Redefining C and D in the Petunia ABC

Abstract

According to the ABC(DE) model for flower development, C-genes are required for stamen and carpel development and floral determinacy, and D-genes were proposed to play a unique role in ovule development. Both C-and D-genes belong to the AGAMOUS (AG) subfamily of MADS box transcription factors. We show that the petunia (Petunia hybrida) C-clade genes PETUNIA MADS BOX GENE3 and FLORAL BINDING PROTEIN6 (FBP6) largely overlap in function, both in floral organ identity specification and floral determinacy, unlike the pronounced subfunctionalization observed in Arabidopsis thaliana and snapdragon (Antirrhinum majus). Some specialization has also evolved, since FBP6 plays a unique role in the development of the style and stigma. Furthermore, we show that the D-genes FBP7 and FBP11 are not essential to confer ovule identity. Instead, this function is redundantly shared among all AG members. In turn, the D-genes also participate in floral determinacy. Gain-of-function analyses suggest the presence of a posttranscriptional C-repression mechanism in petunia, most likely not existing in Arabidopsis. Finally, we show that expression maintenance of the paleoAPETALA3-type B-gene TOMATO MADS BOX GENE6 depends on the activity of C-genes. Taken together, this demonstrates considerable variation in the molecular control of floral development between eudicot species.

Development of DNA Markers Linked to Double-Flower and Hortensia Traits in <i>Hydrangea macrophylla</i> (Thunb.) Ser.

“…Petunias express two such C-class genes, FLORAL BINDING PROTEIN6 (FBP6) and PETUNIA MADS BOX GENE3 (PMADS3). Reduced expression of these genes by PMADS3-RNAi in a mutant fbp6 background results in a double-flowered phenotype (Heijmans et al, 2012). These facts suggest that the gene responsible for controlling d Kira is associated with C-class mutations.…”

Molecular Mechanism Regulating Floral Architecture in Monocotyledonous Ornamental Plants

“…Petunia expresses two C-class genes, FBP6 and PMADS3. Reduction of the expression of these genes by PMADS3-RNAi in a mutant background (fbp6) results in a double-flowered phenotype (Heijmans et al, 2012). Thus, loss of Class C function causes a doubleflowered phenotype in dicot plants.…”

Conservation and Diversification of Floral Homeotic MADS-box Genes in Eustoma grandiflorum

“…Although it is also known that Arabidopsis has two PLE-like genes, SHATTERPROOF1 and 2 (SHP1 and 2), and Antirrhinum has an euAG-like gene, FARINELLI (FAR), these genes do not mainly contribute to their C-functions (Davies et al, 1999;Liljegren et al, 2000). In contrast, in Petunia hybrida and Nicotiana benthamiana, both euAG and PLE sub-clade genes seem to retain C-functions (Fourquin and Ferrándiz, 2012;Heijmans et al, 2012). In E. grandiflorum, all of the putative C-class genes were grouped into the PLE subclade and no euAG sub-clade genes could be identified, suggesting that only PLE sub-clade genes specify the C-function.…”

“…The expression level often correlates with the function. For instance, loss-of-function analysis of two redundant C class genes of Petunia hybrida indicated that one C class gene FBP6 uniquely contributes to style and stigma development, while the other gene PMADS3 exhibited weak expression and did not strongly influence floral organ identity in these organs (Heijmans et al, 2012;Kater et al, 1998).…”