The EDLL motif-containing transcription factor MaERF96L positively regulates starch degradation during banana fruit ripening

Abstract

Starch is an essential natural carbohydrate source for human beings and the main storage carbohydrate for bananas during growth and development. Starch degradation is an indispensable cause of banana fruit softening and flavor formation. Although AP2/ERF transcription factors (TFs) contribute to texture, color, and flavor changes during fruit ripening, the mechanism of AP2/ERF TFs regulating starch degradation in bananas is not fully understood. Here, we identified an EDLL motif-containing AP2/ERF member MaERF96L in banana fruit, and found its expression was upregulated by ethylene during ripening. Meanwhile, MaERF96L was a nuclear-localized protein and acted as a transcriptional activator. Importantly, further in vitro and vivo assays showed that MaERF96L directly bound to the promoter of one starch degradation enzyme gene MaGWD1 and enhanced its transcription. Moreover, MaERF96L transient overexpression in banana fruit up-regulated MaGWD1 expression and promoted starch degradation, which in turn contributed to advance ripening. In summary, these findings demonstrate that MaERF96L could be involved in starch degradation pathway during banana fruit ripening, partly through the positive transcriptional regulation of MaGWD1, thereby expanding our understanding towards the regulatory network of fruit starch degradation.