Overexpression of a Sugarcane BAHD Acyltransferase Alters Hydroxycinnamate Content in Maize Cell Wall

Abstract

The purification of hydroxycinnamic acids [p-coumaric acid (pCA) and ferulic acid (FA)] from grass cell walls requires high-cost processes. Feedstocks with increased levels of one hydroxycinnamate in preference to the other are therefore highly desirable. We identified and conducted expression analysis for nine BAHD acyltransferase ScAts genes from sugarcane. The high conservation of AT10 proteins, together with their similar gene expression patterns, supported a similar role in distinct grasses. Overexpression of ScAT10 in maize resulted in up to 75% increase in total pCA content. Mild hydrolysis and derivatization followed by reductive cleavage (DFRC) analysis showed that pCA increase was restricted to the hemicellulosic portion of the cell wall. Furthermore, total FA content was reduced up to 88%, resulting in a 10-fold increase in the pCA/FA ratio. Thus, we functionally characterized a sugarcane gene involved in pCA content on hemicelluloses and generated a C4 plant that is promising for valorizing pCA production in biorefineries.

Overexpression of the rice BAHD acyltransferase AT10 increases xylan-bound p-coumarate and reduces lignin in Sorghum bicolor

“…Assuming comparable response factors for p CA-Ara and FA-Ara measured under our LC–MS conditions, we can estimate that p -coumaroylation of arabinosyl residues on GAX represent ~ 1% of total arabinose acylation (i.e., feruloylation being more frequent). This is similar to previous values obtained with maize stems showing ratios of acylation of arabinose units by p CA in the range of 2.5% or less [ 7 , 22 ]. In sorghum, acyltransferases responsible for xylan p -coumaroylation and feruloylation are still unknown, but several gene candidates have been proposed based on their higher expression levels in elongating internodes [ 24 ].…”

“…As for p CA transferases, overexpression of OsAT10 in rice results in higher amount of p CA-Ara in young leaves, whereas grain cell walls from barley genotypes mutated in HvAT10 show approximately one-third less p CA than wild-type genotypes [ 19 , 20 ]. Similarly, silencing of SvBAHD05 in S. viridis reduces p CA-Ara content, while overexpression of sugarcane ScAT10 increases p CA-Ara in maize [ 21 , 22 ]. Interestingly, overexpression of these putative p -coumaroyl-CoA GAX transferase AT10 genes is often accompanied with enhancements of cell wall saccharification efficiency, which has promoted their use to improve biomass quality in bioenergy crops [ 22 , 23 ].…”

“…Similarly, silencing of SvBAHD05 in S. viridis reduces p CA-Ara content, while overexpression of sugarcane ScAT10 increases p CA-Ara in maize [ 21 , 22 ]. Interestingly, overexpression of these putative p -coumaroyl-CoA GAX transferase AT10 genes is often accompanied with enhancements of cell wall saccharification efficiency, which has promoted their use to improve biomass quality in bioenergy crops [ 22 , 23 ]. Such reductions of cell wall recalcitrance have been tentatively linked to a decrease of cell wall-bound FA measured in plants overexpressing AT10 transferases [ 19 , 22 , 23 ].…”

“…Interestingly, overexpression of these putative p -coumaroyl-CoA GAX transferase AT10 genes is often accompanied with enhancements of cell wall saccharification efficiency, which has promoted their use to improve biomass quality in bioenergy crops [ 22 , 23 ]. Such reductions of cell wall recalcitrance have been tentatively linked to a decrease of cell wall-bound FA measured in plants overexpressing AT10 transferases [ 19 , 22 , 23 ]. As previously hypothesized, this effect on FA esters might occur if p -coumaroyl-CoA and feruloyl-CoA compete for transfer onto a shared acceptor (e.g., UDP-arabinose) prior to incorporation into xylan chains such that increase of p CA transfer leaves less free acceptor available for FA transfer activity.…”

“…Alternatively, since p -coumaroyl-CoA is a metabolic precursor to feruloyl-CoA, a higher amount of p -coumaroyl-CoA recruited for xylan acylation may indirectly affect the pool of feruloyl-CoA available for such activity [ 20 ]. No effects on lignin monomeric composition and/or lignin content have been observed in rice, switchgrass, and maize lines expressing AT10 transferases [ 19 , 22 , 23 ].…”