Role of grapevine SEPALLATA‐related MADS‐box gene VvMADS39 in flower and ovule development

Seedlessness is one of the most important breeding goals for table grapes; thus, understanding the molecular genetic regulation of seed development and abortion is critical for the development of seedless cultivars. In the present study, we characterized VvMADS39, a class E MADS-box gene of grapevine (Vitis vinifera) orthologous to Arabidopsis SEP2. Heterologous overexpression of VvMADS39 in tomato reduced the fruit and seed size and seed number. Targeted mutagenesis of the homologous SlMADS39 in tomato induced various floral and fruit defects. It could reasonable to suppose that active VvMADS39 expression in "Thompson Seedless" may restrict cellular expansion, resulting in the development of smaller fruits and seeds, VvMADS39 may play a role in the regulation of ovule development in grapevine and contributes to seedless fruit formation. In contrast, VvMADS39 suppression in "Red Globe" was associated with enhanced histone H3 lysine 27 trimethylation in the promoter region of VvMADS39, allowing normal ovule and fruit development; Meanwhile, VvMADS39 interacts with VvAGAMOUS, and the activity of the VvMADS39-VvAGAMOUS dimer to induce integument development requires the activation and maintenance of VvINO expression. The synergistic cooperation between VvMADS39 and related proteins plays an important role in maintaining floral meristem characteristics, and fruit and ovule development.