As the saying goes, people are iron, rice is steel, a meal not to eat hungry panic. For green plants, the most indispensable ” food” is sunshine.
Photosynthesis is the largest and most important chemical reaction on the earth that green plants, algae and bacteria use sunlight. However, human beings have not fully grasped the secrets of plant photosynthesis.
A few days ago, a team from the Institute of Botany of the Chinese Academy of Sciences, led by academician Kuang Tingyun of the Chinese Academy of Sciences and researcher Shen Jianren, published a paper in the form of a long article in Science magazine, which for the first time analyzed the high-resolution structure of diatom’s main light-harvesting antenna protein, revealing the photosynthetic mystery of this extremely widespread phytoplankton that has long been ” prevalent” on earth.
Green Plants Do Not ” Eat” Green Light
About billions of years ago, the first photosynthetic organisms appeared on the earth and gradually adapted to the harsh environment of ancient earth.
They can use solar energy to synthesize organic substances necessary for their growth and development, and release oxygen, gradually transforming the earth’s environment.
After a long process of geological changes and adaptive evolution, photosynthetic organisms reshaped the composition of the earth’s surface and atmosphere, and evolved various life forms. Among them, people are most familiar with all kinds of green plants on land.
However, contrary to people’s intuition, for green plants, photosynthesis mainly absorbs red light and blue-violet light, while green light is hardly utilized by them. ” This phenomenon is related to the basic unit of light absorption by green plants.” Kuang Tingyun said.
In photosynthetic organisms, the functional unit for light absorption is called the light system. Among them, green plants have a structure called a light-harvesting antenna compound outside their light system, which mainly absorbs red light and blue-violet light, while the energy in the green band is basically not utilized by green plants – this is also the main reason why they appear green.
So, is there any photosynthetic organism in nature that can use green light? Scientists have turned their eyes to the vast ocean.
In 2014, Dutch scholars summarized the research progress of light-harvesting antenna proteins in recent decades, pointing out that light-harvesting antenna proteins rich in photosynthetic organisms can combine a large number of pigments and can collect solar energy in a wide light band.
For example, marine algae have colorful light-harvesting proteins, such as phycocyanin of blue algae, phycoerythrin of red algae, fucoxanthin chlorophyll protein of diatoms, etc. They can help algae to utilize solar energy in different wave bands at different seawater depths, especially diatoms that combine a large amount of chlorophyll C and fucoxanthin, and are even more prominent among them.
The ” Invisible Champion” in Plants
Diatoms are a kind of unicellular planktonic photoautotrophs covered with siliceous cell walls, belonging to unequal flagellate groups. At least tens of thousands of diatoms have been found.
” Diatoms can be said to be one of the most’ successful’ phytoplankton in modern oceans.” Shen Jianren said.
Diatoms have strong adaptability and are one of the main groups of marine red tides. They are distributed from the equator to the poles in the ocean and can even live in fresh water, soil and air.
On the other hand, diatoms have great advantages in photosynthesis.
Studies have shown that diatoms contribute about 20% of the earth’s primary productivity every year, that is, their ability to absorb carbon dioxide accounts for about 1 / 5 of the global ecosystem, higher than the contribution of tropical rain forests, and play an important role in the earth’s element cycle and climate change.
This made scientists very curious: why did the seemingly insignificant little diatoms live so ” successfully”?
Previous studies have proved that diatom’s unique light-harvesting antenna protein ” fucoxanthin – chlorophyll a/c protein complex” ( FCP ) has excellent blue-green light capture capability and strong light protection capability, which is one of the important reasons for its prosperity in the ocean.
However, the structure of diatom photosynthetic membrane protein has not been analyzed for a long time, which greatly limits the research on diatom photosynthesis. Kuang Tingyun and Shen Jianren’s team have been working on the structure and function of photosynthetic membrane proteins in higher plants and algae. They decided to jointly solve this unsolved mystery.
The maverick ” light – catching antenna”
In the past few decades, the mainstream view in academia is that the formation of diatom FCP is similar to that of higher plants.
However, Kuang Tingyun and Shen Jianren found that the models of higher plants and green algae could not fully explain the processes of pigment binding, energy capture and transfer, and photoprotection mechanism in diatom FCP protein.
” We are beginning to feel that this problem still needs to be solved by obtaining new experimental models through structural studies.” Kuang Tingyun said.
Relying on the advantages of sample purification and the experience of preparing high-resolution crystals, researchers quickly obtained very regular diatom FCP crystals. However, due to the combination of FCP proteins with a large number of pigments with similar molecular weights to protein polypeptides, it greatly increased the difficulty of analyzing the crystal structure.
Since then, researchers have collected high-precision data through various means, and finally analyzed the fine crystal structure of FCP dimer, a feather class diatom, Phaeodactylum tricornutum.
This study is the first structural analysis of photosynthetic membrane proteins of diatoms. It depicts for the first time the binding details of chlorophyll C and fucoxanthin in photosynthetic membrane proteins, illustrates the spatial arrangement of chlorophyll and fucoxanthin in FCP complexes, and reveals the structural basis for chlorophyll C and fucoxanthin to capture blue-green light and efficiently transfer energy. The binding mode of FCP dimer was revealed for the first time, providing the first clear experimental evidence for the research on the polymerization state of diatom’s main light-harvesting antenna protein in decades.
This high-resolution FCP structural model provides an important structural basis for studying the light energy capture, utilization and light protection mechanism of diatoms.
Reviewers of Science magazine commented that the FCP of diatoms is quite ” unique” and has some unusual characteristics among the light-harvesting antenna complexes of green plants. ” Diatoms are very important to the ecological environment, and their light-harvesting antenna complexes are significantly different from other known green plants, so the protein structure obtained this time is very interesting.”
The results provide new ideas and strategies for guiding the design of new crops and improving the ability of plants to capture light and protect light. Researchers hope that based on this achievement, scientists will design new crops that can utilize the green light band and have high efficiency in capturing light and protecting light, thus providing a new direction for the development of modern intelligent plant factories.