Rubisco and Crop Output: Difference between revisions

Rubisco is the most common protein in the world! Although this is true, just because it is the most abundant doesn’t mean it’s the most useful. Rubisco has some problems working correctly. Compared to other enzymes, the rate of the carboxylation reaction with Rubisco is 3 s-1. This is extremely slow. Another problem with Rubisco is that oxygen, as well as carbon dioxide, can fit into the binding site. This is because they both are similar in size and shape. It is difficult for Rubisco to distinguish which is which. (Goodsell) If this happens, and it does, phosphoglycolate can be made, and this is very toxic. This is Rubisco’s wasteful side chain reaction. To fix these mistakes, it is very costly to the plant, meaning, it costs ATP to fix this. Now the plant has to transport the glycolate across multiple membranes, losing Co2 and making more reactions occur. Depending on varying temperatures Rubisco is working with, its error rate can range from 20- 40%! (Alber, et. Al)

Most plants are categorized into C3 and C4 plants. This is based off of the climate they are found in. C3 plants are more accustomed to cooler temperatures, as opposed to C4 plants that are found in warmer temperatures. Photorespiration is more likely to occur in C4 plants than C3 plants, because C4 plants are more accustomed to warmer temps. As temperatures begin to increase, so does photorespiration. Plants are more likely to dehydrate in the warm weather. This forces them to close the stomata in order to conserve water. When the plant closes the stomata, CO2 is prevented from entering the leaf. Photorespiration is when Rubisco binds O2 instead of CO2. This is contrary to the general pattern of photosynthesis, where Rubisco binds to CO2 instead of O2. Rubisco acts differently in C4 than C3 plants. To reduce photorespiration, C4 plants can “harvest” CO2 in bundle sheath cells. They also are useful at collecting carbon and using less water in warmer climates.  

The major problem researchers have been working to change with Rubisco is the oxygenation instead of the carboxylation. The reason this is a problem is because the plant has to fix this, making this issue energetically unfavorable, by losing around 30% of the plants ATP in that step. When Rubisco binds oxygen instead, crop yield becomes lower, this is because it only makes half the product amount of 3-Phosphoglycerate. This limits how many times a plant can undergo the Calvin Cycle to make sugar. When temperatures begin to increase it is even more of an inconvenience and much more difficult for a plant to fix this problem. If we can fix this issue, Rubisco can not only be more successful with photosynthesis, but extremely successful with changing crop growth and quantity. <ref>PMID: 27935049</ref>

“In recent times, major advances in Rubisco engineering have been achieved through improvement of our knowledge of Rubisco synthesis and assembly, and identifying amino acid catalytic switches in the L-subunit responsible for improvements in catalysis. in crops such as rice will require further advances in chloroplast bioengineering and Rubisco biogenesis.” <ref>PMID: 27935049</ref> Carefully modifying genes in specific major functioning subunits can help change Rubisco to adjust the Calvin cycle and save ATP. This all starts in the chloroplasts, where Rubisco works. Improvements can also be made in C3 plants as well. They can be engineered to harvest Co2 as well, just like C4 plants. There are also alternative pathways that can be created to avoid oxygenation. <ref>PMID: 27935049</ref>