Supercharged biotech rice yields 40% more grain

2022-07-22

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

The yield gain 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 quite like that before.” The approach could be tried in other crops, too, he adds; the new study reports preliminary findings in wheat.

A crop’s yield is fiendishly complex because many genes interact to influence plant productivity. For years, biotechnologists have searched for single genes that augment yield, without much luck. In recent years they’ve shifted their interest to genes that control other genes, and therefore multiple aspects of physiology, such as taking up nutrients from the soil, setting the pace of photosynthesis, and directing resources from leaves to seeds. Modifying one such regulatory gene in maize gives a 10% higher yield—a major gain compared with the 1% increase per year achieved by traditional plant breeding.

To find other candidate yield boosters, 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 encode proteins called transcription factors, that other researchers had previously identified as likely important in photosynthesis. Zhou’s team sought to find out whether any of the genes were activated in rice grown in low-nitrogen soil, because such genes might boost uptake of the nutrient. Increasing their activity in rice grown in regular soil could nudge the plant to draw in even more nitrogen—and make more grain.

The team found 13 genes that turned on when rice plants were grown in nitrogen-poor soil; five led to a fourfold or greater boost in nitrogen uptake. They inserted an extra copy of one of the genes, known as OsDREB1C, into a rice variety called Nipponbare that’s 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 plants without the gene grew less well than control plants, whereas those with extra copies of OsDREB1C grew faster as seedlings and had longer roots.

Good nutrition was one reason: Isotopic tracers revealed the 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 one-third more chloroplasts, the photosynthetic organelles within plant cells, in their leaves and roughly 38% more RuBisCO, a key enzyme in photosynthesis. Planted in the field over 2 to 3 years, the enhanced 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 did 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 boasted both bigger grains and more of them. “What they’ve done is to take a very good [rice variety] and 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 a “lot more convincing” than improving a research variety.

The modified plants also flowered sooner, which gave them more time to devote to making grain. Faster flowering can offer other advantages, depending on the environment, for example allowing farmers to grow more crops per season or to harvest crops before damaging summer heat sets in. However, although the modified Nipponbare flowered up to 19 days earlier, the widely farmed variety of rice bloomed just 2 days earlier.

To demonstrate broader potential, the team added the rice OsDREB1C gene to a research variety of wheat and found the same types of effects. OsDREB1C and similar genes are present not just in rice, wheat, and other grasses, but also in broad-leaved plants. The researchers discovered comparable outcomes from adding an extra copy to the well-studied mustard plant called Arabidopsis. That’s consistent with a common role across the plant kingdom, suggesting other kinds of crops might be amenable to yield boosts from this modification.

Transgenic crops such as the rice Zhou’s team made are unacceptable to some consumers. But Zhou and colleagues say the same yield boost could be accomplished by editing the plant’s own genes, which in some countries is now more lightly regulated than transgenic engineering. Another benefit is that increasing nitrogen efficiency of crops could lessen pollution of streams and lakes from excess fertilizer that runs off fields, Ronald says. And improved photosynthesis will be vital for adding to global food supplies, notes Steven Kelly of the University of Oxford in a commentary. “You can get huge jumps if you’ve got the right transcription factor,” Long says. “I’m sure there’ll be more.”

Science, 22 July 2022
; https://science.org