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DNA engineers solve rice problem

Scientists have discovered gene that can improve grain yield in areas where the soils are poor in phosphorus

Los Angeles TimesSeptember 2, 2012 

Rice, like all plants, needs phosphorus to grow. But there’s a problem for this crop, the most important calorie source in Asia: Much of the soil it’s grown on is low in phosphorus, and yields suffer as a result.

What’s more, world supplies of phosphorus – it comes from phosphate rock – are expensive for poor farmers and won’t last forever.

So it would be very helpful if rice plants could be altered to tolerate low phosphorus levels. After 15 years of work, scientists in the Philippines, Japan and Italy have now reported doing just that.

The trick was to go back to rice varieties from East India that are known to grow better in poor soils than most.

Scientists had identified a strain called Kasalath that they knew could tolerate phosphorus deficiency, but they didn’t know what was behind it. They had narrowed down the effect to a particular part of the genome, though – and DNA sequencing later revealed that this region contained a gene that didn’t exist in the reference rice genome (which is of a Japanese variety) or in other varieties that do poorly in phosphorus-deficient soils.

In the new study, molecular biologist Rico Gamuyao of the International Rice Research Institute in the Philippines and collaborators examined this gene in detail. They concluded that it is indeed responsible for Kasalath’s hardiness in low-phosphorus environments.

They discovered that the gene – which they call Phosphorus Starvation Tolerance, or PSTOL1 – sprang into overdrive when rice was deprived of the mineral.

Then the scientists used genetic engineering to splice the gene into two other strains of rice. With the added gene, the plants boosted their grain yield by more than 60 percent under phosphorus-poor conditions.

Further investigation revealed that the effect of the gene was to greatly enhance the growth of roots, presumably making them more efficient at absorbing what little phosphorus the soil contained.

The scientists then did the experiment in a different way, this time using conventional breeding techniques to introduce the PSTOL1 gene into rice strains that lacked it. They crossed these strains with Kasalath and then bred the hybrids back repeatedly to the non-Kasalath strains so that only small chunks of the Kasalath genome – including PSTOL1 – remained. The result was plants with similarly vigorous root growth.

The results were reported last week in the journal Nature.

“In light of the need to increase rice production for a growing population despite potentially negative impacts of climate change and increasing scarcity of natural resources, it will be critically important to systematically explore traditional rice varieties in which high-value genes such as PSTOL1 are preserved, and to enable breeders to efficiently use these genes in breeding programs,” the scientists wrote.

About half of the world’s agricultural lands are poor in phosphorus, and supplies of rock phosphate could run out in 50 to 100 years, noted Leon V. Kochian, an expert on crop genetics and soil nutrients at the U.S. Department of Agriculture and Cornell University who wrote a commentary that accompanied the study.

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