Phosphorylation of LTF1, A MYB Transcription Factor in Populus, Acts as a Sensory Switch Regulating Lignin Biosynthesis in Wood Cells

Abstract 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 mechanism governing the regulation of lignin biosynthesis remains to be elucidated. Here, we identified a lignin biosynthesis associated transcription factor (LTF) from Populus , LTF1, which binds to the promoter of 4-coumarate-CoA ligase (4CL), a key lignin biosynthetic gene. We showed that LTF1 in its unphosphorylated state functions as a regulator to restrain lignin biosynthesis. When LTF1 becomes phosphorylated by PdMPK6 in response to external stimuli such as wounding, it underwent degradation through a proteasome pathway, resulting in activation of lignification. Expression of the LTF1 phosphorylation-null mutation led to stable LTF1 accumulation and persistent attenuation of lignification in wood cells. The study reveals a mechanism where LTF1 phosphorylation acts as a sensory switch to regulate lignin biosynthesis in response to environmental stimuli. The discovery of novel modulators and mechanisms to modify lignin biosynthesis has important implications for improving the utilization of cell wall biomass.