Mutual interactions between biological timing and innate immunity in Arabidopsis

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We will investigate the interdigitation of two distinct signaling networks that both contribute to plant performance: The endogenous clock system serves to optimally align plant physiology to the periodic changes of light and darkness in the environment and by these means contributes to fitness of the plant, and the innate immune system provides strategies to the plant for self-defense against invading pathogens. A few cases of mutual interactions between circadian rhythmicity and innate immunity have been reported in mammals and flies. Our recent observation that a slave oscillator component in Arabidopsis thaliana is part of the innate immune system suggests a close interaction also in higher plants. Moreover, the circadian transcriptome of Arabidopsis comprises genes involved in pathogen defense. We will address this functional connection from both directions. We will investigate the impact of pathogen challenge on circadian rhythms. First we will test the influence of pathogenassociated molecular patterns (PAMPs) and subsequently the effect of bacterial infection, using the oscillation of selected clock-controlled transcripts as a circadian readout. Conversely, we will analyse the consequences of an impaired endogenous timing system on plant immune responses. A suite of mutants and transgenic plants disrupted in selected components of the circadian system will be tested for their responses to PAMPs and for disease symptom development and survival upon bacterial infection. These experiments will provide insights to what extent the circadian system contributes to plant immunity. This may emerge as an additional benefit of an intact circadian clock for plant performance.