Natural variation-based genetic screen in rice identifies the isopentylamine biosynthetic gene that modulates brown...

We previously identified isopentylamine as a novel defence metabolite accumulated in rice (Oryza sativa L.) infested by brown planthoppers (BPHs, Nilaparvata lugens) and caterpillars, however the key biosynthetic gene(s) remained unknown. An analytical screen of genetically diverse rice cultivars was used to identify natural variation in isopentylamine production in rice, revealing that it can be produced at high levels in cv. Nipponbare but not in cv. Kasalath. Genetic approaches with chromosome fragment substitution lines and backcross inbred lines of Nipponbare and Kasalath were then used to identify genes potentially involved in biosynthesis of isopentylamine. The main candidate biosynthetic gene was knocked out with CRISPR/Cas9 to obtain three independent Nipponbare mutant lines, and correlations between gene function and isopentylamine were examined analytically. The gene Os10g0400500 was identified as the main biosynthetic gene for production of isopentylamine in rice. Furthermore, behavioural responses to isopentylamine in two-choice host assays were examined by placing BPHs in containers with mutant and wild-type Nipponbare leaves. Although BPHs were not always attracted to either wild-type or mutants, more BPHs, at least at some points, were found on the mutant leaves. Our results suggest that BPHs may show a preference for isopentylamine-deprived plants relative to wild types, which further corroborates the potential role of isopentylamine as defence against insect herbivores in chemically diverse rice species.