*3.3. Potential Functions of Tomato MADS-Box Genes during Fruit Development*

To better understand the roles of tomato MADS-box genes in fruit development and ripening, we selected five tomato MADS-box genes (*SlMBP3*, *MADS-RIN*, *TAGL1*, *TM4*, and *SlMBP7*) that were predicted to abundantly expressed at different stages of fruit development and ripening. Then, we detected their relative expression level in fruits samples from five different stages of development by qPCR (Figure 6). As shown in Figure 6A, the expression level of *SlMBP3* was found to be higher at the MG stage than at the other stages. We found that the expression levels of *MADS-RIN* and *TAGL1* exhibited an increasing tendency during the transition from the MG stage to the B+4 stage, and then decreased at the B+7 stage (Figure 6B,C). Moreover, the expression level of *TM4* was found to increase continuously in the process of fruit development (Figure 6D). The *SlMBP7* gene showed a relatively high expression level at the B stage (Figure 6E). Recent reports have identified a number of MADS-box genes that are required for the regulation of fruit development and ripening. One of the most representative is the tomato *MADS-RIN* gene, which is one of the earliest acting ripening regulators, and plays crucial roles in fruit ripening through ethylene dependent and independent ripening regulatory pathways [19,91]. In addition, *TAGL1*, *TM4,* and *SlMBP7* have been found to regulate fruit ripening in tomato [21,22]. Since our results were consistent with the functional research of these genes, the *SlMBP3* gene was predicted to be particularly high in the MG stage, indicating that it might play an important function in fruit development and ripening. These results help to advance our understanding of the function of MADS-box genes in the regulation of fruit developmental and ripening processes in tomato.

## **4. Materials and Methods**
