Department of Entomology, College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China.
Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane, 690-8504, Japan.
Insect Biochem Mol Biol. 2018 Mar;94:18-27. doi: 10.1016/j.ibmb.2018.01.003. Epub 2018 Feb 5.
Insect γ-aminobutyric acid (GABA) receptor (GABAR) is one of the major targets of insecticides. In the present study, cDNAs (CsRDL1A and CsRDL2S) encoding the two isoforms of RDL subunits were cloned from the rice stem borer Chilo suppressalis. Transcripts of both genes demonstrated similar expression patterns in different tissues and developmental stages, although CsRDL2S was ∼2-fold more abundant than CsRDL1A throughout all development stages. To investigate the function of channels formed by CsRDL subunits, both genes were expressed in Xenopus laevis oocytes singly or in combination in different ratios. Electrophysiological results using a two-electrode voltage clamp demonstrated that GABA activated currents in oocytes injected with both cRNAs. The EC value of GABA in activating currents was smaller in oocytes co-injected with CsRDL1A and CsRDL2S than in oocytes injected singly. The IC value of the insecticide fluralaner in inhibiting GABA responses was smaller in oocytes co-injected with different cRNAs than in oocytes injected singly. Co-injection also changed the potency of the insecticide dieldrin in oocytes injected singly. These findings suggested that heteromeric GABARs were formed by the co-injections of CsRDL1A and CsRDL2S in oocytes. Although the presence of Ser at the 2'-position in the second transmembrane segment was responsible for the insensitivity of GABARs to dieldrin, this amino acid did not affect the potencies of the insecticides fipronil and fluralaner. These results lead us to hypothesize that C. suppressalis may adapt to insecticide pressure by regulating the expression levels of CsRDL1A and CsRDL2S and the composition of both subunits in GABARs.
昆虫 γ-氨基丁酸（GABA）受体（GABAR）是杀虫剂的主要靶标之一。在本研究中，从水稻螟虫二化螟中克隆出编码两种 RDL 亚基同工型的 cDNA（CsRDL1A 和 CsRDL2S）。这两个基因的转录本在不同组织和发育阶段表现出相似的表达模式，尽管 CsRDL2S 在所有发育阶段的丰度约为 CsRDL1A 的两倍。为了研究 CsRDL 亚基通道的功能，分别或按不同比例组合在非洲爪蟾卵母细胞中表达这两个基因。使用双电极电压钳的电生理结果表明，GABA 在注射两种 cRNA 的卵母细胞中激活电流。与单独注射相比，在共注射 CsRDL1A 和 CsRDL2S 的卵母细胞中，GABA 激活电流的 EC 值更小。在共注射不同 cRNA 的卵母细胞中，杀虫剂氟虫腈抑制 GABA 反应的 IC 值小于单独注射的卵母细胞。共注射还改变了单独注射的杀虫剂狄氏剂在卵母细胞中的效力。这些发现表明，CsRDL1A 和 CsRDL2S 的共注射在卵母细胞中形成了异源 GABAR。尽管第二跨膜片段 2'位上的 Ser 负责 GABAR 对狄氏剂不敏感，但该氨基酸不影响杀虫剂氟虫腈和氟虫腈的效力。这些结果使我们假设二化螟可能通过调节 GABAR 中 CsRDL1A 和 CsRDL2S 的表达水平以及两种亚基的组成来适应杀虫剂的压力。
