Grass cell wall feruloylation: distribution of bound ferulate and candidate gene expression in Brachypodium distachyon

Abstract

The cell walls of grasses such as wheat, maize, rice, and sugar cane, contain large amounts of ferulate that is ester-linked to the cell wall polysaccharide glucuronoarabinoxylan (GAX). This ferulate is considered to limit the digestibility of polysaccharide in grass biomass as it forms covalent linkages between polysaccharide and lignin components. Candidate genes within a grass-specific clade of the BAHD acyl-coA transferase superfamily have been identified as being responsible for the ester linkage of ferulate to GAX. Manipulation of these BAHD genes may therefore be a biotechnological target for increasing efficiency of conversion of grass biomass into biofuel. Here, we describe the expression of these candidate genes and amounts of bound ferulate from various tissues and developmental stages of the model grass Brachypodium distachyon. BAHD candidate transcripts and significant amounts of bound ferulate were present in every tissue and developmental stage. We hypothesize that BAHD candidate genes similar to the recently described Oryza sativa p-coumarate monolignol transferase (OsPMT) gene (PMT sub-clade) are principally responsible for the bound para-coumaric acid (pCA), and that other BAHD candidates (non-PMT sub-clade) are responsible for bound ferulic acid (FA). There were some similarities with between the ratio of expression non-PMT/PMT genes and the ratio of bound FA/pCA between tissue types, compatible with this hypothesis. However, much further work to modify BAHD genes in grasses and to characterize the heterologously expressed proteins is required to demonstrate their function.

p‐Coumaroyl‐CoA:monolignol transferase (PMT) acts specifically in the lignin biosynthetic pathway in Brachypodium distachyon

“…The predicted protein Bradi2g36910 was found to have the highest sequence homology to OsPMT, sharing 63% amino acid sequence identity and 75% similarity. Recently published phylogenetic trees that contained both Brachypodium and rice BAHD acyltransferases showed that Bradi2g36910 is the most closely related Brachypodium protein to OsPMT (Bartley et al , 2013; Molinari et al , 2013). …”

Breeding maize for silage and biofuel production, an illustration of a step forward with the genome sequence

“…A study of gene deregulation in rice supported the involvement of these putative feruloyl-transferases [103]. Investigations in Brachypodium [96] suggested that the most probable candidates for arabinoxylan feruloylation were the orthologs of BAHD genes in the OsAt1/2/6/7/8/9-like sub-clade. Out of the seven maize orthologs of the rice BAHD genes, only two colocalizations were observed with IVNDFD QTLs, in bins 3.09 and 6.05.…”

“…Several members of the GT61 family (clade A) were shown to be xylan O-3-arabinosyltransferases in wheat and rice [90,95,96]. A mutation in a GT61 gene, involved in arabinoxylan substitution, was shown to improve saccharification in Brachypodium plants, without any significant alteration in plant growth or stem strength [97].…”

Structural Characterization of Lignin and Its Degradation Products with Spectroscopic Methods

“…Gymnosperms contain almost entirely G unit in lignins; dicotyledonous angiosperms contain G and S units in lignins; and all the G, S, and H units can be found in monocotyledonous lignins [5]. Other units with relatively fewer contents were also identified in the lignin of LCBM, such as ferulates and coumarates [6]. Biosynthesis of lignin is a process that monomers undergo radical coupling reactions to form racemic, cross-linked, and phenolic polymer, by which lignin content and composition may vary significantly in different LCBMs [7].…”