A novel ABC gene involved in the interaction between unripe citrus fruits and the tephritid Bactrocera minax larvae

The adaptation of phytophagous insects to host defense is an important aspect of plant–insect interactions. The reciprocal adaptability between specialist insects and their hosts have been adequately explored; however, the mechanisms underlying the adaptation of tephritid fruit fly specialists, a group of notorious pests worldwide, to unripen host fruits remain elusive. Here, plant metabolomes and insect transcriptomes were analyzed for the first time to explore the interaction between unripe citrus fruits and the Chinese citrus fly Bactrocera minax. Eighteen citrus secondary metabolites, mainly flavones, alkaloids and phenylpropanoids, were identified in the unripe citrus fruit metabolome, and they accumulated during larval feeding. Three detoxification genes (1 P450 gene, 2 ABCs genes) were highly expressed in B. minax larvae collected from unripe citrus fruits compared with the ones fed on artificial diets and ripe citrus fruits. Based on omics data, a novel ABC gene was screened through plant allelopathy tests, and the gene was significantly upregulated in B. minax larvae treated with defensive secondary metabolites (N-Methylcytisine, tryptamine, coixol, limonin, nomilin and quercetin), respectively; additionally, the mortality rate of the larvae reached 51% after silencing the ABC gene by RNAi technique. Overall, these results shed light on the mechanisms underlying the biological interactions between tephritid fruit fly specialists and host fruits.