Lignin is specifically deposited in plant secondary cell walls, and initiation of lignin biosynthesis is regulated by a variety of developmental and environmental signals. However, the mechanisms governing the regulation of lignin biosynthesis remain to be elucidated. In this study, we identified a lignin biosynthesis-associated transcription factor (LTF) from Populus, LTF1, which binds the promoter of a key lignin biosynthetic gene encoding 4-coumarate-CoA ligase (4CL). We showed that LTF1 in its unphosphorylated state functions as a regulator restraining lignin biosynthesis. When LTF1 becomes phosphorylated by PdMPK6 in response to external stimuli such as wounding, it undergoes degradation through a proteasome pathway, resulting in activation of lignification. Expression of a phosphorylation-null mutant version of LTF1 led to stable protein accumulation and persistent attenuation of lignification in wood cells. Taken together, our study reveals a mechanism whereby LTF1 phosphorylation acts as a sensory switch to regulate lignin biosynthesis in response to environmental stimuli. The discovery of novel modulators and mechanisms modifying lignin biosynthesis has important implications for improving the utilization of cell-wall biomass.

木质素专门沉积在植物的次生细胞壁中，木质素生物合成的启动受多种发育和环境信号调节。然而，调控木质素生物合成调控的机制仍有待阐明。在这项研究中，我们从杨树中鉴定了木质素生物合成相关转录因子（LTF）。LTF1，它与编码4-香豆酸酯-CoA连接酶（4CL）的关键木质素生物合成基因的启动子结合。我们显示，处于未磷酸化状态的LTF1充当抑制木质素生物合成的调节剂。当LTF1响应外部刺激（例如受伤）而被PdMPK6磷酸化时，它会通过蛋白酶体途径降解，从而导致木质化的激活。LTF1的磷酸化无效突变体版本的表达导致稳定的蛋白质积累和木质细胞中木质化的持续减弱。两者合计，我们的研究揭示了一种机制，其中LTF1磷酸化充当响应环境刺激而调节木质素生物合成的感觉开关。