Transcriptomic sequencing of the wheat pathogen Puccinia striiformis f. sp. tritici isolated from infected wheat across the United States reveals key effectors

Guangxi Wu Becky Lyon Kirk Broders
BSPM, Colorado State University, Fort Collins, CO, USA

Stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases of wheat and is present in all major wheat-growing regions of the world. Within the U.S., stripe rust has traditionally affected cooler regions with higher moisture levels, such as the Pacific Northwest, but in the last 15 years its geographic footprint has expanded. This expansion is associated with suspected incursions of novel Pst races that have unique and broader virulence profiles, are better adapted to warmer environments, and are more aggressive than previously characterized races. Effectors, a group of virulence proteins deployed by the pathogen to manipulate plant cell structures and functions, might contribute to the aforementioned expansion. Furthermore, recent evidence has demonstrated that the pathogen effectors are under strong selective pressure to adapt in order to evade detection by the host resistance mechanisms. Towards the ultimate goal of understanding the diversity, distribution and function of Pst effectors in the pathogen population, we collected 15 field Pst samples from several regions across the U.S. and sequenced their transcriptomes. We further assess the transcriptomes for genome-wide effector diversity and differential expression to identify key effectors that likely contribute to the virulence of Pst. These key effectors could be targets for further molecular characterization as well as be used to devise novel sequence-based tools for the efficient and high-resolution surveillance of outbreaks.