Monitoring circadian rhythms of individual cells in plants
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The circadian clock is an endogenous timing system based on the self-sustained oscillation in individual cells. These cellular circadian clocks compose a multicellular circadian system working at respective levels of tissue, organ, plant body. However, how numerous cellular clocks are coordinated within a plant has been unclear. There was little information about behavior of circadian clocks at a single-cell level due to the difficulties in monitoring circadian rhythms of individual cells in an intact plant. We developed a single-cell bioluminescence imaging system using duckweed as the plant material and succeeded in observing behavior of cellular clocks in intact plants for over a week. This imaging technique quantitatively revealed heterogeneous and independent manners of cellular clock behaviors. Furthermore, these quantitative analyses uncovered the local synchronization of cellular circadian rhythms that implied phase-attractive interactions between cellular clocks. The cell-to-cell interaction looked to be too weak to coordinate cellular clocks against their heterogeneity under constant conditions. On the other hand, under light–dark conditions, the heterogeneity of cellular clocks seemed to be corrected by cell-to-cell interactions so that cellular clocks showed a clear spatial pattern of phases at a whole plant level. Thus, it was suggested that the interactions between cellular clocks was an adaptive trait working under day–night cycles to coordinate cellular clocks in a plant body. These findings provide a novel perspective for understanding spatio-temporal architectures in the plant circadian system.
KeywordsCircadian rhythms Bioluminescence Duckweed Cell-to-cell interaction
We thank Drs. Yuki Kondo and Shigeo Sugano for their kind invitation to this special issue. We also thank for Drs. Shogo Ito and Masaaki Okada for fruitful discussions . This work was supported in part by the Japan Society for the Promotion of Science KAKENHI [Grant numbers 23657033 (T.O.), 25650098 (T.O.), 17KT0022 (T.O.), and 24-1530 (T.M.)], Iwatani Naoji Foundation (T.O.), Japan Science and Technology Agency (JST) ALCA (T.O.), and JST PRESTO (T.O.).
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