Suppression of a tomato SEPALLATA MADS-box gene, SlCMB1, generates altered inflorescence architecture and enlarged sepals

The SEPALLATA (SEP) MADS-box transcription factors play essential roles in reproductive growth, especially in floral organ differentiation. Here, SlCMB1, a tomato SEP MADS-box gene, was isolated. SlCMB1 is noticeably expressed in inflorescences and flowers. Its transcript levels were higher in sepals than in other floral organs and decreased during sepal development. Tomato plants with reduced SlCMB1 mRNA levels displayed longer, branched and indeterminate inflorescences that exhibited a transition from reproductive to vegetative growth and enlarged and abnormally fused sepals. The transcript levels of genes known to regulate the development of inflorescence architecture and sepal size in tomato were dramatically changed. In addition, the expression levels of cell elongation-related and gibberellin biosynthetic genes also showed significant differences between the transgenic lines and the wild type, and the GA content of the peduncle in the transgenic lines was higher than that in the wild type. Yeast two-hybrid assay showed that SlCMB1 could interact individually with MC, J, AP2a and SlMBP21. Overall, our results indicate that SlCMB1 is an important regulator involved in the development of inflorescence architecture and sepal size in tomato plants.