Dance of plants with circadian clock

Abstract

Endogenous oscillator called circadian clock controls many physiological aspects. Since the identification of LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1 ) genes as the 1st candidates for clock components in plants, many clock-associated genes have been identified in Arabidopsis and other plant species. The 1st negative feedback model composed of LHY, CCA1 and TIMING OF CAB EXPRESSION 1 (TOC1) has recently been modified based on possible functions of new players. Photoperiodic flowering is controlled by clock and our knowledge on molecular mechanisms underlying the clock-controlled process has much advanced in this decade. Recently, we have started to understand how the clock regulates organ movements and elongations in a model plant, Arabidopsis. In this short review, i) a history of construction of models on circadian rhythms in Arabidopsis, ii) modified models on circadian system in Arabidopsis, iii) recent progress on understanding molecular mechanisms underlying organ movements controlled by a circadian clock and iv) advantages of using tomato as a model system for chronobiology are summarized and discussed.

Photoperiod pathway regulates expression of MAF5 and FLC that encode MADS-box transcription factors of the FLC family in Arabidopsis

“…Clock mutations such as lhy, cca1, toc1, and gi, affect not only flowering time but also other clock-controlled output pathways such as leaf movement, hypocotyl elongation, and expression of the CCGs (Mizoguchi et al 2002;Mizoguchi et al 2005;Mizoguchi et al 2006;Niinuma et al 2007;Salome and McClung 2004;Searle and Coupland 2004). In contrast, loss-of-function mutations of floral activator genes such as co and ft do not affect the general circadian rhythms (Suarez-Lopez et al 2001).…”

“…Regulation of the MAF5 gene expression by the photoperiod pathway LHY, CCA1, and GI are closely associated with circadian clock functions in Arabidopsis (Fekih et al 2009b;Mizoguchi et al 2002;Mizoguchi et al 2005;Niinuma et al 2007;Salome and McClung 2004), and mutations of these genes alter the expression patterns of the CCGs. Genotypes carrying the mutations in the autonomous pathway, such as fca-1, showed high expression of FLC, whereas mutations in the photoperiod pathway, such as gi, co, and fha, did not affect the transcript level of FLC based on Northern blot analysis (Rouse et al 2002).…”

“…The circadian clock that generates an about 24 h rhythm, is composed of several components (Mizoguchi et al 2006;Niinuma et al 2007;Salome and McClung 2004), including two homologous genes, LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), which encode single myb transcription factors (Mizoguchi et al 2006;Niinuma et al 2007;Salome and McClung 2004). LHY and GI/CO have been shown to have opposite effects on FT expression; over-expression of LHY (lhy-1) lowered the expression level of FT in long-days (LDs), whereas overexpression of GI (35S:GI) or CO (35S:CO) resulted in increased expression (Fowler et al 1999;Fujiwara et al 2005aFujiwara et al , 2005bFujiwara et al , 2005cMizoguchi et al 2005;Samach et al 2000;Suarez-Lopez et al 2001).…”

Increase in vascular pattern complexity caused by mutations in LHY and CCA1 in Arabidopsis thaliana under continuous light

“…Plant growth and metabolism are coordinated with the time of day by rhythmic gene expression with an approximately 24-h period (McClung 2006;Niinuma et al 2007). Flowering time, leaf movement, organ elongation, and stomatal opening are regulated by the circadian clock (de Montaigu et al 2010;Doherty and Kay 2010;Nozue et al 2007;Niinuma et al 2008).…”

Possible involvement of FLC in natural variation of activity to enhance the late flowering phenotype of the clock mutant lhy cca1 under continuous light

“…Photoperiodism was first described in detail by Garner and Allard (1920), who found that many plants flowered in response to changes in day length. The photoperiodic control of flowering time is closely linked to the circadian clock (Mizoguchi et al 2002;Mizoguchi et al 2005;Mizoguchi et al 2006;Niinuma et al 2007;Súarez-López et al 2001;Yanovsky and Kay 2002). In Arabidopsis, LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) encode myb proteins essential for clock function (Schaffer et al 1998;Wang and Tobin 1998).…”