Constant Illumination Boosts Rice Immunity via the Nicotinamide Mononucleotide Signaling Pathway: A Mechanistic Exploration

Light serves as a key input signal for the plant circadian clock, and together they coordinately regulate plant growth and development. However, the nature of their relationship regarding rice immunity remains unclear. The present study aimed to clarify the mechanism by which light modulates rice immunity through the circadian clock. The results indicated that constant light exposure significantly alleviated rice blast symptoms, while constant dark exposure exacerbated them. Transcriptome analysis demonstrated that constant light altered the phases of core circadian clock genes and activated circadian-controlled pathways, including the nicotinamide mononucleotide (NMN)-associated energy metabolism pathway. Metabolomics analysis and experimental validation confirmed that constant light exposure significantly increased the level of NMN, nicotinamide adenine dinucleotide (NAD+), and nicotinamide adenine dinucleotide phosphate (NADP⁺). Notably, exogenous NMN application effectively mitigated rice blast symptoms. Our study provided critical insights into the interplay among light, the circadian clock, and plant immunity, offering potential applications in agricultural production.