RNA-seq Analysis of Meristem Cells Identifies the FaFT3 Gene as a Common Floral Inducer in Japanese Cultivated Strawberry

In Arabidopsis thaliana, the FLOWERING LOCUS T (FT) gene, acting as a floral promoter, is expressed and translated in leaves, and is then transported to the shoot apical meristem. In contrast, the expression pattern of the FaFT3 gene in the crown, which contains the shoot apical meristem, is coordinated with the initiation of the floral bud in the June-bearing type of cultivated strawberry (Fragaria × ananassa) ‘Nyoho’. However, whether the FaFT3 protein functions as a floral promoter and whether the expression pattern of FaFT3 in the crown observed in ‘Nyoho’ is conserved in other strawberry cultivars are not known. In this study, we investigated the floral inducer activity of the FaFT3 gene isolated from the cultivated strawberry ‘Tochiotome’ using FaFT3-overexpressing transgenic Arabidopsis lines and performed expression analysis on the FaFT3 gene in the crown tip of ‘Tochiotome’. Transgenic plants overexpressing the FaFT3 gene exhibited an early-flowering phenotype under both long-day and short-day conditions. Conversely, induction of FaFT3 expression at the crown tip specifically under floral induction conditions was not observed. However, RNA-seq analysis of laser microdissected meristem cells before and after floral bud initiation clearly revealed that the FaFT3 gene is specifically expressed in floral meristem cells. These results suggest that the FaFT3 gene acts as a common floral promoter in June-bearing Japanese cultivated strawberries.