title: Distinct cinnamoyl CoA reductases involved in parallel routes to lignin in Medicago truncatula.
abstract: Cinnamoyl CoA reductases (CCR) convert hydroxycinnamoyl CoA esters to their corresponding cinnamyl aldehydes in monolignol biosynthesis. We identified two CCR genes in the model legume Medicago truncatula. CCR1 exhibits preference for feruloyl CoA, but CCR2 prefers caffeoyl and 4-coumaroyl CoAs, exhibits sigmoidal kinetics with these substrates, and is substrate-inhibited by feruloyl and sinapoyl CoAs. M. truncatula lines harboring transposon insertions in CCR1 exhibit drastically reduced growth and lignin content, whereas CCR2 knockouts grow normally with moderate reduction in lignin levels. CCR1 fully and CCR2 partially complement the irregular xylem gene 4 CCR mutation of Arabidopsis. The expression of caffeoyl CoA 3-O-methyltransferase (CCoAOMT) is up-regulated in CCR2 knockout lines; conversely, knockout of CCoAOMT up-regulates CCR2. These observations suggest that CCR2 is involved in a route to monolignols in Medicago whereby coniferaldehyde is formed via caffeyl aldehyde which then is 3-O-methylated by caffeic acid O-methyltransferase.
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhou
authors.forename: Lisa
authors.initials: L
authors.lastname: Jackson
authors.forename: Gail
authors.initials: G
authors.lastname: Shadle
authors.forename: Jin
authors.initials: J
authors.lastname: Nakashima
authors.forename: Stephen
authors.initials: S
authors.lastname: Temple
authors.forename: Fang
authors.initials: F
authors.lastname: Chen
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000378:metabolism*; D017360:Arabidopsis; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D017343:Genes, Plant / Q000235:genetics*; D017403:In Situ Hybridization; D007700:Kinetics; D008031:Lignin / Q000096:biosynthesis*; D046913:Medicago truncatula / Q000201:enzymology* / Q000235:genetics; D008780:Methyltransferases / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013379:Substrate Specificity
chemical_list: D008031:Lignin; D000445:Aldehyde Oxidoreductases; C019904:cinnamoyl CoA reductase; D008780:Methyltransferases; C059825:caffeoyl-CoA O-methyltransferase