Immunolocalization of the petunia floral binding proteins 7 and 11 during seed development in wild-type and expression mutants of Petunia hybrida

During Petunia hybrida seed development, the MADS-box genes encoding the fl oral binding proteins (FBP) 7 and 11 are expressed in the seed coat and not in the endosperm or embryo. These proteins are thought to function as tran scription factors and are essential for ovule formation in Petunia sop. Imm unocytochemical methods were used to analyze the distribution of FBP7 and F BP11 after fertilization in wild type and ectopic and cosuppression mutants . During the first nine days of seed development the protein was found in t he nuclei of seed coat cells, of both wild-type plants and plants which ect opically expressed FBP11. The signal for FBP7 and -11 proteins diminished d uring seed development, was first lost in the outer epidermis of the seed c oat, then in the endothelium, and finally, at 9 days after pollination (DAP ), the protein could not be detected anymore in the parenchyma cells of the seed coat. Although the distribution patterns in wild-type and FBP11 ectop ically expressing plants are similar, the latter exhibited higher protein l evels. A mild-cosuppression mutant of FBP7 and FBP11, having only a total o f 5% FBP7 and -11 mRNA, showed hardly any FBP7 and -11 proteins. The lack o f FBP7 and -11 caused endosperm degeneration in the mutant at a moment when the protein had already decreased to an undetectable level in the wild typ e and ectopic expression mutant (i.e., at 13 DAP). It is suggested that til l about 9 DAP a minimal amount of FBP7 and -11 is needed for the normal fun ctioning of the seed coat during later stages, i.e., for transfer of nutrie nts to endosperm and embryo. Besides the immunocytochemical data on the FBP 7 and FBP11 MADS-box gene products, the morphological analysis of wild type and mutants contributes details on early seed development in Petunia hybri da.