On March 24th, 2022, team Zhao of Beijing Institute of Life Sciences of China Academy of Sciences and team of Chinese Academy of Sciences jointly published a paper entitled "An Extremely Simplified Macrogenome in Free Life" in the journal Molecular Biology and Evolution. Protozoa Fabrea salina ",reported their research results in the evolution strategy of eukaryotic genome. Starting with the protozoan Dunaliella salina, the team systematically analyzed the minimum genome of free-living heterotrophic eukaryotes for the first time, which provided new insights for the genome simplification theory of eukaryotes and revealed its genetic basis for adapting to high-salt environment.

Ciliates originated about 1 1 100 million years ago. They are a kind of single-celled eukaryotes with the most complex structure and function, and are important materials for studying the genome evolution of eukaryotes. Halophytic wild pea can grow and reproduce at the salinity of 35 ~ 180 ppt, with strong environmental adaptability, fast reproduction cycle and obvious resistance to harsh environment. Previously, the genome data of salt broad bean was blank, which affected the in-depth study of salt tolerance mechanism of salt broad bean. The research team established the culture system of halophyte for the first time, and reconstructed the high-quality megakaryogenome of halophyte by using single cell genome technology and nanopore sequencing technology. Its genome is only 18.35Mb, and 86.5% of the splicing sequences have bilateral telomeres, indicating that its genome is highly complete. In addition, * * * identified 99 18 protein coding genes, the number of which was the least among the published free-living ciliates, only equivalent to that of myxobacteria in prokaryotes. Such a concise and exquisite genome gives it a special position as a research model of biological evolution.

Furthermore, through comparison and evolutionary genomics analysis, the research team systematically revealed the simplified characteristics of halophyte genome, such as high gene density, micro-intron, homologous gene contraction and genome structure related to environmental adaptation, which provided direct evidence for the simplified evolution of eukaryotic predators' genome. Through the exploration of its salt tolerance mechanism, the amplification events and transcriptome level expression characteristics of genes related to high salt stress resistance in the genome were discovered, revealing the adaptive evolution of broad bean to high salt environment. It is found that the accumulation of phosphatidic acid may play an important role in resisting intracellular osmotic pressure. In addition, the team first described the morphological characteristics and transcriptome map of megakaryosome during sexual reproduction of halophyte. In this study, the minimum genome characteristics of free-living ciliates were analyzed for the first time, and the special position of halophyte as an evolutionary model of eukaryotic genome was clarified, which provided a unique perspective for understanding the simplification and evolutionary history of genome.

Zhang Bing, a doctoral student of China Academy of Sciences, and Hou Lina, a master student, are the first authors of the thesis, while Zhao from Beijing Institute of Life Sciences of China Academy of Sciences and Professor Cunji Medical College of China Academy of Sciences are the same authors. The research was supported by the National Natural Science Foundation of China and China Academy of Sciences, and assisted by the Protozoa Laboratory of China Ocean University.

Paper link:

/MBE/advance-article/doi/ 10. 1093/mol bev/msac 062/655389 1