<scp>S</scp> t <scp>HAB</scp> 1‐mediated <scp>ABA</scp> signaling potentiates the sensitivity to long‐distance signal <scp>S</scp> t <scp>SP</scp> 6 <scp>A</scp> to promote tuberization in potato

The plant hormone abscisic acid (ABA) is historically recognized as a tuberization stimulator, with exogenous application significantly enhancing potato tuber formation. However, the physiological significance of endogenous ABA signaling in tuberization and its underlying molecular mechanisms remain poorly understood. Here, by using ABA-insensitive hypermorphic StHAB1^G276D-overexpression mutant and StHAB1 knockdown mutant, we demonstrate that ABA signaling is essential for normal tuber formation in potato. Blocking of ABA signaling by StHAB1^G276D-overexpression reduces underground stolon sensitivity to leaf-derived tuber-inducing signals. Notably, StHAB1 directly interacts with the tuber-forming signal StSP6A and reduces its phosphorylation level. Transcriptomic and quantitative phosphoproteomic analyses proved that StHAB1^G276D modulates gene expression and phosphorylation of key players in the tuberization pathway and gibberellic acid signaling. Collectively, our findings uncover a critical role of endogenous ABA signaling in potato tuber formation and identify a mechanism linking the conserved FLOWERING LOCUS T and ABA pathways, offering molecular insights for accelerating potato tuberization by modulating hormone signaling.