Height is important for plants. Short crops can carry more grain without bending under their own weight, a key trait that helped fuel the Green Revolution in the 1960s. But tall plants are better at surviving long floods. Now, researchers have found two genes that together help control the height of rice plants: one that accelerates stem lengthening and another that acts as a brake. If the system is similar in other plants, scientists say it could be useful in breeding many types of crops.
"This could be one more great tool in the toolbox," says Julia Bailey-Serres, a rice biologist at the University of California, Riverside, who was not involved in the new research.
In the mid-20th century, plant breeders typically selected varieties of wheat and rice with short stems; These plants dedicated more resources to grain and were less likely to fall in strong winds or rain. Later, biologists discovered that these varieties, at certain points in their development, either produce less hormone called gibberellic acid (GA) or are unable to respond to their signals to lengthen their stems. The side effects of those mutations can include young plants that sometimes emerge from the soil too early in drought-prone regions.
Plant molecular geneticist Motoyuki Ashikari from Nagoya University and colleagues have been studying rice varieties that survive long, deep floods by growing taller, and quickly, if necessary, up to 25 centimeters per day. So-called "deep-water rice" is grown in areas of the delta, mainly in Southeast Asia, where slow seasonal flooding can reach 1 meter or more. Previous work had shown that when plants are submerged, ethylene gas accumulates in their tissues and triggers GA production. Ashikari and his colleagues wanted to know how GA makes stems grow in deep-sea rice varieties.
The team compared the DNA of one species of deep-water rice with another variety of rice that can only grow in shallow water. They soon located the two genes, which they called ACE1 (internode lengthening accelerator) and DEC1 (decelerator of the lengthening of the internode). Greenhouse experiments showed what genes did: in deep-water rice, ACE1 turns on when plants are covered in water, stimulating cell division in their stems and helping them to grow, the researchers reported this week in Nature. But a typical variety of shallow water, which has a mutation in ACE1, did not lengthen its stem when it was flooded.
In other experiments, the team showed that DEC1 suppresses stem growth. DEC1 It was active in the shallow water variety, and remained active when those plants were flooded, essentially holding the brakes on stem growth. In contrast, when the deep-water rice was exposed to flooding, the brakes were lifted: DEC1 it stopped expressing itself, further allowing stem growth.
If plant breeders or molecular biologists can control those two genes, they could adjust plant height without having to change GA levels, perhaps even in crops other than rice, says Laura Dixon, a plant biologist at the University of Leeds . That means GA would continue to influence other parts of the plant as normal. The two new genes could act as a simple "attenuation switch" for plant height, says Susan McCouch, a rice biologist at Cornell University, who was also not involved in the research.
The two genes also exist in sugar cane, barley, and well-studied grass. Brachypodium distachyon. Ashikari believes that they could widely occur in other agriculturally important pastures. Another important crop, corn, has an equivalent to ACE1but it has a gene that only partially resembles DEC1. Still, the variety of species with the two genes makes the new discovery "super-sensitive," says McCouch.
The genes could help rice breeders improve low-yielding varieties that can already cope with seasonal flooding, or design new ones from shorter, productive varieties. If this approach works on other plants, it could even help design flood-proof crops for areas experiencing more frequent flooding due to climate change, including the U.S. Midwest, says Bailey-Serras. Such efforts would depend entirely on whether the genes in the target crops are responsive, but, "It would make a huge difference to the farmer."
