Comprehensive analysis of MCTP genes in potato reveals StMCTP9 as a critical regulator of tuber development

The potato (Solanum tuberosum L.) is a vital global staple crop, and recent research has focused on elucidating the molecular mechanisms underlying tuber formation. MULTIPLE C2 DOMAIN AND TRANSMEMBRANE REGION PROTEINs (MCTPs) have emerged as essential regulators of macromolecule transport in plants; however, their roles in potato tuberization remain largely uncharacterized. In this study, we conduct a comprehensive genome-wide analysis of the MCTP family in potato, identifying 17 StMCTP members. Expression profiling reveals tissue-specific and hormone-responsive expression patterns, with dynamic regulation observed during the stolon-to-tuber transition. Subcellular localization assays indicate that StMCTP proteins are distributed in distinct or overlapping patterns in Nicotiana benthamiana leaf epidermal cells. StMCTP9, a homolog of Arabidopsis QUIRKY, is highly expressed in leaves and stolons and interacts with StSP6A, a key tuberigen signal. Knocking down StMCTP9 delays tuber initiation, indicating its role in tuber development. Heterologous expression of StSP6A in Arabidopsis promotes flowering, revealing divergent outcomes of the mobile signal pathway in potato and Arabidopsis. Together, our findings reveal a previously unrecognized role of StMCTP9 in mediating tuber formation, providing a foundation for understanding the broader functional landscape of MCTPs in potato development.