RNAi-mediated plant sterol modification to control insect herbivore pests: insights from Arabidopsis and the diamondback moth

All eukaryotes use sterols as structural components in cell membranes and as precursors for key hormones. However, arthropods are unique among eukaryotes because they cannot synthesize sterols de novo and must acquire sterols through diet. Cholesterol is the dominant sterol in most insects; however, because plants contain little cholesterol, most insect herbivores convert phytosterols to cholesterol. An additional challenge for plant-feeding insects is that only limited types of phytosterols can be converted to cholesterol. In this study, we used RNA interference to modify the plant sterol profile to generate phytosterols that would negatively impact insect herbivores. Specifically, we knocked down the expression of Arabidopsis thaliana Δ8–Δ7-sterol isomerase gene (HYD1), responsible for the conversion of Δ8-sterols into Δ7-sterols. Silenced lines with > 95% transcript reduction showed drastically reduced sterol production and approximately half of the total sterols had a Δ8-configuration. Importantly, these sterol-modified lines exhibited normal growth compared to controls. In contract, the diamondback moth (Plutella xylostella) larvae reared on sterol-modified plants showed reduced growth and survival, while adults showed significantly decreased egg production. Sterol analysis of P. xylostella adults suggests these negative effects were likely a result of reduced cholesterol and the accumulation of Δ8-sterols. Finally, we modeled the effects of sterol-modified plants at the population level using our growth and reproductive data. We observed reduced population size and extended generation time after only two generations. Collectively, our results suggest that modifying plant sterols has potential for management of pest caterpillars, including the globally distributed P. xylostella.