Extending the Toolkit for Beauty: Differential Co-Expression of -Like and Class B MADS-Box Genes during Flower Development.

The molecular basis of orchid flower development is accomplished through a specific regulatory program in which the class B MADS-box genes play a central role. In particular, the differential expression of four class B / genes is responsible for specification of organ identities in the orchid perianth. Other MADS-box genes ( and -like) enrich the molecular program underpinning the orchid perianth development, resulting in the expansion of the original "orchid code" in an even more complex gene regulatory network. To identify candidates that could interact with the genes in orchids, we conducted an in silico differential expression analysis in wild-type and peloric . The results suggest that a YABBY -like gene could be involved in the molecular program leading to the development of the orchid perianth, particularly the labellum. Two YABBY homologs are present in the genome of , and , and both express two alternative isoforms. Quantitative real-time PCR analyses revealed that both genes are expressed in column and ovary. In addition, is more strongly expressed the labellum than in the other tepals of wild-type flowers. This pattern is similar to that of the genes and opposite to that of . In peloric mutant where labellum-like structures substitute the lateral inner tepals, is expressed at similar levels of the genes, suggesting the involvement of in the development of the labellum, together with the genes. Although the yeast two-hybrid analysis did not reveal the ability of PeDL2 to bind the PeMADS2-PeMADS5 proteins directly, the existence of regulatory interactions is suggested by the presence of CArG-boxes and other MADS-box transcription factor binding sites within the putative promoter of the orchid gene.