The MYB transcription factor SmMYB113 directly regulates ethylene-dependent flower abscission in eggplant

Flower abscission is an important developmental process that can significantly reduce the yield of horticultural plants. We previously reported that SmMYB113 is a key transcription factor promoting anthocyanin biosynthesis and improve fruit quality. However, the overexpression of SmMYB113 in eggplant increased flower drop rate and reduced fruit yield. Here, we elucidate the regulatory mechanisms of SmMYB113 on flower abscission in eggplant. RNA-seq analysis indicated that the regulation of flower abscission by SmMYB113 was associated with altered expression of genes related to ethylene biosynthesis and signal transduction, including ethylene biosynthetic genes SmACS1, SmACS8 and SmACO4. Then, the ethylene content in flowers and the function of ethephon (ETH, which promotes fruit ripening) and 1-Methylcyclopropene (1-MCP, which acts as an ethylene perception inhibitor) were analyzed, which revealed that SmMYB113 directly regulates ethylene-dependent flower abscission. Yeast one-hybrid and dual-luciferase assays revealed that SmMYB113 could directly bind to the promoters of SmACS1, SmACS8, and SmACO4 to activate their expression. Through construction of a yeast two-hybrid (Y2H) screening library, the protein SmERF38 was found to interact with SmMYB113, and verified by Y2H, bimolecular fluorescence complementation (BiFC), and luciferase complementation assay. Furthermore, dual-luciferase assays showed that SmERF38 enhanced the role of SmMYB113 on the promoters of SmACS1. Our results provided new insight into the molecular mechanism of flower abscission in eggplant.

CBFs Function in Anthocyanin Biosynthesis by Interacting with MYB113 in Eggplant (Solanum melongena L.)

Eggplant is rich in anthocyanins. R2R3-MYB transcription factors play a key role in the anthocyanin pathway. Low temperature is vital abiotic stress that affects the anthocyanin biosynthesis in plants. CBFs (C-repeat binding factors) act as central regulators in cold response. In this study, we found that SmCBF1, SmCBF2 and SmCBF3, via their C-terminal, physically interacted with SmMYB113, a key regulator of anthocyanin biosynthesis in eggplant. SmCBF2 and SmCBF3 upregulated the expression of SmCHS and SmDFR via a SmMYB113-dependent pathway. In addition, the transient expression assays demonstrated that co-infiltrating SmCBFs and SmMYB113 significantly improved the contents of anthocyanin and the expression levels of anthocyanin structural genes in tobacco. When SmTT8, a bHLH partner of SmMYB113, coexpressed with SmCBFs and SmMYB113, the anthocyanin contents were significantly enhanced compared with SmCBFs and SmMYB113. Furthermore, overexpression of SmCBF2 and SmCBF3 could facilitate the anthocyanin accumulation under cold conditions in Arabidopsis. Taken together, these results shed light on the functions of SmCBFs and potential mechanisms of low-temperature-induced anthocyanin biosynthesis in eggplant.