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Title: The PARVUS gene is expressed in cells undergoing secondary wall thickening and essential for glucuronoxylan biosynthesis

Author
item LEE, C - UGA
item ZHONG, R - UGA
item RICHARDSON, E - UGA
item Himmelsbach, David
item McPhail, Brooks
item YE, Z-H - UGA

Submitted to: Plant and Cell Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2007
Publication Date: 12/12/2007
Citation: Lee, C., Zhong, R., Richardson, E.A., Himmelsbach, D.S., Mcphail, B.T., Ye, Z. 2007. The PARVUS gene is expressed in cells undergoing secondary wall thickening and essential for glucuronoxylan biosynthesis. Plant And Cell Physiology 48: 1659-1672, 2007.

Interpretive Summary: Modification of xylans associated with lignocellulosic cell wall tissue in woody tissue has the potential of making cellulosic biomass more suitable for biofuel production. As such, knowledge of gene roles in xylan biosynthesis is essential. In this work the role of the PARVUS gene in the generation of the 4-unit reducing end sequence of the glucuronoxylan polymer has been identified. Using proton NMR spectroscopy, it has been discovered that mutation of the PARVUS gene can result in the loss of the reducing end 4-sugar unit and in the absence of glucuronic acid side chains generating drastic reduction in cell wall thickening. Thus, control of this gene could enable more efficient conversion of woody biomass to biofuel.

Technical Abstract: Xylan together with cellulose and lignin are the three major components of secondary walls in wood and elucidation of the biosynthetic pathway of xylan is of importance for potential modification of secondary wall composition to produce wood with improved properties. So far, three Arabidopsis glycosyltransferases, FRAGILE FIBER8, IRREGULAR XYLEM8 and IRREGULAR XYLEM9, have been implicated in glucuronoxylan (GX) biosynthesis. In this study, we demonstrate that PARVUS, which is a member of family GT8, is required for the biosynthesis of the tetrasaccharide primer sequence, beta-D-Xyl-(1-3)-alpha-L-Rha-(1'2)-alpha-D-GalA-(1-4)-D-Xyl, located at the reducing end of GX. The PARVUS gene is expressed during secondary wall biosynthesis in fibers and vessels, and its encoded protein is predominantly localized in the endoplasmic reticulum. Mutation of the PARVUS gene leads to a drastic reduction in secondary wall thickening and GX content. Structural analysis of GX using proton NMR spectroscopy revealed that the parvus mutation causes a loss of the tetrasaccharide primer sequence at the reducing end of GX and an absence of glucuronic acid side chains in GX. Activity assay showed that the xylan xylosyltransferase and glucuronyltransferase activities were not affected in the parvus mutant. Together, these findings implicate a possible role of PARVUS in the initiation of biosynthesis of the GX tetrasaccharide primer sequence and provide novel insights into the mechanisms of GX biosynthesis.