Gene could help crops grow in poor soils

9 March 2010 by Tamera Jones

Some crops like barley and wheat survive on poor soils, because they grow special long root hairs to extract nutrients like phosphate and iron. Now scientists have discovered which genes are behind this ability paving the way for plant breeders to develop crops that can grow in infertile soils.

African woman hoeing soil

African woman hoeing poor soil

The ability to grow crops in poor soils will become increasingly important as global demand for food rises alongside a growing population. Most soils in Australia, regions of sub-Saharan Africa and some parts of China aren't very fertile and plants fail to extract enough phosphate and iron from them.

"Long root hairs are important for plants to be able to take up nutrients," says Professor Liam Dolan a botanist from the University of Oxford who led the study.

Plants that can't make long root hairs rely on fungi to release nutrients from soils for them. "Fungi do a lot of this work for a lot of plant species, but plants that don't have a symbiotic relationship with fungi compensate by growing long root hairs," explains Dolan.

We found that root hairs continued to grow until they were around 10 millimetres long when the RSL4 gene was effectively left in the on position.

- Professor Liam Dolan, University of Oxford

Long root hairs are good at getting nutrients from poor soils, because they burrow into the soil, 'like tiny mining machines, releasing acids and other scouring chemicals that crack open rocky minerals to release valuable nutrients," adds Dolan.

Dolan and colleagues developed a series of experiments to look for the genetic mechanisms behind the ability to grow long root hairs. They describe in Nature Genetics how they bred thale cress plants (Arabidopsis thaliana) that could grow either long root hairs or short root hairs.

The team found that a master regulatory gene called RSL4 acts like a switch. Long hairs grow when the gene is switched on and stop growing when it's switched off.

"We found that root hairs continued to grow until they were around 10 millimetres long when the RSL4 gene was effectively left in the on position," explains Dolan.

The gene works with external factors like low phosphate availability and plant growth hormones, called auxins. RSL4 activity and auxin stimulates root hairs to grow. When phosphate is scarce, RSL4 gets switched on so that the root hairs grow longer and the plant can gather sufficient nutrients to grow.

Plants bred with the ability to grow long root hairs may need much less fertiliser than is currently needed. This is good for the farmer, because fertilisers are likely to rise in price as oil reserves diminish. But it's also good for the environment: phosphate fertilisers have been implicated as a major cause of river pollution.

Dolan and his team's finding is the first time researchers have unearthed the genetic mechanisms behind this particular type of cell growth in plants.

"This discovery could represent a general mechanism for regulating cell size in lots of different species, both plants and animals," says Dolan.

'A basic helix-loop-helix transcription factor controls cell growth and size in root hairs' - Keke Yi, Benoît Menand, Elizabeth Bell & Liam Dolan, Nature Genetics, Volume: 42, Pages: 264-267 (2010), doi:10.1038/ng.529, Received 10 August 2009, Accepted 23 December 2009, Published online 7 February 2010