The Arabidopsis ELF3 gene regulates vegetative photomorphogenesis and the photoperiodic induction of flowering

Flowering in Arabidopsis thaliana is promoted by long‐day (LD) photoperiods such that plants grown in LD flower earlier, and after the production of fewer leaves, than plants grown in short‐day (SD) photoperiods. The early‐flowering 3 ( elf 3) mutant of Arabidopsis , which is insensitive to photoperiod with regard to floral initiation has been characterized. elf 3 mutants are also altered in several aspects of vegetative photomorphogenesis, including hypocotyl elongation. When inhibition of hypocotyl elongation was measured, elf 3 mutant seedlings were less responsive than wild‐type to all wavelengths of light, and most notably defective in blue and green light‐mediated inhibition. When analyzed for the flowering‐time phenotype, elf 3 was epistatic to mutant alleles of the blue‐light receptor encoding gene, HY 4. However, when elf 3 mutants were made deficient for functional phytochrome by the introduction of hy 2 mutant alleles, the elf 3 hy 2 double mutants displayed the novel phenotype of flowering earlier than either single mutant while still exhibiting photoperiod insensitivity, indicating that a phytochrome‐mediated pathway regulating floral initiation remains functional in elf 3 single mutants. In addition, the inflorescences of one allelic combination of elf 3 hy 2 double mutants form a terminal flower similar to the structure produced by tfl 1 single mutants. These results suggest that one of the signal transduction pathways controlling photoperiodism in Arabidopsis is regulated, at least in part, by photoreceptors other than phytochrome, and that the activity of the Arabidopsis inflorescence and floral meristem identity genes may be regulated by this same pathway.