Toxin and Genome Evolution in a Drosophila Defensive Symbiosis
Toxin and Genome Evolution in a Drosophila Defensive Symbiosis
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DOI：
10.1093/gbe/evy272
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发表时间：
2019-01-01
影响因子：
3.3
通讯作者：
Perlman, Steve J.
中科院分区：
文献类型：
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作者：
Ballinger, Matthew J.;Gawryluk, Ryan M. R.;Perlman, Steve J.
由微生物共生体赋予的防御在其动物宿主的健康和适应性中起着至关重要的作用。防御性共生研究中一个重要的突出问题是什么决定了防御性共生对不同天敌的长期稳定性和有效性。在这项研究中，我们结合联合收割机基因组和转录组测序，共生体转染和寄生虫保护实验，毒素活性测定，以研究果蝇和垂直传播的螺原体细菌共生体之间的防御性共生关系的演变，特别关注核糖体失活蛋白（RIP），共生体编码的毒素，有牵连的保护对寄生蜂和线虫。尽管许多螺原体菌株，包括黑腹果蝇（Drosophila melanogaster）的雄性杀死共生体（sMel），可以保护免受寄生蜂的侵害，但只有感染食菌蝇（Drosophila neotestacea）的菌株（sNeo）似乎可以保护免受寄生线虫的侵害。我们发现，RIP库是一个主要的区分因素的菌株，不提供线虫的保护，和sMel RIP不显示对线虫核糖体在体内的活动。我们还发现了一种螺旋体菌株感染了一种食菌蚤蝇，黑蚤蝇。虽然宿主和螺原体都与D. neotestacea及其共生体，基因组测序结果表明，M.黑共生体编码丰富多样的RIP，包括质粒编码的毒素，这些毒素与sNeo中的RIP密切相关。我们的研究结果表明，远亲螺原体RIP毒素可能执行专门的功能，寄生虫的特异性，并提出了一个重要的作用，水平基因转移出现新的防御表型。
Defenses conferred by microbial symbionts play a vital role in the health and fitness of their animal hosts. An important outstanding question in the study of defensive symbiosis is what determines long term stability and effectiveness against diverse natural enemies. In this study, we combine genome and transcriptome sequencing, symbiont transfection and parasite protection experiments, and toxin activity assays to examine the evolution of the defensive symbiosis between Drosophila flies and their vertically transmitted Spiroplasma bacterial symbionts, focusing in particular on ribosome-inactivating proteins (RIPs), symbiont-encoded toxins that have been implicated in protection against both parasitic wasps and nematodes. Although many strains of Spiroplasma, including the male-killing symbiont (sMel) of Drosophila melanogaster, protect against parasitic wasps, only the strain (sNeo) that infects the mycophagous fly Drosophila neotestacea appears to protect against parasitic nematodes. We find that RIP repertoire is a major differentiating factor between strains that do and do not offer nematode protection, and that sMel RIPs do not show activity against nematode ribosomes in vivo. We also discovered a strain of Spiroplasma infecting a mycophagous phorid fly, Megaselia nigra. Although both the host and its Spiroplasma are distantly related to D. neotestacea and its symbiont, genome sequencing revealed that the M. nigra symbiont encodes abundant and diverse RIPs, including plasmid-encoded toxins that are closely related to the RIPs in sNeo. Our results suggest that distantly related Spiroplasma RIP toxins may perform specialized functions with regard to parasite specificity and suggest an important role for horizontal gene transfer in the emergence of novel defensive phenotypes.