Identification Of Strategies For Wheat Stripe Rust Pathogenicity By Deep Genome and Transcriptome Sequencing

Stripe rust is a major constraint to wheat production worldwide. The causal agent is the fungus Puccinia striiformis f.sp. tritici (Pst), and the molecular events that underlie host colonisation are largely unknown. The fungus creates a specialized cellular structure within host cells called the haustorium which allows it to obtain nutrients from wheat, and to secrete pathogenicity factors called effector proteins. No effector proteins have been identified to date in Pst. We are using genomic, transcriptomic and proteomic approaches to: 1. Understand how the pathogen establishes a compatible interaction with its host, and 2. Uncover the effector proteins that are synthesised and secreted during infection. We have used next-generation sequencing platforms to characterise the Pst genome, and to generate two contrasting transcriptomes (germinating spores and haustoria). So far we have found ~430 potential secreted protein genes in haustoria which are being tested in vivo to identify those with effector activity. Moreover, digital gene expression analysis comparing spores vs. haustoria has revealed that spores mainly deploy their energy reserves for growth and development, while haustoria extract host nutrients for further growth and use them in biosynthetic pathways for the ultimate production of spores. Finally, we have developed a method to isolate highly purified haustoria which is being tested for proteomics analysis. This technique will be a useful aid to further effector discovery and Pst genome annotation. Together, these studies will substantially increase our knowledge of stripe rust effectors and provide new insights into the pathogenic strategies of this important organism.