Application of Mutant ap3 Allele-based Markers for the Selection of the Long-lasting Flower Phenotype (Misome-shō) in Evergreen Azalea Cultivars

Abstract

There is a long-lasting flower trait with a temporal color change, known as “misome-shō”, in Japanese evergreen azalea. This trait has been found in several wild Japanese evergreen azalea species, such as Rhododendron kaempferi ‘Nikkō-misome’, R. macrosepalum ‘Kochō-zoroi’, R. indicum ‘Chōjyu-hō’, and R. × hannoense ‘Amagi-beni-chōjyu’. The corollas of long-lasting flower cultivars undergo a conversion of normal corollas to sepaloid corollas due to loss of function of the MADS-box B class gene, APETALA3 (AP3) homolog. Also, the long-lasting flower trait was shown to be recessive to normal flowers and controlled by a single gene. To develop a DNA marker for selection of the long-lasting flower phenotype, we carried out a multiplex-PCR approach to detect the ap3 mutant allele related to long-lasting flower traits, and investigated the flower phenotypes in crossed progenies of 23 cross combinations and 245 individuals. The normal flower phenotype individuals in the crossed progenies were homozygous for the normal allele or heterozygous for the normal allele and the ap3 mutant allele. On the other hand, the long-lasting flower phenotype individuals in the crossed progenies were homozygous for the ap3 mutant allele of long-lasting cultivars. These results support the idea that the long-lasting flower trait is caused by a mutation in the AP3 homolog, and it has been newly clarified that any combination of these mutant alleles in long-lasting flower cultivars has the long-lasting flower phenotype. In conclusion, our data indicate that efficient selection of individuals with long-lasting flowers will be possible by using selection DNA markers linked to the long-lasting flower trait.