Fifteen years ago, scientists announced they had finished sequencing the human genome, a monumental task that took decades of research and billions of dollars. After that it would perhaps seem like mapping the genetics of a sedentary plant would be easy. But that wasn’t the case at all. It turns out the DNA of good old garden-variety bread wheat is a tangled, complicated mess, and cracking the code appeared to be an impossible feat—until now.
Researchers have finally sequenced the wheat genome, a breakthrough that could lead to innovations like drought-resistant and vitamin-packed varieties, reports Ed Yong at The Atlantic.
Yong explains that wheat’s genome is so complex because genetically it’s three species in one. Sometime around 500,000 years ago, two of the grassy ancestors of wheat naturally hybridized, creating wild emmer wheat. When early human agriculturalists domesticated the plant, another closely-related grass species also added genetic material to the mix. That means the genome has three pairs of every chromosome. It also means that compared to the human genome, which has 3 billion nucleotides, or genetic letters, wheat has 16 billion. And just one chromosome, Yong says, is larger than the entire genome of the soybean. The whole genome, comprised of 21 chromosomes, also has confusing repeating elements, which make up 85 percent of the sequence.
The effort to understand wheat DNA was just as large as the genome itself. According to Elizabeth Pennisi at Science, it took 200 scientists from 73 institutions in 20 countries (aka the International Wheat Genome Sequencing Consortium) over 13 years and $75 million to crack wheat. In the end, the new fully annotated reference genome, published in the journal Science, includes the precise location of 107,891 genes and 4 million molecular markers from a bread wheat variety called Chinese Spring.
Rudi Appels, a molecular biologist at Agriculture Victoria in Australia who is part of the consortium, says that when the project began, many people believed the sequencing was impossible. But time and technology made the project a reality. “I thought wheat deserved to be as well-defined as the human genome and then the technology really developed enormously,” he tells Melissa Davey at The Guardian. “Suddenly, what was once literally impossible looked achievable, and I wanted to be there and capture new technologies as they came through.”
Breeding wheat with traditional methods has become notoriously difficult because of the plant’s complex genetics. The new reference genome will give researchers a road map of how to improve the plant. Early drafts of the genome have already jumpstarted wheat research. “What took us years in the past now takes us one night,” Jorge Dubcovsky of the University of California, Davis, tells Pennisi. “It’s like walking with a Google map.”
Researchers at the John Innes Centre in Norwich, U.K., have already used the genome to identify genes for grain size. Using CRISPR gene-editing technology they were able to produce wheat with grains 20 percent larger than normal. Other teams are using the genome to produce varieties that don’t need to overwinter in the ground to sprout. Others are looking into the genes that make wheat less vulnerable to insects. Researchers are also looking at the genes that produce allergy-causing proteins in hopes of breeding hypo-allergenic wheat.
The sequencing, however difficult, was necessary. Many farmers were early backers of the project—and with good reason. Currently, wheat makes up about 20 percent of all the calories consumed on Earth. If the population continues to increase farmers will need to produce more and more each year to support humanity by 2050. But converting millions of acres into farmland is costly and would have huge environmental consequences. That means the gains need to come from the wheat itself, through better varieties and hardier resistance to the elements and insects.
The hope now that the genome is out there is that wheat will see some of the innovative booms that other crops have experienced, including corn, the genome of which was published in 2009 and rice, which was completed in 2005.