Scientists have identified genetic variants linked to a higher protein content in wheat, paving the way to more nutritious food. Lead author of the new study, Scott Boden of the University of Adelaide, says it’s the culmination of approximately 10 years of work.
A library of wheat
Wheat is the world’s most widely produced cereal and accounts for about 20% of the world’s dietary protein, so developing wheat variants with higher yield or higher protein content is a major advance.
Boden and his collaborators set out to search for genetic variants that might improve grain yield. They screened a large “library” of approximately 1,500 wheat varieties from the Johnson Centre in Norwich, UK.
This large number of variants is generated by treating wheat with a chemical called ethyl methanosulphate, or EMS, which creates mutations in the wheat genome. Specifically, the EMS randomly causes some of the letters in the wheat DNA to change – in a similar way to how mutations can arise in nature. Each variant can then be tested to see what qualities, or traits, the DNA mutations have created.
Importantly, every wheat variety in the library also had its genome sequenced, so scientists could see exactly what mutations were present in specific genes.
“Previously, we’d have been limited to finding a mutant that was interesting, but not be able to easily find the causal mechanism for that trait,” Boden explains.
The sequencing represents an impressive effort, given that wheat genomes are large and complex, with up to six copies of each chromosome, depending on the species, and a large proportion of repetitive or “junk” DNA.
“If the human genome was the size of the Earth, then the genome would be the size of the Sun,” says Boden.
Searching for improved grain quality
Boden and his colleagues were particularly interested in finding wheat varieties that produced more spikelets, which are the structural support for the plant’s flowers – or florets, as they’re known for cereals like wheat.
“We’ve seen research in other species where if you increase the number of these spikelets, then you can encourage the plant to produce more grain,” Boden explains.
They did find a wheat variant in the library that produced extra spikelets – but when they grew it in the field, it turned out not to have a higher grain yield after all.
However, the grain that the variant produced was about 20% higher in protein compared to a variety that lacked its particular genetic mutation.
“That’s a really significant increase – normally people get excited if there’s a 2-3% increase,” Boden says. In addition, higher protein content in wheat usually comes as part of a tradeoff with reduced yield – but this variant had both high protein and a similar yield to other varieties.
The high-protein wheat of the future?
The team tracked the mutations to a homeobox domain transcription factor gene. The proteins produced by these genes, known as transcription factors, help regulate processes including flower development and leaf shape.
“Just like we have arteries and veins that pump blood around our body, wheat has vasculature which helps distribute carbon, nitrogen and water from the roots and the leaves to the developing grain,” explains Boden. “We found that this variation increases the amount of vasculature in the plant.”
This increased vasculature, he says, allows more nitrogen to be delivered to the grain, which may allow them to produce more protein.
The next step is to cross the high-protein wheat with high-yield wheat varieties that farmers currently grow, in order to transfer the beneficial mutation and hopefully create an improved crop.
“We will then test them to see if this effect on grain protein content is maintained in these varieties,” Boden says. “Some of the early results are promising.”
Boden realised during his undergraduate years that he wanted to use his scientific training to fight famine and help feed the world.
“As I began to look at it further, I realised that as the world’s population is growing, towards 2050 there’s quite a strong risk that we won’t have enough food to feed the world’s population,” he says.