ELF3

EARLY FLOWERING 3 (ELF3) is a plant-specific gene that encodes the hydroxyproline-rich glycoprotein and is required for the function of the circadian clock. ELF3 is one of the three components that make up the Evening Complex (EC) within the plant circadian clock, in which all three components reach peak gene expression and protein levels at dusk. ELF3 serves as a scaffold to bind EARLY FLOWERING 4 (ELF4) and LUX ARRHYTHMO (LUX), two other components of the EC, and functions to control photoperiod sensitivity in plants. ELF3 also plays an important role in temperature and light input within plants for circadian clock entrainment. Additionally, it plays roles in light and temperature signaling that are independent from its role in the EC.

EARLY FLOWERING 3 (ELF3) is a plant-specific gene that encodes the hydroxyproline-rich glycoprotein and is required for the function of the circadian clock. ELF3 is one of the three components that make up the Evening Complex (EC) within the plant circadian clock, in which all three components reach peak gene expression and protein levels at dusk. ELF3 serves as a scaffold to bind EARLY FLOWERING 4 (ELF4) and LUX ARRHYTHMO (LUX), two other components of the EC, and functions to control photoperiod sensitivity in plants. ELF3 also plays an important role in temperature and light input within plants for circadian clock entrainment. Additionally, it plays roles in light and temperature signaling that are independent from its role in the EC. The ELF3 gene encodes a novel, nuclear-localized protein that is 695 amino acids in length. It contains an acidic region (residues 206–320) in its N-terminal, a proline-rich region (440–540) in the middle segment of the peptide sequence, and a glutamine/threonine-rich region (544–653) in its C-terminal. Despite these known characteristics, only one domain of known function has been identified for ELF3. A putative prion-like domain, which is found in intrinsically disordered regions of proteins, has been predicted at amino acid residues 430–609. This prion-like domain is required for protein phase separation of ELF3 and the formation of nuclear speckles. It also contains a glutamine-rich (polyQ) sequence that might be responsible for ELF3 temperature sensitivity. Aside from this prion-like domain, any other functional domains that the ELF3 protein might contain have yet to be identified. The proline-rich, acidic, and glutamate/threonine regions are characteristics that are frequently associated with transcriptional regulators, but ELF3 lacks a DNA-binding domain, making it unlikely that it binds and regulates DNA on its own. However, these characteristics are hypothesized to permit ELF3 to regulate transcription in concert with LUX and ELF4 as part of the EC. ELF3 is known to be a hub of protein-protein interactions, and the regions of the ELF3 peptide responsible for these interactions have been identified for some of its binding partners. ELF3 uses its N-terminal region to associate with CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) and GIGANTEA (GI) (residues 1–261) as well as with PHYTOCHROME B (PHYB) (residues 1–440). The middle region of ELF3 (residues 261–484) is required for interaction with ELF4, and the C-terminal region (residues 442–695) is required for ELF3 to bind to PHYTOCHROME INTERACTING FACTOR 4 (PIF4). The domain responsible for ELF3 interaction with LUX has not been tested.

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