title: Switchgrass (Panicum virgatum) possesses a divergent family of cinnamoyl CoA reductases with distinct biochemical properties.
abstract: The down-regulation of enzymes of the monolignol pathway results in reduced recalcitrance of biomass for lignocellulosic ethanol production. Cinnamoyl CoA reductase (CCR) catalyzes the first step of the phenylpropanoid pathway specifically dedicated to monolignol biosynthesis. However, plants contain multiple CCR-like genes, complicating the selection of lignin-specific targets. This study was undertaken to understand the complexity of the CCR gene family in tetraploid switchgrass (Panicum virgatum) and to determine the biochemical properties of the encoded proteins. Four switchgrass cDNAs (most with multiple variants) encoding putative CCRs were identified by phylogenetic analysis, heterologously expressed in Escherichia coli, and the corresponding enzymes were characterized biochemically. Two cDNAs, PvCCR1 and PvCCR2, encoded enzymes with CCR activity. They are phylogenetically distinct, differentially expressed, and the corresponding enzymes exhibited different biochemical properties with regard to substrate preference. PvCCR1 has higher specific activity and prefers feruloyl CoA as substrate, whereas PvCCR2 prefers caffeoyl and 4-coumaroyl CoAs. Allelic variants of each cDNA were detected, but the two most diverse variants of PvCCR1 encoded enzymes with similar catalytic activity. Based on its properties and expression pattern, PvCCR1 is probably associated with lignin biosynthesis during plant development (and is therefore a target for the engineering of improved biomass), whereas PvCCR2 may function in defense.
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA.
authors.forename: Luis L
authors.initials: LL
authors.lastname: Escamilla-Treviño
authors.forename: Hui
authors.initials: H
authors.lastname: Shen
authors.forename: Srinivasa Rao
authors.initials: SR
authors.lastname: Uppalapati
authors.forename: Tui
authors.initials: T
authors.lastname: Ray
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Tang
authors.forename: Timothy
authors.initials: T
authors.lastname: Hernandez
authors.forename: Yanbin
authors.initials: Y
authors.lastname: Yin
authors.forename: Ying
authors.initials: Y
authors.lastname: Xu
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D000483:Alleles; D018076:DNA, Complementary; D004926:Escherichia coli; D017343:Genes, Plant; D014644:Genetic Variation; D008031:Lignin / Q000096:biosynthesis / Q000235:genetics*; D005810:Multigene Family; D008897:Panicum / Q000201:enzymology* / Q000235:genetics; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011123:Polyploidy; D013379:Substrate Specificity / Q000235:genetics
chemical_list: D018076:DNA, Complementary; D010940:Plant Proteins; D008031:Lignin; D000445:Aldehyde Oxidoreductases; C019904:cinnamoyl CoA reductase