MYB-mediated regulation of lignin biosynthesis in grasses

Recent analyses of cell wall components of various grass mutant and transgenic lines have provided information on characteristic transcriptional regulation of cell wall formation in grasses, although its knowledge yet remains limited compared with that for eudicot cell wall formation. MYB transcription factors, which are regarded as downstream regulators operating under NAM, ATAF1/2, and CUC2 (NAC) domain transcription factors, have been suggested to be involved in direct regulation of cell wall biosynthesis. In this review, we discuss MYB-mediated transcriptional regulation of the biosynthesis of grass lignins, including grass-specific lignin components such as γ-acyl groups and flavone tricin units. Grass mutant and transgenic lines harboring modified cell-wall-associated MYB genes display altered composition of the γ-acylated and tricin-incorporated lignin units and/or modified expression of enzyme genes involved in the formation of these grass-specific lignin components along with conserved monolignol biosynthetic genes. These findings implicate important roles for MYB transcription factors in coordinated regulation of grass lignin biosynthesis including γ-acylated and tricin-incorporated lignin biosynthesis.