Transcriptional regulation of MbACO2-mediated ethylene synthesis during postharvest banana ripening

Ethylene plays a central role in climacteric fruit ripening. 1-Aminocyclopropane-1-carboxylic acid oxidase (ACO) is a crucial enzyme for ethylene biosynthesis. Edible cultivated banana varieties are mainly composed of the A- or A/B-genome. Nevertheless, the function and regulatory mechanism of ACO genes in the B-genome of banana fruit are unknown. The present study revealed the function and regulatory mechanism of the B-genome-specific gene MbACO2 in ethylene biosynthesis during postharvest banana ripening. MbACO2 expression significantly increased at 6 d postharvest. MbACO2 overexpression in tomato resulted in an increase in ethylene biosynthesis and the acceleration of fruit ripening. MaNAC29 and MbERF71/MbERF113 showed induction during the postharvest periods and directly activated the transcription of MbACO2 through the CGTC-element and GCC-box in its promoter, respectively. In addition, MaMAPK1 interacted with MaNAC29 to further enhance the transcription of MbACO2. Collectively, our findings demonstrate a novel regulatory cascade involving MaMAPK1, MaNAC29, and MbERF71/MbERF113 that promotes MbACO2 transcription during postharvest banana ripening, which helps design breeding strategies to extend the shelf life of fruit.