Overexpression of SlMADS48 Alters the Structure of Inflorescence and the Sizes of Sepal and Fruit in Tomato

MADS-box transcription factors play a vital role in the development of reproductive organs and fruits. However, the mechanisms by which MADS-box transcription factors participate in determining the size of organs remain incompletely understood. This study demonstrated that the overexpression of <i>SlMADS48</i> results in elongated sepals and is accompanied by an elevated gibberellin content, compared with the wild type (WT). The interaction between SlMADS48 and several proteins (SlMC, SlMBP21, SlJOINTLESS, and SlFYFL) involved in sepal development was identified. In addition, the OE<i>-SlMADS48</i> lines exhibited increased branches and total numbers of flowers. Molecular analysis revealed that SlMADS48 interacted with TM29, FUL1, FUL2, and MBP20, which are associated with inflorescence development. Moreover, SlMDS48 directly targeted the promoter of <i>SlTM3</i> via the CArG-box motif, reducing its transcript levels. Additionally, the overexpression of <i>SlMADS48</i> led to a reduction in the size of fruit, together with decreased contents of cytokinins and indole acetic acid (IAA) compared with the WT. Furthermore, SlMADS48 directly combined with the promoters of <i>SlcycD6;1</i> and <i>SlIAA29</i> in the cytokinin and auxin pathways, respectively. This research advanced our understanding of SlMADS48's role in determining organ size and provided valuable insights into target gene selection in tomato breeding programs.