Green corolla segments in a wild Petunia species caused by a mutation in FBP2, a SEPALLATA-like MADS box gene.

A Petunia inflata isolate with a novel phenotype of a purple corolla limb with green corolla segments (GCS) was characterized. The GCS have stomata and trichomes on the adaxial side, and resemble calyx segments in epidermal morphology. The GCS phenotype was inherited in a recessive manner. In the GCS plant, a novel inhibitor/defective spm-like transposable element (dPifTp1) was inserted in the second intron of the Floral Binding Protein 2 (FBP2) gene. The sequence of the resulting transcript contained five silent mutations as compared the corresponding open reading frame of P. x hybrida FBP2 mRNA. The GCS phenotype co-segregated with an FBP2 fragment containing a dPifTp1 insertion. The transcript level of the FBP2 gene in GCS flowers was markedly lower than that in wild-type (WT) flowers, suggesting that partially inhibited FBP2 gene expression caused the morphogenesis of calyx-like tissue in the corolla segments of GCS flowers. Gene expression pattern analysis using a full-length Petunia floral cDNA microarray indicated that some photosynthesis-related genes were expressed at significantly higher levels in the GCS of GCS flowers, but the mRNA levels of most other genes in the GCS were similar to those in the WT corolla. Taken together, these data suggest that the partial loss of FBP2 expression does not shift global gene expression in the corolla segments of the GCS flower toward that of calyx, even though calyx-like morphogenesis was established in the corolla segments.