• Metabolic resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides is a threat in controlling waterhemp (Amaranthus tuberculatus) in the USA. We investigated resistance mechanisms to syncarpic acid-3 (SA3), a nonselective, noncommercial HPPD-inhibiting herbicide metabolically robust to Phase I oxidation, in multiple-herbicide-resistant (MHR) waterhemp populations (SIR and NEB) and HPPD inhibitor-sensitive populations (ACR and SEN).
• Dose–response experiments with SA3 provided ED₅₀-based resistant : sensitive ratios of at least 18-fold. Metabolism experiments quantifying parent SA3 remaining in excised leaves during a time course indicated MHR populations displayed faster rates of SA3 metabolism compared to HPPD inhibitor-sensitive populations.
• SA3 metabolites were identified via LC-MS-based untargeted metabolomics in whole plants. A Phase I metabolite, likely generated by cytochrome P450-mediated alkyl hydroxylation, was detected but was not associated with resistance. A Phase I metabolite consistent with ketone reduction followed by water elimination was detected, creating a putative α,β-unsaturated carbonyl resembling a Michael acceptor site. A Phase II glutathione–SA3 conjugate was associated with resistance.
• Our results revealed a novel reduction–dehydration–GSH conjugation detoxification mechanism. SA3 metabolism in MHR waterhemp is thus atypical compared to commercial HPPD-inhibiting herbicides. This previously uncharacterized detoxification mechanism presents a unique opportunity for future biorational design by blocking known sites of herbicide metabolism in weeds.

中文翻译：

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通过新的还原-脱水-谷胱甘肽共轭在苋菜中抵抗非选择性 4-羟基苯丙酮酸双加氧酶抑制除草剂

• 对 4-羟基苯丙酮酸双加氧酶 (HPPD) 抑制性除草剂的代谢抗性是美国控制水麻 ( Amaranthus tuberculatus ) 的威胁。我们研究了对多除草剂抗性 (MHR) 水麻种群 (SIR 和 NEB) 和 HPPD 抑制剂敏感种群的非选择性、非商业性 HPPD 抑制除草剂 Synarpic acid-3 (SA3) 的抗性机制，该除草剂对 I 期氧化具有代谢稳健性（ACR 和 SEN）。
• SA3 的剂量反应实验提供了至少 18 倍的基于ED _{50的抗性：敏感比。}量化在一段时间内留在切除叶片中的亲本 SA3 的代谢实验表明，与 HPPD 抑制剂敏感的群体相比，MHR 群体显示出更快的 SA3 代谢率。
• SA3 代谢物通过基于 LC-MS 的非靶向代谢组学在整株植物中进行鉴定。检测到可能由细胞色素 P450 介导的烷基羟基化产生的 I 期代谢物，但与耐药性无关。检测到与酮还原和水消除一致的 I 相代谢物，产生类似于迈克尔受体位点的推定 α,β-不饱和羰基。II 期谷胱甘肽-SA3 偶联物与耐药性有关。
• 我们的结果揭示了一种新的还原-脱水-GSH结合解毒机制。因此，与商业 HPPD 抑制除草剂相比，MHR waterhemp 中的 SA3 代谢是非典型的。这种以前未表征的解毒机制通过阻断杂草中已知的除草剂代谢位点，为未来的生物合理设计提供了独特的机会。