Abstract
As most organisms age, their appearance, physiology, and behaviour alters as part of a life history strategy that maximizes their fitness over their lifetime. The passage of time is measured by organisms and is used to modulate these age-related changes. Organisms have an endogenous time measurement system called the circadian clock. This endogenous clock regulates many physiological responses throughout the life history of organisms to enhance their fitness. However, little is known about the relation between ageing and the circadian clock in plants. Here, we investigate the association of leaf ageing with circadian rhythm changes to better understand the regulation of life-history strategy in Arabidopsis. The circadian periods of clock output genes were approximately 1h shorter in older leaves than younger leaves. The periods of the core clock genes were also consistently shorter in older leaves, indicating an effect of ageing on regulation of the circadian period. Shortening of the circadian period with leaf age occurred faster in plants grown under a long photoperiod compared with a short photoperiod. We screened for a regulatory gene that links ageing and the circadian clock among multiple clock gene mutants. Only mutants for the clock oscillator TOC1 did not show a shortened circadian period during leaf ageing, suggesting that TOC1 may link age to changes in the circadian clock period. Our findings suggest that age-related information is incorporated into the regulation of the circadian period and that TOC1 is necessary for this integrative process.
Highlights
Almost all organisms undergo morphological and physiological changes as they age
Our findings suggest that age-related information is incorporated into the regulation of the circadian period and that TIMING OF CAB EXPRESSION 1 (TOC1) is necessary for this integrative process
Sensing the external photoperiod is one mechanism through which the endogenous circadian clock controls flowering in Arabidopsis
Summary
Ageing processes are genetically programmed in almost all higher organisms, from humans to plants (Lim et al, 2007; Mitteldorf and Pepper, 2007) These organisms sense endogenous and exogenous signals for their survival and predict future challenges, such as seasonal changes in climate. In contrast to the highly integrated circadian networks in mammals, plant rhythms appear to be less tightly coupled among cells, tissues, and organs (Thain et al, 2002). This feature allows the individual plant organs to entrain to environmental signals independently (Thain et al, 2000). The circadian clock in the shoot apex can function to the animal master clock of the suprachiasmatic nucleus to synchronize the root circadian rhythm (Takahashi et al, 2015)
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