Researchers discover the genetic mechanism behind stem rust in wheat

Wheat stem rust is a devastating fungal disease of wheat that has reemerged as a worldwide threat to wheat production with the evolution of highly virulent races of the fungus in Africa. For decades, researchers and crop breeders have known that something in wheat’s complex genome was suppressing the plant’s resistance to the fungal pathogen. A study published in Nature Communications sheds new light on the underlying genetic mechanism that causes suppression, potentially removing a barrier to developing crops with stronger immunity using modern genomic tools.

“This is the first identification of a trans-suppressor in wheat, meaning that it’s a gene somewhere in the genome that is impairing the function of other genes somewhere else in the genome,” said lead author Matthew Moscou of The Sainsbury Laboratory, in a press release. “Our study opens the way to a novel approach at improving agriculture through removal of suppressors that negatively interact in wheat.”

The wheat genome is composed of three separate genomes—A, B, and D—derived from three different independently evolved grass species. In the 1960s, Canadian researcher Eric Kerber showed that when the D genome was removed, the plant switched from being susceptible to rust to resistant. Further investigations over 20 years narrowed down the cause of this phenomenon to a gene on a single locus on chromosome 7D that was suppressing the plant’s resistance to stem rust.

In this study, researchers use modern sequencing techniques, genetic mapping, and mutational analysis to identify the gene that suppresses resistance to stem rust. They inoculated wheat plants with stem rust and compared the responses to a range of mutant plants that had lost the suppressor gene.

Typically, wheat responds to stem rust with around 8,000 genes being expressed. In these tests, one mutant responded with about 2,200 genes, another mutant with 55 genes. Critically, these mutant plants are resistant, whereas the parent wheat plant is susceptible.

The next steps of the research are to identify additional genes that contribute to immune suppression in wheat and to understand how these genes broadly impact the wheat genome.

Study