According to the Food and Agricultural Organization, rice is the world's third-largest crop after wheat and maize. It's the staple food in large regions of the world, and with increasing demand and the perceived perils of a changing climate, the vulnerability of rice production to droughts is a growing concern. The RIKEN Center for Sustainable Resource Science (CSRS) is developing new transgenic strains of rice incorporating a gene from the weed thale cress (Arabidopsis thaliana) to make them more drought-resistant.
The CSRS scientists say that plants are able to adapt to drought by generating chemicals called osmoprotectants that include various forms of sugar. By increasing the concentration of the protectants in cells, they retain water better – much in the same way, to make a crude analogy, a damp salt cake dries out more slowly than a dish of water.
The key to producing one protectant sugar called galactinol is the enzyme Galactinol synthase (GolS). Working with the International Center for Tropical Agriculture (CIAT) in Colombia and the Japanese International Research Center for Agricultural Sciences (JIRCAS), the CSRS has introduced the ability to produce GolS in rice by splicing in a gene from the drought- and saline-resistant weed thale cress.
"The Arabidopsis GolS2 gene was first identified with basic research at RIKEN," says RIKEN scientist Fuminori Takahashi. "Using it, we were able to improve resistance to drought-related stress, and increased the grain yield of rice in dry field conditions. This is one of the best model cases in which basic research knowledge has been successfully applied toward researching a resolution to a food-related problem."
To produce the new strains, the team started with Brazilian and African rice, and through gene splicing they made them over-express the GolS2 gene. They then grew the new rice in greenhouses under various controlled conditions and tested the enzymes produced by the transgenic plants compared to an unmodified control group.
The team then tested the transgenic plants under simulated drought conditions, where they found that the modified rice showed less leaf-rolling – an indicator of drought stress. Finally, the test plants were subjected to field tests in Cambodia and in different locations and seasons over a three-year period. In each case, the modified rice produced higher yields, less leaf-rolling, greater biomass, better fertility, higher water content, and more chlorophyll even in mild to severe drought conditions.
"Now, we have begun our next collaborative project, in which we will generate useful rice without [genetically modified] technology." says Takahashi. "It might take five to ten years to reach our goal, but we must keep pressing forward because droughts and climate change might get worse in the future."
The research was published in the Plant Biotechnology Journal.
Source: RIKEN