Wild poinsettia (Euphorbia heterophylla L.) is a troublesome broadleaf weed in grain production areas in South America. Herbicide resistance to multiple sites of action has been documented in this species, including protoporphyrinogen oxidase (PPO) inhibitors. We investigated the physiological and molecular bases for PPO-inhibitor resistance in a E. heterophylla population (RPPO) from Southern Brazil. Whole-plant dose–response experiments revealed a cross-resistance profile to three different chemical groups of PPO inhibitors. Based on dose–response parameters, RPPO was resistant to lactofen (47.7-fold), saflufenacil (8.6-fold), and pyraflufen-ethyl (3.5-fold). Twenty-four hours after lactofen treatment (120 g ha−1) POST, RPPO accumulated 27 times less protoporphyrin than the susceptible population (SPPO). In addition, RPPO generated 5 and 4.5 times less hydrogen peroxide and superoxide than SPPO, respectively. The chloroplast PPO (PPO1) sequences were identical between the two populations, whereas 35 single-nucleotide polymorphisms were found for the mitochondrial PPO (PPO2). Based on protein homology modeling, the Arg-128-Leu (homologous to Arg-98-Leu in common ragweed [Ambrosia artemisiifolia L.] was the only one located near the catalytic site, also in a conserved region of PPO2. The cytochrome P450 monooxygenase inhibitor malathion did not reverse resistance to lactofen in RPPO, and both populations showed similar levels of PPO1 and PPO2 expression, suggesting that metabolic resistance and PPO overexpression are unlikely. This is the first report of an Arg-128-Leu mutation in PPO2 conferring cross-resistance to PPO inhibitors in E. heterophylla.

中文翻译：

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PPO2 中的 Arg-128-Leu 靶位点突变在野生一品红（大戟）中进化，对 PPO 抑制性除草剂具有交叉耐药性

野生一品红 (太子参L.) 是南美洲粮食产区的一种麻烦的阔叶杂草。在该物种中已经记录了对多个作用位点的除草剂抗性，包括原卟啉原氧化酶 (PPO) 抑制剂。我们研究了 PPO 抑制剂耐药性的生理和分子基础。太子参人口（RPPO) 来自巴西南部。全植物剂量反应实验揭示了对三种不同化学组 PPO 抑制剂的交叉耐药谱。基于剂量反应参数，RPPO对乳多芬（47.7 倍）、苯嘧磺草胺（8.6 倍）和 pyraflufen-ethyl（3.5 倍）耐药。乳托芬治疗后 24 小时（120 g ha-1) 邮政，RPPO累积的原卟啉比易感人群少 27 倍（SPPO）。此外，RPPO产生的过氧化氢和超氧化物比 S 少 5 倍和 4.5 倍PPO， 分别。叶绿体 PPO (PPO1) 序列在两个种群之间是相同的，而线粒体 PPO 发现了 35 个单核苷酸多态性 (PPO2）。基于蛋白质同源性模型，Arg-128-Leu（与普通豚草中的 Arg-98-Leu 同源 [青蒿L.]是唯一一个位于催化位点附近的，也在一个保守的区域PPO2. 细胞色素 P450 单加氧酶抑制剂马拉硫磷不能逆转 R 中对乳多芬的耐药性PPO，并且两个人群都表现出相似的水平PPO1和PPO2表达，表明代谢抵抗和PPO不太可能过度表达。这是 Arg-128-Leu 突变的首次报道PPO2赋予 PPO 抑制剂交叉耐药性太子参.