The MfMYB1-MfWRKY51/MfLBD1 regulatory switch modulates anthocyanin biosynthesis under low temperatures

Seasonal leaf coloration, driven by anthocyanin dynamics, is a crucial adaptive response to thermal environments, yet the underlying transcriptional mechanisms remain largely elusive. Here, we utilized the ornamental crabapple Malus 'Fengwu', which exhibits a striking red-to-green transition upon warming, to unravel the thermo-responsive regulatory network. Low temperature maintains red pigmentation and high antioxidant capacity, whereas warming leads to a rapid decline in anthocyanin content. We identified MfWRKY51 and MfLBD1 as crucial transcriptional repressors of anthocyanin biosynthesis, exhibiting elevated expression in green leaves and downregulation under low-temperature conditions. Genetic and biochemical analyses demonstrated that MfWRKY51 and MfLBD1 inhibit anthocyanin accumulation and reduce antioxidant capacity, whereas silencing either gene enhances anthocyanin accumulation and antioxidant capacity. Mechanistically, MfWRKY51 directly binds to the promoters of anthocyanin structural genes (MfDFR, MfANS, and MfUFGT), while MfLBD1 binds to the MfDFR promoter, collectively repressing their transcription. Furthermore, MfMYB1, strongly induced by low temperature and jasmonate (JA), acts as a central positive regulator that directly binds to the promoters of MfWRKY51 and MfLBD1 to repress their transcription. Reciprocally, MfWRKY51 directly suppresses MfMYB1 transcription, forming a mutual-repression feedback loop that functions as a temperature-sensitive switch. This regulatory module is functionally conserved between ornamental crabapple and cultivated apple, where low temperature promotes anthocyanin accumulation by repressing MdWRKY51 and MdLBD1 orthologues. Collectively, our findings reveal a conserved transcriptional network integrating temperature and JA signals to fine-tune anthocyanin metabolism, providing mechanistic insights into plant seasonal adaptation.