Various Hydra species have been employed as model organisms since the 18^th 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 (species name has been changed to H. vulgaris) was sequenced a decade ago (Chapman et al., 2010) and the updated genome assembly, Hydra 2.0, was made available by the National Human Genome Research Institute in 2017. While H. vulgaris belongs to the non-symbiotic brown hydra lineage, the green hydra, Hydra viridissima, harbors algal symbionts and belongs to an early diverging clade that separated from the common ancestor of brown and green hydra lineages at least 100 million years ago (Schwentner and Bosch 2015; Khalturin et al., 2019). While interspecific interactions between H. viridissima and endosymbiotic unicellular green algae of the genus Chlorella have been a subject of interest for decades, genomic information about green hydras was nonexistent. Here we report a draft 280-Mbp genome assembly for Hydra viridissima strain A99, 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 H. viridissima assembly provides an important hydrozoan genome reference that will facilitate symbiosis research and better comparisons of metazoan genome architectures.

自¹⁸世纪以来，各种水螅物种已被用作模式生物。转基因和敲低技术的引入使它们成为研究再生、体轴形成、衰老、共生和全生的细胞和分子机制的理想实验系统。为了给遗传学研究提供重要参考，十年前对Hydra magnipapillata （种名已改为H. vulgaris ）基因组进行了测序（查普曼等人。 , 2010 ）和更新的基因组组装，Hydra 2.0，由国家人类基因组研究所于 2017 年提供。虽然H. vulgaris属于非共生棕色水螅谱系，但绿色水螅（Hydra viridissima ）拥有藻类共生体，属于至少在一亿年前从棕色和绿色九头蛇谱系的共同祖先中分离出来的早期分歧分支（施温特纳和博世 2015 ;哈尔图林等人。 , 2019 ）。虽然H. viridissima和小球藻属内共生单细胞绿藻之间的种间相互作用几十年来一直是人们感兴趣的主题，但有关绿水螅的基因组信息并不存在。在这里，我们报告了Hydra viridissima菌株 A99 的 280-Mbp 基因组组装草案，支架 N50 为 1.1 Mbp。 H. viridissima基因组包含估计 21,476 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幽门螺杆菌的特征。 viridissima ，例如对宿主-共生体相互作用很重要的先天免疫基因的多样化。因此， H. viridissima组装提供了重要的水螅动物基因组参考，将促进共生研究和更好地比较后生动物基因组结构。