Flower colour as a model in azalea for integration of phenotype, genotype and gene expression

Flower colour is inherited as a semi-qualitative trait in azalea. A two-gene model is used to explain the phenotypic variation between white, brick red and carmine red colour: W for anthocyanins and Q for the co-pigmentation of flavonols. However, the presence of the latter in white flowers cannot be detected visually. Also, the existence of pink flowers is not explained by this model. Therefore, flower colour was determined on a crossing population using image analysis software. Integration of the image analysis data as QTLs on a genetic map could be enlightening, hence a map of 16 linkage groups was constructed. Besides AFLP and SSR markers also a set of functional markers was used. EST-markers were developed for 4 genes coding for enzymes in the flavonoid biosynthesis pathway. MYB-profiling generated 15 dominant markers. In this way, phenotypic and genetic data were both integrated on the genetic map of azalea. In case both are located at the same position, the genes are assumed to be directly involved in the creation of the phenotype. Nevertheless, not the genes themselves but transcription factors are often the switches for phenotypic variation. In that case phenotype is expected to map together with gene expression. Therefore, expression profiles of 5 flavonoid biosynthesis genes were generated in petals of part of the crossing population using RT-qPCR and eQTL mapping integrated these data with the genetic map.