Researchers have shed light on the mystery of what makes bread wheat susceptible to the devastating disease stem rust. For decades, researchers knew that something in the wheat's genome was suppressing the plant's resistance to stem rust. Now, researchers at The Sainsbury Laboratory (TSL) have identified the underlying genetic mechanism that is causing this suppression, removing a stubborn barrier to developing crops with stronger immunity using modern genomic tools.
At the heart of the mystery is the notoriously complex bread wheat genome which is composed of three separate genomes A, B, and D. These came 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. More research 20 years later proved that the cause of this phenomenon was a gene on a single locus on chromosome 7D that was suppressing wheat's resistance to stem rust.
In the TSL study, researchers inoculated wheat plants with stem rust and compared the responses to a range of mutant plants without the suppressor gene. Normally, wheat responds to stem rust with around 8,000 genes being expressed. In the TSL tests, a mutant responded with around 2,200 genes, another mutant with 55 genes. Critically, these mutant plants are resistant, whereas the parent wheat plant is susceptible.
Dr. Matthew Moscou, one of the lead authors of the study, explains that while plants responding to the pathogen would be a good thing, it does not make it resistant. This is the opposite. The plant that is responding is the susceptible one and the one not responding is the resistant one.
(Source: Crop Biotech Update, International Service for Acquisition of Agri-Biotech Applications. www.isaaa.org)