Ancient roots of wheat virus resistance

The DNA sequence of a gene responsible for resistance to a devastating virus in wheat has been discovered, providing important clues for managing more resistant crops and maintaining a healthy food supply.

Wheat crops in the Americas, Asia, Europe, and Africa are regularly damaged by wheat yellow mosaic virus (WYMV), and there is a high demand for wheat varieties or cultivars that are resistant to this virus.

The study, published in the Proceedings of the National Academy of Sciences, found that the resistance gene originated in an ancient Mediterranean relative of wild wheat.

Dr Mohammad Pourkheirandish from the University of Melbourne, lead researcher of the study, said: "This discovery could help develop more resistant wheat varieties, improve crop yields and reduce the use of harmful fungicides. It also highlights the need to conserve biodiversity necessary to protect the food supply."

WYMV reduces food production by 80%, causing major economic losses. The virus is hosted and spread by a soil-living fungus that colonizes the roots of wheat plants, discolors wheat leaves and stunts plant growth.

Microscopic fungal spores containing WYMV can survive in soil for up to 10 years. Although fungicides can kill spores and stop transmission, fungicide treatments are neither cost-effective nor ecologically sustainable.

"A viable alternative is to selectively breed or genetically modify wheat for resistance to WYMV," Dr Pourkheirandish said.

"Prior to this study, we knew that a dominant gene called Ym2 could reduce the effects of WYMV in wheat plants by more than 70 percent, but we didn't know how the gene did this."

The research team used a technique called positional cloning to locate the Ym2 gene on the bread wheat chromosome and found that its DNA sequence encodes a protein called NBS-LRR. These proteins are the "guardians" that detect pathogens and trigger an immune response in plants.

Dr Pourkheirandish said: "Now that we know the DNA sequence of the gene, we can select for breeding lines that carry Ym2 by simply analyzing the DNA from a small leaf, even without virus inoculation."

"It will also make it easier for us to find variants of Ym2 in wild relatives of wheat, which may provide better disease resistance for further crop improvement."

The DNA of modern wheat is chimeric, meaning that its genetic material came from several ancestral plants through natural crosses, or hybrids, and then selective breeding by humans.

By comparing the DNA sequences of related species, the researchers discovered that the Ym2 gene in modern bread wheat came from an ancient wild plant called Aegilops sharonensis, native to the eastern Mediterranean countries. There is a similar gene in Aegilops speltoides, another wild ancestor of bread wheat.

Dr Pourkheirandish said: "These wild species may have hybridized with cultivated wheat at some point and passed on the genetic resistance that is now commercially important."

"Original wild plants are rich sources of useful traits such as disease resistance that plant breeders and geneticists can exploit to protect modern crops and maintain a healthy food supply—including bread, pasta, noodles, couscous, pastries, cakes and other wheat products that many of us rely on and enjoy."

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