Transcription factor EjMYBF1 positively regulates flavonol biosynthesis in loquat (Eriobotrya japonica)

Loquat ( Eriobotrya japonica ) is rich in flavonols with health-promoting functions. However, regulatory mechanisms of flavonol biosynthesis in loquat are unclear. This study functionally characterized an R2R3-MYB, EjMYBF1 from loquat. Expression level of EjMYBF1 is positively correlated with flavonol content at different stages of fruit development and in ten accessions with differential flavonol accumulation. Dual-luciferase assays and EMSA indicated that EjMYBF1 transactivated the promoters of structural genes involved in flavonol biosynthesis by binding to promoter regions containing MYBCORE elements. Transient overexpression and virus-induced gene silencing assays of EjMYBF1 in loquat fruit peels and leaves, as well as heterologous constitutive expression of EjMYBF1 in Nicotiana tabacum confirmed that EjMYBF1 is a positive regulator of flavonol biosynthesis in loquat. These results demonstrate that EjMYBF1 is a functional flavonol-specific activator in loquat and explain one reason for its high flavonol content from the perspective of transcriptional regulation. This work provides a potential target for improving loquat nutrition and for applications in secondary metabolic engineering.