Molecular Basis of Crosstalk between the Circadian Clock and Innate Immunity in Arabidopsis

Author/Creator

Author/Creator ORCID

Date

2015-01-01

Department

Biological Sciences

Program

Biological Sciences

Citation of Original Publication

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Distribution Rights granted to UMBC by the author.

Abstract

Pathogens-induced plant diseases cause tremendous losses in crop production and severely impact global economy. Successful control of plant diseases relies on a thorough understanding of mechanisms of disease resistance in plants. The timing of effective defense responses against invading pathogens is crucial for plant fitness. The circadian clock integrates temporal information with environmental cues, such as light and temperature, in regulating plant growth and development. Recently, the circadian clock has been shown to affect plant responses to biotic cues. To further examine the role of the circadian clock in regulating plant immunity, we tested disease resistance in mutants disrupted in CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), two critical components of the central oscillator synergistically contributing to the circadian clock. We found that cca1 and lhy mutants synergistically affect basal and resistance gene-mediated defense against the bacterial pathogen Pseudomonas syringae and the oomycete pathogen Hyaloperonospora arabidopsidis (Hpa). Arrhythmicity of the circadian clock caused by overexpression of CCA1 or LHY also resulted in severe susceptibility to P. syringae. We identified a downstream target of CCA1 and LHY, GLYCINE-RICH RNA-BINDING PROTEIN (GRP7), previously shown to influence plant defense and stomatal activity and as a key constituent of a slave oscillator regulated by the circadian clock. We show that the defense role of CCA1, LHY, and GRP7 against P. syringae is at least partially through circadian control of stomatal aperture. We also showed that a salicylic acid regulator, phosphate transporter PHT4;1 who has been reported to play an important role in Arabidopsis defense is likely controlled by CCA1. In addition, we tested a mutant disrupting another clock component LUX ARRHYTHMO (LUX) and found that LUX could also be involved in defense regulation. Both SA-mediated defense and flg22 response were impaired in lux-1 mutants. The expression of LUX was found to be CCA1-dependent and suppressed by pathogen infection. We also showed that two of downstream targets of LUX, PRR7 and PRR9, could modulate plant defense response. Furthermore, we found defense activation by P. syringae infection and treatment with flg22 (an elicitor of basal defense) can also feedback-regulate clock activity. Together these data strongly support a role of the circadian clock in defense control and reveal reciprocal crosstalk between the circadian clock and plant innate immunity. Plant innate immunity is intimately connected with the circadian clock.