Circadian Regulation of the Rice Immune Response during Rice Blast Infection via Metabolic and Calcium Signaling

The circadian clock is crucial in plant immunity and metabolism, yet the coordinating mechanisms remain elusive. In the present study, transcriptome analysis of <i>M. oryzae</i>-infected rice leaves and rhythmic analysis showed reduced amplitudes of circadian and phytochrome genes, impacting immune response, metabolic pathways, and calcium signaling. The amplitudes of pattern-triggered immunity (PTI)-related genes declined, while the rhythmicity of effector-triggered immunity (ETI)-related genes disappeared. Moreover, alterations in the phases of metabolic pathways were observed, potentially involved in immune response regulation like phytohormone biosynthesis. Calcium signaling exhibited a circadian pattern similar to that of the whole-transcriptome analysis. The administration of CaCl₂ alleviated, whereas the calcium ion chelator EGTA aggravated, the phenotypes of rice blasts, suggesting their role in regulating the circadian clock-mediated immune response in rice. Our study highlighted the significance of circadian regulation in rice blast-induced immune modulation, which may contribute to developing immunomodulators and the formulation of chronobiology-based precise therapeutic regimens.