The next green revolution for rice

Researchers at the University of Oxford and the Chinese Academy of Sciences have discovered a gene that improves the yield and fertiliser use efficiency of rice.

A ‘Green Revolution’ in the late-20th century led to significant increases in global grain yields of rice and other cereals; it was fuelled by increased fertiliser use and high-yielding dwarfed Green Revolution Varieties (GRVs) that are still used today. GRVs have a higher number of grain-bearing branches (‘tillers’) per plant, which are enhanced by increased nitrogen fertiliser use. However, fertilisers can be expensive, and can also cause environmental damage. Researchers have discovered a gene that can help develop new GRVs that combine increased tiller number and grain yield with reduced nitrogen use, to help reach a global sustainable agriculture goal.

“This study is a prime example of how pursuing fundamental plant science objectives can lead rapidly to potential solutions to global challenges. It discovers how plants coordinate their growth in response to soil nitrogen availability, then shows how that discovery can enable breeding strategies for sustainable food security and future new green revolutions,” Professor Harberd said.

The study, published as the cover story of the journal Science, was led by Professor Xiangdong Fu from the Chinese Academy of Sciences’ Institute of Genetics and Developmental Biology and Professor Nicholas Harberd from the Department of Plant Sciences at the University of Oxford. Researchers identified a rice gene that responds to nitrogen and increases the accumulation of a protein called NGR5 in plant cells. Nitrogen-stimulated NGR5 accumulation changes the structure of genes that inhibit tiller growth, thereby increasing the numbers of yield-enhancing tillers.

“Discovering how nitrogen stimulates tiller growth was exciting in itself. But our discovery was particularly exciting because NGR5 controls the activity (via a mechanism known as chromatin modulation) of multiple genes in the rice genome, genes likely responsible for many different rice responses to soil nitrogen in addition to tiller growth,” Professor Harberd said.

Soil nitrogen promotes rice branching. Nitrogen fertilisers (High N, right) increase the number of rice plant flowering branches (compared with Low N, left), thus boosting grain yield. The researchers have now discovered the underlying gene that controls this nitrogen-responsive increase in branch number. Image credit: Kun Wu/Xiangdong Fu, Chinese Academy of Sciences.

GRVs also increase tiller numbers by accumulating another branch-promoting protein called DELLA — an accumulation that is reduced by the plant hormone gibberellin (GA). The study revealed that GA also reduces NGR5 accumulation, and that tiller growth is the product of complex interactions between BGR5 and DELLA proteins.

“We next reasoned that further increase in the accumulation of NGR5 might increase tiller number and yield with reduced fertiliser use. To our delight, we found that increasing NGR5 accumulation caused an increase in both tiller number and grain yield of a current elite rice GRV, especially at low fertiliser levels,” Professor Harberd said.

Researchers say NGR5 could become a major target for plant breeders in enhancing crop yield and fertiliser use efficiency, to achieve global grain yield increases at a reduced environmental cost.

Image credit: ©stock.adobe.com/au/WR.LILI