On March 24, 2022, Zhao Fangqing's team from the Beijing Institute of Life Sciences, Chinese Academy of Sciences, and Miao Miao's team from the University of Chinese Academy of Sciences collaborated to publish a study titled "An extremely streamlined macronuclear genome in the free-living protozoan Fabrea salina" in the journal Molecular Biology and Evolution.
paper, reporting their research results on eukaryotic genome evolution strategies.
Starting from the protozoan Fabrea salina, the team systematically analyzed for the first time the smallest genome of a currently known free-living heterotrophic eukaryote, providing new insights into the theory of eukaryotic genome streamlining and revealing its high-salt environment.
Genetic basis of environmental adaptation.
Ciliates originated about 1.1 billion years ago and are a class of single-cell eukaryotes with the most complex structures and functions. They are important materials for studying the evolution of eukaryotic genomes.
The salt bean beetle can grow and reproduce at a salinity of 35 to 180 ppt. It has strong environmental adaptability, a fast reproduction cycle, and significant resistance to harsh environments.
Previously, the genome data of salt broad bean has been blank, which has affected the in-depth research on the salt tolerance mechanism of salt broad bean.
The research team first established a culture system for the salt fava bean, and used a combination of single-cell genome technology and Nanopore sequencing technology to reconstruct a high-quality salt fava bean macronuclear genome.
Its genome is only 18.35Mb, and 86.5% of the spliced ??sequences have bilateral telomeres, indicating that its genome is highly complete.
In addition, *** identified 9918 protein-coding genes, which is the smallest number among published free-living ciliates and is only equivalent to the number of genes in myxobacteria in prokaryotes.
Such a simple and elegant genome gives it a special status as a model for studying biological evolution.
The research team further used comparative and evolutionary genomics analysis to systematically reveal the high gene density, microintrons, homologous gene shrinkage and other genome streamlined features of the salt faba bean, as well as the genome structure related to environmental adaptation, providing insights into eukaryotic predators.
Direct evidence for the evolution of genome simplicity.
By exploring its salt tolerance mechanism, we found amplification events and transcriptome-level expression characteristics of genes related to high-salt stress resistance in the genome, revealing the adaptive evolution of the salt faba bean to high-salt environments.
Studies have found that the accumulation of phosphatidic acid may play an important role in resisting high intracellular osmotic pressure.
In addition, the team described for the first time the morphological characteristics and transcriptome profile of the macronucleus during sexual reproduction in the salt fava bean.
This study is the first to analyze the minimalist genome characteristics of a free-living ciliate, clarifies the special status of the salt faba bean as a model for studying eukaryotic genome evolution, and provides a unique perspective for understanding the simplification and evolutionary history of the genome.
Zhang Bing, a doctoral candidate at the University of Chinese Academy of Sciences, and Hou Lina, a master's student at the University of Chinese Academy of Sciences, are the co-first authors of the paper. Researcher Zhao Fangqing of the Beijing Academy of Biological Sciences, Chinese Academy of Sciences, and Professor Miao Miao of Cunji Medical College of the Chinese Academy of Sciences are the co-corresponding authors.
The research received financial support from the National Natural Science Foundation of China and the Chinese Academy of Sciences, and received help from the Protozoa Laboratory of Ocean University of China.