Periodic Reporting for period 2 - PhotoRedesign (Redesigning the Photosynthetic Light Reactions)
Période du rapport: 2021-10-01 au 2023-03-31
Photosynthesis is central to life on Earth because it uses the energy of sunlight to generate the oxygen we breathe and the food we eat. However, the fraction of the energy of sunlight reaching a plant which ends up as biomass or crop yield is only a few percent and even less under stressful conditions. Moreover, when analysing the efforts of plant breeding over the last decades it became clear that many characteristics of plants have already reached a state that is close to being optimal for agricultural use, while for photosynthesis there apparently exists a lot of space for further improvement.
Therefore, the PhotoRedesign project aims at enhancing photosynthesis, and to be more precise, the light reactions of photosynthesis that capture light and convert the captured light energy into molecules that can then be used to convert carbon dioxide from the atmosphere into organic biomolecules. As a matter of fact, nature has invented several types of organisms that can perform photosynthesis. Since they all trace back to a common ancestor, these organisms are still genetically compatible, meaning that their genes should work also in the other organisms. We selected three very distantly related organisms that can utilise very different parts of the sun light for photosynthesis, namely cyanobacteria with a blue-green coloration, plants that are green and purple bacteria that have the colour purple. As mentioned before, their different colours indicate already that they can use very different portions of the sun light for photosynthesis.
Our goal is to combine the different components of these three organisms responsible for light capture. Ideally, this will create an organism which becomes black, because it uses all parts of the sunlight. As a test laboratory to achieve this we are using the cyanobacterium Synechocystis because it is easily accessible to genetic manipulation.
Generating such a black cyanobacterium would represent on itself already a breakthrough in the research field of enhancing photosynthesis. Cyanobacteria are important model organisms for biotechnological applications and such black cyanobacteria might provide the basis for a better production of biofuels and other valuable compounds. Equally important is that results obtained in the cyanobacterium can be transferred to plants which provide our food. To this end, the cyanobacterium can be used as a test laboratory for enhanced photosynthesis which will then be rebuilt in its optimized form in plants.
Therefore, the PhotoRedesign project aims at enhancing photosynthesis, and to be more precise, the light reactions of photosynthesis that capture light and convert the captured light energy into molecules that can then be used to convert carbon dioxide from the atmosphere into organic biomolecules. As a matter of fact, nature has invented several types of organisms that can perform photosynthesis. Since they all trace back to a common ancestor, these organisms are still genetically compatible, meaning that their genes should work also in the other organisms. We selected three very distantly related organisms that can utilise very different parts of the sun light for photosynthesis, namely cyanobacteria with a blue-green coloration, plants that are green and purple bacteria that have the colour purple. As mentioned before, their different colours indicate already that they can use very different portions of the sun light for photosynthesis.
Our goal is to combine the different components of these three organisms responsible for light capture. Ideally, this will create an organism which becomes black, because it uses all parts of the sunlight. As a test laboratory to achieve this we are using the cyanobacterium Synechocystis because it is easily accessible to genetic manipulation.
Generating such a black cyanobacterium would represent on itself already a breakthrough in the research field of enhancing photosynthesis. Cyanobacteria are important model organisms for biotechnological applications and such black cyanobacteria might provide the basis for a better production of biofuels and other valuable compounds. Equally important is that results obtained in the cyanobacterium can be transferred to plants which provide our food. To this end, the cyanobacterium can be used as a test laboratory for enhanced photosynthesis which will then be rebuilt in its optimized form in plants.
In the first two years of the project we have gained important insights into what is needed to rebuild photosystems from plants into the model cyanobacterium Synechocystis. Having a cyanobacterium with plant photosystems will be important to us when testing enhanced variants of photosynthesis for a later use in crop plants. So far, we have been able to transfer one plant photosystem into Synechocystis and we are working now on bringing this photosystem to full activity. In addition, we have done experiments that pave the way to produce pigments and photosystems from purple bacteria into Synechocystis and to rebuild modules that capture light in plants in Synechocystis. Last not least, we have grown Synechocystis cells for a long time under very intensive light to prepare them for the expected effects of enhanced photosynthesis, i.e. more influx of light energy. The Synechocystis cells responded to this by adapting, i.e. by evolving changes in their genes that made them more tolerant to high light without losing much performance under low light. This „hardened“ cyanobacteria will be the ideal host for the enhanced photosynthesis that we are developing.
Transferring photosystems from plants to prokaryotes and making them functional again in this distantly related but still very different environment is very challenging and has not been attempted or succeeded before. We expect to further enhance the activity of this foreign photosystem in the course of the project. The transfer of purple bacterial pigments and photosystems into a cyanobacterium is even more difficult than transferring a plant photosystem into a cyanobacterium, but we have identified tentative obstacles and are working our way around those. With respect to creating a chassis for hosting the enhanced photosynthesis we have already provided strains that can easily cope with much more influx of energy such that we are well prepared for embedding a super-performing photosynthesis in such strains. Although the concept to use evolution in the laboratory is known for some time in model microorganisms, our experiments have been the first of its kind for high light tolerance of a microorganisms that performs photosynthesis.