No circadian clock-gene circuit in the generation of cellular bioluminescence rhythm of CaMV35S::PtRLUC in duckweed

Abstract

Physiological circadian rhythms are coordinated in the plant body in an orderly manner. The coordination of time information has been studied from the aspects of cell-cell local coupling and long-distance communication between tissues. These studies were based on the idea that the behavior of the clock gene circuit represents the physiological rhythms. Here we report the cellular circadian rhythm of a bioluminescence reporter which is not governed by the clock gene circuit in the expressing cells. Using a dual-color bioluminescence monitoring system in Lemna minor transfected with the AtCCA1::LUC+ and CaMV35S::PtRLUC reporters, cellular bioluminescence rhythms with different free-running periods (FRPs) were detected in the same cells. Co-transfection experiments with the two reporters and a clock gene overexpressing effector revealed that the circadian properties of the AtCCA1::LUC+ rhythm, but not those of the CaMV35S::PtRLUC rhythm, were altered in the cells with a dysfunctional clock gene circuit. This indicates that the AtCCA1::LUC+ rhythm is a direct output of the cellular circadian clock while the CaMV35S::PtRLUC rhythm is not. After plasmolysis, the CaMV35S::PtRLUC rhythm disappeared while the AtCCA1::LUC+ rhythm persisted. The plant circadian system consists of both cell-autonomous rhythms and non-cell-autonomous rhythms that are unaffected by the cellular clock.