Abstract
Plants experience specific stresses at particular, but predictable, times of the day. The circadian clock is a molecular oscillator that increases plant survival by timing internal processes to optimally match these environmental challenges. Clock regulation of jasmonic acid (JA) action is important for effective defenses against fungal pathogens and generalist herbivores in multiple plant species. Endogenous JA levels are rhythmic and under clock control with peak JA abundance during the day, a time when plants are more likely to experience certain types of biotic stresses. The expression of many JA biosynthesis, signaling, and response genes is transcriptionally controlled by the clock and timed through direct connections with core clock proteins. For example, the promoter of Arabidopsis transcription factor MYC2, a master regulator for JA signaling, is directly bound by the clock evening complex (EC) to negatively affect JA processes, including leaf senescence, at the end of the day. Also, tobacco ZEITLUPE, a circadian photoreceptor, binds directly to JAZ proteins and stimulates their degradation with resulting effects on JA root-based defenses. Collectively, a model where JA processes are embedded within the circadian network at multiple levels is emerging, and these connections to the circadian network suggest multiple avenues for future research.
Highlights
The circadian clock is a molecular oscillator that increases plant survival by timing internal processes to optimally match these environmental challenges
The expression of many jasmonic acid (JA) biosynthesis, signaling, and response genes is transcriptionally controlled by the clock and timed through direct connections with core clock proteins
The classic view of the circadian system consists of three parts: (1) input signals from the environment that give time-of-day cues and set the clock, (2) a core molecular oscillator that keeps 24-h time, and (3) rhythmic physiological outputs that are often manifested through cyclic gene expression programs [6,7]
Summary
The daily rotation of planet Earth and resulting day/night cycles affect nearly every location on the terrestrial surface. To match these cycles, organisms have an endogenous timekeeping mechanism called the circadian clock that confers 24-h rhythmicity to life processes. Clocks enable anticipation of daily changes in environmental conditions, match and coordinate internal processes with the external environment, and allow for efficient allocation of cellular resources [1,2]. Important external conditions might occur with certainty, such as dawn or day length, and these events can help predict more variable environmental challenges, such as excessive temperatures or the presence of day-active pests. Recent work shows multiple molecular mechanisms by which the clock directly controls important aspects of JA action in plant growth and defense
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