Cis-regulation of the CYP6CS1 gene and its role in mediating cross-resistance in a pymetrozine-resistant strain of Nilaparvata lugens

Pymetrozine is currently one of the primary insecticides used to control the brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae), but the long-term effectiveness of this chemical is threatened by growing issues of resistance. Previous studies in a laboratory selected strain of N. lugens, Pym-R, have shown that resistance to pymetrozine can evolve without target-site mutations. A key candidate gene identified is the cytochrome P450 gene CYP6CS1, which is overexpressed in the resistant Pym-R strain compared to the laboratory susceptible strain, Pym-S. In this study, we provide a deeper characterization of the regulatory mechanism and phenotypic effects of CYP6CS1 by comparing the resistant and susceptible variants of this gene. Using artificial constructs in Luciferase activity assays, we elucidate the role of indels in the overexpression of CYP6CS1 in the resistant strain. Additionally, transgenic Drosophila experiments also revealed that the CYP6CS1 gene not only contributes to resistance against pymetrozine, but is able to confer moderate to low cross-resistance to several other pesticides. This research provides vital insights into the possible genetic mechanisms that may contribute to pymetrozine resistance in field populations. Future work will aim to examine the relevance of CYP6CS1 variation in the field with the aim of developing diagnostic markers of resistance.