The Nitrogen Regulatory Gene ntrC Modulates Virulence and Nitrogen Metabolism in Burkholderia glumae

Burkholderia glumae, the causal agent of bacterial panicle blight in rice, is a major threat to global rice production. Although the NtrB-NtrC two-component system is a well-established regulator of nitrogen assimilation in many bacteria, its role in B. glumae has remained undefined. In this study, we constructed a ntrC deletion mutant of B. glumae BGR1 to investigate the contribution of NtrC to nitrogen metabolism and virulence. Under nitrogen-limited conditions in minimal medium supplemented with a single nitrogen source, the mutant exhibited markedly impaired growth, particularly when ammonium or glutamine served as the sole nitrogen source. Loss of ntrC also resulted in significant reductions in swimming motility, biofilm formation, and toxoflavin production, while extracellular protease activity was unaffected. In pathogenicity assays, the mutant caused substantially milder symptoms in both rice seedlings and flowering panicles, despite showing no difference in bacterial population levels in planta compared with the wild-type. These findings demonstrate that NtrC is essential for efficient nitrogen utilization and for full virulence expression in rice. This study provides evidence that the NtrB-NtrC system links nitrogen metabolism with virulence expression in B. glumae.