| Summary: | The phenomenon of multi-carpel and multi-ovule exists in the grapevine cultivar ‘Xiangfei’, but the mechanism of ovule formation is seldom reported. In this study, we observed the ovule formation process by using ‘Xiangfei’ grapes. The role of the <i>VvAG2</i> (<i>VvAGAMOUS</i>) gene in ovule formation was identified, and we explored the relationship between VvAG2, VvSEP3(VvMADS4) and VvAGL11(VvMADS5) proteins. The results showed that the ovule primordium appeared when the inflorescence length of ‘Xiangfei’ grapes were 4–5 cm long; the relative expression levels of <i>VvAG2</i>, <i>VvAGL11</i> and <i>VvSEP3 </i>genes were higher during ovule formation, and the expression levels of <i>VvAG2</i> gene was the highest. Transgenic tomato (<i>Solanum lycopersicum</i>) plants expressing <i>VvAG2</i> produced higher numbers of ovules and carpels than the wild type. Moreover, yeast two-hybrid and yeast three-hybrid experiments demonstrated that VvSEP3 acts as a bridge and interacts with VvAG2 and VvAGL11 proteins, respectively. Meanwhile, a homodimer can be formed between VvSEP3 and VvSEP3, but there was no interaction between VvAG2 and VvAGL11. These findings suggest that the <i>VvAG2</i> gene is involved in the formation of ovules, and VvAG2/VvSEP3 together with VvAGL11/VvSEP3 can form a tetrameric complex. In summary, our data showed that <i>VvAG2 </i>along with <i>VvSEP3 </i>and <i>VvAGL11</i> jointly regulate the ovule formation of ‘Xiangfei’ grapes.
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