A new "green revolution" may come: Chinese scholars find ways to produce high yields and fewer fertilizers

In the early morning of August 16th, Beijing time, Fu Xiangdong, a researcher at the Institute of Genetics and Development of the Chinese Academy of Sciences and director of the Center for Molecular Agricultural Biology, as a corresponding author, published a six-year new output online in the top academic journal Nature. This achievement may herald the arrival of a new "green revolution": crops can achieve high yield and low fertilizer.

In the 1960s, the first "green revolution" featuring the reduction of crop height and semi-dwarf breeding has doubled the world's rice and wheat production and solved the problem of food and clothing.

More than half a century later, rice and wheat branded with the "green revolution" made experts in the agronomy field troubled by another new problem. "The height of semi-dwarf crops has become shorter, making it insensitive to chemical fertilizers. The consequence is that the utilization efficiency of nitrogen fertilizers has also decreased, so that our farmers now fertilize in large quantities, but they do not get the output they really want. At the same time, it also caused environmental problems. "Fu Xiangdong said in an interview with Peng Mei News reporter ().

The team led by Fu Xiangdong has long studied how to obtain high-yield and less-fertile crops. Fu Xiangdong said, "This is a common goal of breeding experts, but it has not been resolved for a long time." The results published this time, the transcription factor GRF4 (GROWTH-REGULATING FACTOR 4), which is no stranger to the agricultural field, has not been discovered before. The functions of the show are displayed, bringing the above goals closer to the possibility of achieving them.

"It turns out that it is not clear why the efficiency of nitrogen fertilizer use of 'green revolution' varieties will decline, so our research is directed at this problem. GRF4 has enabled us to find a new strategy that is to maintain the height of crops and make it resistant Lodging, while improving the efficiency of nitrogen fertilizer utilization, achieved the goal of less input and more output. "Fu Xiangdong said.

In a review article published simultaneously by Nature, Fanmiao Wang and Makoto Matsuoka, two industry experts from the Bioscience and Biotechnology Center of Nagoya University in Japan, commented on the results of Fu Xiangdong and others, "A new green revolution is coming. "They believe that this research will inspire other researchers to discover more genes and molecules related to nitrogen use.

Fu Xiangdong himself said, "This work not only maintains the semi-dwarf advantages of the green revolutionary varieties, but also improves the efficiency of nitrogen fertilizer utilization. We should stand on the shoulders of giants and take a step forward. This is also in line with the current domestic The breeding concept of less input, more output, and environmental protection, I personally feel that the impact on the breeding of major crops is still quite large. "

The merits and demerits of the "green revolution"

Around the 1960s, chemical fertilizers were widely used in the agricultural field. The use of fertilizers promotes the growth and development of crops, and the crops that are growing happily theoretically will result in higher yields.

But at the same time there was a drawback. The higher the plant height, the larger the ears, the heavier the crop load, especially in the harsh environment of storms and rains, it is easy to fall. That is to say, after the use of chemical fertilizers, the problem of crop lodging has occurred, and the occurrence of lodging has naturally decreased.

"This has led to the breeding of semi-dwarf crops, and the crop's center of gravity has collapsed. This has doubled the world's rice and wheat production, which is the so-called first 'green revolution.' Fu Xiangdong said .

Fu Xiangdong mentioned, "All rice and wheat varieties now carry the 'Green Revolution' gene."

While solving lodging resistance and fertilizer resistance, another problem was gradually realized in the 1990s.

"From the 1960s to the 1990s, with the increase in the use of chemical fertilizers, production increased. However, after the 1990s, an inflection point appeared. The use of chemical fertilizers has been rising, but the output has not increased," Fu Xiangdong said Farmers all hope to apply a larger amount of fertilizer to obtain higher yields, but it is counterproductive.

It is from that time onwards that the inefficient use of nitrogen fertilizers by existing major crops has become a long-awaited puzzle. At present, the average utilization rate of rice nitrogen fertilizer in China is only 35%.

At the same time, environmental problems caused by the large-scale use of nitrogen fertilizers are increasing. "Domestic use of fertilizers is three times the world average. This pressure is very large. Especially in China, it is very important to improve the efficiency of nitrogen fertilizer utilization."

At present, China's rice cultivation area accounts for 20% of the world's rice cultivation area, but China's rice nitrogen fertilizer consumption accounts for 37% of the global rice nitrogen fertilizer consumption. Sustaining a large amount of nitrogen fertilizer investment not only wastes resources and energy, but also aggravates a series of ecological and environmental pollution problems such as soil acidification, water eutrophication and agricultural greenhouse gas emissions.

"In order to increase the output a little bit, a lot of fertilizer needs to be applied. After 50 years, we have encountered new problems." Fu Xiangdong said.

The key to the problem: GRF4

This research started six years ago, and Fu Xiangdong's group set out to find the cause of the low nitrogen utilization efficiency.

Taking rice as an example, the research team compared a large number of varieties with the "green revolution" gene (SD1, allele mutations will cause semi-dwarfing), and studied their absorption and assimilation of nitrogen fertilizer (the conversion of inorganic nitrogen in the plant into organic Process of nitrogen).

"We found that some varieties have a higher nitrogen absorption capacity and some varieties have a lower absorption capacity, but they all carry the 'Green Revolution' gene, which is used by breeders." Fu Xiangdong said.

In the paper, the research team selected 36 indica rice varieties. Hydroponic cultivation under sufficient nitrogen fertilizer conditions was used to measure the nitrogen uptake of various varieties for 4 weeks. Similarly, various varieties were planted in soil under high fertilizer conditions to collect yield data. The results show that there is a maximum three-fold difference in nitrogen absorption efficiency among 36 varieties.

