Transient Overexpression of VvMYBPA1 in Grape Berries Enhances Susceptibility to Botrytis cinerea Through ROS Homeostasis Modulation

Gray mold disease, caused by <i>Botrytis cinerea</i>, severely impacts grape production worldwide. Although proanthocyanidins (PAs) contribute to fungal pathogen resistance, their role in grape defense against <i>B. cinerea</i> remains unclear. Here, we demonstrate that VvMYBPA1, a key transcriptional regulator of PA biosynthesis, negatively modulates <i>B. cinerea</i> 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 <i>VvRBOHs'</i> expression and reduced peroxidase (POD) activity, resulting in excessive hydrogen peroxide (H₂O₂) accumulation and more cell death. Our results reveal that VvMYBPA1 negatively regulates <i>B. cinerea</i> resistance by disrupting antioxidant enzyme activity and ROS homeostasis, providing new insights into the interplay between PA biosynthesis and fungal defense mechanisms.