LUX ARRHYTHMO mediates crosstalk between the circadian clock and defense in Arabidopsis

Abstract

The circadian clock is known to regulate plant innate immunity but the underlying mechanism of this regulation remains largely unclear. We show here that mutations in the core clock component LUX ARRHYTHMO (LUX) disrupt circadian regulation of stomata under free running and Pseudomonas syringae challenge conditions as well as defense signaling mediated by SA and JA, leading to compromised disease resistance. RNA-seq analysis reveals that both clock- and defense-related genes are regulated by LUX. LUX binds to clock gene promoters that have not been shown before, expanding the clock gene networks that require LUX function. LUX also binds to the promoters of EDS1 and JAZ5 , likely acting through these genes to affect SA- and JA-signaling. We further show that JA signaling reciprocally affects clock activity. Thus, our data support crosstalk between the circadian clock and plant innate immunity and imply an important role of LUX in this process.

Coronatine is More Potent than Jasmonates in Regulating Arabidopsis Circadian Clock

“…To further test the clock regulatory role of COR, we performed the luciferase (LUC) assay with plants expressing the LUC gene driven by promoters of different clock genes, including CCA1, TOC1, PRR7, and GRP7. Similar to MJ, we found that COR suppressed seedling growth in our clock assay condition ( Figure S5 and [5]). After normalizing the LUC amplitude to relative leaf area of seedlings, we observed that COR dampened the amplitude and lengthened the period of all four reporters largely in a dosage dependent manner, regardless COR was applied at 25 or 37 h after light onset (subjective dawn or subjective dusk, respectively) ( Figure 2).…”

“…We then transferred the seedlings to continuous light (LL) for 1 d and treated them with MJ (100µM) or COR (10µM) for gene expression analysis. qRT-PCR results showed that both MJ and COR suppressed expression of selected core clock genes ( Figure S4 and [5]), supporting that both MJ and COR regulate clock activity.…”

“…One way that COR promotes bacterial virulence is through interfering with JA signaling. A number of studies demonstrated crosstalk between JA signaling and the circadian clock [3][4][5]17]. We are interested in elucidating in this report whether P. syringae-derived COR can regulate plant circadian clock.…”

“…The JA level and expression of some key JA biosynthetic and signaling genes oscillate in a day [3,4]. Two Arabidopsis clock genes, LUX [5] and TIC [4] were shown to regulate clock output to affect JA signaling. In turn, JA signal activation dampens the amplitude and lengthens the period of some clock reporters [5], suggesting a reciprocal regulation of the circadian clock by JA signaling.…”

“…Two Arabidopsis clock genes, LUX [5] and TIC [4] were shown to regulate clock output to affect JA signaling. In turn, JA signal activation dampens the amplitude and lengthens the period of some clock reporters [5], suggesting a reciprocal regulation of the circadian clock by JA signaling. Such a reciprocation relationship is also found between the circadian clock and other biological processes, including nutrient uptake and signaling mediated by salicylic acid, reactive oxygen species, and phytohormones [6][7][8][9], and it suggests an adaptive nature of plants to coordinate limited resources for growth, development, and environmental stimuli.…”