Two MYB transcription factors interact to inhibit the expression of cell wall metabolism and starch degradation genes in banana.

Banana (Musa acuminata, AAA group) fruit softening severely affects postharvest quality, yet the molecular regulatory networks governing this process remain incompletely understood. In this study, we found that the overexpression of MaMYB44 in bananas and tomatoes delayed fruit firmness loss and starch degradation. In addition, MaMYB44 interacted with MaMYB73 (another member of the R2R3-MYB transcription factor [TF] family), which also functioned as a repressor of fruit firmness loss and starch degradation. To elucidate the regulatory network of these TFs, we performed a genome-wide co-target gene analysis using DNA affinity purification sequencing (DAP-Seq). The results showed that MaMYB44 and MaMYB73 co-targeted the cell wall metabolism gene expansin A15 (MaEXPA15) and the starch degradation gene β-amylase3 (MaBAM3). Notably, the interaction of MaMYB44 and MaMYB73 enhanced their binding affinity and inhibitory effects on MaEXPA15 and MaBAM3. This study uncovers a regulatory mechanism in which MaMYB44 and MaMYB73 form a complex to inhibit the expression of genes involved in fruit firmness loss and starch degradation. These findings provide perspectives on controlling fruit softening and identify important targets for improving postharvest quality.