Identification of flowering genes in strawberry, a perennial SD plant

BackgroundWe are studying the regulation of flowering in perennial plants by using diploid wild strawberry (Fragaria vescaL.) as a model. Wild strawberry is a facultative short-day plant with an obligatory short-day requirement at temperatures above 15°C. At lower temperatures, however, flowering induction occurs irrespective of photoperiod. In addition to short-day genotypes, everbearing forms of wild strawberry are known. In 'Baron Solemacher' recessive alleles of an unknown repressor,SEASONAL FLOWERING LOCUS(SFL), are responsible for continuous flowering habit. Although flower induction has a central effect on the cropping potential, the molecular control of flowering in strawberries has not been studied and the genetic flowering pathways are still poorly understood. The comparison of everbearing and short-day genotypes of wild strawberry could facilitate our understanding of fundamental molecular mechanisms regulating perennial growth cycle in plants.ResultsWe have searched homologs for 118Arabidopsisflowering time genes fromFragariaby EST sequencing and bioinformatics analysis and identified 66 gene homologs that by sequence similarity, putatively correspond to genes of all known genetic flowering pathways. The expression analysis of 25 selected genes representing various flowering pathways did not reveal large differences between the everbearing and the short-day genotypes. However, putative floral identity and floral integrator genesAP1andLFYwere co-regulated during early floral development.AP1mRNA was specifically accumulating in the shoot apices of the everbearing genotype, indicating its usability as a marker for floral initiation. Moreover, we showed that flowering induction in everbearing 'Baron Solemacher' and 'Hawaii-4' was inhibited by short-day and low temperature, in contrast to short-day genotypes.ConclusionWe have shown that many central genetic components of the flowering pathways inArabidopsiscan be identified from strawberry. However, novel regulatory mechanisms exist, likeSFLthat functions as a switch between short-day/low temperature and long-day/high temperature flowering responses between the short-day genotype and the everbearing 'Baron Solemacher'. The identification of putative flowering gene homologs andAP1as potential marker gene for floral initiation will strongly facilitate the exploration of strawberry flowering pathways.