A petunia MADS box gene involved in the transition from vegetative to reproductive development

We have identified a novel petunia MADS box gene, PETUNIA FLOWERING GENE (P FG), which is involved in the transition from vegetative to reproductive de velopment. PFG is expressed in the entire plant except stamens, roots and s eedlings. Highest expression levels of PFG are found in vegetative and infl orescence meristems, Inhibition of PFG expression in transgenic plants, usi ng a cosuppression strategy, resulted in a unique nonflowering phenotype, H omozygous pfg cosuppression plants are blocked in the formation of inflores cences and maintain vegetative growth. In these mutants, the expression of both PFG and the MADS box gene FLORAL BINDING PROTEIN26 (FBP26), the putati ve petunia homolog of SQUAMOSA from Antirrhinum, are down-regulated. In hem izygous pfg cosuppression plants initially a few flowers are formed, after which the meristem reverts to the vegetative phase. This reverted phenotype suggests that PFG, besides being required for floral transition, is also r equired to maintain the reproductive identity after this transition. The po sition of PFG in the hierarchy of genes controlling floral meristem develop ment was investigated using a double mutant of the floral meristem identity mutant aberrant leaf and flower (alf) and the pfg cosuppression mutant. Th is analysis revealed that the pfg cosuppression phenotype is epistatic to t he alf mutant phenotype, indicating that PFG acts early in the transition t o flowering, These results suggest that the petunia MADS box gene, PFG, fun ctions as an inflorescence meristem identity gene required for the transiti on of the vegetative shoot apex to the reproductive phase and the maintenan ce of reproductive identity.