Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, USA.
Department of Agronomy, Kansas State University, Manhattan, KS, USA.
Pest Manag Sci. 2018 Oct;74(10):2306-2315. doi: 10.1002/ps.4778. Epub 2017 Dec 29.
Resistance to the synthetic auxin herbicide dicamba is increasingly problematic in Kochia scoparia. The resistance mechanism in an inbred dicamba-resistant K. scoparia line (9425R) was investigated using physiological and transcriptomics (RNA-Seq) approaches.
No differences were found in dicamba absorption or metabolism between 9425R and a dicamba-susceptible line, but 9425R was found to have significantly reduced dicamba translocation. Known auxin-responsive genes ACC synthase (ACS) and indole-3-acetic acid amino synthetase (GH3) were transcriptionally induced following dicamba treatment in dicamba-susceptible K. scoparia but not in 9425R. Chalcone synthase (CHS), the gene regulating synthesis of the flavonols quertecin and kaemperfol, was found to have twofold higher transcription in 9425R both without and 12 h after dicamba treatment. Increased CHS transcription co-segregated with dicamba resistance in a forward genetics screen using an F population.
Prior work has shown that the flavonols quertecin and kaemperfol compete with auxin for intercellular movement and vascular loading via ATP-binding cassette subfamily B (ABCB) membrane transporters. The results of this study support a model in which constitutively increased CHS expression in the meristem produces more flavonols that would compete with dicamba for intercellular transport by ABCB transporters, resulting in reduced dicamba translocation. © 2017 Society of Chemical Industry.
节节草对合成生长素除草剂麦草畏的抗性日益成为一个问题。本研究采用生理学和转录组学（RNA-Seq）方法研究了 9425R 节节草这一纯合麦草畏抗性株系的抗性机制。
9425R 与麦草畏敏感株系在麦草畏吸收或代谢方面没有差异，但 9425R 的麦草畏转运明显减少。在麦草畏敏感节节草中，ACC 合酶（ACS）和吲哚-3-乙酸氨基酸合成酶（GH3）等已知的生长素响应基因在麦草畏处理后转录被诱导，但在 9425R 中则没有。调控类黄酮槲皮素和堪皮素合成的查尔酮合酶（CHS）基因在未经和经麦草畏处理 12 h 后，在 9425R 中的转录水平均提高了两倍。在利用 F 群体进行正向遗传学筛选时发现，CHS 转录的增加与麦草畏抗性共分离。
先前的研究表明，类黄酮槲皮素和堪皮素与生长素竞争通过 ABCB 膜转运蛋白进行细胞间运动和血管加载。本研究结果支持这样一种模式，即在分生组织中持续增加 CHS 的表达会产生更多的类黄酮，这些类黄酮会与 ABCB 转运蛋白竞争细胞间运输的麦草畏，从而导致麦草畏转运减少。 © 2017 英国化学学会
