title: Novel seed coat lignins in the Cactaceae: structure, distribution and implications for the evolution of lignin diversity.
abstract: We have recently described a hitherto unsuspected catechyl lignin polymer (C-lignin) in the seed coats of Vanilla orchid and in cacti of one genus, Melocactus (Chen et al., Proc. Natl. Acad. Sci. USA. 2012, 109, 1772-1777.). We have now determined the lignin types in the seed coats of 130 different cactus species. Lignin in the vegetative tissues of cacti is of the normal guaiacyl/syringyl (G/S) type, but members of most genera within the subfamily Cactoidae possess seed coat lignin of the novel C-type only, which we show is a homopolymer formed by endwise β-O-4-coupling of caffeyl alcohol monomers onto the growing polymer resulting in benzodioxane units. However, the species examined within the genera Coryphantha, Cumarinia, Escobaria and Mammillaria (Cactoideae) mostly had normal G/S lignin in their seeds, as did all six species in the subfamily Opuntioidae that were examined. Seed coat lignin composition is still evolving in the Cactaceae, as seeds of one Mammillaria species (M. lasiacantha) possess only C-lignin, three Escobaria species (E. dasyacantha, E. lloydii and E. zilziana) contain an unusual lignin composed of 5-hydroxyguaiacyl units, the first report of such a polymer that occurs naturally in plants, and seeds of some species contain no lignin at all. We discuss the implications of these findings for the mechanisms that underlie the biosynthesis of these newly discovered lignin types.
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK, 73401, USA.|DOE Bioenergy Sciences Center, Oak Ridge, TN, USA.
authors.forename: Fang
authors.initials: F
authors.lastname: Chen
authors.affiliation: Department of Biochemistry, Enzyme Institute, University of Wisconsin-Madison, 1710 University Avenue, Madison, WI, 53726, USA.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Tobimatsu
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK, 73401, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Jackson
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK, 73401, USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Nakashima
authors.affiliation: Department of Biochemistry, Enzyme Institute, University of Wisconsin-Madison, 1710 University Avenue, Madison, WI, 53726, USA.|DOE Great Lakes Bioenergy Research Center, Madison, WI, USA.|Wisconsin Bioenergy Initiative, Madison, WI, USA.
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK, 73401, USA.|DOE Bioenergy Sciences Center, Oak Ridge, TN, USA.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D029421:Cactaceae / Q000235:genetics / Q000502:physiology*; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D008031:Lignin / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D010802:Phylogeny; D012639:Seeds / Q000737:chemistry* / Q000502:physiology; D013045:Species Specificity
chemical_list: D008031:Lignin