CONSTANS alters the circadian clock inArabidopsis thaliana

Abstract

Plants are sessile organisms that have acquired highly plastic developmental strategies to adapt to the environment. Among these processes, the floral transition is essential to ensure reproductive success and is finely regulated by several internal and external genetic networks. The photoperiodic pathway, which controls the plant response to day length, is one of the most important pathways controlling flowering. In Arabidopsis photoperiodic flowering, CONSTANS (CO) is the central gene activating the expression of the florigen FLOWERING LOCUS T (FT) in the leaves at the end of a long day. CO expression is strongly regulated by the circadian clock. However, to date, no evidence has been reported regarding a feedback loop from the photoperiod pathway back to the circadian clock. Using transcriptional networks, we have identified relevant network motifs regulating the interplay between the circadian clock and the photoperiod pathway. Gene expression, chromatin immunoprecipitation experiments and phenotypic analysis allowed us to elucidate the role of CO over the circadian clock. Plants with altered CO expression showed a different internal clock period, measured by daily rhythmic movements in the leaves. We show that CO is able to activate key genes related to the circadian clock, such as CCA1, LHY, PRR5 and GI, at the end of a long day by binding to specific sites on their promoters. Moreover, a significant number of PRR5 repressed target genes are upregulated by CO, and this could explain the phase transition promoted by CO. The CO-PRR5 complex interacts with the bZIP transcription factor HY5 and helps to localize the complex in the promoters of clock genes. Our results indicate that there may be a feedback loop in which CO communicates back to the circadian clock, feeding seasonal information to the circadian system.

CONSTANS, a HUB for all seasons: How photoperiod pervades plant physiology regulatory circuits

“…Other complex components of the clock, however, that also regulate photoperiod, such as ZTL and GI, were incorporated as the system became more complex and robust ( Serrano-Bueno et al 2017 ; Ferrari et al 2019 ). However, a loop back from CO to the clock in Arabidopsis was recently described, so that photoperiod signaling can adjust the circadian system, communicating daylength information to the time keeper ( de los Reyes et al 2023 ). As this system involves the Arabidopsis bZIP TF HY5, which is present and commonly coexpressed with COLs in coexpression gene networks in algae ( de los Reyes et al 2017 ), it is highly probable that a compensation of the clock by daylength was introduced very early in the evolution of light sensing in plants.…”

“…CO has been considered the key regulatory gene controlling the timing of flowering through the photoperiod, but in recent years, increasing evidence points to new roles of CO as a hub gene/protein integrating a set of inputs and outputs involved in different developmental and physiological processes, not only in the flowering transition ( Romero-Campero et al 2013 ). In this way, CO has a predominant role in a regulatory network that can provide daylength information to processes such as carbon metabolism ( Ortiz-Marchena et al 2014 ), responses to hormones ( Wang et al 2016 ; Xu et al 2016 ), stomatal opening ( Ando et al 2013 ), stresses, photoprotection ( Gabilly et al 2019 ; Tokutsu et al 2019 ; Park et al 2023 ), proline synthesis ( Mattioli et al 2009 ), lipid metabolism ( Deng et al 2015 ), floral organ senescence, and abscission ( Serrano-Bueno et al 2021 , 2022 ) and can interact with elements of the circadian clock ( de los Reyes et al 2023 ).…”

Genome-Wide Identification, Characterization and Expression Profiling of the CONSTANS-like Genes in Potato (Solanum tuberosum L.)

“…CO gene expression is consistent with light rhythms, which promotes flowering only under long-day (LD) conditions [ 19 , 20 ]. FLOWERING LOCUS T ( FT ) is the florigen gene that researchers had long sought [ 21 , 22 ], and FT is a direct downstream gene of the transcription factor CO regulating plant flowering.…”