The resistance to dieldrin gene (Rdl) encodes a subunit of the insect γ-amino butyric acid (GABA) receptor, and the encoded Rdl subunit is a major target site for cyclodiene and phenylpyrazole insecticides. Since the substitution of a single amino acid (Ala to Ser/Gly at position 302) of the Drosophila melanogaster Rdl gene was first identified to confer high level resistance to dieldrin, mutations at the equivalent positions have been reported to confer resistance to dieldrin and/or fipronil in a wide range of different insects. In the cotton bollworm Helicoverpa armigera, there are two Rdl homologs (HaRdl-1 and HaRdl-2) in close proximity on the Z chromosome, which as wild-type sequences, encode alanine and serine respectively at amino acid position 302. In the present study, we used the CRISPR/Cas9 gene editing approach to knock out HaRdl-1 and HaRdl-2 and establish two homozygous knockout strains (ΔRdl-1 and ΔRdl-2). The ΔRdl-1 strain showed low levels of resistance (8.0- to 9.3-fold) to three cyclodiene insecticides (endosulfan, aldrin and dieldrin) compared with the background SCD strain. In contrast, toxicity of the three cyclodiene insecticides to the ΔRdl-2 strain increased significantly (3.6- to 6.3-fold) when compared with the SCD strain. Genetic analysis indicated the obtained resistance to endosulfan and dieldrin in the ΔRdl-1 strain was sex-linked, which is consistent with the fact that HaRdl-1 locus is located on the Z chromosome. The above results demonstrate that both HaRdl-1 and HaRdl-2 are important determinants for the susceptibility of H. armigera SCD strain to the three cyclodiene insecticides, but have opposite effects. It was also found that HaRdl-1 and HaRdl-2 are involved, to some extent, in mediating sensitivity of H. armigera to avermectin and fipronil respectively. We speculate that the HaRdl-1 and HaRdl-2 subunits have different pharmacological properties, which contribute to the differential sensitivities of H. armigera to the tested cyclodienes and other insecticides.

中文翻译：

---

反向遗传学揭示棉铃虫的两种 Rdl 同源 GABA 受体对环二烯杀虫剂毒性的相反影响

狄氏剂抗性基因（Rdl）编码昆虫γ-氨基丁酸（GABA）受体的一个亚基，编码的Rdl亚基是环二烯和苯基吡唑类杀虫剂的主要靶位点。由于首先鉴定出黑腹果蝇 Rdl 基因的单个氨基酸（位置 302 处的 Ala 到 Ser/Gly）可赋予对狄氏剂的高水平抗性，因此据报道，等效位置的突变可赋予狄氏剂抗性和/或氟虫腈在各种不同的昆虫中。在棉铃虫Helicoverpa armigera中，Z染色体上有两个Rdl同源物（HaRdl-1和HaRdl-2）紧邻，作为野生型序列，分别在302位氨基酸编码丙氨酸和丝氨酸。学习，我们使用 CRISPR/Cas9 基因编辑方法敲除 HaRdl-1 和 HaRdl-2，并建立两个纯合敲除菌株（ΔRdl-1 和 ΔRdl-2）。与背景 SCD 菌株相比，ΔRdl-1 菌株对三种环二烯杀虫剂（硫丹、艾氏剂和狄氏剂）的抗性水平较低（8.0 至 9.3 倍）。相反，与 SCD 菌株相比，三种环二烯杀虫剂对 ΔRdl-2 菌株的毒性显着增加（3.6 至 6.3 倍）。遗传分析表明，ΔRdl-1 菌株获得的硫丹和狄氏剂抗性是性连锁的，这与 HaRdl-1 基因座位于 Z 染色体上的事实一致。上述结果表明，HaRdl-1 和 HaRdl-2 都是棉铃虫 SCD 菌株对三种环二烯杀虫剂敏感性的重要决定因素，但有相反的效果。还发现HaRdl-1和HaRdl-2在一定程度上参与介导棉铃虫分别对阿维菌素和氟虫腈的敏感性。我们推测 HaRdl-1 和 HaRdl-2 亚基具有不同的药理学特性，这导致棉铃虫对测试的环二烯和其他杀虫剂的不同敏感性。