Furthermore, CSS line plants demonstrated a higher photosynthetic rate than unmodified (wild type) rice under high CO 2 conditions, even though the amount of Rubisco in their leaves was over 30% less. Although many researchers have been able to improve Rubisco's catalytic characteristics, there have been no examples of such a large increase being achieved. This approximately doubled the catalytic rate to that which is equivalent to C 4 plants. In this CSS line (sorghum RbcS transferred/rice RbcS knocked out), the rice RbcS was completely replaced by sorghum RbcS, producing hybrid Rubisco. Next, the rice RbcS gene was knocked out in the sorghum RbcS incorporated rice plants using CRISPR/Cas9 gene editing. This rice with sorghum RbcS inserted (SS line), produced a chimera form of Rubisco from both sorghum RbcS and rice RbcS. They genetically modified rice (a C 3 plant) by transferring RbcS from the C 4 plant sorghum, successfully increasing the catalytic rate of rice Rubisco 1.5 times. This team has been focusing on conducting research into RbcS. The sequence of the amino acids in RbcS varies greatly between species. Rubisco is made up of two types of protein- large subunits (RbcL) and small subunits (RbcS). However, as the amount of atmospheric CO 2 is continuing to increase, it is believed that if C 3 plants had the same highly active type of Rubisco as C 4 plants then this could be utilized to improve photosynthetic ability. Rubisco with high catalytic activity tends to be inhibited easily by oxygen, therefore it cannot function effectively in atmospheric conditions where there is a low concentration of CO 2 if the plant doesn't have a CO 2-concentrating mechanism. The catalytic rate is low in C 3 plants, whereas in C 4 plants it tends to be high. C 4 plants, such as corn and sugarcane, on the other hand, have acquired a mechanism to concentrate CO 2 (the C 4 photosynthetic pathway). Most major crops, such as rice, wheat and soybean are C 3 plants that use regular photosynthesis. Rubisco's catalytic activity varies depending on the type of plant. Rubisco can mistakenly fix to O 2 molecules instead of CO 2 molecules, creating a toxic compound that needs to be recycled by the plant). However, Rubisco has two major drawbacks which limit photosynthesis: its catalytic activity is very low, and it can be inhibited by O 2 (ie. In photosynthesis, Rubisco is an enzyme that acts as the initial catalyst for the reaction which turns CO 2 into organic carbon. Thus improving photosynthesis in agricultural crops can increase their yield. Growth speed in plants is mainly determined by photosynthetic ability. It is hoped that the method to improve photosynthesis demonstrated in this study could be applied to many other crops which, like rice, have low Rubisco activity such as wheat, soybean and potato.Analysis of the protein structures indicated the possibility that the difference in amino acid type could affect the catalytic activity. The 102 amino acid found inside RbcS is isoleucine in rice and leucine in sorghum.This is believed to be the first time in the world that such a large increase in Rubisco activity has been achieved. A hybrid Rubisco consisting of rice RbcL and sorghum RbcS demonstrated a catalytic rate that was approximately 2 times higher than that of rice Rubisco.RbcS is an important factor for determining the speed of the catalyst. Rubisco consists of two types of protein large subunits (RbcL) and small subunits (RbcS).The low activity of the enzyme Rubisco, which is the catalyst for the reaction that turns CO 2 into organic carbon, limits the rate of photosynthesis. Photosynthesis determines a plant's growth rate.These results were published in the international scientific journal Molecular Plant on August 31. In the future, it is hoped that increasing the photosynthetic ability of agricultural crops will lead to increased yields.
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