Metabolome profiling reveals the resistance mechanisms of rice against brown planthopper

Rice (Oryza sativa L.) is a crucial global cereal crop, severely threatened by the brown planthopper (BPH), which causes extensive damage through direct feeding and virus transmission. To elucidate the resistance mechanism mediated by the BPH-resistance gene Bph6, metabolic responses to BPH infestation were compared between the resistant rice line G6 and the susceptible cultivar Nipponbare using LC-MS-based metabolomics combined with quantitative real-time PCR analysis. The Bph6 gene conferred both antixenotic and antibiotic resistance to BPH. A total of 673 metabolites were identified across all samples. BPH infestation induced more pronounced metabolic alterations in susceptible Nipponbare than in the resistant G6 line. Compared with Nipponbare, G6 exhibited a more coordinated defense response characterized by enhanced accumulation of amino acid-derived metabolites, flavonoids, and serotonin-associated compounds. Consistently, the expression levels of key biosynthetic genes, including TDC and CYP71A1 involved in serotonin biosynthesis and CHS and F3H associated with flavonoid biosynthesis, were significantly upregulated in G6. These findings demonstrate that Bph6 mediates a more stable and effective defense metabolism in rice through coordinated regulation of primary and secondary metabolism, particularly flavonoid- and serotonin-related pathways.