Synchronization of Circadian Clock Gene Expression inArabidopsisandHyaloperonospora arabidopsidisand its Impact on Host-Pathogen Interactions

Abstract

AbstractOrganisms across all kingdoms have an internal circadian clock running in 24h cycles. This clock affects a variety of processes, including innate immunity in plants. However, the role of pathogen circadian clocks had not been extensively explored. We previously showed that light can influence infection of the oomyceteHyaloperonospora arabidopsidis(Hpa, downy mildew disease) on its natural hostArabidopsis thaliana. Here, we identifiedHpaorthologs of known circadian clock genes (CCGs)Drosophila TIMELESS (TIM)andArabidopsis Sensitive to Red Light Reduced 1 (AtSRR1)genes. Expression of bothHpaTIMandHpaSRR1showed a circadian rhythm whenHpawas exposed to constant light. Contrastingly, these two genes were negatively regulated by constant dark exposure. Furthermore, the expression patterns ofHpaTIMandHpaSRR1correlate with those ofAtCCA1andAtLHY, indicating a synchronisation of biological clock genes between the host and the pathogen. In addition, screening mutants ofArabidopsisClock Regulated Genes (AtCRGs) with three virulentHpaisolates revealed that mutations inAtCRGsinfluencedHpaTIMandHpaSRR1expression andHpadevelopment, indicating a functional link between the plant biological clock and virulence. Moreover, sporulation ofHpawas reduced by targetingHpaTIMandHpaSRR1with short synthesized small interfering RNAs, indicating that the pathogen clock is also relevant to virulence. We propose that plant and pathogen clocks are synchronized during infection and that proper regulation of both clocks are genetically necessary for pathogen virulence.