Newswise — A pioneering study undertaken at the Institute of Evolution has identified a new protein family, which is present in most of the cereal species and is responsible for fighting harmful diseases. In the case of wheat, the functional gene is present in wild emmer wheat, the progenitor of wheat, while domesticated bread and pasta wheats contain only non-functional copies of the gene. Accordingly, future incorporation of the gene into the cultivated varieties will protect them against yellow rust disease that currently cause damages totaling around one billion dollars annually. “Our discovery is an outcome of a long research project that lasted 25 years. However, as soon as we managed to identify the sequence of the gene that provides resistance against yellow rust in wild emmer wheat, we also discovered genes that are structurally similar in almost all plant species. This is a real breakthrough that open new ways to reduce the yield losses caused by plant pathogens, as part of the efforts to secure the global supply of food,” explains Prof. Tzion Fahima, who headed the research.
Over the past year, a consortium of a large number of scientists from around the world, including researchers from Tel Aviv University and the University of Haifa, managed to decipher the genomes of domesticated and wild wheats. At an early stage of the work the researchers announced that sequencing of the genome would enable them to rapidly identify important genes, thereby permitting a significant breakthrough in the struggle against hunger that threatens humankind. Just a few months later, Prof. Fahima, who was one of the researchers in the international consortium, explains how the reference genome sequences helped him to complete a study he has been working on for more than two decades with the goal of finding new ways to develop disease resistant varieties of wheat.
Yellow rust is a diseases caused by the fungus that leads to the loss of around five million tons of wheat per year. The wild emmer wheat gene Yr15 provides resistance against more than 3000 yellow rust strains from around the globe. Today, following the emergence of new and more virulent strains of the disease, almost 90 percent of cultivated wheat production are under the danger of being struck by the disease. This situation threatens the global food supply, since wheat accounts for 20 percent of the protein and calorie uptake of human consumption.
Although the researchers knew that the Yr15 gene provides resistance against this destructive disease, the enormous size of the wheat genome – which comprises around 16 billion letters – made it almost impossible to find the precise sequence of this gene. The researchers compare this task to finding a needle in a haystack. “Discovery of the molecular mechanism of a particular gene requires determination of its location (e.g. genetic mapping) within the gigantic wheat genome, which is five times larger than the human genome, followed by the identification of the sequence of amino acids that compose the protein coded by the gene and sends the necessary commands to activate resistance to disease. This information also enables us to incorporate the gene into other wheat varieties or to transfer it efficiently using classical breeding methods,” explains Prof. Abraham Korol of the Institute of Evolution.
As noted above, Prof. Fahima has been attempting to crack the Yr15 mystery for long time. In a study undertaken together with his team, including Valentina Klymiuk, Elitsur Yaniv, Lin Huang, Dina Raats, and Andrii Fatiukha, the task has finally been completed. The researchers found that the gene is located on the 1B chromosome of wheat, and they successfully revealedthe 4500 genetic code letters that compose the gene. They also discovered that the protein coded by the gene is comprised of two important domains (kinase-pseudokinase), both are crucial for proper activation of the plant immune response.
“As soon as the plant is attacked by the yellow rust fungus, the resistance protein activates programmed cell death of the infected cells. It basically cause the infected plant cells to ‘commit suicide,’ along with the disease-causing agent that is attempting to invade them. This immune response is sacrificing only the infected cells in order to stop the harmful parasitic invasion, while the rest of the plant cells stay healthy” explains Valentina Klymiuk from Prof. Fahima’s laboratory, who investigated this aspect in her doctoral thesis.
However, the deciphering of the specific wheat gene has also opened up much broader horizons for the researchers. Following their discovery, they identified a similarity between the tandem kinase-pseudokinase protein of Yr15 and proteins found in humans. “These proteins, which form part of the immune system of the human body, activate programmed cell death in human cells infected by agents such as viruses and bacteria in order to destroy them. When we recognized this evolutionary similarity, we thought of checking whether this protein architecture is also found in other plant species,” recalls doctoral student Andrii Fatiukha from Prof. Fahima’s laboratory.
In an examination of numerous plant species, the researchers indeed found that almost all of them contain proteins with such kinase-pseudokinase structure. The researchers believe that this protein family plays an important role in protecting plants against diseases caused by fungi, and hope that in the future it will be possible to exploit them to this end. The researchers called the new protein family Tandem Kinase-Pseudokinases (TKPs). “This is a new family of proteins that we have identified for the first time. These proteins share a similar structure and operate in a similar way. It’s fascinating to see how the evolution of the immune system generated similar solutions in such different species - plants and animals,” Prof. Fahima concluded.
The paper describing these results was published in Nature Communications:
Klymiuk V, Yaniv E, Huang L, Raats D, Fatiukha A, Chen S, Feng L, Frenkel Z, Krugman T, Lidzbarsky G, Chang W, Jääskeläinen MJ, Schudoma C, Paulin L, Laine P, Bariana H, Sela H, Saleem K, Sørensen CK, Hovmøller MS, Distelfeld A, Chalhoub B,Dubcovsky J, Korol AB, Schulman AH, Fahima T. 2018. Cloning of the wheat Yr15 resistance gene sheds light on the plant tandem kinase-pseudokinase family. Nature Communications 9:3735.
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