Photoreceptor Regulation of CONSTANS Protein in Photoperiodic Flowering

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.

Signalling for developmental plasticity

“…Thus, signalling appears to converge to several parallel transcription factors and not to concentrate on a single player. The photoperiodic and low red to far-red signals converge upstream FT by stabilizing CO [29]. The shape of the network emerges as a consequence of multiple points of parallel and sequential signalling convergence.…”

“…In Arabidopsis plants grown under long days, the presence of light perceived by photoreceptors such as cry2 and phyA coincides with high mRNA levels of the CONSTANS (CO) gene (Accession number X94937), whose expression is under circadian control [26,27]. Light is required for the stabilization of CO, which in darkness undergoes proteasome-mediated degradation [29]. As a result of this coincidence, the expression of the FLOWERING LOCUS T (FT) gene (Accession number AB027504) is dramatically increased and this leads to the promotion of flowering.…”

PSEUDO RESPONSE REGULATORs stabilize CONSTANS protein to promote flowering in response to day length

“…Through this regulation, transcripts of CO accumulate in the afternoon under LDs when plants are exposed to light. This coincidence between CO mRNA and light exposure allows stabilization of translated CO protein at these times, causing CO to accumulate under LDs and achieving recognition of LDs (Appendix Fig S1; Valverde et al , 2004). CO then directly promotes floral transition through its capacity to activate transcription of the “florigen” gene FLOWERING LOCUS T ( FT ) specifically under LDs (Andres & Coupland, 2012; Song et al , 2014).…”

“…CO then directly promotes floral transition through its capacity to activate transcription of the “florigen” gene FLOWERING LOCUS T ( FT ) specifically under LDs (Andres & Coupland, 2012; Song et al , 2014). By contrast, under SDs, CO transcription occurs only in the dark, and under these conditions, CO protein does not accumulate (Valverde et al , 2004). …”

Differential effects of light-to-dark transitions on phase setting in circadian expression among clock-controlled genes in Pharbitis nil

“…9,10 Information on light exposure is thereby integrated at CO, leading to its accumulation under LDs and accomplishing measurement of day length. 7,8,10–12 Temporal regulation of CO transcription through the clock-controlled blue light photoreceptor FLAVIN-BINDING, KELCH REPEAT, F-BOX1 (FKF1), clock-controlled flowering regulators CYCLING DOF FACTORs (CDFs), and the clock protein GIGANTEA (GI) determines the proper daily accumulation pattern of CO transcript, ensuring that its accumulation coincides with light exposure only under LDs and CO accumulation occurs specifically under these conditions. 13-15 These proteins thereby link CO transcription and the circadian clock, which comprises transcriptional negative feedback-loops with particular clock genes such as LATE ELONGATED HYPOCOTYL ( LHY ) and TIMING OF CAB EXPRESSION 1 ( TOC1 ) in Arabidopsis.…”