Rapid wheat genome sequencing offers hope for disease resistance

The wheat genome is difficult to sequence because it is around five times larger than the human genome. Until 2018, when the first complete wheat genome was sequenced, it was considered an impossible task.

Simon Krattinger, of King Abdullah University of Science and Technology  in Saudi Arabia, and colleagues. used a new technology called circular consensus sequencing – which can read long stretches of DNA far more accurately and quickly than before – to sequence the genome of the South African wheat cultivar, Kariega . This cultivar is unique in having long-lasting resistance to the fungal stripe rust disease, while many other disease-resistant cultivars lose their resistance after several years.

“What we want to understand is, what are the genetic components of this resistance, what are the genes that confer this resistance, and how can we deploy these?” Krattinger says. 

To identify the genes associated with resistance to stripe rust, the researchers bred the resistant Kariega cultivar with another non-resistant cultivar, then looked to see which of the progeny had resistance. They then treated the resistant progeny with a chemical that causes DNA mutations, to look for those that lost their resistance and where the mutations occurred in the genome.

They identified three genes associated with stripe rust resistance, including the Yr27 gene, which codes for an immune receptor that recognises the stripe rust fungus. A similar version of this gene, called Lr13, is associated with resistance to the related leaf rust disease.

The discovery provides valuable information as it can guide selective breeding for those genes. It could also inform more targeted engineering of disease-resistant wheat, Krattinger says. 

Ravi Singh, from the International Maize and Wheat Improvement Center in Texcoco, México , who was not involved in the study, says wheat engineered with the Yr27 gene had lost its resistance to stripe and leaf rust infection in many countries, but this study identifies an important region of the gene associated with resistance against both diseases.

“This information can be useful in creating, or searching for, additional variation in this region and then phenotyping progenies for resistance,” Singh says. “This could be a good gene-editing project as a follow-up. Let’s hope it will succeed.”

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