Regulation of major phase transitions in woodland strawberry (Fragaria vesca L.)

Plant’s life cycle is characterized by several phase changes. Two of them, juvenile to adult and vegetative to reproductive shifts, have a major role to ensure reproductive success. In juvenile phase, plants are unable to flower, but after attaining adult vegetative phase they become competent to respond to flowering inducing signals. After the competence to flower is attained, diverse endogenous and environmental signals finally induce flowering.
Molecular control of flowering induction has been extensively studied in Arabidopsis, whereas the genetic mechanism of juvenile to adult transition has begun to emerge only recently. In Arabidopsis, two sequentially acting small RNA species, miR156 and miR172, control juvenile to adult transition. After plants have attained the adult stage, four major genetic pathways mediate environmental (photoperiod, vernalization) and endogenous (plant hormone gibberellin, developmental stage) signals to induce flowering (vegetative to reproductive phase transition). More than 100 flowering time genes have been functionally characterized in Arabidopsis. Many of these genes are conserved between species including perennials. However, only fragmentary information about the flowering pathways exists in perennials, and the mechanisms controlling juvenile to adult phase transition are almost completely unknown.
We aim at revealing molecular mechanisms controlling juvenile to adult and vegetative to reproductive phase transitions in woodland strawberry (Fragaria vesca L.), which has a potential to become one of the major perennial model species. F. vesca is induced to flowering either under SD conditions or regardless of the daylength when the temperature is low. Interestingly, continuously flowering (everbearing, EB) mutants of F. vesca show completely opposite response to photoperiod and temperature. We have shown that recessive alleles of one unknown gene, SFL (Seasonal Flowering Locus) causes EB phenotype in five F. vesca genotypes originating from Europe and America. Obviously, SFL is a major flowering time gene in F. vesca and it provides a key for understanding flowering gene pathway in this species. Moreover, our results indicate that SFL controls also juvenile to adult phase transition. In this project, we are using positional cloning to identify SFL gene. After identification, SFL will be functionally characterized by using transgenic plants and its environmental regulation will be studied in controlled conditions. Moreover, another selected flowering time genes will be functionally characterized and their locations in the F. vesca flowering gene pathway in relation to SFL will be explored. For identification of novel regulators of flowering time in F. vesca, we will develop a high-throughput screening system for the identification of induced mutations and generate the mutagenized population (EMS mutagenesis) for further studies.
The knowledge gained in this project will be utilized in the connected applied projects to develop molecular markers for the selection of desirable flowering characters (early/continuous flowering). This work will have a strong impact also on marker assisted breeding of other ornamental and fruit species of Rosaceae, since many genetic markers are transferable within Rosaceae.