Abstract
The circadian clock in plants synchronizes biological processes that display cyclic 24-h oscillation based on metabolic and physiological reactions. This clock is a precise timekeeping system, that helps anticipate diurnal changes; e.g., expression levels of clock-related genes move in synchrony with changes in pathogen infection and help prepare appropriate defense responses in advance. Salicylic acid (SA) is a plant hormone and immune signal involved in systemic acquired resistance (SAR)-mediated defense responses. SA signaling induces cellular redox changes, and degradation and rhythmic nuclear translocation of the non-expresser of PR genes 1 (NPR1) protein. Recent studies demonstrate the ability of the circadian clock to predict various potential attackers, and of redox signaling to determine appropriate defense against pathogen infection. Interaction of the circadian clock with redox rhythm promotes the balance between immunity and growth. We review here a variety of recent evidence for the intricate relationship between circadian clock and plant immune response, with a focus on the roles of redox rhythm and NPR1 in the circadian clock and plant immunity.
Highlights
Most eukaryotic and some prokaryotic organisms have some type of circadian clock that functions as an internal timing mechanism for the control of various normal physiological reactions under light/dark cycle, such as metabolism, hormone levels, body temperature, permitting vision, and brain activities processes [1,2,3,4,5]
We review interactions between circadian clock and plant immune system, we focus on recent advances in rhythmic oscillation of both redox and clock, and on metabolic and physiological reactions that promote balance of plant immunity and growth
CCA1 and LHY have transcript and protein levels that peak in the morning, TOC1 peaks in early evening and acts as a repressor that directly binds to CCA1 and LHY promoters. ~40% of TOC1 target genes have an early morning phase regulated by the circadian clock
Summary
Most eukaryotic and some prokaryotic organisms have some type of circadian clock that functions as an internal timing mechanism for the control of various normal physiological reactions under light/dark cycle, such as metabolism, hormone levels, body temperature, permitting vision, and brain activities processes [1,2,3,4,5]. The circadian clock is a rather robust system, especially in detecting the precise time of day processes in many metabolic and physiological reactions to help plants make the right reaction at the right time. It drives an endogenous oscillating rhythm strictly observe a period of approximately 24 h even if it is under continuous light or dark [6,7,8,9]. We review interactions between circadian clock and plant immune system, we focus on recent advances in rhythmic oscillation of both redox and clock, and on metabolic and physiological reactions that promote balance of plant immunity and growth
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