Orchidaceae includes many species with petaloid sepals, as well as several genera, such as Cypripedium and Habenaria, with distinct sepals and petals. Since the morphological differentiation of sepals and petals is observed in different orchid groups, it likely evolved independently in Orchidaceae. The flower of Habenaria radiata has green sepals and white petals in the perianth. Among the cultivars of H. radiata, the floral homeotic mutant cultivar 'Hishou' exhibits an altered flower morphology, with petaloid organs in whorl 1. Class B MADS-box genes play an important role in petal and petaloid organ development in dicots and monocots. We isolated and characterized three class B genes from H. radiata, termed HrGLOl, HrGLO2 and HrDEF. HrGLOl and HrGLO2 were expressed in sepals, petals and columns, whereas HrDEF was expressed only in petals and columns, and not in sepals. In the petaloid-sepal cultivar, all three class B genes were expressed in sepals, petals and columns. These results suggest that the distinctive expression of HrDEF plays a role in the differentiation of sepals and petals in H. radiata. We carried out an intraspecific cross between wild-type and petaloid-sepal H. radiata cultivars. Intraspecific hybrids had two types of flowers; some individuals had petaloid-sepal flowers, similar to 'Hishou', and the rest had wild-type flowers. The results of the current study suggest that the petalization of sepal phenotype of 'Hishou' is a dominant phenotype, and that the expansion of DEF-like gene expression in whorl 1 is a gain-of-function mutation.
|出版社||Nova Science Publishers, Inc.|
|出版ステータス||Published - 2010 1月 1|
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