Cnidarians are one of the oldest eumetazoan taxa, and are thought to be a sister group to all bilaterians. In spite of comparatively simple morphology, cnidarians exhibit diverse body forms and life histories. In addition, many cnidarian species establish symbiotic relationships with microalgae. Various Hydra species have been employed as model organisms since the 18th century. Introduction of transgenic and knock-down technologies made them ideal experimental systems for studying cellular and molecular mechanisms involved in regeneration, body-axis formation, senescence, symbiosis, and holobiosis. In order to provide an important reference for genetic studies, the Hydra magnipapillata genome was sequenced. However, the initial published version of the H. magnipapillata genome did not achieve assembly continuity comparable to those of other model systems, due mainly to a large number of transposable elements. For almost a decade, the highly fragmented genome assembly of H. magnipapillata (scaffold N50=128Kb) has remained the only genomic resource for this genus with several dozen species. Here we report a draft 280-Mbp genome assembly for Hydra viridissima strain A99, a symbiotic, early diverging member of the Hydra clade, with a scaffold N50 of 1.1 Mbp. The H. viridissima genome contains an estimated 21,476 protein-coding genes. Comparative analysis of Pfam domains and orthologous proteins highlights characteristic features of H. viridissima, such as diversification of innate immunity genes that are important for host-symbiont interactions. Thus, the Hydra viridissima assembly provides an important hydrozoan genome reference that will facilitate symbiosis research and better comparisons of metazoan genome architectures.

中文翻译：

---

来自共生水生动物Hydra viridissima的参考基因组

平民是最古老的杜鹃花类群之一，被认为是所有双语者的姊妹团体。尽管形态比较简单，但刺胞动物仍表现出多样的身体形态和生活史。此外，许多cnidarian物种与微藻建立了共生关系。自18世纪以来，已将各种九头蛇物种用作模型生物。转基因和基因敲除技术的引入使它们成为研究涉及再生，体轴形成，衰老，共生和整体病的细胞和分子机制的理想实验系统。为了给遗传研究提供重要参考，对九头蛇九头蛇基因组进行了测序。但是，H。magnipapillata的初始发布版本基因组不能实现与其他模型系统相当的装配连续性，这主要归因于大量的转座因子。近十年来，高分枝吸虫（H. magnipapillata）（支架N50 = 128Kb）的高度碎片化的基因组组装一直是该属的唯一基因组资源，有数十种。在这里，我们报告了九头蛇绿色菌种A99（一种共生的，九头蛇分支的早期分歧成员）的草稿280-Mbp基因组装配草案，其支架N50为1.1 Mbp。该H. viridissima基因组包含估计21476个蛋白质编码基因。Pfam结构域和直系同源蛋白的比较分析突出了H. viridissima的特征，例如对宿主共生体相互作用至关重要的先天免疫基因的多样化。因此，Hydra viridissima大会提供了重要的水生动物基因组参考，这将有助于共生研究和后生动物基因组结构的更好比较。