Heat-induced expression of BnMYB6 represses lignin biosynthesis

Lignin is a key component affecting the quality of raw fibers in ramie. Although high temperature suppresses lignin accumulation in ramie bark, the underlying regulatory mechanism remains unclear. This study identified BnMYB6 as a heat-sensitive R2R3-MYB repressor of lignin formation. High temperature significantly reduced lignin accumulation in ramie bark, accompanied by induction of BnMYB6 expression and repression of multiple lignin biosynthetic genes. Further analyses revealed that heat stress directly activated the BnMYB6 promoter. Subcellular localization and transcriptional activity assays confirmed that BnMYB6 protein localizes to the nucleus and exhibits transcriptional repressive activity. Heterologous expression of BnMYB6 in Arabidopsis thaliana significantly reduced the transcription levels of lignin-associated genes without impairing growth. Moreover, yeast one-hybrid and EMSA confirmed that BnMYB6 directly binds to the promoter regions of the key lignin biosynthesis genes BnC4H , BnPAL , and BnCCoAOMT . These findings support BnMYB6 as a heat-inducible transcriptional suppressor of lignin biosynthesis, providing a promising genetic target for molecular breeding of heat-resilient, low-lignin ramie.