Australian Herbicide Resistance Initiative, School of Agriculture and Environment, The University of Western Australia, Crawley, Australia.
Centre for Plant Genetics and Breeding, School of Agriculture and Environment, The University of Western Australia, Crawley, Australia.
Ann Bot. 2018 Sep 24;122(4):627-640. doi: 10.1093/aob/mcy097.
Resistance to synthetic auxin herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) is increasing in weed populations worldwide, which is of concern given the recent introduction of synthetic auxin-resistant transgenic crops. Due to the complex mode of action of the auxinic herbicides, the mechanisms of evolved resistance remain largely uncharacterized. The aims of this study were to assess the level of diversity in resistance mechanisms in 11 populations of the problem weed Raphanus raphanistrum, and to use a high-throughput, whole-genome transcriptomic analysis on one resistant and one susceptible population to identify important changes in gene expression in response to 2,4-D.
Levels of 2,4-D and dicamba (3,6-dichloro-2-methoxybenzoic acid) resistance were quantified in a dose-response study and the populations were further screened for auxin selectivity, 2,4-D translocation and metabolism, expression of key 2,4-D-responsive genes and activation of the mitogen-activated proein kinase (MAPK) pathway. Potential links between resistance levels and mechanisms were assessed using correlation analysis.
The transcriptomic study revealed early deployment of the plant defence response in the 2,4-D-treated resistant population, and there was a corresponding positive relationship between auxinic herbicide resistance and constitutive MAPK phosphorylation across all populations. Populations with shoot-wide translocation of 2,4-D had similar resistance levels to those with restricted translocation, suggesting that reduced translocation may not be as strong a resistance mechanism as originally thought. Differences in auxin selectivity between populations point to the likelihood of different resistance-conferring alterations in auxin signalling and/or perception in the different populations.
2,4-D resistance in wild radish appears to result from subtly different auxin signalling alterations in different populations, supplemented by an enhanced defence response and, in some cases, reduced 2,4-D translocation. This study highlights the dangers of applying knowledge generated from a few populations of a weed species to the species as a whole.
在全球范围内，杂草种群对合成生长素除草剂（如 2,4-二氯苯氧乙酸（2,4-D））的抗性不断增强，这令人担忧，因为最近引入了合成生长素抗性转基因作物。由于生长素除草剂的作用模式复杂，进化抗性的机制在很大程度上仍未得到充分描述。本研究的目的是评估 11 个问题杂草萝卜（Raphanus raphanistrum）种群中抗性机制的多样性，并对一个抗性种群和一个敏感种群进行高通量全基因组转录组分析，以确定对 2,4-D 响应时基因表达的重要变化。
在剂量反应研究中定量测定了 2,4-D 和二甲四氯（3,6-二氯-2-甲氧基苯甲酸）的抗性水平，进一步筛选了生长素选择性、2,4-D 转运和代谢、关键 2,4-D 响应基因的表达以及丝裂原激活蛋白激酶（MAPK）途径的激活情况。使用相关分析评估了抗性水平与机制之间的潜在联系。
转录组研究表明，在 2,4-D 处理的抗性种群中，植物防御反应的早期部署，以及在所有种群中，生长素除草剂抗性与组成型 MAPK 磷酸化之间存在正相关关系。具有 2,4-D 全株转运的种群与具有限制转运的种群具有相似的抗性水平，这表明与最初的想法相比，减少转运可能不是一种很强的抗性机制。种群之间生长素选择性的差异表明，不同种群中生长素信号转导和/或感知可能存在不同的抗性赋予改变。
野生萝卜对 2,4-D 的抗性似乎是由于不同种群中生长素信号转导的微妙改变，辅以增强的防御反应，在某些情况下，减少 2,4-D 的转运。本研究强调了将从杂草物种的少数几个种群中获得的知识应用于整个物种所带来的危险。
