THE ARABIDOPSIS ELF3 GENE REGULATES VEGETATIVE PHOTOMORPHOGENESIS ANDTHE PHOTOPERIODIC INDUCTION OF FLOWERING

Flowering in Arabidopsis thaliana is promoted by long-day (LD) photope riods such that plants grown in LD flower earlier, and after the produ ction of fewer leaves, than plants grown in short-day (SD) photoperiod s. The early-flowering 3 (elf3) mutant of Arabidopsis, which is insens itive to photoperiod with regard to floral initiation has been charact erized. elf3 mutants are also altered in several aspects of vegetative photomorphogenesis, including hypocotyl elongation. When inhibition o f hypocotyl elongation was measured, elf3 mutant seedlings were less r esponsive 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, elf3 was epistatic to mutant alleles of the blue-light receptor encoding gene, HY4. However, when elf3 mut ants were made deficient for functional phytochrome by the introductio n of hy2 mutant alleles, the elf3 hy2 double mutants displayed the nov el phenotype of flowering earlier than either single mutant while stil l exhibiting photoperiod insensitivity, indicating that a phytochrome- mediated pathway regulating floral initiation remains functional in el f3 single mutants. In addition, the inflorescences of one allelic comb ination of elf3 hy2 double mutants form a terminal flower similar to t he structure produced by tfl1 single mutants. These results suggest th at 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 infloresce nce and floral meristem identity genes may be regulated by this same p athway.