Hs) define O-glycosylation sites on hydroxyproline rich-proteins (HRGPs) in root hairs as a single cell system. Only few AtP4Hs are highly expressed in root hair, for each one of them a single homozygous T-DNA mutant was isolated. Among these mutants: p4h2.1 and p4h2.2, p4h5 and p4h13 showed drastically reduced root hair lengths. In agreement with that, complete loss of transcript was confirmed by RT-PCR for p4h5 and p4h13 and much lower transcripts were detected in p4h2.1 and p4h2.2. To verify that disruption of root, P4Hs specifically blocked elongation growth of root hairs, each rhP4H protein coding sequence GFP-tagged was expressed, driven by their own native promoter in their respective mutant background. The 3 constructs P4H2pro::P4H2-GFP, P4H13pro::P4H13-GFP and P4H5pro::P4H5-GFP were able to fully complement the root hair phenotype. Next, rhP4Hs were constitutively expressed under the control of 35S CaMV promoter. The constitutively expression of P4Hs in Wt background did not increase further more the length of the root hairs. At tissue level, localization of rhP4H2 is focalized only in tricoblast cells whereas rhP4H5 and rhP4H13 localize in both trichoblast and atricoblast cell types in roots suggesting that there is not a complete overlap between rhP4Hs expression. All the previously described results demonstrate that AtP4H2, AtP4H5 and AtP4H13 are crucial players for root hair growth. The control of growth by O-glycosylated EXTs may represent a more general mechanism for regulating cell expansion in different plant cell types.