Regulatory role of the SmMYB44-l gene in anthocyanin synthesis in Solanum melongena L.

Eggplant (Solanum melongena L.), a major crop of the Solanaceae family, is valued for its rich nutritional profile, particularly the high anthocyanin content in the purple peel. Anthocyanin biosynthesis is primarily regulated by a network of transcription factors. Current research on MYB transcription factors in eggplant has predominantly focused on their roles as positive regulators, with limited insight into negative regulatory mechanisms. In this study, we cloned the SmMYB44-l gene. Bioinformatic and phylogenetic analyses revealed the presence of an EAR (LxLxL) repressor motif at the C-terminus of its encoded protein, and high sequence homology to StMYB44-l from potato. Expression analysis indicated a negative correlation between SmMYB44-l transcript levels and pericarp anthocyanin content. Subcellular localization experiment showed that SmMYB44-l localized to the nucleus. Transient expression assays demonstrated that SmMYB44-l repressed anthocyanin biosynthesis in tobacco (Nicotiana benthamiana) by downregulating both the MYB activator SmMYB75, and structural genes (NbCHS, NbF3H). Luciferase complementation imaging confirmed the absence of physical interaction between SmMYB44-l and SmMYB75. Overexpression of SmMYB44-l in both tobacco and eggplant suppressed anthocyanin accumulation. Yeast one-hybrid and luciferase reporter assays validated its direct repressive role in the regulation of anthocyanin biosynthesis.