Characterization of the roles of MiSPL4a and MiSPL4b in flowering time and drought resistance in Arabidopsis

SQUAMOSA promoter-binding protein-like 3/4/5 (SPL3/4/5) genes are involved mainly in regulating plant flowering through the gibberellin and age pathways. In our previous study, two SPL4-like genes, MiSPL4a and MiSPL4b (MiSPL4a/b), were identified and analyzed in mango, and their highest expression levels were detected in flowers. However, the functions of MiSPL4a and MiSPL4b in mango remain unclear. In this study, bioinformatics, expression, function and interacting proteins were analyzed. The results revealed that MiSPL4a was highly expressed in leaves at the early stage of the flower induction period, while MiSPL4b increased the highest expression peak during the vegetative period. MiSPL4a/b genes were induced by drought treatment. Overexpression of MiSPL4a/b accelerated early flowering and increased the expression levels of several flowering-related genes, such as APETALA1 (AtAP1), FRUITFULL (AtFUL), and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (AtSOC1) in Arabidopsis thaliana. The MiSPL4a/b transgenic plants presented increased resistance to drought and abscisic acid (ABA) treatment, and the MiSPL4b transgenic plants were sensitive to prohexadione-calcium (Pro-Ca) treatment. In addition, MiSPL4a and MiSPL4b interact with MiSOC1, Mi14–3–3, and several stress-related proteins. In summary, these findings indicated that in transgenic Arabidopsis, MiSPL4a/b genes have the function of accelerating flowering and enhancing stress resistance.