Scientists around the world will need to review their most cherished notion that species are distinct entities, after Western Australia research revealed new diseases can emerge when microbial species swap genes.

In the Southern Hemisphere’s largest genome project, the Grains Research and Development Corporation (GRDC) supported research found the same gene associated with two different fungal wheat diseases, Yellow Spot and Septoria nodorum blotch.

Yellow spot, also known as tan spot, causes yield losses of 5-10 percent in the main wheat areas of Australia, while S. nodorum blotch annually costs the nation’s grain industry more than $60 million in lost production.

GRDC Western Panel Member, Professor Richard Oliver said the research, through the Australian Centre for Necrotrophic Fungal Pathogens at Murdoch University, showed fungal species could swap genes and acquire characteristics of another species.

“It happened through interspecific gene transfer, where a gene encoding a critical virulence factor transferred from one species of fungal pathogen to another.

“Interspecific gene transfer is the smouldering fire undermining our most cherished notion in biology that species are distinct entities,” he said.

Professor Oliver made the amazing discovery while scrolling through 17,000 genes thought to be produced by the S. nodorum fungus, Stagnospora.

As part of the GRDC project into mapping the genetic structure of S. nodorum, Professor Oliver was struck by the similarity of gene number 16571 and the ToxA gene causing the disease Yellow Spot.

ToxA is host-specific, only affecting wheat and wheat cultivars carrying a particular susceptibility gene, Tsn1.

Meanwhile, strains of the Yellow Spot fungus, Pyrenophora trici-repentis (PTR), without ToxA, caused only a weak disease.

PTR was considered a mild pathogen until 1941 when it became what is now known as Yellow Spot, recognised wherever wheat is grown.

The GRDC project was a collaboration with the Eidgenössische Technische Hochschule Zürich (ETH), Switzerland and the US Department of Agriculture.

Swiss research provided some startling clues to the origin of the gene responsible for Yellow Spot that the researcher believe originated in S. nodorum.

Bruce MacDonald and student Eva Stuckenbroek, who conducted the research in Switzerland, believed interspecific or horizontal gene transfer from S. nodorum to PTR enabled it to colonise wheat cultivars containing the Tsn1 gene.

“Yellow Spot with the S. nodorum gene could have overcome wheat defences and successfully caused disease,” Professor Oliver said.

“Our findings now prove that fungal species can swap genes and acquire properties characteristic of another fungal species

“A gene fairly marginal for pathogenicity in Stagonospora was critical for promoting Yellow Spot from an also-ran to a major player.

“This finding and others showed interspecific gene transfer occurs in nature.

“It’s only if a gene gives a recipient organism a significant fitness advantage that the transferred gene survives in the new host.”

Professor Oliver said these necrotrophic fungal plant diseases were so important that the GRDC initiated a major project in 2000 to investigate all aspects of S. nodorum, with a major focus on determining their entire genome sequence in 2005.

RELATED RELEASE: Research provides first evidence of gene transfers between fungal diseases