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Keywords:

  • biofuel;
  • cell wall;
  • convergent evolution;
  • diversification;
  • land colonization;
  • lycophyte;
  • P450;
  • phenylpropanoid

Contents

 Summary273
I.Introduction273
II.Emergence of the monolignol biosynthetic scaffold274
III.Occurrence and elaboration of lignification in tracheophytes280
IV.Concluding remarks282
 Acknowledgements282
 References282

Summary

Lignin, a phenolic polymer derived mainly from hydroxycinnamyl alcohols, is ubiquitously present in tracheophytes. The development of lignin biosynthesis has been considered to be one of the key factors that allowed land plants to flourish in terrestrial ecosystems. Lignin provides structural rigidity for tracheophytes to stand upright, and strengthens the cell wall of their water-conducting tracheary elements to withstand the negative pressure generated during transpiration. In this review, we discuss a number of aspects regarding the origin and evolution of lignin biosynthesis during land plant evolution, including the establishment of its monomer biosynthetic scaffold, potential precursors to the lignin polymer, as well as the emergence of the polymerization machinery and regulatory system. The accumulated knowledge on the topic, as summarized here, provides us with an evolutionary view on how this complex metabolic system emerged and developed.