Often the evolution or diversification of life is likened to the shape of a tree. The branches from the trunk further branch, and basically, the branches never cross each other. But in the evolution of organisms, two completely different lineages may merge into one. Endosymbiotic evolution between two organisms at the cellular level, which eventually integrate them into a single organism, has given rise to mitochondria in present-day eukaryotes and chloroplasts in plant cells, and had a major impact on the diversity of organisms on Earth. In fact, this kind of symbiotic evolution is not rare but is occurring in the current natural environment. I am focusing on microbial systems that are considered to be in the middle of the evolution of cellular symbiosis and trying to elucidate how the integration of two different organisms proceeds and what kind of biological significance there is in the symbiosis, mainly using genome/transcriptome analysis.
Genome Evolution in Cellular Symbiosis
In the course of the evolution in the cellular symbiosis, the genomes of the two different organisms are thought to change dynamically influencing each other. I’m trying to unveil the principles of the genome evolution by analyses on the genomes of organisms from various stages of the symbiotic evolution.
- Report of a complete genome sequence of cyanobacterial symbiont in diatom cells (Nakayama et al. 2014 PNAS, Nakayama and Inagaki 2017 Sci. Rep.
- Discovery of relic nuclear genomes of symbiotic algae in dinoflagellate cells (Sarai et al. 2020 PNAS)
Understanding the role of cellular symbiotic relationships
Although many cases of microbial symbiosis have been reported, their ecological roles and biological significance are poorly understood. I am working with a variety of cellular symbiotic relationships, trying to understand the biological context that led them to the deep symbiotic relationships and the impact that the symbioses have on ecosystems.
- Discovery of cyanobacterial lineage hidden by a dinoflagellate host (Nakayama et al. 2019 PNAS)