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 p etunia, designated floral binding protein (fbp) genes 7 and 11. The pu tative protein products of these genes have similar to 90% of their ov erall amino acid sequence in common. In situ RNA hybridization experim ents revealed that both genes are expressed in the center of the devel oping gynoecium before ovule primordia are visible. At later developme ntal stages, hybridization signals were observed only in the ovules, s uggesting that these genes are involved in ovule formation. To test th is hypothesis, we raised transgenic petunia plants in which both fbp7 and fbp11 expression was inhibited by cosuppression. In the ovary of t hese transformants, spaghetti-shaped structures developed in positions normally occupied by ovules. These abnormal structures morphologicall y and functionally resemble style and stigma tissues. Our results show that these MADS box genes belong to a new class of MADS box genes inv olved in proper ovule development in petunia.