Photoreceptor Regulation of CONSTANS Protein in Photoperiodic Flowering

TLDR

Plants flower in response to day length; in Arabidopsis, the CONSTANS gene promotes flowering in long days by aligning CO mRNA expression with light exposure, yet the mechanism of CO activation remains unclear, and photoreceptors modulate CO stability to generate daily rhythms that refine the circadian CO mRNA pattern and are central to day‑length control of flowering. Light stabilizes nuclear CO protein in the evening, whereas in the morning or in darkness the protein is degraded by the proteasome.

Abstract

Many plants flower in response to seasonal fluctuations in day length. The CONSTANS (CO) gene of Arabidopsis promotes flowering in long days. Flowering is induced when CO messenger RNA expression coincides with the exposure of plants to light. However, how this promotes CO activity is unknown. We show that light stabilizes nuclear CO protein in the evening, whereas in the morning or in darkness the protein is degraded by the proteasome. Photoreceptors regulate CO stability and act antagonistically to generate daily rhythms in CO abundance. This layer of regulation refines the circadian rhythm in CO messenger RNA and is central to the mechanism by which day length controls flowering.