What are your goals?

Cyanobacteria, the forerunners of today’s photosynthetic organisms, are thought to have existed at least two billion years ago. After their appearance, photosynthetic organisms brought about major changes in the global environment, and conversely, they also had to withstand environmental change through constant evolution, producing as a result the huge diversity of photosynthetic organisms adapted to different environments that exists today. We are endeavoring to study the various mechanisms of photosynthesis used by different photosynthetic organisms, and compare those mechanisms to develop an understanding of how they evolved and adapted to different environments, with the aim also of conducting applied research based on our findings. To such an end, we are focusing in particular on protein complexes.

Figure 1. Plant photosystem complexes separated out using electrophoresis

Proteins have individual functions, but they are also known to frequently bond with other proteins to create complexes that have their own functions. As such, it’s important to our understanding of how organisms live that we study not only the functions of individual proteins, but also those of protein complexes. Particularly the photosynthetic apparatuses that carry out photosynthesis, namely photosystems I and II and light-harvesting antennae complexes, are extremely sophisticated molecular machines composed of multiple proteins combined with chlorophyll and carotenoid pigments. Learning about the functions and structure of these apparatuses along with their evolution and current environment is essential to our understanding of the way photosynthetic organisms function.

 

What kind of methods do you use in your research?

We use electrophoresis to separate out the protein complexes of plants, algae, cyanobacteria and other photosynthetic organisms (Figure 1). We then comprehensively identify the separated protein complexes using mass spectrometers. Lastly, we analyze and compare the separation patterns of individual proteins to predict protein complex structures. This method has enabled us to predict the existence of protein complexes that have not yet been discovered. We are also using bioinformatics, the computer-based analysis of complex biological data, to combine our findings with other biological knowledge to boost the precision of our prediction of unknown protein complexes.

We use genetic, molecular biological, biochemical, spectroscopic and other approaches to conduct detailed analysis of any newly discovered protein complexes that we find particularly interesting so as to try to reveal their functions.

Figure 2. An example of protein complex prediction by comparing the protein separation pattern.

In our research group, we are equipped to separate out photosynthetic apparatus components by electrophoresis while maintaining their photosynthetic activity. This lets us isolate the photosynthetic apparatuses of various photosynthetic organisms to investigate their protein and pigment composition and photosynthetic characteristics in detail. Through our analyses, we’re learning more and more about the structure and functions of photosynthetic apparatuses that have been unknown up to now. We’re currently comparing the photosynthetic apparatuses of different photosynthetic organisms to investigate the specific roles played by those apparatuses in the lives of the organisms concerned, and the evolutionary significance to those organisms of acquiring such apparatuses.

 

What do you plan to do next?

There is a very close relationship between the evolution of photosynthetic organisms and global environmental changes, so much so that you could say that they have coevolved. We’re currently focusing on analyzing the evolution of photosynthetic organisms in relation to glacial periods. Photosynthetic organisms can’t survive without photosynthesizing, and so we’re interested in finding out how green algae in particular managed to survive the severe conditions of glacial periods, and how their survival affected their subsequent evolution, particularly how it contributed to their invasion of terrestrial environments.

Also, our comprehensive analysis of protein complexes of photosynthetic organisms has, albeit quite by coincidence, revealed a new mechanism used by plants to control nitrogen metabolism. Nitrogen metabolism in plants is closely related to photosynthesis, and furthering our understanding of it is important also from the agricultural perspective. Hopefully, we will be able to contribute to understanding of nitrogen metabolism in plants by conducting further research to elucidate this mechanism.

Another task that we are engaged in is the creation of our own public online database of the results of our comprehensive analyses of the protein complexes of photosynthetic organisms. It is my hope that allowing photosynthesis researchers throughout the world to use this database will help them to find new protein complexes from the perspective of their particular interests.