Plant-parasitic nematodes are one of the most economically important pests of crops. It is widely accepted that Horizontal Gene Transfer (HGT) - the natural acquisition of foreign genes in parasitic nematodes - contributes to parasitism. However, an apparent paradox has emerged from HGT analyses: On one hand, distantly related organisms with very dissimilar genetic structures (i.e. bacteria), and only transient interactions with nematodes as far as we know, dominate the list of putative donors; while on the other hand, considerably more closely related organism (i.e. the host plant), with similar genetic structure (i.e. introns) and documented long-term associations with nematodes, are rare among the list of putative donors. Given that these nematodes ingest cytoplasm from a living plant cell for several weeks, there seems to be a conspicuous absence of plant-derived cases. Here we used comparative genomic approaches to evaluate possible plant-derived HGT events in plant parasitic nematodes. Our evidence supports a cautionary message for plant-derived HGT cases in the sugar beet cyst nematode, Heterodera schachtii. We propose a four step model for HGT from plant to parasite in order to evaluate why the absence of plant-derived HGT cases is observed. We find that the plant genome is mobilised by the nematode during infection, but that uptake of said “mobilome” is the first major barrier to HGT from host to nematode. These results provide new insight into our understanding of the prevalence/role of nucleic acids exchange in the arms race between plants and plant parasites.

中文翻译：

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对从植物到寄生胞囊线虫的 DNA 转移的严格评估

植物寄生线虫是经济上最重要的农作物害虫之一。人们普遍认为，水平基因转移（HGT）——寄生线虫中自然获得的外源基因——会导致寄生。然而，HGT 分析中出现了一个明显的悖论：一方面，具有非常不同遗传结构的远亲生物（即细菌），并且据我们所知，与线虫仅存在短暂的相互作用，在假定的供体列表中占主导地位；另一方面，具有相似遗传结构（即内含子）且有记录的与线虫长期关联的、关系更密切的生物体（即宿主植物）在假定的供体名单中很少见。鉴于这些线虫在数周内从活植物细胞中摄取细胞质，因此似乎明显缺乏植物源性病例。在这里，我们使用比较基因组方法来评估植物寄生线虫中可能的植物源性 HGT 事件。我们的证据支持对甜菜胞囊线虫 Heterodera schachtii 中植物源性 HGT 病例的警示信息。我们提出了从植物到寄生虫的 HGT 的四步模型，以评估为什么没有观察到植物源性 HGT 病例。我们发现，植物基因组在感染过程中被线虫动员，但对所述“动员组”的吸收是 HGT 从宿主到线虫的第一个主要障碍。这些结果为我们理解核酸交换在植物和植物寄生虫之间的军备竞赛中的普遍性/作用提供了新的见解。