Wheat Gene Resistant to Deadly Fungus Identified

In a recent study with worldwide repercussions, researchers have identified a gene capable of giving wheat plants resistance to one of the most deadly races of the wheat stem rust pathogen - called Ug99 - first discovered in Uganda in 1999.

The discovery may help scientists develop new wheat varieties and strategies that protect the world's food crops against the disease currently making its way to the breadbaskets of Asia, according to the researchers.

In so doing, countless crops and very possibly lives could be saved.

Published in the journal Science, the study identifies the resistant gene Sr35, and appears alongside a study from an Australian team of researchers identifying another effective resistance gene called Sr33.

"This gene, Sr35, functions as a key component of plants' immune system," Eduard Akhunov, associate professor of plant pathology at Kansas State University and lead researcher, said in a statement. "It recognizes the invading pathogen and triggers a response in the plant to fight the disease."

Wheat stem rust is caused by a fungal pathogen that, according to Akhunov, wheat breeders were able to combat starting in the 1950s via resistant wheat varieties. That changed, however, upon the arrival of Ug99, which devastated local crops before spreading to Kenya, Ethiopia, Sudan and Yemen.

"Until that point, wheat breeders had two or three genes that were so efficient against stem rust for decades that this disease wasn't the biggest concern," Akhunov said. "However, the discovery of the Ug99 race of pathogen showed that changes in the virulence of existing pathogen races can become a huge problem."

As a first line of defense, wheat breeders and researchers began looking for resistance genes among those that had already been discovered in the existing germplasm repositories, he explained.

"The Sr35 gene was one of those genes that was discovered in einkorn wheat grown in Turkey," Akhunov said. "Until now, however, we did not know what kind of gene confers resistance to Ug99 in this wheat accession."

All told, the scientists spent nearly four years trying to identify the location of the Sr35 gene in the wheat genome nearly twice as dense as the human genome.

Once a list of likely candidates was formulated, they used two complimentary approaches to find the Sr35 gene, including chemically mutagenizing the resistant accession of wheat to identify plants that become susceptible to the stem rust pathogen.

"It was a matter of knocking out each candidate gene until we found the one that made a plant susceptible," Akhunov said. "It was a tedious process and took a lot of time, but it was worth the effort."

Next, they isolated the candidate gene and used biotechnical approaches to develop transgenic plants that carried the Sr35 gene and showed resistance to the Ug99 race of the stem.

At this point, with the resistance gene located, Akhunov and his colleagues are looking at what proteins are transferred by the fungus into the wheat plants and recognized by the protein encoded by the Sr35 gene.

By doing this, the scientists will be able to better understand the molecular mechanisms behind infection and develop new approaches for controlling the devastating pathogen.