Functional testing of a PF02458 homologue of putative rice arabinoxylan feruloyl transferase genes in Brachypodium distachyon

Main conclusion We show that changing the expression of a putative feruloyl transferase gene belonging to the BAHD acyl-transferase family alters the levels of cell wall esterified ferulates and diferulates in Brachypodium distachyon cell walls. While the potential of grass cell walls for biofuel production has been realized, the technology for lignocellulosic biomass conversion for the production of ethanol is still inefficient because of structural mechanisms that plants have evolved to make the cell wall recalcitrant to enzymatic attack. One of these mechanisms in grasses involves the esterification of arabinoxylans in the cell wall with ferulic acid via an ester linkage to arabinose side chains on xylans. These ferulates undergo oxidative coupling reactions to form ferulate dimers, thus crosslinking polysaccharides. Arabinoxylan feruloylation is an important factor that determines cell wall recalcitrance because it directly cross-links xylans and because ferulates act as nucleating sites for the formation of lignin and for the linkage of lignin to the xylan/cellulose network. Here we report on the effects of changing the expression of Bradi2g43520 (BdAT1), a homologue of the rice feruloyl transferase gene Os01g42880 belonging to the Pfam PF02458 family, in Brachypodium distachyon. Down regulation in several independent RNAi:: BdAT1 lines, resulted in up to a 35 % reduction of ferulate levels in both leaves and stems compared to control plants, over 2-3 generations of selfing. In contrast, overexpression of putative BdAT1 resulted in an increase of up to 58 and 47 % of ferulate levels in leaves and stems, respectively, compared to control plants and analyzed over 2-3 generations of selfing. These findings suggest that Bradi2g43520 may be a good candidate for feruloylation of AX in Brachypodium.