Typically, geneticists sequence genomes by breaking DNA into small segments, reading them separately, and assembling the pieces back together. But if each chromosome occurs six times, how do you know where to put any given piece?
Worse still, 85 percent of wheat’s DNA consists of repetitive sequences, so even if you narrow a piece down to the right chromosome, it’s still a chore to work out where exactly it should sit. It’s like solving a giant jigsaw puzzle that depicts the same patch of blue sky three times over.
“You have no idea where things go,” says Kellye Eversole, who leads the International Wheat Genome Sequencing Consortium, or IWGSC—a group of researchers from 19 countries who have been trying to crack the genome since 2005. After 14 years, around $75 million, and a few incomplete drafts, the team has now published the nearly complete genome of a wheat variety called Chinese Spring, mapping more than 107,000 of its genes. “It’s really a miracle that we finished,” Eversole says.
Unexpectedly, a much smaller six-person team, led by Steven Salzberg from Johns Hopkins University, released its own version of a near-complete wheat genome last year, by using new technologies that read out very long stretches of DNA. But while Eversole applauds the small team’s accomplishment, she notes that its version “doesn’t have the level of detail that we have in ours, and it’s that detail that makes a difference for breeders.”
“The genome sequence of maize had a big impact on creating better varieties,” Eversole notes. By contrast, wheat production has lagged behind, and the crop’s profitability has recently dropped. That’s problematic because researchers estimate that the world will need to grow 60 percent more wheat by 2050 to feed its booming population.
“Whatever your views on a wheat-based diet, there is no escaping its importance in global food security,” says Alison Bentley, who was not part of the consortium. Bentley is the director of genetics and breeding at the United Kingdom’s National Institute of Agricultural Botany, and although she says that people have made huge progress in breeding wheat in the absence of a genome, having one will speed everything up.
Traditionally, it has taken a lot of trial and error to create new varieties of wheat that, say, tolerate cold or resist fungal diseases. “You throw things together and go through this long process of annual breeding in the hope that your variety has the right package of genes—and that takes years,” says Eversole, who grew up in Oklahoma as part of a farming family. But with a full genome at hand, breeders can identify the genes behind particular traits, and ensure that these are present in their crops. “The goal is to build a better breeder’s toolbox and increase profitability for growers,” she says.