The genes that make roots grow down

A US-based team of researchers has identified four genes in corn that makes their roots grow downwards.

While it seems trivial, the direction of a plant’s roots play a key role in the plant’s water and nutrient acquisition.

The discovery also has implications for growing food in space.

When a seedling is turned sideways, sometimes the roots turn down suddenly, and sometimes they follow a more gentle curve towards gravity.

A plant’s gravitropism – its response to gravity – makes it more or less drought tolerant and sustainable to grow, because of the way its roots grow and spread.

The researchers have published details of how they isolated the genes in PNAS.

They examined root directions in thousands of corn seedlings, and compared this information to each seedling’s genetic data.

“Because we had previously performed the same experiment with the distantly related Arabidopsis plant, we were able to match genes within the relevant regions of the genome in both species,” says senior author Professor Edgar Spalding, from the Department of Botany at the University of Wisconsin, US.

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More on plant root genetics: Gene determines how far down roots go

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Arabidopsis, or thale cress, is a tiny flowering plant that is popular among biologists as a model organism.

Once the researchers found genetic regions in corn that influenced gravitropism, they could compare with the Arabidopsis genomes to pinpoint exactly which genes were responsible for the trait.

“Follow-up tests verified the identity of four genes that modify root gravitropism. The new information could help us understand how gravity shapes root system architectures,” says Spalding.

The technique they used could also help to spot the genes that cause other plant traits.

“I thought it was super cool that we could identify genes we wouldn’t have found otherwise just by comparing genomic intervals in unrelated plant species,” says co-author Professor Matt Hudson, from the department of crop sciences at the University of Illinois, US.

“We were pretty confident they were the right genes when they popped right out of this analysis, but Spalding’s group then spent seven or eight more years getting solid biological data to verify they do, indeed, play a role in gravitropism. Having done that, I think we’ve validated the whole approach such that in future, you could use this method for many different phenotypes.”

Beyond drought tolerance, knowing more about plant gravitropism will be important the more we grow plants in space.

“NASA is interested in growing crops on other planets or in space and they need to know what you’d have to breed for to do that,” says Hudson.

“Plants are pretty discombobulated without gravity.”