Crop diseases are a severe threat to global food security. Around one-fifth of the global wheat harvest is lost each year to pests and diseases. That’s enough to make around 290 billion loaves of bread.
Stripe rust, or yellow rust, which creates yellow coloured stripes on leaf blades, is one of the three major wheat rust diseases, along with stem rust of wheat and leaf rust and, is of increasing concern for global wheat production, according to researchers at King Abdullah University of Science & Technology (KAUST).
In research that they say will help eradicate major wheat diseases, the KAUST researchers along with collaborators from South Africa, France and the US have assembled the genome of bread wheat and identified the gene responsible for stripe rust resistance. This is a key South African wheat cultivar called Kariega, which has robust resistance to stripe rust. Using this genome, the researchers identified and cloned a key gene that confers stripe rust resistance.
“Rust spores are dispersed by winds and can travel thousands of kilometres, meaning new and highly virulent strains spread rapidly,” explained Naveenkumar Athiyannan, who worked on the project alongside KAUST's Michael Abrouk and Simon Krattinger. “Unlike humans, plants don’t have an adaptive immune system that helps them ‘memorize’ past infections. Instead, their ability to withstand specific diseases is encoded by disease resistance genes.”
“Wheat has a dynamic and complex genome, five times larger than the human genome. This makes it extremely challenging to pinpoint the location of a specific gene,” said Abrouk. Moreover, disease resistance genes often differ between wheat cultivars. Sequencing the Kariega genome, in particular, is important for understanding stripe rust resistance.
The team combined the latest DNA sequencing techniques to assemble the genome, before conducting extensive analysis using molecular markers to identify the exact chromosomal region that confers stripe rust resistance.
“The Kariega assembly allowed us to look in detail at the DNA sequence of this region and identify all possible candidate genes,” said Abrouk. “This step would have taken months or even years in the past.”
The team identified the stripe rust resistance gene as Yr27, which they then cloned to study the gene function and molecular mechanisms of resistance. In the future, the cloned genes could be transferred to cultivars during breeding, and could even be modified to alter a plant’s disease recognition and resistance.
“We were excited to discover that Yr27 is a version, or allele, of a known leaf rust resistance gene,” said Athiyannan. “Now that we know the exact sequences of both alleles, we may be able to engineer a new version of the gene that recognizes both diseases simultaneously.”
“We’ve developed a fast and cost-effective strategy to clone disease resistance genes,” added Krattinger. “The long-term goal is to clone the 400 resistance genes found in wheat, providing scientists with a real shot at eradicating major wheat diseases.”