title: Convergent evolution of syringyl lignin biosynthesis via distinct pathways in the lycophyte Selaginella and flowering plants.
abstract: Phenotypic convergence in unrelated lineages arises when different organisms adapt similarly under comparable selective pressures. In an apparent example of this process, syringyl lignin, a fundamental building block of plant cell walls, occurs in two major plant lineages, lycophytes and angiosperms, which diverged from one another more than 400 million years ago. Here, we show that this convergence resulted from independent recruitment of lignin biosynthetic cytochrome P450-dependent monooxygenases that route cell wall monomers through related but distinct pathways in the two lineages. In contrast with angiosperms, in which syringyl lignin biosynthesis requires two phenylpropanoid meta-hydroxylases C3'H and F5H, the lycophyte Selaginella employs one phenylpropanoid dual meta-hydroxylase to bypass several steps of the canonical lignin biosynthetic pathway. Transgenic expression of the Selaginella hydroxylase in Arabidopsis thaliana dramatically reroutes its endogenous lignin biosynthetic pathway, yielding a novel lignin composition not previously identified in nature. Our findings demonstrate a unique case of convergent evolution via distinct biochemical strategies and suggest a new way to genetically reconstruct lignin biosynthesis in higher plants.
authors.affiliation: Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Jing-Ke
authors.initials: JK
authors.lastname: Weng
authors.forename: Takuya
authors.initials: T
authors.lastname: Akiyama
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Bonawitz
authors.forename: Xu
authors.initials: X
authors.lastname: Li
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: Clint
authors.initials: C
authors.lastname: Chapple
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics; D002473:Cell Wall / Q000737:chemistry; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D005816:Genetic Complementation Test; D008031:Lignin / Q000096:biosynthesis*; D009682:Magnetic Resonance Spectroscopy; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D032503:Selaginellaceae / Q000201:enzymology / Q000235:genetics*
chemical_list: D010940:Plant Proteins; D018749:RNA, Plant; D008031:Lignin; D003577:Cytochrome P-450 Enzyme System