Complete Genomes of Symbiotic Cyanobacteria Clarify the Evolution of Vanadium-Nitrogenase
Complete Genomes of Symbiotic Cyanobacteria Clarify the Evolution of Vanadium-Nitrogenase
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DOI：
10.1093/gbe/evz137
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发表时间：
2019-07-01
影响因子：
3.3
通讯作者：
Li, Fay-Wei
中科院分区：
文献类型：
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作者：
Nelson, Jessica M.;Hauser, Duncan A.;Li, Fay-Wei
植物与固氮蓝藻的内共生现象在不同植物谱系中独立演化，为研究植物 - 微生物相互作用的演化及遗传学提供了独特视角。然而，植物蓝藻共生体的完整基因组极为稀少，因此我们对其基因组及功能多样性知之甚少。在此，我们展示了从苔藓植物中分离出的四种蓝藻的完整基因组。纳米孔长读长测序技术使我们能够获得所有主染色体及大多数质粒的环形重叠群。我们发现，尽管这四种分离株的16S rRNA序列差异较小，但它们在基因组重排和基因内容上表现出显著差异。此外，四种分离株中有三种拥有编码钒（V） - 固氮酶（vnf）的基因，这在固氮生物中并不常见，且此前在植物蓝藻共生体中未见报道。在两个案例中，vnf基因位于质粒上，这意味着可能存在质粒介导的水平基因转移。对含vnf基因的蓝藻进行比较基因组分析，进一步确定了一个保守的基因簇。该基因簇中的许多基因尚未进行功能表征，有望成为未来研究阐明钒 - 固氮酶功能及调控机制的候选基因。
Plant endosymbiosis with nitrogen-fixing cyanobacteria has independently evolved in diverse plant lineages, offering a unique window to study the evolution and genetics of plant-microbe interaction. However, very few complete genomes exist for plant cyanobionts, and therefore little is known about their genomic and functional diversity. Here, we present four complete genomes of cyanobacteria isolated from bryophytes. Nanopore long-read sequencing allowed us to obtain circular contigs for all the main chromosomes and most of the plasmids. We found that despite having a low 16S rRNA sequence divergence, the four isolates exhibit considerable genome reorganizations and variation in gene content. Furthermore, three of the four isolates possess genes encoding vanadium(V)-nitrogenase (vnf), which is uncommon among diazotrophs and has not been previously reported in plant cyanobionts. In two cases, the vnf genes were found on plasmids, implying possible plasmid-mediated horizontal gene transfers. Comparative genomic analysis of vnf-containing cyanobacteria further identified a conserved gene cluster. Many genes in this cluster have not been functionally characterized and would be promising candidates for future studies to elucidate V-nitrogenase function and regulation.