Abstract
Plant growth responses to cues such as light, temperature, and humidity enable the entrainment of the circadian rhythms with diurnal cycles. For example, the temperature variations between day and night affect plant growth and accompany the time lag to light cycle. Despite its importance, there has been no systematic investigation into time lags, and the mechanisms behind the entrainment of the circadian rhythms with multiple cycles remain unknown. Here, we investigated systemically the effects of the time lag on the circadian rhythm and growth in Arabidopsis thaliana. To investigate the entrainment status of the circadian clock, the rhythm of the clock gene CIRCADIAN CLOCK ASSOCIATION 1 (CCA1) was measured with a luciferase reporter assay. As a result, the rhythm was significantly modulated by the time lag with +10°C heating for 4 h every day but not −10°C cooling. A model based on coupled cellular oscillators successfully described these rhythm modulations. In addition, seedling growth depended on the time lag of the heating cycle but not that of the cooling cycle. Based on the relationship between the CCA1 rhythms and growth, we established an estimation method for the effects of the time lag. Our results found that plant growth relates to the CCA1 rhythm and provides a method by which to estimate the appropriate combination of light–dark and temperature cycles.
Highlights
Organisms on earth have been found to have circadian clocks that are adapted to 24 h periods for environmental cycles
In nature and horticultural practices, the light–dark cycle is usually accompanied by a temperature cycle, which is associated with a day temperature that is higher than the night temperature
There has been no systematic investigation into the time lag of temperature cycles and the entrainment behavior of circadian rhythms under dual-zeitgeber cycles
Summary
Organisms on earth have been found to have circadian clocks that are adapted to 24 h periods for environmental cycles. Most plants exhibit optimal growth with the in-phase regime, in which the day temperature is higher than the night temperature (which we have termed +DIF) (Xiong et al, 2011, Xiao et al, 2018). The spatial unevenness under lighting or air conditioning and the thermal conductivity of air and soil/water might generate a spatial time lag in DIF. As such time lags might affect plant production yields, the elucidation of their effects is required to improve horticultural practices. There has been no systematic investigation into the time lag of temperature cycles and the entrainment behavior of circadian rhythms under dual-zeitgeber cycles
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