CO-SUPPRESSION OF THE PETUNIA HOMEOTIC GENE FBP2 AFFECTS THE IDENTITYOF THE GENERATIVE MERISTEM

The function of the petunia MADS box gene fbp2 in the control of flora l development has been investigated. Inhibition of fbp2 expression in transgenic plants by a co-suppression approach resulted in the develop ment of highly aberrant flowers with modified whorl two, three and fou r organs. This mutant flower phenotype inherited as a single Mendelian trait. The flowers possess a green corolla which is reduced in size. Furthermore, the stamens are replaced by green petaloid structures and the inner gynoecial whorl is dramatically reduced. No ovules or place nta are formed and instead two new inflorescences developed in the axi ls of the carpels. These homeotic transformations are accompanied by a complete down-regulation of the petunia MADS box gene fbp6 which is h ighly homologous to the Arabidopsis and Antirrhinum genes agamous (ag) and plena (ple). In contrast to this, two other petunia MADS box gene s, exclusively expressed in whorls two and three, are still transcribe d. Our results indicate that the fbp2 gene belongs to a new class of m orphogenesis genes involved in the determination of the central part o f the generative meristem.