Genetic modification increases grain yields, shortens rice growing time

By giving a Chinese rice variety a second copy of one of its own genes, researchers increased its yield by up to 40%. The change helps the plant take up more fertilizer, boosts photosynthesis and hastens flowering, which could contribute to bigger harvests, the group reports today in Science.

The yield gain from a single gene coordinating these multiple effects is "truly impressive," says Matthew Paul, a plant breeder 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 also be tried in other cultures, he adds; the new study reports preliminary results on wheat.

Crop yield is devilishly complex because many genes interact to influence plant productivity. For years, biotechnologists have searched for single genes that increase yield, without much luck. In recent years, they have shifted their interest to genes that control other genes, and thus multiple aspects of physiology, such as the uptake of nutrients from the soil, the rate of photosynthesis, and the orientation of plant resources. leaves to seeds. Modifying such a regulatory gene in maize results in a 10% higher yield, a major gain over the 1% increase per year achieved by traditional plant breeding.

To find other yield-boosting candidates, a team led by plant biologist Wenbin Zhou of the Chinese Academy of Agricultural Sciences (CAAS) combed through 118 rice and maize regulatory genes, which code for proteins called transcription factors, which other researchers had previously identified. probably important in photosynthesis. Zhou's team investigated whether any of the genes were activated in rice grown in low-nitrogen soil, as these genes might boost uptake of the nutrient. Increasing their activity in rice grown in ordinary soil could prompt the plant to take up even more nitrogen and produce more grain.

The team found 13 genes that turned on when rice plants were grown in nitrogen-poor soil; five resulted in a four- or more-fold increase in nitrogen uptake. They inserted an extra copy of one of the genes, known as OsDREB1C, into a variety of rice called Nipponbare which is being 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 grew faster as seedlings and had longer roots.

Good nutrition was one of the reasons: Isotope tracers revealed that plants with extra copies of OsDREB1C 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 about 38% more RuBisCO, a key enzyme in photosynthesis. Planted in the field for 2-3 years, the improved rice gave higher yields at three sites in China with climates ranging from temperate to tropical.

Importantly, the researchers also transformed a high-yielding rice variety often planted by farmers by adding an extra copy of the gene. These modified modern rice plants produced up to 40% more grain per plot than the controls, the researchers report. "That's a big number," says Pam Ronald, a rice geneticist at the University of California, Davis. "Amazing."

As in the greenhouse experiments, the modified plants in the field had both larger and more numerous grains. “What they did was take a very good [rice variety] and show that they can improve it,” says Steve Long, a plant physiologist at the University of Illinois, Urbana. -Champaign, who adds that the result is a "much more compelling" than improving a variety of research.

Altered plants also flowered earlier, giving them more time to spend on making grain. Faster flowering can provide other benefits, depending on the environment, such as allowing farmers to grow more crops per season or harvest crops before the summer heat sets in. However, although the modified Nipponbare flowered up to 19 days earlier, the widely grown variety of rice flowered only 2 days earlier.

To demonstrate broader potential, the team added the rice gene OsDREB1C to a research wheat variety and found the same kinds of effects. OsDREB1C and similar genes are present not only in rice, wheat and other grasses, but also in broadleaf plants. The researchers found comparable results by adding an extra copy to the well-studied mustard plant called Arabidopsis. This is consistent with a common role in acro...