A new study published in Science by a team of scientists across five continents led by King Abdullah University of Science and Technology (KAUST) Associate Professor Brande Wulff reports a previously unknown molecular event that initiates the immune response to a major wheat disease. The findings provide strategies to engineer wheat that has stronger immunity against infection.
As the main food staple for billions of people and one of the main sources of animal feed, wheat is one of the most important food commodities in the world. This importance is why a wheat pandemic can be even more devasting than a human pandemic.
"Climate change is causing diseases to appear in places previously unseen. We need more study of plant immunity to develop technologies that will protect valuable food crops," said Wulff.
Like animals, plants have immune systems but very different ones. Vertebrates, including humans, rely on blood cells for their immunity. These cells emit specific types of proteins that bind to and kill a pathogen. Lacking a circulatory system, plants have evolved a different immune approach but one that is equally effective. The challenge is understanding the specific molecular reactions that lead to the plant killing and thus surviving an invading pathogen.
The study shows the first molecular events to occur inside plant cells in response to stem rust, a fungus given its name because infected plants show brown pustules on their stems and leaves when infected. Sometimes referred to as the "polio of wheat", historically stem rust has been the cause of many famines. While farming practices have produced wheat that is resistant, the unexpected spread of stem rust can wipe out harvests.
The immune reaction begins when stem rust interacts with a specific type of protein known as "tandem kinases". Kinases are universal molecules that operate in human immunology too, as well as contribute to glucose uptake, the formation of blood vessels, neural development and more. Tandem kinases get their names because they are physically linked together. They also are known for their role in plant immunity.
While their importance in stem rust immunity does not come as a surprise, the study shows the initial molecular reactions tandem kinases conduct to achieve an immune response. This response ultimately kills the cell, denying the pathogen of the nutrients it parasitically extracts. Thus, the pathogen fails to proliferate and infect more cells, instead dying with its morbid host.
In the absence of the pathogen, Wulff and his colleagues found that the tandem kinases are bound to each other, almost like wearing handcuffs, keeping them inactive. However, when a pathogen binds to one of the kinases, it effectively unlocks the cuffs, freeing the other kinase to switch on the immune response. This mechanism had never been previously observed and gives insights on ways to engineer wheat that have stronger resistance against threatening disease.
Because of the evolutionary conservation of the immune mechanism across cereals and against other pathogens, the study provides a framework for strengthening cereal crops against many diseases.
"A majority of countries see wheat as critical to their food policy and food security. The more we understand how wheat reacts to pathogens the more we can sustainably secure the food supply for the world's growing population," said Wulff.
The ease at which it can be grown, stored, and processed, as well as its nutritional value, has made wheat the most produced and traded crop in the world. In the last ten years, more than 750 million tons has been grown annually. In contrast, rice, another major food staple, has barely exceeded 500 million tons over the same time.
Wulff is also co-chair of the Center of Excellence for Sustainable Food Security. This center is conducting scientific research to enhance sustainable food production, especially in arid environments.
