Department of Entomology, University of Arizona, Tucson, AZ 85721, USA.
Department of Biology, Austin Peay State University, Clarksville, TN 37040, USA.
Genetics. 2022 May 5;221(1). doi: 10.1093/genetics/iyac037.
Crops genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis have advanced pest management, but their benefits are diminished when pests evolve resistance. Elucidating the genetic basis of pest resistance to Bacillus thuringiensis toxins can improve resistance monitoring, resistance management, and the design of new insecticides. Here, we investigated the genetic basis of resistance to Bacillus thuringiensis toxin Cry1Ac in the lepidopteran Helicoverpa zea, one of the most damaging crop pests in the United States. To facilitate this research, we built the first chromosome-level genome assembly for this species, which has 31 chromosomes containing 375 Mb and 15,482 predicted proteins. Using a genome-wide association study, fine-scale mapping, and RNA-seq, we identified a 250-kb quantitative trait locus on chromosome 13 that was strongly associated with resistance in a strain of Helicoverpa zea that had been selected for resistance in the field and lab. The mutation in this quantitative trait locus contributed to but was not sufficient for resistance, which implies alleles in more than one gene contributed to resistance. This quantitative trait locus contains no genes with a previously reported role in resistance or susceptibility to Bacillus thuringiensis toxins. However, in resistant insects, this quantitative trait locus has a premature stop codon in a kinesin gene, which is a primary candidate as a mutation contributing to resistance. We found no changes in gene sequence or expression consistently associated with resistance for 11 genes previously implicated in lepidopteran resistance to Cry1Ac. Thus, the results reveal a novel and polygenic basis of resistance.
经过基因工程改造、可产生苏云金芽孢杆菌杀虫蛋白的作物，在害虫管理方面取得了进展，但当害虫产生抗药性时，它们的益处就会减少。阐明害虫对苏云金芽孢杆菌毒素的抗药性的遗传基础，可以改善抗药性监测、抗药性管理和新杀虫剂的设计。在这里，我们研究了鳞翅目昆虫烟夜蛾（Helicoverpa zea）对苏云金芽孢杆菌毒素 Cry1Ac 抗性的遗传基础，烟夜蛾是美国破坏性最大的农作物害虫之一。为了便于这项研究，我们构建了该物种的第一个染色体水平基因组组装，该基因组有 31 条染色体，包含 375Mb 和 15482 个预测蛋白。通过全基因组关联研究、精细图谱绘制和 RNA-seq，我们在一个已经在田间和实验室中选择具有抗性的烟夜蛾品系中，鉴定出 13 号染色体上与抗性强烈相关的 250kb 数量性状位点。该数量性状位点上的突变导致但不足以引起抗性，这意味着至少有一个以上基因的等位基因参与了抗性。该数量性状位点不包含先前报道的与苏云金芽孢杆菌毒素抗性或敏感性相关的基因。然而，在具有抗性的昆虫中，该数量性状位点中的一个驱动蛋白基因出现了一个提前终止密码子，这是一个可能导致抗性的突变候选基因。我们没有发现 11 个先前被认为与 Cry1Ac 抗性有关的基因的序列或表达与抗性一致的变化。因此，结果揭示了一种新的、多基因的抗性基础。
