title: Ancient origin of the biosynthesis of lignin precursors.
abstract: BACKGROUND
  Lignin plays an important role in plant structural support and water transport, and is considered one of the hallmarks of land plants. The recent discovery of lignin or its precursors in various algae has raised questions on the evolution of its biosynthetic pathway, which could be much more ancient than previously thought. To determine the taxonomic distribution of the lignin biosynthesis genes, we screened all publicly available genomes of algae and their closest non-photosynthetic relatives, as well as representative land plants. We also performed phylogenetic analysis of these genes to decipher the evolution and origin(s) of lignin biosynthesis.
  
  
  RESULTS
  Enzymes involved in making p-coumaryl alcohol, the simplest lignin monomer, are found in a variety of photosynthetic eukaryotes, including diatoms, dinoflagellates, haptophytes, cryptophytes as well as green and red algae. Phylogenetic analysis of these enzymes suggests that they are ancient and spread to some secondarily photosynthetic lineages when they acquired red and/or green algal endosymbionts. In some cases, one or more of these enzymes was likely acquired through lateral gene transfer (LGT) from bacteria.
  
  
  CONCLUSIONS
  Genes associated with p-coumaryl alcohol biosynthesis are likely to have evolved long before the transition of photosynthetic eukaryotes to land. The original function of this lignin precursor is therefore unlikely to have been related to water transport. We suggest that it participates in the biological defense of some unicellular and multicellular algae.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, , T6G 2E9, , Canada. labeeuw@ualberta.ca.
authors.forename: Leen
authors.initials: L
authors.lastname: Labeeuw
authors.affiliation: Department of Botany and Biodiversity Research Centre, University of British, Columbia, BC, , V6T 1Z4, , Canada. patrick.martone@botany.ubc.ca.
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Martone
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, , T6G 2E9, , Canada. yboucher@ualberta.ca.
authors.forename: Yan
authors.initials: Y
authors.lastname: Boucher
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, , T6G 2E9, , Canada. rcase@ualberta.ca.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Case
mesh_terms: D000438:Alcohols / Q000737:chemistry; D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics; D005075:Biological Evolution; D002696:Chlamydomonas / Q000235:genetics*; D002708:Chlorella / Q000235:genetics*; D019295:Computational Biology; D004141:Dinoflagellida / Q000235:genetics; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D058087:Haptophyta / Q000235:genetics; D008031:Lignin / Q000096:biosynthesis*; D016013:Likelihood Functions; D010788:Photosynthesis; D010802:Phylogeny; D032503:Selaginellaceae / Q000235:genetics
chemical_list: D000438:Alcohols; D008031:Lignin; D000445:Aldehyde Oxidoreductases; C019904:cinnamoyl CoA reductase