title: p-Coumaroyl-CoA:monolignol transferase (PMT) acts specifically in the lignin biosynthetic pathway in Brachypodium distachyon.
abstract: Grass lignins contain substantial amounts of p-coumarate (pCA) that acylate the side-chains of the phenylpropanoid polymer backbone. An acyltransferase, named p-coumaroyl-CoA:monolignol transferase (OsPMT), that could acylate monolignols with pCA in vitro was recently identified from rice. In planta, such monolignol-pCA conjugates become incorporated into lignin via oxidative radical coupling, thereby generating the observed pCA appendages; however p-coumarates also acylate arabinoxylans in grasses. To test the authenticity of PMT as a lignin biosynthetic pathway enzyme, we examined Brachypodium distachyon plants with altered BdPMT gene function. Using newly developed cell wall analytical methods, we determined that the transferase was involved specifically in monolignol acylation. A sodium azide-generated Bdpmt-1 missense mutant had no (<0.5%) residual pCA on lignin, and BdPMT RNAi plants had levels as low as 10% of wild-type, whereas the amounts of pCA acylating arabinosyl units on arabinoxylans in these PMT mutant plants remained unchanged. pCA acylation of lignin from BdPMT-overexpressing plants was found to be more than three-fold higher than that of wild-type, but again the level on arabinosyl units remained unchanged. Taken together, these data are consistent with a defined role for grass PMT genes in encoding BAHD (BEAT, AHCT, HCBT, and DAT) acyltransferases that specifically acylate monolignols with pCA and produce monolignol p-coumarate conjugates that are used for lignification in planta.
authors.affiliation: School of Biological Sciences, Illinois State University, Normal, IL, 61790, USA; Department of Energy Great Lakes Bioenergy Research Center, Madison, WI, 53706, USA.
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Petrik
authors.forename: Steven D
authors.initials: SD
authors.lastname: Karlen
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Cass
authors.forename: Dharshana
authors.initials: D
authors.lastname: Padmakshan
authors.forename: Fachuang
authors.initials: F
authors.lastname: Lu
authors.forename: Sarah
authors.initials: S
authors.lastname: Liu
authors.forename: Philippe
authors.initials: P
authors.lastname: Le Bris
authors.forename: Sébastien
authors.initials: S
authors.lastname: Antelme
authors.forename: Nicholas
authors.initials: N
authors.lastname: Santoro
authors.forename: Curtis G
authors.initials: CG
authors.lastname: Wilkerson
authors.forename: Richard
authors.initials: R
authors.lastname: Sibout
authors.forename: Catherine
authors.initials: C
authors.lastname: Lapierre
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: John C
authors.initials: JC
authors.lastname: Sedbrook
mesh_terms: D058431:Brachypodium / Q000201:enzymology*; D003373:Coumaric Acids / Q000378:metabolism; D008031:Lignin / Q000096:biosynthesis*; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000378:metabolism; D011422:Propionates
chemical_list: D003373:Coumaric Acids; D010940:Plant Proteins; D011422:Propionates; D008031:Lignin; C495469:p-coumaric acid
keywords: BAHD acyltransferase; Brachypodium distachyon; DFRC method; NMR; biomass; grass; lignin; lignin acylation; thioacidolysis