Summary
ELF3 and GI are two important components of the Arabidopsis circadian clock. They are not only essential for the oscillator function but are also pivotal in mediating light inputs to the oscillator. Lack of either results in a defective oscillator causing severely compromised output pathways, such as photoperiodic flowering and hypocotyl elongation. Although single loss of function mutants of ELF3 and GI have been well-studied, their genetic interaction remains unclear. We generated an elf3 gi double mutant to study their genetic relationship in clock-controlled growth and phase transition phenotypes. We found that ELF3 and GI repress growth differentially during the night and the day, respectively. Circadian clock assays revealed that ELF3 and GI are essential Zeitnehmers that enable the oscillator to synchronize the endogenous cellular mechanisms to external environmental signals. In their absence, the circadian oscillator fails to synchronize to the light-dark cycles even under diurnal conditions. Consequently, clock-mediated photoperiod-responsive growth and development is completely lost in plants lacking both genes, suggesting that ELF3 and GI together convey photoperiod sensing to the central oscillator. Since ELF3 and GI are conserved across flowering plants and represent important breeding and domestication targets, our data highlight the possibility of developing photoperiod-insensitive crops by adjusting the allelic combination of these two key genes.
One sentence summary ELF3 and GI are essential for circadian clock mediated photoperiod sensing.
Footnotes
Funding information We thank Dr. Rachael Oakenfull for her help in the luciferase assays. The funding for this work was provided by a Biotechnology and Biological Sciences Research Council grant to SJD (BBSRC grant code BB/N018540/1), a grant by the Deutsche Forschungsgemeinschaft to MQ (Qu 141/6-1), and the Leibniz Association.
New data are added to further substantiate the essential role of ELF3 and GI in clock-mediated photoperiod sensing. All figures are modified.