Transcription factor SmMYC2 regulates secondary cell wall thickening to enhance drought resilience in eggplant

SmMYC2 promotes SmNST1 expression and inhibits the expression of SmMYB108 and SmMYC2 itself in vivo, then thickens secondary cell wall and enhances drought resilience of eggplant. As climate change worsens, drought stress has emerged as a critical limiting factor for crop productivity. Members of the basic helix-loop-helix (bHLH) transcription factor family exhibit multifunctional regulatory roles in plant adaptation mechanisms. Nevertheless, the operational dynamics of bHLH-mediated genetic networks in Solanum melongena L. during water deficit conditions remain poorly characterized. This study focused on the molecular characterization of SmMYC2, a nuclear-localized bHLH transcription factor isolated from 'March eggplant' cultivar. Tissue-specific expression profiling revealed predominant transcript abundance in foliar tissues in comparison with other organs. Transgenic overexpression lines showed higher tolerance under drought treatment by increasing SOD content and decreasing MDA content with no significant change in POD activity in comparison with WT (wild-type) plants. Notably, SmMYC2-OE plants displayed significant stem diameter enlargement. In vivo protein interaction analyses employing bimolecular fluorescence complementation and luciferase-based imaging confirmed physical associations between SmMYC2 and SmJAZ1/SmJAZ3/SmMYB21. Functional genomic investigations through yeast one-hybrid systems and luciferase reporter analyses uncovered an autoregulatory mechanism where SmMYC2 binds to its autologous promoter to suppress transcriptional activity. Furthermore, SmMYC2 demonstrated differential regulatory effects by suppressing SmMYB108 promoter activity. Although SmMYC2 did not directly bind the SmNST1 promoter in vitro, it altered ProSmNST1 activity in vivo, suggesting an indirect regulatory mechanism. This comprehensive analysis reveals that SCW structural reinforcement correlates with improved drought adaptation in eggplant, elucidating a multilayered transcriptional framework with potential applications in eggplant productivity enhancement.