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Endogenous circadian clock integrates cyclic signals of environment and daily and seasonal behaviors of organisms to achieve spatiotemporal synchronization, which greatly improves genetic diversity and fitness of species. This review addresses recent studies on the plant circadian system in the field of chronobiology, covering topics on molecular mechanisms, internal and external Zeitgebers, and hierarchical regulation of physiological outputs. The architecture of the circadian clock involves the autoregulatory transcriptional feedback loops, post‐translational modifications of core oscillators, and epigenetic modifications of DNA and histones. Here, light, temperature, humidity, and internal elemental nutrients are summarized to illustrate the sensitivity of the circadian clock to timing cues. In addition, the circadian clock runs cell‐autonomously, driving independent circadian rhythms in various tissues. The core oscillators responds to each other with biochemical factors including calcium ions, mineral nutrients, photosynthetic products, and hormones. We describe clock components sequentially expressed during a 24‐h day that regulate rhythmic growth, aging, immune response, and resistance to biotic and abiotic stresses. Notably, more data have suggested the circadian clock links chrono‐culture to key agronomic traits in crops. [ABSTRACT FROM AUTHOR]

As sessile organisms, plants perceive, respond, and adapt to the environmental changes for optimal growth and survival. The plant growth and fitness are enhanced by circadian clocks through coordination of numerous biological events. In legume species, nitrogen‐fixing root nodules were developed as the plant organs specialized for symbiotic transfer of nitrogen between microsymbiont and host. Here, we report that the endogenous circadian rhythm in nodules is regulated by MtLHY in legume species Medicago truncatula. Loss of function of MtLHY leads to a reduction in the number of nodules formed, resulting in a diminished ability to assimilate nitrogen. The operation of the 24‐h rhythm in shoot is further influenced by the availability of nitrogen produced by the nodules, leading to the irregulated nyctinastic leaf movement and reduced biomass in mtlhy mutants. These data shed new light on the roles of MtLHY in the orchestration of circadian oscillator in nodules and shoots, which provides a mechanistic link between nodulation, nitrogen assimilation, and clock function. [ABSTRACT FROM AUTHOR]

It was noted that circadian components function in plant adaptation to diurnal temperature cycles and freezing tolerance. Our genome-wide transcriptome analysis revealed that evening-phased COR27 and COR28 mainly repress the transcription of clock-associated evening genes PRR5, ELF4 and cold-responsive genes. Chromatin immunoprecipitation indicated that CCA1 is recruited to the site containing EE elements of COR27 and COR28 promoters in a temperature-dependent way. Further genetic analysis shows COR28 is essential for the circadian function of PRR9 and PRR7. Together, our results support a role of COR27 and COR28 as nighttime repressors integrating circadian clock and plant cold stress responses. [ABSTRACT FROM AUTHOR]