E3 ubiquitin ligase MaRZF1 modulates high temperature‐induced green ripening of banana by degrading MaSGR1

High temperatures (>24°C) prevent the development of a yellow peel on bananas called green ripening, owing to the inhibition of chlorophyll degradation. This phenomenon greatly reduces the marketability of banana fruit, but the mechanisms underlining high temperature-repressed chlorophyll catabolism need to be elucidated. Herein, we found that the protein accumulation of chlorophyll catabolic enzyme MaSGR1 (STAY-GREEN 1) was reduced when bananas ripened at high temperature. Transiently expressing MaSGR1 in banana peel showed its positive involvement in promoting chlorophyll degradation under high temperature, thereby weakening green ripening phenotype. Using yeast two-hybrid screening, we identified a RING-type E3 ubiquitin ligase, MaRZF1 (RING Zinc Finger 1), as a putative MaSGR1-interacting protein. MaRZF1 interacts with and targets MaSGR1 for ubiquitination and degradation via the proteasome pathway. Moreover, upregulating MaRZF1 inhibited chlorophyll degradation, and attenuated MaSGR1-promoted chlorophyll degradation in bananas during green ripening, indicating that MaRZF1 negatively regulates chlorophyll catabolism via the degradation of MaSGR1. Taken together, MaRZF1 and MaSGR1 form a regulatory module to mediate chlorophyll degradation associated with high temperature-induced green ripening in bananas. Therefore, our findings expand the understanding of posttranslational regulatory mechanisms of temperature stress-caused fruit quality deterioration.