Photosynthesis is the process by which green plants use light energy to convert carbon dioxide and water into energy-rich organic matter while releasing oxygen. Photosynthesis, which involves more than 100 steps, is surprisingly inefficient, and scientists have been trying to improve it for years. For the first time, scientists have recently modified the genes of soybean plants in an effort to improve their photosynthetic efficiency and increase soybean production.
Plants react slowly, and humans don’t get enough to eat
Nearly 10 percent of the world’s population will still be hungry in 2021, according to a new United Nations report. UNICEF projects that by 2030, more than 660 million people will face food shortages and malnutrition. The two main reasons for this are inefficient food production methods and poor growing conditions due to climate change.
Plants need light energy for photosynthesis, but under full light conditions, no plant can use all the light energy it absorbs. Excessive light, on the other hand, can potentially harm plants by inhibiting photosynthesis, reducing its efficiency and maximum photosynthetic rate (known as photoinhibition), and, in severe cases, destroying photosynthesis-related structures.
In fact, plants have developed a variety of photoprotective mechanisms during their evolution, among which heat dissipation dependent on the lutein cycle has attracted widespread attention in recent years. It plays an important role in dissipating excess energy and is considered as the main pathway of photoprotection.
Under low light conditions such as cloud cover, the reversal of lutein cycle direction often takes several minutes to complete
The lutein cycle mainly involves three components: violet xanthin (V), anther xanthin (A) and zeaxanthin (Z). In higher plants, V is first converted into intermediate product A and then Z is formed under strong light conditions. Among them, Z can directly quench the photoactive state of chlorophyll, allowing the excess light energy absorbed by plants to be lost in the form of heat energy. When the sun goes down or there are clouds in the sky covering the sun, the direction of transformation of lutein cycle needs to be reversed, that is, Z is finally converted back to V through A, so as to reduce the content of Z, so that leaves can continue to carry out full photosynthesis under the weak light intensity. However, the reversal of the direction of the lutein cycle often takes several minutes to complete, wasting valuable time that could otherwise be used for photosynthesis.
Improve plant efficiency
Among the many genes involved in photosynthesis, three genes (collectively known as VPZ) are key to the rate at which photoprotective mechanisms switch.
A 2016 study showed that upregulating VPZ in tobacco (because it’s easy to change its genes and because a single plant can produce a large number of seeds) can speed up the Z-V conversion process and thus increase its photosynthetic efficiency, And ultimately increase tobacco biomass (the amount of organic matter contained per unit area at any given time). However, in recent years, the academic community has been controversial on the effect of VPZ. Some researchers believe that the positive effect caused by VPZ may be related to the change of hormone content, and this increase effect may be limited by plant species, so it is difficult to apply in food production.
In order to resolve the above controversy, scientists further conducted field experiments on soybean, the world’s fourth largest food crop, to explore the effects of VPZ on photosynthesis and crop yield. They found that overexpression of VPZ significantly increased soybean seed yields, up to 33% higher than average. The study also found that not only did the seed yield increase, but the protein and oil content of individual soybeans also did not change, thus “adding quantity without losing quality,” underscoring the potential for this type of bioengineering to increase crop yields.
Tobacco crops modified by synthetic biology have greatly improved the efficiency of photosynthesis, and the plant size has also increased
The microscopic study of photosynthetic efficiency showed that, although there were some differences between different varieties and different years, the overexpression of VPZ in soybean accelerated the photoprotection shut-off speed in the shade-light transition process, thus improving the photosynthetic efficiency under the condition of unstable light intensity. In addition, although VPZ was overexpressed, the V content of soybean was still decreased and Z content was still increased under intense light conditions. In other words, this did not affect the initiation of the necessary photoprotection mechanism.
The yields of two very different crops, tobacco and soyabeans, both showed large increases under experimental conditions, suggesting that the approach is universally applicable. Can say, this method once mature, agriculture will usher in a qualitative leap.