The Role of MaWRKY70 in Regulating Lipoxygenase Gene Transcription during Chilling Injury Development in Banana Fruit

Banana is a typical cold-sensitive fruit; it is prone to chilling injury (CI), resulting in a quality deterioration and commodity reduction. However, the molecular mechanism underlying CI development is unclear. In this study, cold storage (7 °C for 5 days) was used to induce CI symptoms in bananas. As compared with the control storage (22 °C for 5 days), cold storage increased the CI index and cell membrane permeability. Moreover, we found that the expression levels of the WRKY transcription factor MaWRKY70 were increased consistently with the progression of CI development. A subcellular localization assay revealed that MaWRKY70 was localized in the nucleus. Transcriptional activation analyses showed that MaWRKY70 processed a transactivation ability. Further, an electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter (DLR) assays showed that MaWRKY70 was directly bound to the W-box motifs in the promoters of four lipoxygenase (LOX) genes associated with membrane lipid degradation and activated their transcription. Collectively, these findings demonstrate that MaWRKY70 activates the transcription of MaLOXs, thereby acting as a possible positive modulator of postharvest CI development in banana fruit.