Transient Overexpression of in Grape Berries Enhances Susceptibility to Through ROS Homeostasis Modulation.

Gray mold disease, caused by , severely impacts grape production worldwide. Although proanthocyanidins (PAs) contribute to fungal pathogen resistance, their role in grape defense against remains unclear. Here, we demonstrate that VvMYBPA1, a key transcriptional regulator of PA biosynthesis, negatively modulates resistance in grape berries. While infection suppressed endogenous VvMYBPA1, its agroinfiltration-mediated transient overexpression in berries elevated susceptibility, paralleling reduced β-1,3-glucanase (BGL) and polyphenol oxidase (PPO) activities. Additionally, VvMYBPA1 overexpression elevated expression and reduced peroxidase (POD) activity, resulting in excessive hydrogen peroxide (HO) accumulation and more cell death. Our results reveal that VvMYBPA1 negatively regulates resistance by disrupting antioxidant enzyme activity and ROS homeostasis, providing new insights into the interplay between PA biosynthesis and fungal defense mechanisms.