Circadian rhythms in Arabidopsis: time for nuclear proteins

Abstract

To be prepared for the periodic alterations of light and darkness in their environment, plants utilise an endogenous clock to anticipate these changes and to time physiological processes appropriately. Large-scale screens for mutants with perturbed circadian output rhythms, as well as characterisation of mutants with altered flowering time in Arabidopsis thaliana (L.) Heynh., have led to advances in our knowledge of the molecular basis of this internal timing system. The repertoire of proteins, mostly nuclear-localised, that play a crucial role in clock regulation, as well as of the photoreceptors involved in transmitting light information to synchronise the endogenous clock with the outside world, has expanded considerably and is the subject of this review.

The mammalian circadian timing system: from gene expression to physiology

“…Since then negative feedback loops of clock gene expression have been uncovered in all genetic model systems for circadian oscillators, including cyanobacteria, neurospora, plants, and mammals. Excellent and detailed reviews are available on all of these systems (Albrecht and Eichele 2003;Froehlich et al 2003;Golden 2003;Reppert and Weaver 2002;Roenneberg and Merrow 2003;Staiger 2002;Stanewsky 2003); here we will concentrate on a brief discussion of some recent findings about the mammalian circadian timing system. The identification of mammalian clock genes has greatly profited from genetic studies in the fruit fly Drosophila melanogaster, as most essential Drosophila clock genes have orthologs in mammals.…”

Plant Circadian Rhythms

“…Arabidopsis exhibits myriad rhythmic outputs or ''hands'' of the clock (McClung, 2001;McClung et al, 2002;Staiger, 2002). Like many plants, Arabidopsis displays rhythmic cotyledon and leaf movement, although this rhythm in Arabidopsis is based on differential growth and thus differs from the rhythmic turgordriven expansion and contraction of the pulvinus that underlies rhythmic leaf movement in legumes, including Tamarindus and Mimosa (Kim et al, 1993).…”

PCC1 : a merging point for pathogen defence and circadian signalling in Arabidopsis

“…Here, interlocked negative and positive transcriptional feedback loops ensure a rhythmic expression of the components required for the inner clock. Fluctuating levels of these regulatory proteins, which make up the central oscillator, are responsible for the various physiological and biochemical outputs (Barak et al 2000;Lakin-Thomas 2000;Merrow 2000, 2001;Roden and Carre 2001;Staiger 2001Staiger , 2002. CCA1 (circadian clock associated 1) is believed to be one of the components of the central oscillator since its mRNA and protein levels show robust rhythms in constant light, the protein exerts a negative feedback on its own expression and plants overexpressing CCA1 (CCA1-ox) stop overt circadian rhythms (Wang and Tobin 1998).…”