Horizontal gene transfer (HGT) is frequent in parasitic plant mitochondria as a result of vascular connections established in host-parasite relationships. Recent studies of the holoparasitic plant Lophophytum mirabile (Balanophoraceae) revealed the unprecedented acquisition of a large amount of mitochondrial sequences from its legume host. We focused on a close relative, the generalist holoparasite Ombrophytum subterraneum, to examine the incidence of HGT events in the mitochondrial genome (mtDNA). The mtDNA of O. subterraneum assembles into 54 circular chromosomes, only 34 of which contain the 51 full-length coding regions. Numerous foreign tracts (totaling almost 100 kb, ~ 14% of the mtDNA), including 12 intact genes, were acquired by HGT from the Asteraceae hosts. Nine chromosomes concentrate most of those regions and eight are almost entirely foreign. Native homologs of each foreign gene coexist in the mtDNA and are potentially functional. A large proportion of shorter regions were related to the Fabaceae (a total of ~ 110 kb, 15.4%), some of which were shared with L. mirabile. We also found evidence of foreign sequences donated by angiosperm lineages not reported as hosts (Apocynaceae, Euphorbiaceae, Lamiaceae, and Malvales). We propose an evolutionary hypothesis that involves ancient transfers from legume hosts in the common ancestor of Ombrophytum and Lophophytum followed by more recent transfer events in L. mirabile. Besides, the O. subterraneum mtDNA was also subjected to additional HGT events from diverse angiosperm lineages, including large and recent transfers from the Asteraceae, and also from Lamiaceae.

中文翻译：

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Ombrophytum地下（Balanophoraceae）线粒体基因组中的多染色体结构和异物。

水平基因转移（HGT）在寄生植物线粒体中很常见，这是由于宿主与寄生虫之间建立了血管联系而导致的。最近对全寄生寄生植物Lophophytum mirabile（Balanophoraceae）的研究表明，从其豆类宿主中获得了前所未有的大量线粒体序列。我们专注于近亲全寄生的Ombrophytum地下，检查线粒体基因组（mtDNA）中HGT事件的发生率。地下隐孢子虫的mtDNA组装成54个环形染色体，其中只有34个包含51个全长编码区。HGT从菊科宿主中获得了许多异物（总计近100 kb，约占mtDNA的14％），包括12个完整基因。九个染色体集中了这些区域的大部分，而八个则几乎完全是外来的。每个外源基因的天然同源物共存于mtDNA中，并且可能具有功能。很大一部分较短的区域与Fabaceae有关（总计〜110 kb，15.4％），其中一些与奇异乳杆菌共有。我们还发现了被子植物谱系捐赠的外来序列的证据，没有报告为宿主（夹竹桃科，大戟科，唇形科和锦葵科）。我们提出了一个进化假说，其中涉及在豆科植物和麦草植物的共同祖先中从豆类宿主进行的古老转移，然后是最近发生的神奇的L. mirabile转移事件。此外，O.submtneum mtDNA还遭受了来自不同被子植物谱系的其他HGT事件的影响，包括菊科的大量和近期转移，