Wild rice gene gives yield boost

Richard Black BBC News 22 Aug 12;

A gene from wild Indian rice plants can significantly raise the yield of common varieties in nutrient-poor soils.

Scientists from the International Rice Research Institute (Irri) identified a gene that helps uptake of phosphorus, nitrogen and potassium, and transferred it into commercial strains.

Their yield was about 60% above normal in phosphorus-poor soils, the team reports in the journal Nature.

Large swathes of Asia have soil that is phosporus-deficient.

The gene came from a variety called Kasalath, native to nutrient-poor soils of eastern India.

About 10 years ago, scientists deduced that Kalasath contained one or more genes that allowed it to grow successfully in low-phosphorus conditions.

It took the Irri team three years to identify the gene responsible, which they have named PSTOL1.

"We got the [DNA] sequence of this region, but the region is very complex and it was very difficult to identify what is an actual gene and what is not," lead researcher Sigrid Heuer told BBC News.

"There's so much work being done on phosphorus pathways and we could never find the genes and the mechanisms, and actually it's very simple - the gene promotes larger root growth, so the plant takes up nutrients more easily."

In phosporus-poor soils, PSTOL1 switches on during an early stage of root development.

This increases the area of root in contact with the soil, enabling the plant to scavenge more phosphorus.

Although the researchers focussed on this one key nutrient, they found the faster root growth also helped uptake of nitrogen and potassium, which are also vital for the plant's development.
Breeding success

The scientists then used genetic engineering to transfer PSTOL1 into plants from two main rice lineages - indica and japonica.

When they were raised in phosphorus-poor soils, their yields were about 60% higher than un-modified plants.

Subsequently, the team was able to cross-breed Kasalath with conventionally used strains, using molecular markers to guide the process.

These also produced high yields in poor soil.

Commenting on the research in Nature, Prof Leon Kochian from Cornell University, US, said phosphorus was "probably the most limiting mineral nutrient for plants".

About half of the world's agriculural land is deficient in the substance. This does not mean the element is absent, but that it is locked up in forms from which plant roots are poor at liberating it.

Usually, farmers combat the issue by deploying fertilisers containing phosphate compounds and other essential nutrients.

But there are concerns that the supply will be difficult to maintain in the long term, as it comes principally from rock types that are not very common.
Super ambition

The Irri team next plans to share the marker-assisted breeding process with other scientists in rice-growing areas of the world, so they can cross Kasalath with locally used varieties and see how they perform.

The package of science is all openly published and publicly accessible with no intellectual property rights involved, which was a condition of funding from the Generation Challenge Program.

The longer term ambition is to create "super-tolerant" strains that can grow successfully in a range of conditions.

Genes involved would confer tolerance to drought, salinity, and inundation - the last using the Sub1A gene, which was also discovered in a wild rice variety six years ago and allows plants to survive entirely underwater for at least two weeks.

The team believes that these useful genes are likely to exist in wild varieties such as Kalasath.

"This group [of varieties] is a real treasure chest - there are lots of stress genes preserved in it," said Dr Heuer.

"The aim is super-tolerance - we're working on this, and within the next five to 10 years this will be a reality."

The research illustrates the usefulness of studying a variety of crop strains. PSTOL1 and Sub1A are completely absent from the varieties that have had their entire genomes sequenced.

The Irri team is also working with other scientists to target phosphorus-tolerance genes in other important food crops such as sorghum.