Functional characterization and spatial interaction of TERMINAL FLOWER 1 in Hemerocallis

In horticulture, continuous flowering (CF) is a popular trait introduced into a wide range of cultivated varieties. To explore the mechanism of continuous flowering, this study first cloned the continuous flowering gene, named HkTFL1, from Hemerocallis fulva 'H2006001'. Based on real-time PCR, HkTFL1 was expressed higher in the vegetative growth phase than in the reproductive growth phase, and the expression level was greatest in the shoot apex, followed by the leaf and pedicel. With Hemerocallis 'Golden Doll' and 'H2006001' as the core parents, their hybrid offspring showed that the expression level of the HkTFL1 gene in the continuous flowering population was lower than that in the single flowering (SF) population. Subcellular localization of onion and tobacco epidermal cells showed that HkTFL1 was located in the cytoplasm. The expression level of HkTFL1 was highest in the petal differentiation stage and then decreased gradually. In addition, the heterologous expression of HkTFL1 in Arabidopsis thaliana resulted in delayed flowering, increased rosette number, increased basal inflorescence branch number, inhibition of inflorescence formation, and failure to form a normal inflorescence. HkTFL1 is not only involved in flowering time and floral meristem differentiation but also regulates inflorescence architecture.