Graft-transmissible action of Arabidopsis FLOWERING LOCUS T protein to promote flowering.

Day length perceived by a leaf is a major environmental factor that controls the timing of flowering. It has been believed that a mobile, long-distance signal called florigen is produced in the leaf, and is transported to the shoot apex where it triggers floral morphogenesis. Grafting experiments have shown that florigen is transmissible from a donor plant that has been subjected to inductive day length to an un-induced recipient plant. However, the nature of florigen has long remained elusive. Recent studies have provided evidence that the FLOWERING LOCUS T (FT) protein in Arabidopsis and corresponding proteins in other species are an important part of florigen. Our work showed that the FT activity, either from overexpressing or inducible transgenes or from the endogenous gene, to promote flowering is transmissible through a graft junction, and that an FT protein with a T7 tag (FT-T7) is transported from a donor scion to the apical region of recipient stock plants and becomes detectable within a short period of 24-48 h. That the FT-green fluorescent protein (GFP) fusion protein (FT:GFP) retains limited ability for graft-transmissible action was confirmed.