July 24, 2002

A team of CSIRO Plant Industry scientists has isolated the gene that produces the shorter, more productive, varieties of rice that led the 'green revolution' in the 1960s.

With funding from Graingene* and using information from the publicly available rice genome sequence, the team was able to isolate the 'semi-dwarfing' (sd-1) gene, and develop 'perfect' markers to identify it.

Team leader, Dr Wolfgang Spielmeyer, says isolating the gene will speed up the process of breeding new rice varieties and help to identify semi-dwarfing genes in other cereal crops like wheat.

"In terms of yield, the 'green revolution' gene is probably the single most important gene in modern rice breeding," he says.

"Today it is still the main semi-dwarfing gene present in most rice varieties but, until now, it has never been isolated."

The 'green revolution' saw new varieties of rice with shorter stems producing record crop yields throughout Asia. The semi-dwarf varieties were less likely to fall over and responded better to nitrogen fertilisers.

"Because we were able to use the publicly available rice genome sequence, we were able to isolate this gene significantly faster than by conventional methods," Dr Spielmeyer says.

"Previous research had identified a region within the rice genome where the sd-1 gene was located.

"We also knew that semi-dwarf plants were deficient in an important plant hormone called gibberellins, which determines plant height.

"We focused our search for sd-1 on the genes involved in gibberellins production that were located within the previously identified region.

"That's when we found that the sd-1gene was defective, restricting the synthesis of gibberellins, creating a semi-dwarf rice plant.

"It's a great example of how information from the publicly available rice genome sequence can be used to isolate genes that are important to agriculture."

Once the semi-dwarfing gene had been isolated, Dr Spielmeyer's team developed a perfect marker directly from the gene sequence, which will enable rice breeders to produce new varieties of semi-dwarf rice more efficiently.

"A perfect marker is like a molecular flag. It is an easily detectable piece of DNA that identifies a gene, or group of genes. In this case it marks the location of the sd-1 gene for semi-dwarfing."

Breeding a new variety of rice can take many years, as successive generations must be grown to near-maturity before it is known if the dwarfing gene is present.

The perfect marker developed by Dr Spielmeyer and his team will fast-track breeding of new rice varieties by enabling breeders to screen for the semi-dwarfing gene at a much earlier stage of plant development, saving valuable time and resources.

Knowledge gained by isolating the sd-1 gene will assist further research into cereal crops.

"We will be able to use our knowledge of the sd-1 gene to study and isolate related gene sequences that are responsible for semi-dwarfing in other cereal crops such as wheat and barley.

"We hope this will lead to further advances in improving these important crops."

A detailed description of the work by Dr Spielmeyer and his colleagues, Dr Marc Ellis and Dr Peter Chandler, is published in the prestigious US scientific journal, Proceedings of the National Academy of Science, and is available online at: http://www.pnas.org/cgi/content/full/99/13/9043 

* Graingene is a strategic alliance involving three of Australia's leading agricultural organisations - AWB Limited, CSIRO and the Grains Research and Development Corporation (GRDC).