Arabidopsis EARLY FLOWERING 4 recruits EARLY FLOWERING 3 to the nucleus to facilitate gene repression

The evening complex (EC) is a protein complex composed of ELF3, ELF4 and LUX that accumulates at dusk to repress gene expression. ELF3 functions as a scaffold around which the other EC components assemble, while LUX facilitates EC binding to DNA. Although ELF4 is essential for the activity of the EC, its precise role within the complex is unclear. Earlier studies indicated that mutations within the ELF4-binding domain of ELF3 reduced the nuclear accumulation of ELF3. However, it has remained unknown whether ELF4 directly contributes to these phenotypes. To investigate this further, we quantified the cellular and subnuclear distribution of Arabidopsis ELF3 across the evening in hypocotyl nuclei with or without a functional ELF4 allele. These results highlight a critical requirement for ELF4 in recruiting ELF3 to hypocotyl nuclei at dusk. Reduced nuclear accumulation in the elf4 mutant correlated with a failure of ELF3 to repress gene expression and inhibit hypocotyl elongation, particularly under short-day conditions. We also observed that ELF4 was necessary to recruit ELF3 to foci in root nuclei, but these foci displayed different temporal properties from those in the hypocotyl. In summary, our results support a model in which ELF4 recruits ELF3 to the nucleus at dusk to enhance ELF3 repressive activity.