StuPPO9 Enhances Drought Tolerance in Potato (Solanum tuberosum) by Coordinating Photosynthetic Stability and Secondary Metabolism Reprogramming

Drought stress is a primary abiotic constraint limiting potato productivity. While polyphenol oxidase (PPO) is known to participate in stress responses, the specific role of StuPPO9 in drought tolerance remains poorly understood. In this study, we generated StuPPO9-overexpressing (OE) and CRISPR/Cas9-mediated knockout (C4) lines in the potato cultivar ‘Atlantic’. Under sustained drought stress, OE lines exhibited significantly superior growth phenotypes compared to wild-type (WT) and C4 plants, characterized by increased leaf and root relative water content, root number and enhanced photosynthetic efficiency (Pn and Gs). OE plants also maintained lower levels of MDA and ROS through elevated antioxidant enzyme activities. Notably, transcriptomic analysis revealed that StuPPO9 triggers a global reprogramming of metabolic pathways. Key drought-responsive genes associated with phenylpropanoid biosynthesis (e.g., anthocyanin acyltransferase), terpenoid metabolism, and hormone signaling (e.g., HPt protein) were significantly upregulated in OE plants. These findings suggest that StuPPO9 confers drought resilience through a multi-layered network involving optimized carbon allocation, reinforced cell wall integrity, and enhanced ROS scavenging capacity. This study provides a promising genetic target and theoretical foundation for breeding drought-resistant potato varieties.