Kamikawa Ryoma, Mochizuki Takako, Sakamoto Mika, Tanizawa Yasuhiro, Nakayama Takuro, Onuma Ryo, Cenci Ugo, Moog Daniel, Speak Samuel, Sarkozi Krisztina, Toseland Andrew, van Oosterhout Cock, Oyama Kaori, Kato Misako, Kume Keitaro, Kayama Motoki, Azuma Tomonori, Ishii Ken-Ichiro, Miyashita Hideaki, Henrissat Bernard, Lombard Vincent, Win Joe, Kamoun Sophien, Kashiyama Yuichiro, Mayama Shigeki, Miyagishima Shin-Ya, Tanifuji Goro, Mock Thomas, Nakamura Yasukazu
Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Department of Informatics, National Institute of Genetics, Research Organization of Information and Systems, Shizuoka 411-8540, Japan.
Sci Adv. 2022 Apr 29;8(17):eabi5075. doi: 10.1126/sciadv.abi5075.
Secondary loss of photosynthesis is observed across almost all plastid-bearing branches of the eukaryotic tree of life. However, genome-based insights into the transition from a phototroph into a secondary heterotroph have so far only been revealed for parasitic species. Free-living organisms can yield unique insights into the evolutionary consequence of the loss of photosynthesis, as the parasitic lifestyle requires specific adaptations to host environments. Here, we report on the diploid genome of the free-living diatom (35 Mbp), a nonphotosynthetic osmotroph whose photosynthetic relatives contribute ca. 40% of net oceanic primary production. Comparative analyses with photosynthetic diatoms and heterotrophic algae with parasitic lifestyle revealed that a combination of gene loss, the accumulation of genes involved in organic carbon degradation, a unique secretome, and the rapid divergence of conserved gene families involved in cell wall and extracellular metabolism appear to have facilitated the lifestyle of a free-living secondary heterotroph.
在几乎所有真核生物生命之树中带有质体的分支中都观察到了光合作用的次生丧失。然而，到目前为止，基于基因组对从光合生物向次生异养生物转变的洞察仅在寄生物种中得以揭示。自由生活的生物体能够为光合作用丧失的进化后果提供独特的见解，因为寄生生活方式需要对宿主环境进行特定的适应。在此，我们报告了自由生活的硅藻（35兆碱基对）的二倍体基因组，这是一种非光合渗透营养生物，其光合亲属贡献了约40%的海洋净初级生产力。与光合硅藻和具有寄生生活方式的异养藻类进行比较分析表明，基因丢失、参与有机碳降解的基因积累、独特的分泌组以及参与细胞壁和细胞外代谢的保守基因家族的快速分化似乎共同促成了自由生活的次生异养生物的生活方式。
