McMYB52 drives tepal coloration via activating anthocyanin and lignin biosynthesis in Michelia crassipes.

Purple flower coloration in Michelia crassipes represents a rare pigmentation trait within the genus Michelia. Therefore, investigating the regulatory mechanisms of purple flowers in M. crassipes holds significant breeding value. Here, MYB52, a novel R2R3-MYB transcription factor in the M. crassipes flower, was isolated and functionally characterized. ‌Heterologous expression of McMYB52 in tobacco triggered dark-red petal, which was driven by anthocyanin, flavonoid, and lignin accumulation‌. Histological comparison confirmed that the morphology of transgenic tobacco petal cells changed from flat to conical, with significantly denser papillate protrusions, consistent with the dome-shaped cell changes observed in M. crassipes purple tepals. Transient overexpression in M. crassipes tepals replicated this phenotype and coordinately activated phenylpropanoid pathway genes, notably McCCoAOMT, which exhibited a 763-fold transcriptional induction relative to controls‌. Conversely, in McMYB52-silenced tepals, the expression of McPALs, McC4H, McF3H-2, McLDOXs, McCCoAOMT was drastically suppressed. Further yeast one-hybrid and dual-luciferase reporter assays showed that McMYB52 directly binds to and significantly activates the McCCoAOMT promoter, suggesting its potential role in jointly regulating flavonoid and lignin biosynthesis.‌ All in all, our findings demonstrate that McMYB52 acts as a positive regulator in M. crassipes purple tepals, providing mechanistic insights into the homeostatic regulation of flavonoid and lignin biosynthesis in woody species. Furthermore, it offers a molecular breeding reference for manipulating floral coloration in Magnoliaceae‌. Moreover, the development of transient overexpression and VIGS systems in M. crassipes flower provides a strategic framework for addressing the challenge of gene function validation in Michelia species.