Abstract
Photoperiodic induction of flowering requires light perception in leaves, followed by transmission of mobile signal from leaves to the shoot apex, where floral meristems are initiated. However, the nature of the mobile signal has remained unknown.
In Arabidopsis, floral pathway integrator FT acts mainly in the photoperiod pathway. FT encodes a 20kD protein of the PEBP/RKIP family. FT is expressed in vasculature of cotyledon and leaf where light is perceived. FT requires flowering-time gene FD which encodes a bZIP protein and is expressed in shoot apex. These suggest that the site of FT action is likely to be the shoot apex.
To examine the transmissibility of promoting effect of FT, we performed micrografting experiments in Arabidopsis. Using 4-day-old seedlings, two-shoot, 'Y-shaped' grafts were assembled on hypocotyl of recipient plants. Grafted 35S::FT plants partially rescued the late-flowering phenotype of ft-1 recipient plants, suggesting that floral promotion by FT is graft-transmissible.
