Background: Basic region/leucine zippers (bZIPs) are transcription factors (TFs) encoded by a large gene family in plants. ABF3 and ABI5 are Group A bZIP TFs that are known to be important in abscisic acid (ABA) signaling. However, questions of whether ABF3 regulates ABI5 are still present.
Results: In vitro kinase assay results showed that Thr-128, Ser-134, and Thr-451 of ABF3 are calcium-dependent protein kinase phosphorylation sites. Bimolecular fluorescence complementation (BiFC) analysis results showed a physical interaction between ABF3 and 14-3-3ω. A Thr-451 to Ala point mutation abolished the interaction but did not change the subcellular localization. In addition, the Arabidopsis protoplast transactivation assay using a luciferase reporter exhibited ABI5 activation by either ABF3 alone or by co-expression of ABF3 and 14-3-3ω. Moreover, chromatin immunoprecipitation-qPCR results showed that in Arabidopsis, ABI5 ABA-responsive element binding proteins (ABREs) of the promoter region (between - 1376 and - 455) were enriched by ABF3 binding under normal and 150 mM NaCl salt stress conditions.
Conclusion: Taken together, our results demonstrated that ABI5 expression is regulated by ABF3, which could contribute to salt stress tolerance in Arabidopsis thaliana.
Keywords: 14-3-3; ABF3; ABI5; Abscisic acid; Calcium; Phosphorylation; Salt.