Metabolomic profiling reveals the anti-herbivore mechanism of rice (Oryza sativa) induced by silicon

Annual loss of rice caused by insect pests accounts for about 30% of total production, and the use of traditional pesticides has brought about environmental pollution, food safety, and other problems. The use of secondary metabolites of rice to control pests has become a research hotspot, but little is known about the mechanism of rice self-resistance. Rice is a typical silicon accumulating crop. Previous study showed that silicon can significantly enhance the resistance of rice to Chilo suppressalis, but anti-insect active substances in silicon-treated rice were unknown. In current study, metabolomics analysis has been performed on two groups of rice (T1, treated with silicon and insect; T3, treated with only insect). A total of 151 significantly different metabolites were obtained, compared with T3 group, 23 metabolites in T1 were significantly up-regulated and 128 metabolites were significantly down-regulated. Different metabolites were mainly enriched to tryptophan metabolism, lipoic acid metabolism, linoleic acid metabolism, isoflavone biosynthesis, and indole alkaloid biosynthesis. The different metabolites (p < 0.1) enriched to lipoic acid metabolism and fatty acid biosynthesis were all significantly up-regulated. Ten significantly up-regulated different metabolites were selected from T1. These were 3-hydroxy-palmitic acid methyl ester (1), octanoic acid (2), 3-hydroxyoctadecanoic acid (3), 12-hydroxyoctadecanoic acid (4), 2-linoleoylglycerol (5), methyleugenol (6), alpha-asarone (7), 2,4,5-trimethoxybenzaldehyde (8), acitretin (9), and menatetrenone (10), and their anti-insect activity was evaluated. Compounds 1–5 and 7–10 could significantly inhibit the growth of Chilo suppressalis. Compounds 2 and 3 inhibited growth of the insect by 35.5 and 64.5%, respectively. Compound 2 belongs to lipoic acid metabolism and fatty acid biosynthesis. We speculate that silicon positively regulated the metabolic pathway of lipoic acid and fatty acid to enhance the resistance of rice to insects.