Nitrogen fertilizer is made from natural gas. Extracting and burning natural gas harms life on our planet, so we should probably stop doing it (or at least try to cut back drastically). But food crops, like all plants, need this nitrogen. This is quite a puzzle, especially since the human population dependent on these crops is expected to increase over the next few decades, while the area of arable land is expected to decline.
In response, genetic engineers in China have developed crops that can thrive with less nitrogen, and they have created a variety of rice that yields 40-70% more than regular rice. It has more grains per branch, each grain particle is larger and denser, and the plants flower earlier. Most breeding methods currently used in cereal crops can only generate a yield increase of less than 1%, so this is a big problem.
One gene modifies several
Scientists began by studying proteins called transcription factors, which often control the expression of a set of genes often involved in various aspects of the same physiological function. In this case, the focus was on transcription factors already known to regulate photosynthesis.
To find the perfect target, the researchers screened a set of 118 transcription factors previously identified to regulate photosynthesis in rice and maize to find those that were also upregulated in response to light and at low levels. nitrogen. When they found one, they generated transgenic rice lines that produced many. Overexpressing a transcription factor like this instead of the individual genes it controls is like demanding to speak to the manager instead of being tossed around between various customer service reps in different departments.
The rice plants obtained were placed in fields with different environmental conditions: temperate fields near Beijing, tropical fields in Hainan province and subtropical fields in Zhejiang province.
Over three years, all rice plants showed increased photosynthetic capacity and improved nitrogen use efficiency. They had more chlorophyll and more and larger chloroplasts than wild-type rice. They also had more efficient nitrogen uptake in their roots than wild-type rice, and they had more efficient transport of that nitrogen from their roots to their shoots than wild-type rice. This increased their grain yield, even when the plants were grown with less nitrogen fertilizer.
Other experiments have been done with transgenic plants grown hydroponically and in rice paddies, and they have also performed well. Overexpressing the same transcription factor in a more sophisticated strain of rice (japonica, as opposed to the plebeian Oryza sativa which was used in most of the other experiments) as well as in wheat and Arabidopsis (the most commonly used model organism in plant biology) had similar effects on these important plants.
This transcription factor upregulates the activity of 345 genes, most of which are known to respond to salt, drought and cold. When scientists overexpressed one of these genes, a gene involved in early flowering, plants flowered earlier, but were stunted and had reduced grain yields. This is likely because the early flowering trait, isolated from the increased carbon and nitrogen utilization conferred by the transcription factor, did not allow the plants to accumulate sufficient resources in their growing time. shortcut.
The authors suggest that genome editing could be used rather than the transgenic techniques they relied on to overexpress this transcription factor in other crops so that they, too, can achieve a higher yield. Such cultivars could be useful in cases where growing seasons and field space can become limited and nitrogen fertilizers can become scarce – by, you know, rare scenarios like wildfires, floods and droughts. And the war.
Science, 2022. DOI: 10.1126/science.abi8455