BASF SE, Ludwigshafen, Germany.
Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR, USA.
Pest Manag Sci. 2022 Jun;78(6):2258-2264. doi: 10.1002/ps.6850. Epub 2022 Mar 16.
Resistance to protoporphyrinogen oxidase (PPO)-inhibiting herbicides is endowed primarily by target-site mutations at the PPX2 gene that compromise binding of the herbicide to the catalytic domain. In Amaranthus spp. PPX2, the most prevalent target mutations are deletion of the G210 codon, and the R128G and G339A substitutions. These mutations strongly affect the dynamic of the PPO2 binding pocket, resulting in reduced affinity with the ligand. Here we investigated the likelihood of co-occurrence of the most widespread target site mutations in the same PPX2 allele.
Plants carrying R128G+/+ ΔG210+/-, where + indicates presence of the mutation, were crossed with each other. The PPX2 of the offspring was subjected to pyrosequencing and E. coli-based Sanger sequencing to determine mutation frequencies and allele co-occurrence. The data show that R128G ΔG210 can occur in one allele only; the second allele carries only one mutation. Double mutation in both alleles is less likely because of significant loss of enzyme activity. The segregation of offspring populations derived from a cross between heterozygous plants carrying ΔG210 G399A also showed no co-occurrence in the same allele. The offspring exhibited the expected mutation distribution patterns with few exceptions.
Homozygous double-mutants are not physiologically viable. Double-mutant plants can only exist in a heterozygous state. Alternatively, if two mutations are detected in one plant, each mutation would occur in a separate allele. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
对原卟啉原氧化酶（PPO）抑制剂除草剂的抗性主要是由 PPX2 基因靶位突变赋予的，这些突变会损害除草剂与催化结构域的结合。在苋属植物中，最常见的靶位突变是 G210 密码子缺失，以及 R128G 和 G339A 取代。这些突变强烈影响 PPO2 结合口袋的动力学，导致与配体的亲和力降低。在这里，我们研究了同一 PPX2 等位基因中最广泛的靶位突变同时发生的可能性。
携带 R128G+/+ΔG210+/-的植物（其中+表示存在突变）相互杂交。后代的 PPX2 进行焦磷酸测序和基于 E. coli 的 Sanger 测序，以确定突变频率和等位基因共发生。数据表明，R128GΔG210 只能存在于一个等位基因中；第二个等位基因仅携带一个突变。由于酶活性显著丧失，双突变在两个等位基因中不太可能发生。来自携带ΔG210G399A 杂合植物杂交的后代群体的分离也显示在同一等位基因中没有共发生。除了少数例外，后代表现出预期的突变分布模式。
纯合双突变体在生理上是不可行的。双突变体植物只能存在于杂合状态。或者，如果在一株植物中检测到两个突变，那么每个突变都会发生在一个单独的等位基因中。© 2022 作者。害虫管理科学由 John Wiley & Sons Ltd 代表化学工业协会出版。
