The Arabidopsis thaliana clock consists of a central loop and two peripheral (morning and evening) loops. The central loop includes transcription factors CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), CCA1 HIKING EXPEDITION (CHE), and TIMING OF CAB EXPRESSION 1 (TOC1). TOC1 positively regulates expression of CCA1 and LHY that have redundant but non-overlapping functions, while CCA1 and LHY bind to the promoter of TOC1 and inhibit its expression. CHE interacts with TOC1 and binds to CCA1 promoter and promotes its expression, whereas CCA1 and LHY repress CHE expression. In A. thaliana, circadian regulators affect rhythms and period of the clock as well as its input and output pathways. At least ~10% of genes, including those involved in photosynthesis and starch metabolism, and up to 90% of transcriptome are affected by the circadian rhythms. Moreover, day-length and circadian effects on transitory starch metabolism correlate with diurnal expression of these metabolic genes. Hence, maintaining circadian regulation increases CO2 fixation and growth, whereas disrupting circadian rhythms reduces fitness. Using Arabidopsis hybrids and allopolyploids as experimental systems, we are testing how and why circadian rhythms are altered to promote growth vigor and improve fitness.
Ten selected papers about circadian rhythms and metabolism
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- Harmer SL: The circadian system in higher plants. Annu Rev Plant Biol 60: 357-77 (2009).
- McClung CR: Plant circadian rhythms. Plant Cell 18: 792-803 (2006).
- Millar AJ, Short SR, Chua NH, Kay SA: A novel circadian phenotype based on firefly luciferase expression in transgenic plants. Plant Cell 4: 1075-87 (1992).
- Ni Z, Kim ED, Ha M, Lackey E, Liu J, Zhang Y, Sun Q, Chen ZJ: Altered circadian rhythms regulate growth vigour in hybrids and allopolyploids. Nature 457: 327-31 (2009).
- Pruneda-Paz JL, Kay SA: An expanding universe of circadian networks in higher plants. Trends Plant Sci 15: 259-65 (2010).
- Wijnen H, Young MW: Interplay of circadian clocks and metabolic rhythms. Annu Rev Genet 40: 409-48 (2006).