Dual disruption of MiMPK4-mediated phosphorylation and interaction with MiRAP2.11 is required for blue light-induced carotenoid biosynthesis in mango fruit.

Light regulates carotenoid biosynthesis in plants at multiple levels. However, the involvement of protein phosphorylation in light-induced carotenoid biosynthesis remains largely unexplored. Our previous studies demonstrated that blue light promotes carotenoid biosynthesis in mango fruit. In this study, we elucidated that blue light induces carotenoid biosynthesis in mango fruit by disrupting the MiMPK4 (MITOGEN-ACTIVATED PROTEIN KINASE 4)-MiRAP2.11 regulatory module. MiRAP2.11, an ERF-subfamily transcription factor induced by blue light, acts as a nucleus-localized transcriptional activator. MiRAP2.11 activates the expression of carotenoid biosynthesis-related gene MiZEP (zeaxanthin epoxidase) by directly binding to its promoter, leading to carotenoid biosynthesis in mango fruit. Conversely, MiMPK4 negatively responds to blue light, interacts with MiRAP2.11 and phosphorylates it, promoting proteasome-dependent degradation of MiRAP2.11. Furthermore, the protein interaction between MiMPK4 and MiRAP2.11, rather than phosphorylation, reduces the binding activity of MiRAP2.11 to the MiZEP promoter, thereby weakening its transcriptional activation of MiZEP. Therefore, MiMPK4 suppresses MiRAP2.11-induced carotenoid biosynthesis through a dual inhibitory mechanism: phosphorylation-triggered protein degradation and interaction-mediated suppression of its transcriptional activation. Collectively, these findings demonstrate that blue light induces carotenoid biosynthesis in mango fruit flesh by disrupting the MiMPK4-MiRAP2.11 signaling module. This study provides new insights into the role of phosphorylation in light-induced carotenoid biosynthesis, further enriching the molecular network of blue light regulation of carotenoid biosynthesis pathways.