Sourgrass (Digitaria insularis) is one of the most problematic weeds in South America because glyphosate resistance is widespread across most crop production regions. Acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides have been intensively used to manage D. insularis, which substantially increased selection pressure for this class of herbicides. We confirmed resistance to ACCase herbicides in a D. insularis population from Brazil and characterized its molecular basis. Resistant plants showed high level of resistance to haloxyfop (resistance factor, RF = 613-fold), low level of resistance to pinoxaden (RF = 3.6-fold), and no resistance to clethodim. A target-site mutation, Trp2027Cys, was found in the ACCase sequence from resistant plants. A protein homology model shows that the Trp2027Cys mutation is near the herbicide-binding pocket formed between two ACCase chains, and is predicted to obstruct the access of aryloxyphenoxypropionates (FOP) herbicides to the binding site. A qPCR-based single nucleotide polymorphism genotyping method was validated to discriminate susceptible (wild-type Trp2027) and resistant (mutant Cys2027) alleles. All resistant plants were homozygous for the mutation and the assay could be used for early detection of resistance in D. insularis field samples with suspected resistance to ACCase inhibitors.

中文翻译：

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Trp2027Cys 突变在 Digitaria insularis 中进化，对 ACCase 抑制剂具有交叉耐药性

酸草（Digitaria insularis）是南美洲最成问题的杂草之一，因为草甘膦抗性在大多数作物生产地区普遍存在。乙酰辅酶 A 羧化酶 (ACCase) 抑制性除草剂已被广泛用于管理 D. insularis，这大大增加了对此类除草剂的选择压力。我们确认了来自巴西的 D. insularis 种群对 ACCase 除草剂的抗性，并表征了其分子基础。抗性植物对氟啶虫胺表现出高水平的抗性（抗性因子，RF = 613 倍），对唑草胺的抗性水平低（RF = 3.6 倍），对烯草酮无抗性。在抗性植物的 ACCase 序列中发现了一个靶位点突变 Trp2027Cys。蛋白质同源性模型表明，Trp2027Cys 突变位于两条 ACCase 链之间形成的除草剂结合口袋附近，预计会阻碍芳氧基苯氧基丙酸酯 (FOP) 除草剂进入结合位点。验证了基于 qPCR 的单核苷酸多态性基因分型方法来区分易感（野生型 Trp2027）和抗性（突变型 Cys2027）等位基因。所有抗性植物对于突变都是纯合的，并且该测定可用于在怀疑对 ACCase 抑制剂具有抗性的 D. insularis 田间样品中早期检测抗性。验证了基于 qPCR 的单核苷酸多态性基因分型方法来区分易感（野生型 Trp2027）和抗性（突变型 Cys2027）等位基因。所有抗性植物对于突变都是纯合的，并且该测定可用于在怀疑对 ACCase 抑制剂具有抗性的 D. insularis 田间样品中早期检测抗性。验证了基于 qPCR 的单核苷酸多态性基因分型方法来区分易感（野生型 Trp2027）和抗性（突变型 Cys2027）等位基因。所有抗性植物对于突变都是纯合的，并且该测定可用于在怀疑对 ACCase 抑制剂具有抗性的 D. insularis 田间样品中早期检测抗性。