StHAB1, a negative regulatory factor in abscisic acid signaling, plays crucial roles in potato drought tolerance and shoot branching.

Abscisic acid (ABA) is critical in drought tolerance and plant growth. Group A protein type 2C phosphatases (PP2Cs) are negative regulators of ABA signaling and plant adaptation to stress. However, our knowledge about the functions of potato group A PP2Cs is limited. Here, we report that potato group A PP2C StHAB1 is broadly expressed in potato plants and strongly induced by ABA and drought. Suppression of StHAB1 enhanced potato ABA sensitivity and drought tolerance, whereas overexpression of the dominant mutant StHAB1G276D compromised ABA sensitivity and drought tolerance. StHAB1 interacts with almost all ABA receptors and the Snf1-Related Kinase OST1. Suppressing StHAB1 and overexpressing StHAB1G276D alter potato growth morphology; notably, overexpression of StHAB1G276D causes excessive shoot branching in potato. RNA-seq analyses identified that auxin efflux carrier genes, StPIN3, StPIN5, and StPIN8, were upregulated in StHAB1G276D-overexpressed axillary buds. Correspondingly, auxin concentration was reduced in StHAB1G276D-overexpressed axillary buds, consistent with the repressing role of auxin in lateral branch outgrowth. The expression of BRANCHED1s (StBRC1a and StBRC1b) does not change in StHAB1G276D-overexpressed axillary buds, suggesting that overexpression of StHAB1G276D caused axillary bud outgrowth is not due to regulating BRC1 expression. Our findings demonstrate that StHAB1 is vital in potato drought tolerance and shoot branching.