Editors' ChoiceCircadian Rhythms

Infection alters circadian rhythm

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Sci. Signal.  06 Mar 2018:
Vol. 11, Issue 520, eaat4604
DOI: 10.1126/scisignal.aat4604

The response to bacterial infection alters the circadian rhythm of Arabidopsis thaliana.

Circadian rhythms control diverse processes, including behavior, physiology, and the immune response. Whereas endogenous factors generate the oscillations of gene expression patterns that define the circadian clock, external cues, such as light and temperature, set the periodicity and amplitude of these oscillations. Li et al. found that the circadian clock of the plant Arabidopsis thaliana also responded to pathogen infection. Local infection of Arabidopsis leaves with Pseudomonas syringae reduced the amplitude and increased the periodicity of circadian oscillations in tissues distant from the infection site. In response to infection, plants produce the hormone salicylic acid (SA), which exerts some of its effects by stimulating the production of reactive oxygen species (ROS). The transcription factor NPR1 mediates SA-induced responses but can also inhibit SA biosynthesis. Treating uninfected plants with single transient dose of SA or hydrogen peroxide mimicked pathogen-induced reduction in the circadian rhythm amplitude but did not affect the clock’s periodicity. Plants lacking NPR1 function exhibited a greater reduction in circadian amplitude when treated with SA compared with wild-type plants, and overexpression of NPR1 reduced the amount by which the circadian amplitude decreased in response to SA treatment or P. syringae infection. The enzyme RBOHD, which produces ROS specifically in the apoplastic space between the plasma membrane and cell wall, was involved in lengthening of the circadian period in response to infection or SA treatment but did not entirely account for the response, indicating that other sources of ROS also likely contribute. In addition to demonstrating that infection can alter the circadian rhythm of plants, this work also identifies ROS as a previously unappreciated regulator of the plant circadian clock.

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