Moretti Marcelo L, Alárcon-Reverte Rocio, Pearce Stephen, Morran Sarah, Hanson Bradley D
Department of Plant Sciences, University of California, Davis, California, United States of America.
Department of Horticulture, Oregon State University, Corvallis, Oregon, United States of America.
PLoS One. 2017 Jul 10;12(7):e0180794. doi: 10.1371/journal.pone.0180794. eCollection 2017.
Herbicide resistance is a challenge for modern agriculture further complicated by cases of resistance to multiple herbicides. Conyza bonariensis and Conyza canadensis are invasive weeds of field crops, orchards, and non-cropped areas in many parts of the world. In California, USA, Conyza populations resistant to the herbicides glyphosate and paraquat have recently been described. Although the mechanism conferring resistance to glyphosate and paraquat in these species was not elucidated, reduced translocation of these herbicides was observed under experimental conditions in both species. Glyphosate and paraquat resistance associated with reduced translocation are hypothesized to be a result of sequestration of herbicides into the vacuole, with the possible involvement of over-expression of genes encoding tonoplast transporters of ABC-transporter families in cases of glyphosate resistance or cationic amino acid transporters (CAT) in cases of paraquat resistance. However, gene expression in response to herbicide treatment has not been studied in glyphosate and paraquat resistant populations. In the current study, we evaluated the transcript levels of genes possibly involved in resistance using real-time PCR. First, we evaluated eight candidate reference genes following herbicide treatment and selected three genes that exhibited stable expression profiles; ACTIN, HEAT-SHOCK-PROTEIN-70, and CYCLOPHILIN. The reference genes identified here can be used for further studies related to plant-herbicide interactions. We used these reference genes to assay the transcript levels of EPSPS, ABC transporters, and CAT in response to herbicide treatment in susceptible and resistant Conyza spp. lines. No transcription changes were observed in EPSPS or CAT genes after glyphosate or paraquat treatment, suggesting that these genes are not involved in the resistance mechanism. Transcription of the two ABC transporter genes increased following glyphosate treatment in all Conyza spp. lines. Transcription of ABC transporters also increased after paraquat treatment in all three lines of C. bonariensis. However, in C. canadensis, paraquat treatment increased transcription of only one ABC transporter gene in the susceptible line. The increase in transcription of ABC transporters after herbicide treatment is likely a stress response based on similar response observed across all Conyza lines regardless of resistance or sensitivity to glyphosate or paraquat, thus these genes do not appear to be directly involved in the mechanism of resistance in Conyza spp.
抗除草剂是现代农业面临的一项挑战，而对多种除草剂产生抗性的情况则使这一挑战更加复杂。南美蟛蜞菊和加拿大蓬是世界许多地区大田作物、果园及非种植区的入侵杂草。在美国加利福尼亚州，最近已报道了对除草剂草甘膦和百草枯具有抗性的南美蟛蜞菊种群。虽然尚未阐明这些物种对草甘膦和百草枯产生抗性的机制，但在实验条件下观察到这两个物种中这些除草剂的转运减少。与转运减少相关的草甘膦和百草枯抗性被推测是除草剂被隔离到液泡中的结果，在草甘膦抗性情况下可能涉及ABC转运蛋白家族编码液泡膜转运蛋白的基因过表达，在百草枯抗性情况下可能涉及阳离子氨基酸转运蛋白（CAT）。然而，尚未在草甘膦和百草枯抗性种群中研究除草剂处理后的基因表达情况。在本研究中，我们使用实时PCR评估了可能参与抗性的基因的转录水平。首先，我们在除草剂处理后评估了八个候选内参基因，并选择了三个表现出稳定表达谱的基因；肌动蛋白、热休克蛋白70和亲环素。此处鉴定的内参基因可用于与植物 - 除草剂相互作用相关的进一步研究。我们使用这些内参基因来检测敏感和抗性南美蟛蜞菊品系中5-烯醇丙酮酰莽草酸-3-磷酸合酶（EPSPS）、ABC转运蛋白和CAT对除草剂处理的转录水平。在草甘膦或百草枯处理后，EPSPS或CAT基因未观察到转录变化，这表明这些基因不参与抗性机制。在所有南美蟛蜞菊品系中，草甘膦处理后两个ABC转运蛋白基因的转录增加。在所有三个南美蟛蜞菊品系中，百草枯处理后ABC转运蛋白的转录也增加。然而，在加拿大蓬中，百草枯处理仅使敏感品系中的一个ABC转运蛋白基因的转录增加。除草剂处理后ABC转运蛋白转录的增加可能是一种应激反应，因为在所有南美蟛蜞菊品系中都观察到了类似的反应，无论对草甘膦或百草枯的抗性或敏感性如何，因此这些基因似乎并不直接参与南美蟛蜞菊属植物的抗性机制。
