Expression of MADS-box Genes in Narrow-petaled Cultivars of Rhododendron macrosepalum Maxim.

Japanese old azalea cultivars have various floral mutations. We isolated MADS-box class C homologous genes from wild-type Rhododendron macrosepalum to analyze the expression patterns in the floral organs of the narrow-petal mutational cultivars ‘Hanaguruma’, ‘Gin-no-zai’, and ‘Seigaiha’. The AG homologous genes RmAG1-1/-2/-3 were 99–100% identical to RkAG1-1/-2, which was isolated from R. kaempferi. In ‘Hanaguruma’, ‘Seigaiha’, and the wild type, the relative expression level of RmAG in whorl 2 was much lower than that in whorl 3. In contrast, the relative expression level of RmAG in whorl 2 of ‘Gin-no-zai’ was approximately 15.5% of that in whorl 3. In ‘Gin-no-zai’, the petals with mutations were categorized as 1 of these 3 types: type 1, consisting of narrow petals with traces of anthers; type 2, consisting of narrow petals only; and type 3, consisting of petals that coalesced with the neighboring petals. The relative expression levels of RmAG gradually increased from type 3 to type 1 petals. These results suggest that the degree of staminoidy for the petals in whorl 2 is attributable to the expression levels of RmAG.