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

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, <i>Nilaparvata lugens</i>, were used to test this hypothesis. Bioassays revealed that two representative cardenolides, ouabain, and digoxin, demonstrated significant toxicity against <i>N. lugens</i>. 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 <i>N. lugens</i>. However, the knockdown of certain Oatp and Mdr genes significantly enhances the oral toxicity of ouabain and digoxin to <i>N. lugens</i>. The findings of our study support that Oatps and Mdrs are key transporters in <i>N. lugens</i> protection against dietary cardenolides.