MabZIP74 interacts with MaMAPK11-3 to regulate the transcription of MaACO1/4 during banana fruit ripening

Fruit ripening is an economically important process of many edible fruits, which is controlled by a multi-level regulatory network coordinating the spatio-temporal expression of a large array of genes and/or proteins. In banana, ethylene orchestrates the ripening process, but the regulatory mechanism(s) controlling the expression of genes encoding ethylene biosynthesis-related enzymes is not fully understood. Here, we report the identification and characterization of a basic leucine zipper (bZIP) transcription factor MabZIP74 from banana fruit. Its gradually decreased with the progression of banana fruit ripening, implying a negative role for MabZIP74 in banana fruit ripening. MabZIP74 is localized in the nucleus and displays transcriptional inhibitory activity. More specifically, MabZIP74 was found to be a transcriptional repressor of ethylene biosynthetic genes MaACO1 and MaACO4, the accumulation of which paralleled ethylene production during banana ripening. Importantly, a protein kinase MaMAPK11-3 interacted with and phosphorylated MabZIP74, which attenuated MabZIP74-mediated transcriptional repression of MaACO1 and MaACO4 during ripening. Taken together, our findings reveal a novel MabZIP74-mediated regulatory network involved in ethylene biosynthesis and fruit ripening in banana. These results advance our knowledge on fruit ripening and provide additional opportunities for genetic improvement of banana fruit ripening.