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Horizontal Transfer of Microbial Toxin Genes to Gall Midge Genomes
Genome Biology and Evolution ( IF 3.3 ) Pub Date : 2021-08-27 , DOI: 10.1093/gbe/evab202
Kirsten I Verster 1 , Rebecca L Tarnopol 2 , Saron M Akalu 1 , Noah K Whiteman 1, 3
Affiliation  

A growing body of evidence has underscored the role of horizontal gene transfer (HGT) in animal evolution. Previously, we discovered the horizontal transfer of the gene encoding the eukaryotic genotoxin cytolethal distending toxin B (cdtB) from the pea aphid Acyrthosiphon pisum secondary endosymbiont (APSE) phages to drosophilid and aphid nuclear genomes. Here, we report cdtB in the nuclear genome of the gall-forming “swede midge” Contarinia nasturtii (Diptera: Cecidomyiidae) via HGT. We searched all available gall midge genome sequences for evidence of APSE-to-insect HGT events and found five toxin genes (aip56, cdtB, lysozyme, rhs, and sltxB) transferred horizontally to cecidomyiid nuclear genomes. Surprisingly, phylogenetic analyses of HGT candidates indicated APSE phages were often not the ancestral donor lineage of the toxin gene to cecidomyiids. We used a phylogenetic signal statistic to test a transfer-by-proximity hypothesis for animal HGT, which suggested that microbe-to-insect HGT was more likely between taxa that share environments than those from different environments. Many of the toxins we found in midge genomes target eukaryotic cells, and catalytic residues important for toxin function are conserved in insect copies. This class of horizontally transferred, eukaryotic cell-targeting genes is potentially important in insect adaptation.

中文翻译:

微生物毒素基因向瘿蚊基因组的水平转移

越来越多的证据强调了水平基因转移 (HGT) 在动物进化中的作用。以前,我们发现编码真核基因毒素细胞致死膨胀毒素 B (cdtB) 的基因从豌豆蚜虫 Acyrthosiphon pisum 次级内共生体 (APSE) 噬菌体水平转移到果蝇和蚜虫核基因组。在这里,我们通过 HGT 报告了胆囊形成“瑞典蠓”Contarinia nasturtii(双翅目:Cecidomyiidae)的核基因组中的 cdtB。我们搜索了所有可用的瘿蚊基因组序列,寻找 APSE 到昆虫 HGT 事件的证据,并发现五个毒素基因(aip56、cdtB、溶菌酶、rhs 和 sltxB)水平转移到 cecidomyiid 核基因组。出奇,HGT 候选者的系统发育分析表明 APSE 噬菌体通常不是 cecidomyiids 毒素基因的祖先供体谱系。我们使用系统发育信号统计来检验动物 HGT 的邻近转移假设,这表明微生物到昆虫的 HGT 更可能发生在共享环境的类群之间,而不是来自不同环境的类群之间。我们在蠓基因组中发现的许多毒素都以真核细胞为目标,而对毒素功能很重要的催化残基在昆虫拷贝中是保守的。这类水平转移的真核细胞靶向基因在昆虫适应中具有潜在的重要意义。这表明微生物到昆虫的 HGT 更可能发生在共享环境的类群之间,而不是来自不同环境的类群之间。我们在蠓基因组中发现的许多毒素都以真核细胞为目标,而对毒素功能很重要的催化残基在昆虫拷贝中是保守的。这类水平转移的真核细胞靶向基因在昆虫适应中具有潜在的重要意义。这表明微生物到昆虫的 HGT 更可能发生在共享环境的类群之间,而不是来自不同环境的类群之间。我们在蠓基因组中发现的许多毒素都以真核细胞为目标,而对毒素功能很重要的催化残基在昆虫拷贝中是保守的。这类水平转移的真核细胞靶向基因在昆虫适应中具有潜在的重要意义。
更新日期:2021-08-27
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