The MaASR3-MaHDT1 module modulates high-temperature-inhibited chlorophyll breakdown in banana fruit by suppressing the E3 ligase MaNIP1.

The ripening of banana fruit at high temperature (HT) exceeding 24°C impedes developing yellow peels, causing green ripening, which considerably lowers its marketability. Our recent study found that HT induces E3 ubiquitin ligase MaNIP1 (NYC1 interacting protein 1)-mediated degradation of MaNYC1 (NON-YELLOW COLORING 1) to inhibit chlorophyll breakdown during banana fruit ripening, but MaNIP1's upstream regulatory mechanism is still unclear. Herein, the ASR transcription factor (TF) MaASR3, which is repressed in green-ripened fruit compared to yellow-ripened fruit, was identified as the potential binding protein for the MaNIP1 promoter. MaASR3 promoted chlorophyll degradation in banana fruit by repressing MaNIP1 expression. More importantly, the histone deacetylase MaHDT1 interacted with MaASR3 and enhanced MaASR3-mediated repression of MaNIP1. Overexpression of MaASR3 in banana fruit reduced the histone acetylation levels in the MaNIP1 promoter and repressed MaNIP1 expression, thereby weakening the HT-inhibited degreening of banana fruit. Our study reveals an innovative regulatory cascade comprising the MaASR3-MaHDT1-MaNIP1 complex, which modulates HT-inhibited chlorophyll degradation. This explains the green ripening in bananas exposed to such conditions and enhances the comprehension of transcriptional and epigenetic regulations of fruit quality deterioration due to temperature stresses.