Molecular characterization of a stress-response bZIP transcription factor in banana

Increasing evidence has demonstrated that basic leucine zipper (bZIP) transcription factors (TFs) are functional and involved in plant stress response, but few bZIP TFs have thus far been investigated in economically important fruit crops, such as bananas. In our present work, a novel 43.4 kDa bZIP transcription factor, MabZIP3, with a conserved bZIP domain, and a theoretical isoelectric point of 9.96 was isolated and characterized from banana fruit. Phylogenetic analysis showed that MabZIP3 belonged to the AREB subfamily of the bZIP family and was most closely related to BnABF2 and PsABF2. Transient expression analysis of the MabZIP3-GFP fusion protein in tobacco BY2 protoplasts revealed that the MabZIP3 protein is localized in the nucleus. Real-time PCR and promoter analysis of MabZIP3 indicated that it was responsive to methyl jasmonate, abscisic acid, chilling stress and pathogen Colletotrichum musae infection. More importantly, to further understand the regulatory network of MabZIP3 in response to stress, proteins physically interacting with MabZIP3 were identified by screening a cDNA expression library of banana fruit using the yeast two-hybrid system. Several interacting proteins related to stress responses were obtained, including a Saposin-Bdomain-containing protein, MaSAP, and their interaction was further confirmed by bimolecular fluorescence complementation assay (BiFC). Taken together, our results suggest that MabZIP3 is a stress-responsive transcription factor, which might be functionally linked to stress related proteins.