Rice is a staple food for billions of people worldwide, but environmental and climate changes threaten the agricultural yields necessary to support the needs of an ever growing human population.
Many researchers have explored how to increase rice yield sustainably, detail the genetic variation between cultivated and wild rice, identify engineering opportunities, and develop genetically modified variants of multiple plants, including rice. New research has taken a step back to get a broader view of the interaction between the plants and the soils in which they grow.
An international team from the University of Oxford, Nanjing Agricultural University, and Institute of Genetics and Developmental Biology (Chinese Academy of Sciences) has published their work exploring the genetics behind rice’s response to nitrogen levels in the soil.
Their paper entitled, “OsWRI1a coordinates systemic growth responses to nitrogen availability in rice” was published in Science.
Conventional farming practices often rely on the use of nitrogenous fertilizers to increase yield, but the use of these fertilizers is costly both financially and environmentally. However, plants grown in areas with low levels of nitrogen in the soil produce less edible yield. The molecular and genetic cause of this yield differential has been unknown.
To address the question of how plants respond to nitrogen levels in the soil, researchers explored the genetic variants in rice plants. They identified that rice plants with a non-function variant of the OsWRI1a (WRINKLED1a) gene were unable to increase root growth in nitrogen poor soils, reducing shoot growth and thus reducing yield. Over-expression of WRINKLED1a increased the growth of roots and shoots in low-nitrogen soils, as well as in other soils with varied nitrogen levels.
The team screened the genetics of over 3000 rice cultivars, identifying natural variants of the gene that were expressed at differing levels. They crossed plants with the allele variants that were more strongly expressed into rice plants that had weaker allele variants of the WRINKLED1a gene.
Field trials in Hainan and Anhui provinces in China showed that rice plants from crosses with the stronger allele had a stronger root-to-shoot ratio regardless of the nitrogen levels and had higher grain yields with lower fertilizer applications. This resulted in a 23.7% increase in yield under low nitrogen fertilizer application (120 kg/ha) and a 19.9% increase under high fertilizer application (300 kg/ha).
“Our study clearly shows that this regulator is a promising target for sustainable crop improvement. It was extraordinary to see the difference that the improved version of the gene had on rice yields during our field trials,” said corresponding author Zhe Ji, PhD, a postdoctoral researcher at the University of Oxford.
[University of Oxford]
Further exploration of the function of WRINKLED1a showed that there are differing functions of the protein in root and shoot tissues. In the roots, WRINKLED1a activated genes involved in nitrogen uptake, while in the shoot, it functions as an activator, turning on the regulatory gene NGR5, which promotes shoot branching. It’s function in the roots is tied to WRINKLED1a’s disruption of the formation of a protein complex that normally stops the accumulation of auxin, which typically would promote root growth. This disruption is not seen in the shoot tissues, suggesting that the role of WRINKLED1a is tissue specific.
“WRINKLED1a helps rice avoid the usual ‘more roots, less shoot’ trade-off under nitrogen limitation, supporting stable yields with lower nitrogen inputs,” said lead author Shan Li, PhD, at Nanjing Agricultural University.
This work shows promise for improving rice yields without the need for high tech interventions, but by utilizing standard selective breeding practices, informed by genetic understanding. Many plants have similar mechanisms for growth, so the positive progress in rice may open an opportunity to study other plants at the foundation of diets around the world.
“The next step is to investigate whether homologous genes in other crops, such as wheat and maize, can be leveraged to achieve similar outcomes,” concluded Li.
