Pigment composition patterns and expression of anthocyanin biosynthesis genes in Rhododendron kiusianum, R. kaempferi, and their natural hybrids on Kirishima mountain mass, Japan

We compared anthocyanidin composition patterns and the expression of anthocyanin biosynthesis genes in Rhododendron kiusianum, R. kaempferi, and their natural hybrids from the Kirishima mountain mass. Compared with the habitat, phenotypic characteristics including tree height and flower color did not change in the transplanted individuals after cutting propagation. According to flower color measurements, R. kiusianum and R. kaempferi belonged to purple and red series, respectively, and their natural hybrids belonged to either the red or purple series. HPLC analysis showed that the petals of most R. kiusianum and natural hybrids contained both cyanidin and delphinidin series pigments, while the petals of R. kaempferi contained only cyanidin series pigments. However, one R. kiusianum individual in the purple series contained only cyanidin series pigments and one natural hybrid individual in the red series contained both cyanidin and delphinidin series pigments. These individuals were thought to be influenced by co-pigmentation or a lack thereof, respectively. All samples expressed F3′H, DFR, and ANS genes in real-time quantitative RT-PCR, and the F3′5′H gene was always expressed in samples containing delphinidin series pigments. These results suggest that the expression of F3′5′H is essential for R. kiusianun and its natural hybrids to produce delphinidin series pigments. This study showed that interspecific hybridization between wild species with purple series flowers and wild species with red series flowers varied the pigment composition and anthocyanin biosynthesis-related gene expression in the natural hybrids, suggesting that it caused the flower color variation in the wild populations in the Kirishima mountains.