A novel class of MADS box genes is involved in ovule development in petunia

We isolated and characterized two ovule-specific MADS box cDNAs from petunia, designated floral binding protein (fbp) genes 7 and 11. The putative protein products of these genes have approximately 90% of their overall amino acid sequence in common. In situ RNA hybridization experiments revealed that both genes are expressed in the center of the developing gynoecium before ovule primordia are visible. At later developmental stages, hybridization signals were observed only in the ovules, suggesting that these genes are involved in ovule formation. To test this hypothesis, we raised transgenic petunia plants in which both fbp7 and fbp11 expression was inhibited by cosuppression. In the ovary of these transformants, spaghetti-shaped structures developed in positions normally occupied by ovules. These abnormal structures morphologically and functionally resemble style and stigma tissues. Our results show that these MADS box genes belong to a new class of MADS box genes involved in proper ovule development in petunia.