Nielsen K M, Bones A M, Smalla K, van Elsas J D
UNIGEN-Center for Molecular Biology, Norwegian University of Science and Technology, Trondheim, Norway.
FEMS Microbiol Rev. 1998 Jun;22(2):79-103. doi: 10.1111/j.1574-6976.1998.tb00362.x.
Today, 12 years after the first field release of a genetically modified plant (GMP), over 15,000 field trials at different locations have been performed. As new and unique characteristics are frequently introduced into GMPs, risk assessment has to be performed to assess their ecological impact. The possibilities of horizontal gene transfer (HGT; no parent-to-offspring transfer of genes) from plants to microorganisms are frequently evaluated in such risk assessments of GMPs before release into the field. In this review we indicate why putative HGT from plants to terrestrial (soil and plant associated) bacteria has raised concern in biosafety evaluations. Further, we discuss possible pathways of HGT from plants to bacteria, outline the barriers to HGT in bacteria, describe the strategies used to investigate HGT from plants to bacteria and summarize the results obtained. Only a few cases of HGT from eukaryotes such as plants to bacteria have been reported to date. These cases have been ascertained after comparison of DNA sequences between plants and bacteria. Although experimental approaches in both field and laboratory studies have not been able to confirm the occurrence of such HGT to naturally occurring bacteria, recently two studies have shown transfer of marker genes from plants to bacteria based on homologous recombination. The few examples of HGT indicated by DNA sequence comparisons suggest that the frequencies of evolutionarily successful HGT from plants to bacteria may be extremely low. However, this inference is based on a small number of experimental studies and indications found in the literature. Transfer frequencies should not be confounded with the likelihood of environmental implications, since the frequency of HGT is probably only marginally important compared with the selective force acting on the outcome. Attention should therefore be focused on enhancing the understanding of selection processes in natural environments. Only an accurate understanding of these selective events will allow the prediction of possible consequences of novel genes following their introduction into open environments.
如今，在首次对转基因植物进行田间释放12年后，已在不同地点进行了超过15000次田间试验。由于新的独特性状经常被引入转基因植物中，因此必须进行风险评估以评估其生态影响。在将转基因植物释放到田间之前，其向微生物水平基因转移（HGT；基因非亲代至子代转移）的可能性在这类风险评估中经常得到评估。在本综述中，我们指出了为何植物向陆生（土壤及与植物相关的）细菌的假定水平基因转移在生物安全评估中引发了关注。此外，我们讨论了植物向细菌水平基因转移的可能途径，概述了细菌中水平基因转移的障碍，描述了用于研究植物向细菌水平基因转移的策略并总结了所得结果。迄今为止，仅报道了少数几例从植物等真核生物向细菌的水平基因转移情况。这些情况是在比较植物和细菌的DNA序列后确定的。尽管田间和实验室研究中的实验方法均未能证实此类水平基因转移在自然细菌中的发生，但最近有两项研究表明基于同源重组的标记基因从植物转移到了细菌中。DNA序列比较表明的少数水平基因转移实例表明，从植物到细菌进化上成功的水平基因转移频率可能极低。然而，这一推断是基于少数实验研究及文献中的迹象得出的。转移频率不应与环境影响的可能性相混淆，因为与作用于结果的选择力相比，水平基因转移频率可能仅具有微不足道的重要性。因此，应将注意力集中在增强对自然环境中选择过程的理解上。只有准确理解这些选择事件，才能预测新基因引入开放环境后的可能后果。
