Hydroxylation of HPPD facilitates its PUB11-mediated ubiquitination and degradation in response to oxidative stress in Arabidopsis

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays a critical role in plant photosynthesis, and is essential for enhancing tolerance to oxidative stress. However, the precise mechanisms through which plants regulate HPPD in response to oxidative stress remain largely unknown. Here, we report that the Arabidopsis thaliana HPPD (AtHPPD) undergoes an uncharacterized post-translational modification, namely phenylalanine hydroxylation, in response to excessive hydroxyl radicals (·OH), thereby mediating oxidative stress tolerance. Biochemical analyses reveal that this hydroxylation impairs the normal function of AtHPPD, leading to its accelerated degradation. Furthermore, we identified PUB11 as a key interactor with AtHPPD. In vitro and in vivo assays show that PUB11 enhances its interaction with AtHPPD under oxidative stress, promoting ubiquitination and facilitating rapid degradation of AtHPPD via the 26S proteasome pathway to balance the ROS levels. Overall, this work provides new insights into how plants balance photosynthetic efficiency and the repair of oxidative damage, while uncovering key processes in oxidative stress regulation, providing a foundation for crop breeding to meet abiotic challenges.