At the same time, the research team found an interesting phenomenon, that is, all the current high-product species, their nitrogen absorption capacity is not the highest. "We were still very happy to see this result at the time, which means that there is room for improvement in all varieties now."

The research team used the above varieties to build a genetic group to understand which gene can determine the increased absorption capacity of nitrogen fertilizer. Finally, the research team found the key gene for efficient use of nitrogen fertilizer, namely GRF4, through QTL mapping and map cloning.

In fact, scientists are not new to GRF4. Previous studies have shown that GRF4 can regulate ear size and growth molecule cytokinin levels, which are all related to yield. Some studies also believe that GRF4 may be involved in gibberellin (a plant hormone) signal transmission pathway, which plays an important role in regulating plant growth and development. However, the specific molecular mechanism is not very clear.

After finding the key genes, the research team transformed rice on the basis of the "green revolution" varieties and up-regulated the expression of GRF4. The results showed that, compared with the control group "Green Revolution" varieties, rice with up-regulated GRF4 expression had enhanced nitrogen absorption capacity.

GRF4 and "ally" are provoked in semi-dwarf rice

The next question for the research team is what is the mechanism by which GRF4 determines nitrogen absorption efficiency?

The paper proposed the interaction between GRF4 and SLR1, a member of the DELLA protein family in rice.

What is DELLA protein? This will go back to the "green revolution" mechanism. "During my PhD and postdoctoral studies (around 2000), many research groups, including my mentor, were looking for the mechanism of the 'green revolution' variety and which genes regulate plant growth accordingly." Fu Xiangdong said.

After a long time, it was discovered that the "green revolution" is basically the increase in the accumulation of DELLA protein, and DELLA protein will inhibit the growth of plant height, and the plant will naturally become semi-dwarfed.

Specifically in rice, it shows the mutation of SD1 allele, and in wheat, it is the mutation of Rht allele. Under normal circumstances, gibberellin promotes crop growth by destroying the DELLA protein. However, in the case of the above-mentioned gene mutation, the gibberellin activity of crops is reduced.

In the latest achievement of Fu Xiangdong and others, it was found that GRF4 can bind to the promoter of genes involved in nitrogen absorption and metabolism, and increase nitrogen absorption and metabolism by activating these downstream genes. At the same time, GRF4 needs the help of another key "ally" GIF1.

SLR1, a member of the DELLA protein family in rice, has a role similar to "provocation of allies", inhibiting the role between GRF4 and GIF1, thereby inhibiting the transcriptional activation activity of GRF4, and ultimately inhibiting nitrogen absorption and metabolism.

In addition, because of the interaction between GRF4 and the DELLA protein family, the research team confirmed that GRF4 is also a key element of the gibberellin signal transduction pathway. Gibberellin promotes the degradation of DELLA protein, thereby enhancing the transcriptional activation activity of GRF4, and realizes the coordinated regulation of photosynthetic carbon fixation capacity of plant leaves and root nitrogen absorption capacity, thereby maintaining the balance of plant carbon-nitrogen metabolism.

The study finally confirmed that GRF4 is a positive regulator of carbon-nitrogen metabolism in plants, which can promote nitrogen absorption, assimilation and transport pathways, as well as photosynthesis, sugar metabolism and transport, etc., and thus promote plant growth and development.

Fu Xiangdong and others believe that the discovery of new functions of GRF4 not only enriches the understanding of the molecular mechanism of gibberellin signaling, but also clarifies the reasons for the low efficiency of nitrogen fertilizer utilization in the "green revolution" dwarf rod breeding at the molecular level, and proposes a clear solution.

New "green revolution" may come

It is worth noting that this is not the first time Fu Xiangdong's team has found a secret to improve the efficiency of nitrogen use.

In 2014, the research team found another key gene, DEP1, which can also improve the efficiency of nitrogen use. "The two discovered molecular mechanisms are different. This time is the gibberellin signaling pathway, which was the G protein signaling pathway at the time. The two mechanisms will not antagonize each other (inhibition), so when combined together It has a good effect. "

Fu Xiangdong believes that the combination of the above two genes used in rice, the future application prospects may be greater.

While the aforementioned Fanmiao Wang and Makoto Matsuoka commented on the results of Fu Xiangdong and others, the research will inspire other researchers to discover more genes and molecules related to nitrogen utilization.

When there are more and more options for improving nitrogen utilization efficiency, a new "green revolution" will come. Fanmiao Wang et al.

Fu Xiangdong and his long-term research work, "Our laboratory's philosophy is that there are many ways to reduce the amount of fertilizer used, but it must be to reduce the amount of fertilization on the premise of ensuring that the yield is not reduced, because this can really be used by breeders. And farmers accept. "

And this latest achievement or a highly accepted breeding option. "First, it is more efficient at absorbing and utilizing nitrogen; second, it can increase yield; third, it can make plant stems thicker and more resistant to lodging. These three traits are very beneficial to agricultural production. "Fu Xiangdong said.

How to evaluate this 6-year work? Fu Xiangdong lamented that the first "green revolution" solved the problem of yield, but left the problem of nitrogen fertilizer utilization efficiency. Now our work not only maintains the semi-dwarf advantages of the "green revolution" varieties, but also improves the efficiency of nitrogen fertilizer utilization. "It should be standing on the shoulders of giants and taking another step forward. It is also in line with the current domestic breeding philosophy of less input, more output and environmental protection. I personally feel that the impact on the breeding of major crops is still quite large."

However, Fu Xiangdong emphasized that this is only a theoretical breakthrough. "Told us that there is such an application prospect, and the real application prospect still needs to be proven by the breeder's frontline practice." His team is currently working with breeding experts to carry out related work, "We hope to find more excellence, etc. Alleles are selected by breeders. Although each breeder has his own philosophy, we hope to provide them with some good materials. "

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