Quantitative phosphoproteomics profiling reveals the regulatory mechanisms underlying high light stress in maize and rice.

High light stress seriously compromises crop yields and food security. Protein phosphorylation plays a key regulatory role in high light responses; however, their complexity hinders a full understanding of these processes. To address this, we performed a system-wide quantitative phosphoproteomic analysis in maize and rice over a four-hour high light exposure. By comparing site-specific phosphorylation dynamics between the two species, we identified both conserved and species-specific phosphorylation events associated with light harvesting, electron transport, metabolism, ROS scavenging, and signal transduction. Enhanced phosphorylation of LHCB4 at a conserved phosphosite was observed for both plants, indicating a shared mechanism for light-harvesting complex remodeling. Specifically, maize showed unique phosphorylation regulation of D1 and the PSI subunit PsaE, implying a mechanism for restoring photodamaged reaction centers. In contrast, rice rapidly attenuated electron supply via reduced plastocyanin phosphorylation, concurrent with the early induced phosphorylation of phototropin and a receptor-like kinase. Furthermore, we found that phosphorylation dynamics of metabolic enzymes affect their activities, maize preferentially enhanced photosynthetic efficiency, whereas rice exhibited more tunable regulation across primary metabolism. Overall, this study provides a comprehensive phospho-signaling atlas, revealing convergent and divergent phosphorylation process that underlie differential high light acclimation in maize and rice.