FPF1 modulates the competence to flowering in Arabidopsis

During the transition to flowering the FPF1 gene is expressed in the periph eral zone of apical meristems and in floral meristems of Arabidopsis. Const itutive expression of FPF1 causes early flowering in Arabidopsis under both long-day and short-day conditions and leads to a shortened juvenile phase as measured by the trichome distribution on the abaxial leaf surface. In th e classical late flowering mutants, overexpression of FPF1 compensates part ially for the late flowering phenotype, indicating that FPF1 acts downstrea m or in a parallel pathway to the mutated genes. The co-overexpression of 3 5S::API with 35S::FPF1 leads to a synergistic effect on the shortening of t he time to flowering under short-day conditions. The co-overexpression of 3 5S::FPF1 and 35S::LFY, however, shows only an additive reduction of floweri ng time and the conversion of nearly every shoot meristem, except the inflo rescence meristem, to a floral meristem under the same light conditions. In addition, the constitutive expression of FPF1 attenuates the severe Ify-1 phenotype under short days and phenocopies to a great extent the Ify-1 muta nt grown under long-day conditions. Thus, we assume that FPF1 modulates the competence to flowering of apical meristems.