The role of glycosyltransferase 61 and BAHD genes in determining ferulate & para-coumarate content of the cell walls of the Poaceae

Lignocellulosic biomass, composed largely of plant cell walls, of economically important cereal crops is remarkably recalcitrant to digestion, both in second generation biofuel production and ruminant nutrition applications. Ferulic acid (FA) esterified to arabinoxylan (AX) forms oxidatively linked dimers and oligomers which cross-link polysaccharide chains. FA is also a nucleation site for lignin formation. These cross-links are major inhibitors of enzymatic digestion, and therefore FA is a key target for improving the digestibility of grass cell walls. Also, para coumaric acid (pCA) esterified to AX may be involved in the polymerisation of lignin. Despite the importance of cell wall bound hydroxycinnamic acids, many of the genes and enzymes responsible for the esterification of pCA and FA to AX remain to be elucidated. The BAHD and glycosyltransferase (GT)61 gene families have previously been identified as likely to be involved in the process (Mitchell et al., 2007). Here, the role of candidate genes within the BAHD and GT61 families in pCA and FA esterification to AX is investigated in the model organism Brachypodium distachyon (Brachypodium). Jasmonic acid induced large increases in cell wall-esterified pCA, and moderate increases in FA and FA dimer in Brachypodium callus, accompanied by up-regulation of genes within the BAHD and GT61 families. Furthermore, transformation of Brachypodium with RNAi constructs designed to knock-down expression of paralogues BdGT61.9p1 and BdGT61.9p2 resulted in decreased cell wall-esterified FA. Overexpression of BdGT61.9p1 in Brachypodium resulted in a small increase in the 8-8-coupled FA dimer. These findings complemented the existing body of evidence for the involvement of genes within the BAHD and GT61 families in hydroxycinnamic acid esterification to AX.