title: Role of bifunctional ammonia-lyase in grass cell wall biosynthesis.
abstract: L-Phenylalanine ammonia-lyase (PAL) is the first enzyme in the biosynthesis of phenylpropanoid-derived plant compounds such as flavonoids, coumarins and the cell wall polymer lignin. The cell walls of grasses possess higher proportions of syringyl (S)-rich lignins and high levels of esterified coumaric acid compared with those of dicotyledonous plants, and PAL from grasses can also possess tyrosine ammonia-lyase (TAL) activity, the reason for which has remained unclear. Using phylogenetic, transcriptomic and in vitro biochemical analyses, we identified a single homotetrameric bifunctional ammonia-lyase (PTAL) among eight BdPAL enzymes in the model grass species Brachypodium distachyon. (13)C isotope labelling experiments along with BdPTAL1-downregulation in transgenic plants showed that the TAL activity of BdPTAL1 can provide nearly half of the total lignin deposited in Brachypodium, with a preference for S-lignin and wall-bound coumarate biosynthesis, indicating that PTAL function is linked to the characteristic features of grass cell walls. Furthermore, isotope dilution experiments suggest that the pathways to lignin from L-phenylalanine and L-tyrosine are distinct beyond the formation of 4-coumarate, supporting the organization of lignin synthesis enzymes in one or more metabolons.
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203, USA.|Department of Biological Sciences, University of North Texas, Denton, Texas 76203, USA.
authors.forename: Jaime
authors.initials: J
authors.lastname: Barros
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203, USA.|Department of Biological Sciences, University of North Texas, Denton, Texas 76203, USA.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Serrani-Yarce
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203, USA.|Department of Biological Sciences, University of North Texas, Denton, Texas 76203, USA.|BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Fang
authors.initials: F
authors.lastname: Chen
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203, USA.
authors.forename: David
authors.initials: D
authors.lastname: Baxter
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203, USA.
authors.forename: Barney J
authors.initials: BJ
authors.lastname: Venables
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203, USA.|Department of Biological Sciences, University of North Texas, Denton, Texas 76203, USA.|BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D058431:Brachypodium / Q000235:genetics* / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D008031:Lignin / Q000096:biosynthesis*; D010650:Phenylalanine Ammonia-Lyase / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D010940:Plant Proteins; D008031:Lignin; D010650:Phenylalanine Ammonia-Lyase