Mutant PI/GLO Homolog Confers the Hose-in-hose Flower Phenotype in Kurume Azaleas

To analyze hose-in-hose flowers of Kurume azaleas, floral morphologies and homeotic MADS genes were investigated in single and hose-in-hose cultivars. In floral morphological analysis, single flowers are comprised of four whorls of floral organs: sepals, petals, stamens, and carpels. Hose-in-hose flowers, in contrast, produced petaloid sepals instead of sepals in the first whorl. Based on molecular analysis, we isolated PISTILLATA (PI)/GLOBOSA (GLO) homologs in the hose-in-hose flower cultivar ‘Kirin’ and analyzed their expression in single flower and hose-in-hose flower cultivars. The mRNA sequences of two RoPI genes, RoPI-1 and RoPI-2, differed in terms of a 6 bp deletion. Based on genomic analysis, an insertion sequence was found in the second intron of RoPI-1 in hose-in-hose flowers. These RoPI genes were mainly expressed in the second and third whorls of single flowers, whereas these genes were expressed in all whorls of hose-in-hose flowers. These results suggest that the up-regulation of RoPI-1 expression contributed to the petaloid sepal formation of hose-in-hose flowers of Kurume azaleas.