MaWLIM2-MaZFP6 transcriptional regulatory module directly represses E3 ligase gene MaRZF1 to regulate high temperature-suppressed chlorophyll catabolism in banana fruit

Banana (Musa acuminata, AAA group) fruit ripening at high temperatures (HTs) exceeding 24 °C prohibits the yellow peel development and leads to green ripening, which dramatically diminishes its marketability. Our recent study found that HT induced MaRZF1 (RING Zinc Finger 1)-mediated degradation of MaSGR1 (STAY-GREEN 1) to inhibit chlorophyll breakdown, but how HT activates MaRZF1's expression is completely unclear. The present study identifies two transcription factors (TFs), MaWILIM2 (widely expressed LIM) and MaZFP6 (zinc finger protein), as potential binding proteins for the MaRZF1 promoter. Both MaWILIM2 and MaZFP6 expression levels were lower in 30 °C green-ripened fruit than in 20 °C yellow-ripened fruit. In banana fruit, overexpressing MaWLIM2 and MaZFP6 suppressed MaRZF1 expression and mitigated chlorophyll catabolism inhibition caused by HTs. More importantly, MaWLIM2 interacted with MaZFP6 to synergistically repress the MaRZF1 promoter activity. Our findings demonstrate that MaWLIM2 and MaZFP6 form a dynamic transcriptional regulatory module that represses MaRZF1 and controls HTs-inhibited chlorophyll degradation in banana fruit. These findings enhance our understanding of transcriptional regulation in fruit quality decline due to temperature stress and are expected to aid in developing strategies to manage banana green-ripening.