[Advances in research on lignin biosynthesis and its genetic engineering]

Lignin, one of the main components in vascular plants, is important for the adaptation of terrestrial plants to environment during evolution. However, its presence in plants has negative effects on wood processing during pulping and stock breeding. Therefore much attention has been focused on the regulation of lignin biosynthesis. The pathways leading to the synthesis of lignin polymers have been studied for decades. Much understanding of lignin biosynthesis has been advanced. This paper reviewed the recent progress made in the various steps associated with monolignol biosynthesis. It includes the catalysis by three enzymes, i.e. p-coumarate-3-hydroxylase (C3H), ferulate-5-hydroxylase (F5H) and caffeic acid 3-O-methyltransferase (COMT); the multiform biosynthetic pathway of syringyl (S) lignin in angiosperms; the biosynthesis route of guaiacyl (G) and syringyl (S) lignin specifically regulated by cinnamyl alcohol dehydrogenase (CAD) and sinapyl alcohol dehydrogenase (SAD) and the formation of the lignin macromolecule. Based on the elucidation of lignin biosynthesis pathway, it has also been given the achievements in lignin gene engineering. Many studies were concentrated on the modification of lignin content and composition. In some cases, the potential value of transgenic plants with modified lignin beneficial for pulping has been demonstrated. To better understand the mechanism of lignin biosynthesis and improve the properties of plants, new biotechnological strategies can be developed, which include combinatorial modification of multiple lignin traits in plants through multigene cotransformation, transcriptional control of lignin biosynthesis and the application of RNA interference. The identification of novel genes by molecular and genetic approaches will be useful in opening up new avenues of lignin modification in the future.