Towards functional characterization of CAZy family GT77 Glycosyltransferases

BENT LARSEN PETERSEN, JOSE M. ESTEVEZ, BODIL JØRGENSEN, SASCHA GILLE, JESPER HARHOLDT, YANG ZHANG, TADASHA ISHII, STEVEN B. LEVERY, MARKUS PAULY, PETER ULVSKOV

Bryant University Smithfield, RI

Congreso; Plant Cell Wall, Gordon Conference; 2009

Gordon Conference

Two GT-family-77 Arabidopsis mutants, rra-1 and rra-2, were shown to have areduced residual arabinose phenotype in a fraction that is not readily releasedfrom the cell wall. Involvement of the corresponding wild type genes RRA1and RRA2 in arabinosylation of extensins was suggested (Egelund et al. 2007,Plant Mol. Biol. 64:439-451). Recently, a xyloglucanase based screen onArabidopsis T-DNA-mutants identified a mutant, xeg113, where the extensincomponernt of the cell wall was under-arabinosylated (Gille et al. 2009,P.N.A.S., in press). Interestingly XEG113 (At2g35610) is also classiflied inGT-family-77. The similarity of RRA1-3 and XEG113 to glycosyltransferases fromChlamydomonas reinhardtii has prompted us to propose that the reducedarabinose phenotype of the mutants shall be explained in terms ofcompromised extensin arabinosylation.The following scenarios are considered: The RRAs and XEG113 are: 1. not arabinosyltransferases. The reduced arabinose phenotype is a pleiotropic effect. 2. inverting arabinosyltransferases (contrary to what is expected of GT77s) and thus create á-arabinans. 3. retaining UDP-araf : extensin Hyp â-AraTs and hence add the innermost Araf to extensin Hyp residues. 4. retaining UDP-araf : extensin (Ara)1-2 â-AraTs and hence transfer the second or third arabinofuranosyl residue of extensin arabinans.