Knockdown of Oatp and Mdr Transporter Genes Enhances Cardenolide Toxicity to the Noncardenolide Feeder, Nilaparvata lugens

Insect adaptation to toxic cardenolides has been a model system to study convergent evolution between plants and herbivores. It was hypothesized that Organic anion-transporting polypeptides (Oatps) and multidrug transporters (Mdrs) provide basal resistance against cardenolides in a nonadapted insect. However, there is still little evidence to support this hypothesis. A noncardenolide feeder and an important rice pest, Nilaparvata lugens, were used to test this hypothesis. Bioassays revealed that two representative cardenolides, ouabain, and digoxin, demonstrated significant toxicity against N. lugens. The suppression of the expression levels of six Oatp genes and three Mdr genes by the RNAi did not result in any significant lethal phenotype in N. lugens. However, the knockdown of certain Oatp and Mdr genes significantly enhances the oral toxicity of ouabain and digoxin to N. lugens. The findings of our study support that Oatps and Mdrs are key transporters in N. lugens protection against dietary cardenolides.