A Small RNA Sequencing Analysis of the Wheat-Powdery Mildew Interaction

In plant pathogenic fungi, little is known about the role of small RNAs in the interaction with the host. Powdery mildews are highly specialized obligate biotrophs and major fungal pathogens of cereals. The objective of this work is to explore the role of small RNAs in disease development during the interaction between wheat (Triticum aestivum) and wheat powdery mildew (Blumeria graminis f.sp. tritici). Based on sequence homology to known components of RNA silencing machineries in eukaryotes, we have identified the proteins likely to be involved in this mechanism in wheat powdery mildew. We used a preliminary set of RNAseq data to analyze the transcriptional activation of the RNA silencing pathway in the pathogen during the early stages of the interaction. We have also applied powdery mildew infected and non-infected leaf material to small RNA sequencing, and analyzed the compatible interaction between three mildew isolates and wheat. Samples were collected 48 hours post infection, a critical stage for the establishment and the development of the disease. Small RNA libraries were analyzed for the origin, size distribution and preferential mapping of small RNA reads. We have also explored the relationships between small RNA mapping, transposable elements content, and gene expression in three genetically characterized loci in the pathogen. In another set of analyses, we have annotated candidate microRNAs and microRNA precursors in powdery mildew, and predicted their targets in wheat.