By giving a Chinese variety of rice a second copy of one of its own genes, researchers increased its yield by up to 40%. The change helps the plant absorb more fertilizer, boosts photosynthesis and speeds up flowering, all of which can contribute to bigger harvests, the group reported today in Science.
The increase in yield from a single gene coordinating these multiple effects is “really impressive,” says Matthew Paul, a plant geneticist at Rothamsted Research, who was not involved in the work. “I don’t think I’ve ever seen anything like this before.” The approach could be tried in other crops, he adds; the new study reports preliminary findings in wheat.
Breeding a crop is fiendishly complicated because many genes interact to affect plant productivity. For years, biotechnologists have searched for single genes that increase yield without much success. In recent years, they have shifted their interest to genes that control other genes and therefore multiple aspects of physiology, such as nutrient uptake from the soil, determining the rate of photosynthesis, and channeling resources from leaves to seeds. Modifying one such regulatory gene in corn produced a 10 percent higher yield—a major gain compared to the 1 percent increase per year achieved by traditional plant breeding.
To find other yield-enhancing candidates, a team led by plant biologist Wenbin Zhou of the Chinese Academy of Agricultural Sciences (CAAS) studied 118 rice and maize regulatory genes that encode proteins called transcription factors that other researchers previously had identified as possibly important in photosynthesis. Zhou’s team sought to find out whether any of the genes were activated in rice grown in low-nitrogen soil, as such genes can increase nutrient uptake. Increasing their activity in rice grown in ordinary soil can prompt the plant to absorb even more nitrogen and make more grain.
The team found 13 genes that are turned on when rice plants are grown in nitrogen-poor soil; five resulted in a fourfold or greater increase in nitrogen uptake. They inserted an extra copy of one of the genes, known as OsDREB1C, in a rice variety called Nipponbare that is used for research. They also knocked out the gene in other individual rice plants. Greenhouse experiments by Shaobo Wei and Xia Li of CAAS showed that plants without the gene grew worse than control plants, while those with extra copies of OsDREB1C they grow faster as seedlings and have longer roots.
Good nutrition was one reason: isotopic markers revealed plants with extra copies of OsDREB1C they took up extra nitrogen through their roots and moved more of it to the shoots. The modified plants were also better equipped for photosynthesis; they had about a third more chloroplasts, the photosynthetic organelles in plant cells, in their leaves and roughly 38% more RuBisCO, a key enzyme in photosynthesis. Planted in the field for 2 to 3 years, the improved rice produced higher yields at three locations in China with climates ranging from temperate to tropical.
Importantly, the researchers also transformed a high-yielding rice variety commonly planted by farmers by adding an extra copy of the gene. These modified modern rice plants produced up to 40 percent more grain per plot than controls, the researchers reported. “That’s a big number,” says Pam Ronald, a rice geneticist at the University of California, Davis. “Unbelievable.”
As in the greenhouse experiments, the modified plants in the field boasted both larger grains and more of them. “What they’ve done is take a lot of good [rice variety] and they’ve shown they can make it better,” says Steve Long, a plant physiologist at the University of Illinois, Urbana-Champaign, who adds that the result is “much more compelling” than improving a research variety.
The modified plants also flower earlier, giving them more time to devote to grain production. Faster flowering can offer other advantages depending on the environment, such as allowing farmers to grow more crops per season or harvest before damaging summer heat sets in. However, although the modified Nipponbare flowered up to 19 days earlier, the widely cultivated rice variety flowered only 2 days earlier.
To demonstrate a broader potential, the team added rice OsDREB1C gene to a research wheat variety and found the same types of effects. OsDREB1C similar genes are present not only in rice, wheat and other grasses, but also in deciduous plants. The researchers found comparable results from adding an extra copy to the well-studied mustard plant, called mustard Arabidopsis. This is consistent with a general role in the plant kingdom, suggesting that other crop species may be susceptible to increased yield from this modification.
Transgenic crops like the rice that Zhou’s team made are unacceptable to some consumers. But Zhou and his colleagues say the same increase in yield can be achieved by editing the plant’s own genes, which in some countries is now more lightly regulated than transgenic engineering. Another benefit is that increasing the nitrogen efficiency of crops can reduce pollution of streams and lakes from excess fertilizer that runs off fields, Ronald says. And improved photosynthesis will be vital to adding to global food supplies, notes Stephen Kelly of the University of Oxford in a commentary. “You can get huge jumps if you have the right transcription factor,” says Long. “I’m sure there will be more.”