Gene expression profiling of candidate genes for flowering in Belgian pot azalea

Pot azalea (R. simsii hybrids) production in the Ghent area (Belgium) accounts approximately 40 million plants per year. The past decade, growers and their associations have made efforts to improve both the quality of the vegetative as well as the flowering plants; however, suboptimal flowering is often observed. Different potential causes have been quoted but a clear cut direct cause is seldom found; interaction between several elements related to the culture conditions should be at the base. Therefore we aimed at identifying the influential factors related to flowering quality by an integrated approach focusing on the induction of processes at the gene expression level and physiological measurements. Candidate genes for flower initiation (FT, TOC, CO, LFY, AG, AP3 and CRY) have been isolated in azalea, as well as genes potentially involved in the process of dormancy breaking (ELIP, dehydrin, ARP), the carbohydrate metabolism (SUSY and ?-amylase) and gibberellic acid biosynthesis (GA20-oxidase, GA2-oxidase and GA3-oxidase). The expression of these genes was determined in several cultivars under different culture conditions. Flower initiation was stimulated by the application of growth regulators in combination with day length conditions (8h and 16h). The expression profiles of both FT and LFY clearly indicated when bud formation was initiated, but day-length was not a determining factor for initiation. To evaluate gene expression under cold treatment, plants with fully developed buds (stage 7) were grown at 7°C and 18°C for 6 weeks. The expression of ELIP, ARP and dehydrin is clearly upregulated under cold conditions and decreases again after 5 weeks when dormancy has been released. When we look at the sugar metabolism, the expression of both SUSY and ?-amylase appears to be upregulated in plants grown at cold temperatures compared to plants kept in the greenhouse. At anthesis, the expression of the genes of the carbohydrate pathway indicates the photosynthetic capacity of the plants and also the expression of the GA-genes differed between treatments. Results of the 3 experiments (initiation, dormancy and anthesis) will be presented.