Wheat Genetics Resource Center and Department of Plant Pathology, Kansas State University, Manhattan, KS 66506.
Crop Production Systems Research Unit, US Department of Agriculture-Agricultural Research Services, Stoneville, MS 38776.
Proc Natl Acad Sci U S A. 2018 Mar 27;115(13):3332-3337. doi: 10.1073/pnas.1719354115. Epub 2018 Mar 12.
Gene amplification has been observed in many bacteria and eukaryotes as a response to various selective pressures, such as antibiotics, cytotoxic drugs, pesticides, herbicides, and other stressful environmental conditions. An increase in gene copy number is often found as extrachromosomal elements that usually contain autonomously replicating extrachromosomal circular DNA molecules (eccDNAs). , a crop weed, can develop herbicide resistance to glyphosate [-(phosphonomethyl) glycine] by amplification of the 5-enolpyruvylshikimate-3-phosphate synthase () gene, the molecular target of glyphosate. However, biological questions regarding the source of the amplified , the nature of the amplified DNA structures, and mechanisms responsible for maintaining this gene amplification in cells and their inheritance remain unknown. Here, we report that amplified copies in glyphosate-resistant (GR) are present in the form of eccDNAs with various conformations. The eccDNAs are transmitted during cell division in mitosis and meiosis to the soma and germ cells and the progeny by an as yet unknown mechanism of tethering to mitotic and meiotic chromosomes. We propose that eccDNAs are one of the components of McClintock's postulated innate systems [McClintock B (1978) ] that can rapidly produce soma variation, amplify genes in the sporophyte that are transmitted to germ cells, and modulate rapid glyphosate resistance through genome plasticity and adaptive evolution.
基因扩增已在许多细菌和真核生物中被观察到，作为对各种选择压力的反应，如抗生素、细胞毒性药物、杀虫剂、除草剂和其他应激环境条件。基因拷贝数的增加通常作为染色体外元件发现，这些元件通常包含自主复制的染色体外环状 DNA 分子（eccDNA）。一种农作物杂草，可以通过扩增 5-烯醇丙酮酰莽草酸-3-磷酸合酶（EPSPS）基因对草甘膦[（膦酰基甲基）甘氨酸]产生抗药性，该基因是草甘膦的分子靶标。然而，关于扩增的来源、扩增 DNA 结构的性质以及负责在细胞中维持这种基因扩增及其遗传的机制等生物学问题仍然未知。在这里，我们报告说，在草甘膦抗性（GR）中，扩增的 EPSPS 拷贝以具有各种构象的 eccDNA 的形式存在。eccDNA 通过一种未知的与有丝分裂和减数分裂染色体连接的机制，在有丝分裂和减数分裂期间传递到体细胞和生殖细胞及其后代。我们提出，eccDNA 是 McClintock 假设的先天系统的组成部分之一[McClintock B（1978）]，可以快速产生体细胞变异，扩增在孢子体中传递给生殖细胞的基因，并通过基因组可塑性和适应性进化调节快速草甘膦抗性。
