Nitrogen fertilization is essential for crop yield but can increase susceptibility to rice blast, a phenomenon known as Nitrogen-Induced Susceptibility (NIS). The genetic architecture governing natural variation in NIS remains poorly characterized. To address this, we performed a genome-wide association study (GWAS) using a diverse panel of 268 rice accessions from the rice diversity panel 2, under controlled nitrogen regimes 0N (control),1N (100 mg/L NH₄NO₃), 2N (200 mg/L NH₄NO₃). Our analyses defined a NIS Index (NISI), which revealed extensive polymorphism. GWAS identified several significant loci, including a novel locus on chromosome 8 (NIS4) harboring F-box protein genes. Physiological dissection showed that a 'negative NIS' phenotype (enhanced resistance under high nitrogen) correlated with a rapid, pathogen-triggered defense response, characterized by immediate induction of peroxidase activity and lignin biosynthesis. Conversely, susceptible lines exhibited delayed defense. Gene expression analysis linked active nitrogen assimilation (GS/GOGAT cycle) to susceptibility. We conclude that NIS polymorphism is genetically controlled and hinges on the host's ability to redirect nitrogen resources toward early defense activation during pathogen invasion.
Yanfang et al. (Tue,) studied this question.