# Conserved eukaryotic factors XCT and COP1 work together to control circadian clock function and reproductive timing in plants

## TL;DR

This study shows how two conserved proteins, XCT and COP1, work together to control the plant's internal clock and timing of reproduction.

## Contribution

The study reveals a novel interaction between XCT and COP1 in regulating the circadian clock and flowering time in plants.

## Key findings

- XCT and COP1 genetically and physically interact in Arabidopsis.
- XCT and COP1 regulate the oscillator component ELF3 to modulate circadian function.
- The collaboration of XCT and COP1 helps maintain circadian integrity and developmental timing.

## Abstract

Circadian rhythms align biological processes with environmental cycles to enhance fitness. Eukaryotic circadian oscillators rely on transcriptional–translational feedback loops, although specific oscillator components vary among lineages. The plant oscillator consists of a uniquely complex network of transcriptional regulators. These clock genes regulate each other’s expression and influence key developmental processes such as the transition from vegetative to reproductive growth. Here, we investigate the function of XAP5 CIRCADIAN TIMEKEEPER (XCT), a protein conserved across eukaryotes and previously implicated in RNA processing and circadian regulation in Arabidopsis thaliana. We show that XCT genetically and physically interacts with CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), an E3 ubiquitin ligase also conserved across eukaryotes. Both XCT and COP1 regulate the abundance and activity of the oscillator component EARLY FLOWERING3 (ELF3) to modulate circadian function and flowering time. These findings demonstrate how broadly conserved factors collaborate with plant-specific regulators to maintain circadian integrity and coordinate developmental timing.