Analysis of the Function and Regulatory Mechanisms of the AmFLS Gene, Encoding the Flavonol Synthase in Abelmoschus manihot L.

Abelmoschus manihot L. (Jinhuakui, JHK) is a Malvaceae plant with ornamental, medicinal, and edible value. It is rich in flavonoids, with a particularly high content of flavonols; however, current research on the molecular mechanisms underlying flavonol biosynthesis in JHK, particularly the upstream transcriptional regulatory networks, remains limited. In this study, JHK was used as the model plant to determine the patterns of flavonol accumulation in different tissues and during the flowering period. We cloned the AmFLS gene to validate its function and screened for and identified its upstream transcriptional regulators and interacting proteins. The results indicate that flavonols in JHK are primarily concentrated in floral organs, with the highest level observed during the budding stage. Furthermore, we found that AmFLS positively regulates flavonol biosynthesis and serves as the central rate-limiting gene. Additionally, AmMYB111 is a nuclear-localized R2R3-MYB repressor that directly binds to the AmFLS promoter and inhibits its transcription, thereby negatively regulating flavonol accumulation. Finally, the DELLA family proteins AmRGL2 and AmMYB111 can specifically interact with each other and actively promote the accumulation of flavonols. This study provides a preliminary elucidation of the molecular mechanism by which upstream transcriptional regulation of the AmFLS gene controls flavonol biosynthesis, offering a theoretical basis for further elucidating the regulatory network of flavonol metabolism in JHK and accelerating its industrial development.