Rice farming has a nitrogen problem. Modern rice depends heavily on fertilizer. That dependence helped drive the Green Revolution and the spectacular rise in yields that followed. It has also given agriculture a costly habit. Farmers need nitrogen to push up production, but less than half of what is applied to the field ends up inside the plant. The rest is lost to the air, water and soil, with consequences for farm budgets, pollution, and climate. In India, where the annual fertilizer subsidy runs to roughly 1.7 lakh crore rupees, any credible path to using less nitrogen without sacrificing yields is a step towards sustainable food security.
What makes the finding immediately useful is that there is already a version of this gene in existing rice varieties. (File photo)
A new study in Science by researchers at Nanjing Agricultural University, the University of Oxford, and the Chinese Academy of Sciences points to one such path. The team, led by Chengbo Shen, Zhe Ji, and Shan Li, identified a rice gene that helps the rice plant keep its balance when nitrogen is scarce. In field trials, plants carrying a stronger natural version of this gene produced nearly 24 percent higher yields under low fertilizer conditions and about 20 percent higher yields even under high fertilizer conditions.
The story begins with a basic plant dilemma. When nitrogen runs short, the rice plant shifts into survival mode. It diverts energy into roots to hunt for nutrients and cuts back on shoots, where the grain comes from. In the wild, this makes sense. But in a monoculture paddy field where every neighboring plant is doing the same thing underground, it is less than ideal. Less shoot growth usually means lower yield.
Scientists have known about this trade-off for more than a century. What they had not found was the biological genetic switch controlling it. The new paper identifies a gene (called OsWRI1a, previously known only for its role in seed oil biosynthesis). This gene helps rice decide how much to invest above and below ground.
In the shoot, this gene switches on a pathway that promotes tillering, the branching that helps determine how many grain-bearing stalks a rice plant produces. In the root, it interferes with the biological machinery that normally slows down the hormone that pushes forward roots. The net result is a plant that does not hit the alarm bells when faced with nitrogen shortage. Instead of devoting extra energy into roots and starving off shoots, it keeps growth evenly balanced.
What makes the finding immediately useful is that there is already a version of this gene in existing rice varieties. The researchers screened more than 3,000 cultivated varieties and found that many indica lines carry a naturally stronger version than japonica varieties. A tiny difference in the gene’s “biological switch” helps make a stronger version. The researchers moved the stronger version into a japonica variety through conventional breeding and tested it across three field trials in Hainan and Anhui provinces in China. The improved plants held a more stable balance between root and shoot growth and delivered higher yields across different nitrogen conditions.
There is an evolutionary angle here too. When the team mapped the gene variants against soil nitrogen content across 42 countries and regions, the stronger indica version turned up more often in low-nitrogen soils. That suggests local nitrogen conditions may have helped shape where different versions of the gene persisted.
This is an exciting study that could make a meaningful difference in how nitrogen is used. That said, no single gene will fix decades of heavy fertilizer use in agriculture. Field performance depends on soil, climate, farming practices and the many other genes that shape a crop so further testing of this approach is needed. But for India, where indica rice predominates, the research shows the way because the trait breeders want does not need to be genetically engineered from other crop plants, it is already in rice, and in the field.
Anirban Mahapatra is a scientist and author. His most recent book is When the Drugs Don’t Work. The views expressed are personal.
