ELF4 Regulates GIGANTEA Chromatin Access through Subnuclear Sequestration

Many organisms, including plants, use the circadian clock to measure the duration of day and night. Daily rhythms in the plant circadian system are generated by multiple interlocked transcriptional/translational loops and also by spatial regulations such as nuclear translocation. GIGANTEA (GI), one of the key clock components in Arabidopsis, makes distinctive nuclear bodies like other nuclear-localized circadian regulators. However, little is known about the dynamics or roles of GI subnuclear localization. Here, we characterize GI subnuclear compartmentalization and identify unexpected dynamic changes under diurnal conditions. We further identify EARLY FLOWERING 4 (ELF4) as a regulator of GI nuclear distribution through a physical interaction. ELF4 sequesters GI from the nucleoplasm, where GI binds the promoter of CONSTANS (CO), to discrete nuclear bodies. We suggest that the subnuclear compartmentalization of GI by ELF4 contributes to the regulation of photoperiodic flowering. [Display omitted] ► GI forms dynamic subnuclear structures ► GI and ELF4 physically interact at nuclear bodies ► ELF4 regulates subnuclear localization of GI ► ELF4 sequesters GI to nuclear bodies from the CO promoter GIGANTEA (GI), a key component of the plant circadian oscillator, can form subnuclear bodies, but the dynamics and functions of these inclusions are poorly understood. Somers, Nam, and colleagues show that formation of GI subnuclear structures changes dynamically under diurnal conditions and that the clock-associated protein ELF4 regulates GI nuclear distribution by sequestering GI to these nuclear bodies. This restricts GI access to the promoter of the key flowering locus CONSTANS, suggesting a regulatory mechanism to control photoperiodic flowering.