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Novel seed coat lignins in the C actaceae: structure, distribution and implications for the evolution of lignin diversity
Author(s) -
Chen Fang,
Tobimatsu Yuki,
Jackson Lisa,
Nakashima Jin,
Ralph John,
Dixon Richard A.
Publication year - 2013
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.12012
Subject(s) - lignin , trichome , botany , subfamily , coat , biology , cactus , biochemistry , gene , ecology
Summary We have recently described a hitherto unsuspected catechyl lignin polymer ( C ‐lignin) in the seed coats of V anilla orchid and in cacti of one genus, M elocactus (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 C actoidae 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 C oryphantha, C umarinia , E scobaria and M ammillaria ( C actoideae) 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 C actaceae, as seeds of one M ammillaria species ( M . lasiacantha ) possess only C ‐lignin, three E scobaria 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.