Abstract
Light is one of several major environmental stimuli that determine timing of the transition from vegetative to reproductive phase. In Arabidopsis , phytochrome B (phyB), cryptochrome 2 (cry2) and phyA are major photoreceptors that regulate flowering. PhyB delays flowering by reducing the expression of flowering activators, FLOWERING LOCUS T (FT) and subsequent SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1). However, the mechanism by which phyB signaling is modified remains unclear. Here we identify a novel PHYTOCHROME-DEPENDENT LATE-FLOWERING (PHL) gene that is involved in flowering regulation by phyB. The phl mutants exhibited a late-flowering phenotype under various light conditions. However, the phl phenotype was completely suppressed by the phyB mutation, indicating that PHL accelerates flowering by suppressing phyB signaling. Accordingly, the expression of FT and SOC1 was reduced in the phl mutant. In addition, the PHL protein is a nuclear protein that interacts with phyB. Taken together, the present work has identified a novel component of the system by which light signals are perceived, processed and transduced to the downstream pathway that regulates flowering.
