Uncovering new mechanisms for wheat rust resistance

Research highlights the emerging role of unusual kinase fusion proteins in wheat disease resistance.

Thuwal, Saudi Arabia, 23rd May 2023 / Sciad Newswire / Researchers have cloned the wheat rust resistance genes Lr9 and Sr43 and identified that they encode unusual kinase fusion proteins^[1][2]. Their research will enable new options for addressing resistance to disease in bread wheat.

Each year about 20 percent of global wheat production is lost to pests and disease, the equivalent of 3,500 grain ships. Breeding resistant cultivars is one of the most economical and environmentally friendly ways to address the problem.

The wild relatives of wheat provide a reservoir of genetic diversity for crop improvement. The Lr9 leaf rust resistance gene, for example, was originally identified in a wild goatgrass (Aegilops umbellulata). In a pioneering experiment conducted in the 1950s, Dr Ernest Sears succeeded in transferring a tiny Lr9-carrying segment of an Aegilops chromosome into bread wheat, demonstrating that it is possible to stably cross small chromosome segments from distant wild relatives.

Nearly 40 percent of the resistance genes found in bread wheat today have been crossed into wheat from wild relatives over the last 60 years. Wheat cultivars carrying Lr9 were released in the late 1960s, and Lr9 is still effective in many wheat growing areas. However, this type of breeding can lead to co-introduction of unfavorable versions of other genes from the wild relative, known as “linkage drag.”

KAUST researcher Yajun Wang used long-read sequencing to sequence the genomes of an Lr9-containing bread wheat cultivar and Ae. umbellulata. Comparison of the two genomes allowed the full reconstruction of this historic translocation. “We found that Lr9 had been introduced into wheat along with about 536 other genes from Aegilops umbellulata. Moreover, the process led to the deletion of a small fragment of the wheat genome containing 87 genes,” says Wang.

Similar to Lr9, the stem rust resistance gene Sr43 came from the wild tall wheatgrass (Thinopyrum elongatum).

Two teams led by Simon Krattinger and Brande Wulff cloned Lr9 and Sr43, respectively, by generating mutants and comparing their sequence to the parent genomes.

“The cloned genes can now be used to engineer bread wheat lines without linkage drag. More importantly, the genes can be combined with other cloned rust resistance genes into multigene stacks to create lines with superior and more durable resistance,” says Guotai Yu, lead researcher on the Sr43 project.

To clone Lr9, Wang developed a novel method called MutIsoSeq based on sequencing mRNA rather than genomic DNA. It combines long-read sequencing of mRNA from wild-type parental lines and short-read mRNA sequencing of mutant plants to identify candidate genes. Compared to other gene-cloning methods based on DNA sequencing, MutIsoSeq allows cheaper and faster cloning of causal genes without tedious genetic mapping, and the method can be easily applied in any basic molecular biology lab.

The cloning of Lr9 and Sr43 also revealed that the genes encode unusual kinase fusion proteins. Wheat kinases have recently emerged as a prominent new player involved in disease resistance in wheat and barley. The researchers combined large- scale mutational analysis and AlphaFold protein modeling to interpret the protein function.

“A kinase is a common enzyme that plays important roles in many cellular processes in both plants and animals, including in immunity," says Krattinger.

“Pathogens secrete proteins that sabotage host processes, subverting the host and causing disease. Our work suggests that the fusion of these proteins to kinases may allow the host to more easily detect the presence of pathogens and trigger defense responses,” he adds.

REFERENCE

1. Wang, Y., Abrouk, M., Gourdoupis, S., Koo, D., Karafiátová, M., Molnár, I., Doležel, J., Athiyannan, N., Cavalet-Giorsa, E., Jaremko, Ł., Poland, J., Krattinger, S.G. An unusual tandem kinase fusion protein confers leaf rust resistance in wheat. Nature Genetics. | article
2. Yu, G., Matny, O., Gourdoupis, S., Johnson, R., Aljedaani, F.R., Blilou, I., Gardener, C., Yue, Y., Kangara, N., Steuernagel, B., Hayta, S., Smedley, M., Harwood, W., Patpour, M., Wu, S., Poland, J.A., Jones, J., Reuber, L., Ronen, M., Sharon, A., Rouse, M., Xu, S., Holušová, K., Bartos, J., Molnár, I., Karafiátová, M., Jaremko, L., Doležel, J., Steffenson, B., Wulff, B.B.H. The wheat stem rust resistance gene Sr43 encodes an unusual protein kinase. Nature Genetics. | article

ENDS

For further information, please contact:

Sciad Communications
Amy Thomas and Jasmin Shearan
E: kaust@sciad.com
T: +44 (0)20 3405 7892

Notes to Editors

Photo caption:
From left: Professor Brande Wulff, Guotai Yu, Yajun Wang and Professor Simon Krattinger collaborated to reveal new insights into wheat rust resistance. © 2023 KAUST; Anastasia Serin.

About KAUST

Established in 2009, KAUST is a graduate research university devoted to finding solutions for some of the most pressing scientific and technological challenges in the world, as well as Saudi Arabia, in the areas of food and health, water, energy, environment and the digital domain. 

KAUST brings together the best minds from around the world to advance research. More than 120 different nationalities live, work and study on campus. KAUST is also a catalyst for innovation, economic development and social prosperity, with research resulting in novel patents and products, enterprising startups, regional and global initiatives, and collaboration with other academic institutions, industries and government agencies.  

For additional information, visit www.kaust.edu.sa.