The StMYB55/StPYL8-StEXLB1 Module Is Associated With Drought Tolerance and Stomatal Regulation in Potato

Potato growth and development are inhibited by drought stress, which in extreme situations jeopardises tuber yield and quality. Despite progress in understanding drought stress responses, the full regulatory network remains unclear. In this study, we found that the cell wall-localised expansin gene StEXLB1 was significantly induced by polyethylene glycol 6000 (PEG6000) and abscisic acid (ABA). StEXLB1-Overexpression (OE) reduced stomatal density and aperture, accompanied by enhancing drought tolerance. Conversely RNA interference (RNAi) lines exhibited the opposite effects. Further investigation revealed that the transcription factor StMYB55 directly promotes StEXLB1 transcription. Notably, StMYB55-OE resulted in stomatal phenotypes similar to those in StEXLB1-OE lines. Conversely, StMYB55-RNAi increased stomatal density and aperture, as well as reduced drought tolerance. StMYB55 interacts with the ABA receptor StPYL8 and the molecular chaperone StDnaJ3, respectively. This complex then acts to differentially suppress the transcript levels of key stomatal development factors (StSPCH and StFAMA). Genetic evidence showed that StPYL8-RNAi resulted in increased stomatal density and aperture, which was associated with decreased drought tolerance in potato. Collectively, this study suggests that the StMYB55/StPYL8-StEXLB1 module may participate in drought stress response, potentially via stomatal regulation, and provides candidate genes for breeding drought-tolerant potato varieties.