Functional identification of apple MdJAZ2 in Arabidopsis with reduced JA-sensitivity and increased stress tolerance

Here, we report the decrease of JA-sensitivity and enhancement of tolerance to salt and PEG stresses in Arabidopsis overexpressing apple MdJAZ2. As signalling molecules, jasmonates (JAs) play significant roles in plant development and stress responses. JAZ proteins are the targets of the SCF^COI1 complex and act as the negative regulators in JA signalling pathway. However, there are no reports regarding the biological function of apple JAZ genes. In this study, one JAZ gene, MdJAZ2 from apple, was functionally characterized in detail. The expression of MdJAZ2 was up-regulated by MeJA and wounding treatments. MdJAZ2-GFP fusion protein was observed in nucleus in transient expression assay. Yeast two-hybrid and bimolecular fluorescence complementation assays revealed that MdJAZ2 could form homo- and heteromers, and also interact with F-box protein MdCOI1. Overexpression of MdJAZ2 conferred impaired JA-sensitivity in transgenic Arabidopsis, including JA-mediated root growth inhibition, susceptibility to the bacterial pathogen Pst DC3000, and the expression of JA response genes. Additionally, MdJAZ2 overexpression also improved tolerance to NaCl and PEG treatments in transgenic Arabidopsis. Together, our findings suggest that apple MdJAZ2 was not only involved in the JA response but also played roles in stress tolerance.