Group led by Kyoto University discovers Pias protein in rice that induces resistance to rice blast

A research group led by Professor Ryohei Terauchi of the Graduate School of Agriculture, Kyoto University, and Senior Researcher Motoki Shimizu of the Iwate Biotechnology Research Center, in collaboration with Tokyo University of Agriculture, the National Agriculture and Food Research Organization, the Sainsbury Laboratory (UK) and the John Innes Centre (UK), announced the discovery of Pias, a protein that induces resistance in rice by recognizing a protein secreted by rice blast fungus. Pias was found to have an additional domain, DUF761, bound to its structure. The group found that this additional domain attracts blast fungal proteins like pseudo-bait and induces resistance. The results are expected to lead to the creation of a wide range of disease-resistant crop varieties and were published in the June 30 issue of the Proceedings of the National Academy of Sciences.

Rice blast is considered one of the world's 10 major crop diseases and identifying the resistance mechanism of this disease is expected to contribute greatly to the stable production of food. In the process of searching for new resistance genes against rice blast fungus, the research group focused on a foreign rice variety, Keiboba, which is resistant to the 2012-1 rice blast fungus. The research group crossed the resistant Keiboba with Hitomebore, which is susceptible to rice blast (does not have a resistance gene), and looked for resistance genes using the RaIDEN method, a genome analysis technology developed independently.

As a result, they found a resistance gene and named it "Pias." The amino acid sequence of the protein produced by the resistance gene was inferred to be an NLR-type immunoreceptor protein composed of a pair of similar proteins. The protein is composed of Pias-1 and Pias-2. These pairs of proteins are thought to bind and work in concert. The group also succeeded in identifying a factor of blast fungus recognized by the protein and named it "AVR-Pias."

Furthermore, the amino acid sequence shows that an additional domain DUF761 is bound to the end of Pias-2 in addition to its basic structure. They also found that the blast fungus AVR-Pias binds to this additional domain. The Pias protein was thought to exert resistance by attracting and recognizing the blast fungus like a pseudo-bait in its additional domain.

A search for genes similar to Pias-2 using a number of rice lines as material revealed a variety of additional domains in the same position as DUF761. The research group confirmed that a system that uses additional domains as pseudo-bait to exert resistance is widely conserved in rice strains. Rice is thought to have incorporated some of the rice proteins targeted by pathogens during evolution and made it an additional domain. The study also confirmed traces of additional domains detached from the genome analysis.

"We believe that the NLR-type immune receptor protein consisting of Pias-1 and 2 we discovered acts as a sensor (sensor NLR) and exerts resistance by conveying information to another NLR protein (helper NLR)," explains Dr. Terauchi. "Such modular systems are easy for humans to imitate, and we expect that in the future, by artificially designing additional domains, we will be able to expand the range of resistance and produce crops that are resistant to pathogens. Moving forward, we would like to analyze the three-dimensional structure of proteins composed of Pias-1 and 2 and identify the binding mechanism."