Tunicates occupy the evolutionary position at the boundary of invertebrates and vertebrates. It exhibits adaptation to broad environmental conditions and is distributed globally. Despite hundreds of years of embryogenesis studies, the genetic basis of the invasive habits of ascidians remains largely unknown. The leathery sea squirt, Styela clava, is an important invasive species. We used the chromosomal‐level genome and transcriptome of S. clava to explore its genomic‐ and molecular‐network‐based mechanisms of adaptation to environments. Compared with Ciona intestinalis type A (C. robusta), the size of the S. clava genome was expanded by 2‐fold, although the gene number was comparable. An increase in transposon number and variation in dominant types were identified as potential expansion mechanisms. In the S. clava genome, the number of genes encoding the heat‐shock protein 70 family and members of the complement system was expanded significantly, and cold‐shock protein genes were transferred horizontally into the S. clava genome from bacteria. The expanded gene families potentially play roles in the adaptation of S. clava to its environments. The loss of key genes in the galactan synthesis pathway might explain the distinct tunic structure and hardness compared with the ascidian Ciona species. We demonstrated further that the integrated thyroid hormone pathway participated in the regulation of larval metamorphosis that provides S. clava with two opportunities for adapting to their environment. Thus, our report of the chromosomal‐level leathery sea squirt genome provides a comprehensive genomic basis for the understanding of environmental adaptation in tunicates.

中文翻译：

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革质海鞘（Styela clava）环境适应的基因组基础。


被囊动物处于无脊椎动物和脊椎动物边界的进化地位。它表现出对广泛环境条件的适应能力，并分布在全球范围内。尽管胚胎发生研究已经进行了数百年，但海鞘入侵习性的遗传基础仍然很大程度上未知。革质海鞘（ Styela clava ）是一种重要的入侵物种。我们使用了S的染色体水平基因组和转录组。 clava探索其基于基因组和分子网络的环境适应机制。与 A 型玻璃海鞘( C.Robusta ) 相比， S.robusta的大小。尽管基因数量相当，但clava基因组扩大了 2 倍。转座子数量的增加和优势类型的变化被认为是潜在的扩张机制。在S 。 clava基因组中，编码热休克蛋白70家族和补体系统成员的基因数量显着增加，冷休克蛋白基因水平转移到S .来自细菌的棒基因组。扩展的基因家族可能在S的适应中发挥作用。克拉瓦对其环境的影响。半乳聚糖合成途径中关键基因的丢失可能解释了与海鞘相比海鞘的独特外衣结构和硬度。我们进一步证明，整合的甲状腺激素途径参与了幼虫变态的调节，从而提供了S 。 clava有两次适应环境的机会。 因此，我们对染色体水平革质海鞘基因组的报告为了解被囊类动物的环境适应提供了全面的基因组基础。