Environmental responses of the FT/TFL1 gene family and their involvement in flower induction in Fragaria×ananassa

Flowering time control is important for fruit production in Fragaria×. ananassa. The flowering inhibition pathway has been extensively elucidated in the woodland strawberry, Fragaria vesca, whereas the factors involved in its promotion remain unclear. In this study, we investigated the environmental responses of F.×. ananassa FT and TFL1-like genes, which are considered key floral promoters and repressors in many plants, respectively. A putative floral promoter, FaFT3, was up-regulated in the shoot tip under short-day and/or low growth temperature, in accordance with the result that these treatments promoted flowering. FaFT3 mRNA accumulated before induction of a floral meristem identity gene, FaAP1. FaFT2, a counterpart of FvFT2, expressed in the flower bud of F. vesca, was not induced in the shoot tip differentiating sepal or stamen, suggesting that this gene works at a later stage than stamen formation. In F. vesca, FvFT1 transmits the long-day signal perceived in the leaves to the shoot tip, and induces the potent floral inhibitor FvTFL1. FaFT1 was expressed in the leaves under long-day conditions in F.×. ananassa. Expression of FaTFL1 was higher in the shoot tip under long-day than short-day conditions. Independent of day-length, FaTFL1 expression was higher under high temperature than low temperature conditions. These results suggest that FaFT3 induction by short-day or low temperature stimuli is a key step for flowering initiation. As in F. vesca, F.×. ananassa floral inhibition pathways depend on FaTFL1 regulation by day-length via FaFT1, and by temperature.