Suppression of a single BAHD gene in <italic>Setaria viridis</italic> causes large, stable decreases in cell wall feruloylation and increases biomass digestibility.

Summary: Feruloylation of arabinoxylan (AX) in grass cell walls is a key determinant of recalcitrance to enzyme attack, making it a target for improvement of grass crops, and of interest in grass evolution. Definitive evidence on the genes responsible is lacking so we studied a candidate gene that we identified within the BAHD acyl‐CoA transferase family. We used RNA interference (RNAi) silencing of orthologs in the model grasses <italic>Setaria viridis</italic> (<italic>SvBAHD01</italic>) and <italic>Brachypodium distachyon</italic> (<italic>BdBAHD01</italic>) and determined effects on AX feruloylation. Silencing of <italic>SvBAHD01</italic> in <italic>Setaria</italic> resulted in a <italic>c</italic>. 60% decrease in AX feruloylation in stems consistently across four generations. Silencing of <italic>BdBAHD01</italic> in <italic>Brachypodium</italic> stems decreased feruloylation much less, possibly due to higher expression of functionally redundant genes. <italic>Setaria SvBAHD01</italic> RNAi plants showed: no decrease in total lignin, approximately doubled arabinose acylated by <italic>p</italic>‐coumarate, changes in two‐dimensional NMR spectra of unfractionated cell walls consistent with biochemical estimates, no effect on total biomass production and an increase in biomass saccharification efficiency of 40–60%. We provide the first strong evidence for a key role of the <italic>BAHD01</italic> gene in AX feruloylation and demonstrate that it is a promising target for improvement of grass crops for biofuel, biorefining and animal nutrition applications. [ABSTRACT FROM AUTHOR]