The Greenish Flower Phenotype of (Orchidaceae) Is Caused by a Mutation in the -Like MADS-Box Gene .

In , the E-class () genes are generally expressed across all floral whorls. These genes play fundamental roles in floral organ fate determination during development by interacting with other MADS-box gene products, such as those from A-, B-, and C-class genes. However, the function of genes in orchid remains obscure. Here, we analyzed a mutant orchid cultivar with greenish flowers in and found that this phenotype is caused by the absence of SEP function. Wild type flowers contain a column and two perianth whorls consisting of three greenish sepals, two white petals, and a lip (labellum). By contrast, the flowers of cultivar 'Ryokusei' appear greenish, with three normal sepals in whorl 1, two greenish petals and a lip in whorl 2, and several sepaloid organs and a ventral column in whorls 3 and 4. We isolated two -like genes ( and ) and two -like genes ( and ) from wild type and compared their expression in the wild type vs. the mutant cultivar. and were expressed in the column in the wild type, whereas these genes were expressed in the ventral column and in sepaloid organs that had been converted from a column in 'Ryokusei.' and were expressed in all floral organs in the wild type. However, in the mutant cultivar, was expressed in all floral organs, while expression was not detected. Thus, we analyzed the genomic structures of in the wild type and 'Ryokusei' and identified a retrotransposon-like element in its first exon in 'Ryokusei.' Yeast two-hybrid assays demonstrated that HrSEP-1 interacts with HrDEF, HrAG-1, and HrAG-2. These results indicate that the mutant phenotype of 'Ryokusei' flowers is caused by the loss of function of . Therefore, this gene plays an important role in column, lip, and petal development in flowers.