Transcriptional networks for lignin biosynthesis: more complex than we thought?

Lignin is an aromatic heteropolymer and the second most abundant plant biopolymer after cellulose. It is deposited mostly in the secondary cell walls of vascular plants and is essential for water transport, mechanical support and for plant pathogen defense. Lignin biosynthesis is a highly energy-consuming and irreversible process that responds to many developmental and environmental cues, including light, sugar content, circadian clock, plant hormones and wounding. During the past decade, many transcription factors involved in lignin biosynthesis have been identified and characterized. In this review, we assess how these transcriptional activators and repressors modulate lignin biosynthesis, and discuss crosstalk between the lignin biosynthesis pathway and other physiological processes.