title: Independent recruitment of an O-methyltransferase for syringyl lignin biosynthesis in Selaginella moellendorffii.
abstract: Syringyl lignin, an important component of the secondary cell wall, has traditionally been considered to be a hallmark of angiosperms because ferns and gymnosperms in general lack lignin of this type. Interestingly, syringyl lignin was also detected in Selaginella, a genus that represents an extant lineage of the most basal of the vascular plants, the lycophytes. In angiosperms, syringyl lignin biosynthesis requires the activity of ferulate 5-hydroxylase (F5H), a cytochrome P450-dependent monooxygenase, and caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT). Together, these two enzymes divert metabolic flux from the biosynthesis of guaiacyl lignin, a lignin type common to all vascular plants, toward syringyl lignin. Selaginella has independently evolved an alternative lignin biosynthetic pathway in which syringyl subunits are directly derived from the precursors of p-hydroxyphenyl lignin, through the action of a dual specificity phenylpropanoid meta-hydroxylase, Sm F5H. Here, we report the characterization of an O-methyltransferase from Selaginella moellendorffii, COMT, the coding sequence of which is clustered together with F5H at the adjacent genomic locus. COMT is a bifunctional phenylpropanoid O-methyltransferase that can methylate phenylpropanoid meta-hydroxyls at both the 3- and 5-position and function in concert with F5H in syringyl lignin biosynthesis in S. moellendorffii. Phylogenetic analysis reveals that Sm COMT, like F5H, evolved independently from its angiosperm counterparts.
authors: Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA.
authors: Jing-Ke
authors: JK
authors: Weng
authors: Takuya
authors: T
authors: Akiyama
authors: John
authors: J
authors: Ralph
authors: Clint
authors: C
authors: Chapple
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008031:Lignin / Q000096:biosynthesis* / Q000737:chemistry; D019684:Magnoliopsida / Q000201:enzymology; D008780:Methyltransferases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010802:Phylogeny; D010940:Plant Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D017434:Protein Structure, Tertiary; D032503:Selaginellaceae / Q000033:anatomy & histology / Q000201:enzymology*; D016415:Sequence Alignment; D014018:Tissue Distribution
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; C434469:syringyl monolignol; D008031:Lignin; D008780:Methyltransferases; C019608:caffeate O-methyltransferase