An AGAMOUS/SHATTERPROOF homologue (Vvmads1) was isolated from grapevine by differential display between berry and leaf mRNA. The predicted protein sequence of the full-length clone shows a high degree of homology to PLENA (77% identity) and to SHP1 and SHP2 (75% and 74% identity respectively), and is grouped with AGAMOUS/PLENA homologues when the conserved MADS and K domains are compared. Vvmads1 is expressed only in the later stages of flower development and throughout berry development, although expression is reduced after ripening commenced. When Vvmads1 was over-expressed in tobacco, the resulting plants display altered morphologies in the outer two floral whorls. In the most extreme cases, the inner whorls were surrounded by a carpelloid structure created by the modified sepals. Within these sepals were petals which had been split into sections and which were attached at the base of the flower by structures with the appearance of filaments. The results of this study suggest that Vvmads1 has a regulatory role in flower development before fertilisation and a role in fruit development after fertilisation.