Independent action of ELF3 and phyB to control hypocotyl elongation and flowering time

Light regulates various aspects of plant growth, and the photoreceptor phyt ochrome B (phyB) mediates many responses to red light. In a screen for Arab idopsis mutants with phenotypes similar to those of phyB mutants, we isolat ed two new elf3 mutants. One has weaker morphological phenotypes than previ ously identified elf3 alleles, but still abolishes circadian rhythms under continuous light. Like phyB mutants, elf3 mutants have elongated hypocotyls and petioles, flower early, and have defects in the red light response. Ho wever, we found that elf3 mutations have an additive interaction with a phy B null mutation, with phyA or hy4 null mutations, or with a PHYB overexpres sion construct, and that an elf3 mutation does not prevent nuclear localiza tion of phyB. These results suggest that either there is substantial redund ancy in phyB and elf3 function, or the two genes regulate distinct signalin g pathways.