A dual-function PbrMYBL4-PbrMYB10b/PbrSGRL module regulates anthocyanin and chlorophyll metabolism in pear fruit

Abstract R2R3-MYB transcription factors are central regulators of anthocyanin biosynthesis, but their role in coordinating the control of chlorophyll metabolism remains largely unexplored. Here, we identified a novel R2R3-MYB transcriptional repressor from pear, named PbrMYBL4. This nuclear-localized protein contains a canonical EAR repression motif and is predominantly expressed in the fruit pericarp. Functional analyses demonstrated that PbrMYBL4 could simultaneously inhibit anthocyanin accumulation and chlorophyll degradation. Mechanistically, it represses anthocyanin biosynthesis by directly downregulating key structural genes (PbrF3H and PbrANS) and by binding to the promoter of the master activator PbrMYB10b to suppress its transcription. Furthermore, PbrMYBL4 interacts with PbrbHLH3 to form a repressive complex that competitively disrupts the formation of the activating PbrMYB10b-PbrbHLH3 complex, thereby amplifying the repression of anthocyanin pathway genes. Concurrently, PbrMYBL4 could inhibit chlorophyll degradation by directly repressing the chlorophyll degradation gene PbrSGRL. Overall, these findings suggest that PbrMYBL4 could regulate pigment metabolism via distinct regulatory modules, PbrMYBL4-PbrMYB10b and PbrMYBL4-PbrSGRL. Importantly, our findings reveal a dual-function transcriptional regulator that fine-tunes fruit coloration, providing a strategic target for molecular breeding to improve pear fruit quality.