Independent Action of ELF3 and phyB to Control Hypocotyl Elongation and Flowering Time

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Abstract
Light regulates various aspects of plant growth, and the photoreceptor phytochrome B (phyB) mediates many responses to red light. In a screen for Arabidopsis mutants with phenotypes similar to those ofphyB mutants, we isolated two new elf3mutants. One has weaker morphological phenotypes than previously 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. However, we found that elf3 mutations have an additive interaction with a phyB null mutation, with phyA orhy4 null mutations, or with a PHYB overexpression construct, and that an elf3 mutation does not prevent nuclear localization of phyB. These results suggest that either there is substantial redundancy in phyB and elf3 function, or the two genes regulate distinct signaling pathways.