Molecular characterization and expression analysis of the critical floral gene MdAGL24-like in red-fleshed apple

The transition from vegetative to reproductive growth is the most dramatic phase change in plants. To better understand the molecular regulation of floral transition and flower development in red-fleshed apple (Malus sieversii f. niedzwetzkyana), we isolated and characterized a floral MADS-box gene, MdAGL24-like, which shares sequence similarity with AGAMOUS-LIKE 24 (AGL24) from other species. Spatial expression analysis showed that MdAGL24-like dynamically expressed in flowers, followed by roots and fruits. Subcellular localization analysis indicated that, like other transcript factors, MdAGL24-like was localized in the nucleus. Protein interaction analysis showed that MdAGL24-like could interact with MdSOC1 and MdAP1 in vivo and in vitro. MdAGL24-like and MdSOC1 could increase each other's expression by binding the CArG motifs in their promoters. Unlike MdSOC1, MdAGL24-like might indirectly promote the expression of MdLFY by upregulating the expression of MdSOC1. Ectopic expression of MdAGL24-like in wild-type Arabidopsis induced early flowering like the phenotypes induced by other AGL24 genes. Similar to AGL24 in Arabidopsis, MdAGL24-like could rescue the late-flowering phenotype of the agl24 mutant to some extent. These results help clarify the molecular mechanism underlying flowering and provide a means of shortening the juvenile period in red-fleshed apples and other fruit trees.