Study on interaction between circadian clock and aging in Arabidopsis thaliana

Abstract

As most organisms age, their appearance, physiology and behavior alters as part of a life-history strategy that maximizes fitness over their lifetimes. An organism’s age is an important factor in determining proper developmental decision-making. How the age information is incorporated into age-dependent developmental changes? The circadian clock is an endogenous daily time-measurement system and is involved in many physiological responses. Here, I show that the interaction between leaf aging and the circadian clock provides a possible means for changes in the circadian clock system to induce age-dependent developmental changes in the plant. First, I investigate the association between leaf aging and the circadian rhythm to understand the regulation of life history strategy in Arabidopsis. The circadian periods of the output and core clock genes were approximately 1 h shorter in older leaves than in younger leaves, indicating significant effects of aging on circadian regulation. Shortening of the circadian period with leaf aging occurred faster in plant grown under long photoperiod compared with short photoperiod, suggesting that leaf aging differs with the day length and that this correlates to the shortening of the circadian period with leaf aging. By clock mutant screening, I identified for a regulatory gene that links aging and the circadian clock. Interestingly, only toc1 mutants did not show a shortened circadian period length during leaf aging, suggesting that TOC1 may link age to changes in the circadian clock period. Together, these findings suggest that aging information is incorporated into the regulation of circadian period and that TOC1 is necessary for this integrative process. The circadian clock regulates numerous physiological processes, from seedling growth to flowering in Arabidopsis. Photoperiodic control of leaf senescence suggests the involvement of the circadian clock in this process. However, the mechanism by which the circadian clock functions in the senescence pathway is not well understood. ORE1 is a key molecule involved in the leaf aging process in Arabidopsis. In this study, ORE1 expression was found to be controlled by the circadian clock. PRR9, a clock oscillator, binds as a transcriptional activator to the ORE1 promoter. However, ORE1 does not involve the regulation of the circadian clock. Taken together, these results suggest that ORE1 mediates between the circadian clock and control of leaf senescence in Arabidopsis.