Traveling waves of circadian gene expression in lettuce

The circadian clock controls many physiological states in plants by synchronization with environmental changes. The clock can be controlled artificially by imposing various light conditions in a closed system for plant cultivation. The plant circadian rhythm is formed by enormous self-sustained cellular circadian oscillators, so that the synchronization of circadian oscillators is of great importance to the formation of individual circadian rhythms. Therefore, the study of synchronization phenomena is important for precise control of the circadian rhythm. In this study, we have investigated the spatiotemporal dynamics of circadian oscillators in lettuce (Lactuca sativa L.). Bioluminescence of transgenic lettuce carrying a CCA1::LUC construct as a reporter of a circadian gene expression was measured in the leaf and root. We observed phase wave propagation in the leaf with a phase delay in the region of the primary vein, with the primary vein region showing lower amplitude than the other regions. Wave propagation occurred from the edge of the leaf inward. In addition, a striped wave traveled from the base to the tip along the roots, which were grown under continuous dark or light conditions. The features observed in the lettuce plants could be explained by phase oscillator models established in the study of Arabidopsis thaliana. The results of this study show the possibility of applying circadian clock control in a model plant for plant production.