Summary The holoparasitic plant Lophophytum mirabile exhibits remarkable levels of mitochondrial horizontal gene transfer (HGT). Gathering comparative data from other individuals and host plants can provide insights into the HGT process. We sequenced the mitochondrial genome (mtDNA) from individuals of two species of Lophophytum and from mimosoid hosts. We applied a stringent phylogenomic approach to elucidate the origin of the whole mtDNAs, estimate the timing of the transfers, and understand the molecular mechanisms involved. Ancestral and recent HGT events replaced and enlarged the multichromosomal mtDNA of Lophophytum spp., with the foreign DNA ascending to 74%. A total of 14 foreign mitochondrial chromosomes originated from continuous regions in the host mtDNA flanked by short direct repeats. These foreign tracts are circularized by microhomology‐mediated repair pathways and replicate independently until they are lost or they eventually recombine with other chromosomes. The foreign noncoding chromosomes are variably present in the population and likely evolve by genetic drift. We present the ‘circle‐mediated HGT’ model in which foreign mitochondrial DNA tracts become circular and are maintained as plasmid‐like molecules. This model challenges the conventional belief that foreign DNA must be integrated into the recipient genome for successful HGT.

中文翻译：

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水平转移的线粒体 DNA 束通过微同源介导的修复途径变成环状


摘要全寄生植物 Lophophytum mirabile 表现出显着水平的线粒体水平基因转移 (HGT)。收集其他个体和宿主植物的比较数据可以提供对 HGT 过程的深入了解。我们对两种 Lophophytum 个体和含羞草宿主的线粒体基因组 (mtDNA) 进行了测序。我们采用严格的系统发育学方法来阐明整个 mtDNA 的起源，估计转移的时间，并了解所涉及的分子机制。祖先和最近的 HGT 事件取代并扩大了 Lophophytum spp. 的多染色体 mtDNA，外源 DNA 上升至 74%。总共 14 条外源线粒体染色体源自宿主 mtDNA 中的连续区域，两侧是短的同向重复序列。这些外源束通过微同源介导的修复途径环化并独立复制，直到丢失或最终与其他染色体重组。外源非编码染色体在群体中的存在情况各不相同，并且可能通过遗传漂变而进化。我们提出了“环介导的 HGT”模型，其中外源线粒体 DNA 束变成环状并保持为类质粒分子。该模型挑战了传统观念，即外源 DNA 必须整合到受体基因组中才能成功进行 HGT。