December 30, 2020. By Kolemann Lutz
Researchers from the UK and USA genetically engineered the Rubisco enzyme in plants from highly efficient carbon capture and conversion mechanisms in algae cells, representing a key step for assembling algae pyrenoid-based CO2 concentrating mechanisms in plants.
Ribulose‐1,5‐bisphosphate carboxylase/oxygenase, or Rubisco, a key enzyme in photosynthesis, is distributed evenly throughout chloroplast stroma. Rubisco is essential for plants to capture and convert carbon dioxide. The enzyme operates at half its carbon fixation potential in most major stable crops such as rice,wheat, soybean, beats, spinach, potatoes, chlorella, sunflower, and others with the C3 photosynthetic, metabolic pathway.
To overcome this limitation, an international team of researchers became inspired to investigate the feasibility of using algae—tiny single-celled photosynthetic powerhouses living in oceans and other bodies of water where CO2 is scarce—to improve carbon sequestration in stable land-based crops.
Because CO2 spreads 10,000 times slower in H2O than in air and is also slow to equilibrate, aqueous algae species have difficulty accessing CO2. Some non-vascular land plants such as green algae have evolved highly efficient CO2 concentrating mechanisms (CCMs) that condense Rubisco into a liquid-like protein within the chloroplast called a pyrenoid, which acts as a center of carbon dioxide by maintaining a CO2-rich environment around rubisco enzymes. As the most abundant enzyme on Earth’s surface, Rubisco is responsible for about 95% of the carbon fixed in the biosphere.
"The defining feature of a pyrenoid is the matrix, a liquid-like condensate that contains nearly all of the cell's Rubisco," explains Jonikas, an Assistant Professor in the Department of Molecular Biology at Princeton.
Researchers from University of Edinburgh and University of Illinois reconstructed this pyrenoid-like structure by genetically engineering the Rubisco enzyme in plants so that it would behave more like an algal Rubisco. They then injected the Rubisco-binding protein, EPYC1, which has five Rubisco binding sites and is essential to algae’s CO2-concentrating mechanism, into the plant-algal hybrid.
After interaction between the intrinsically disordered EPYC1 protein and the small subunit of Rubisco (SSU), the CCM of alga Chlamydomonas reinhardtii is activated and the pyrenoid undergoes liquid-to-liquid phase separation.
After 32 days of growth under normal lighting, the transgenes of the Chlamydomonas appeared unaffected by the pyrenoid matrix, suggesting the environment inside higher plant chloroplasts is highly compatible with pyrenoid-type bodies.
This discovery represents a key step forward to assemble highly efficient CCM plants with algae-based pyrenoids, which could enhance crop yield potentials by up to 60%. Further research and testing will help understand how internal C3 plant biology within algae-CCM hybrid crops will react to greater amounts of CO2 intake.
Biomass feedstocks of algae on habitable regions in the inner Solar system hold great potential to help crops thrive in poor conditions including drought.
As greenhouses on Mars attempt to similarly replicate how they are grown on Earth, those greenhouses become much easier to construct and operate if their interior pressure is also very low.
As the Martian atmosphere is comprised of 95% CO2 and receives half the solar irradiance of Earth, adapting stable crops to help deactivate drought-sensing genes in hypobaria conditions and designing plants with highly efficient CO2 concentrating mechanisms will play an important role in increasing biomass production for food.
Research Paper. Nicky Atkinson, et al. Condensation of Rubisco into a proto-pyrenoid in higher plant chloroplasts. Nature Communications. December 9, 2020
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