A Virus-Induced Assay for Functional Dissection and Analysis of Monocot and Dicot Flowering Time Genes

Virus-induced flowering (VIF) uses virus vectors to express Flowering Locus T (FT) to induce flowering in plants. This approach has recently attracted wide interest for its practical applications in accelerating breeding in crops and woody fruit-trees. However, the insight into VIF and its potential as a powerful tool for dissecting florigenic proteins remained to be elucidated. Here, we describe the mechanism and further applications of Potato virus X (PVX)-based VIF in the short-day Nicotinana tabacum cultivar Maryland Mammoth. Ectopic delivery of Arabidopsis AtFT by PVX/AtFT did not induce the expression of the endogenous FT orthologue NtFT4, however it was sufficient to trigger flowering in Maryland Mammoth plants grown under non-inductive long-day conditions. Infected tobacco plants developed no systemic symptoms and the PVX-based VIF did not cause transgenerational flowering. We showed that the PVX-based VIF is a much more rapid method to examine the impacts of single amino-acid mutations on AtFT for floral induction than making individual transgenic Arabidopsis lines for each mutation. We also used the PVX-based VIF to demonstrate that adding histidine- or FLAG-tag to the N- or C-terminal of AtFT could affect its florigenic activity, and that this system can be applied to assay the function of FT genes from heterologous species including tomato SFT and rice Hd3a. Thus the PVX-based VIF represents a simple and efficient system to identify individual amino acids that are essential for FT-mediated floral induction, and to test the ability of mono- and dicotyledonous FT genes and FT fusion proteins to induce flowering.