Overexpression of Two MADS-Box Genes from Lagerstroemia speciosa Causes Early Flowering and Affects Floral Organ Development in Arabidopsis

Lagerstroemia speciosa is an important ornamental plant, and there is only one double-petaled variety, ‘Yunshang’, produced by natural mutation, in the whole genus of Lagerstroemia. The members of the MADS-box family play important roles in floral organ development. However, little is known about the biological function of the MADS-box gene in L. speciosa. In our study, two MADS-box genes (LsAG2 and LsDEF1) were isolated from L. speciosa, and their expression levels in different tissues and developmental stages were analyzed by RT-qPCR. Subcellular localization showed that LsAG2 and LsDEF1 are localized in the nucleus. The overexpression of LsAG2 and LsDEF1 in Arabidopsis thaliana caused transgenic plants to exhibit different phenotypes, such as floral organ aberrations, early flowering, and dwarf plants, and resulted in the up-regulation of endogenous genes related to flowering (i.e., AP1, PI, FLC, FUL, LFY, and FT). Our results provide a theoretical basis for the flowering time, flower development, and genetic improvement of double-petaled flowers in the genus of Lagerstroemia.