Transcriptome of an Armillaria root disease pathogen reveals candidate genes involved in host substrate utilization at the host­-pathogen interface

Summary Armillaria species display diverse ecological roles ranging from beneficial saprobe to virulent pathogen. Armillaria solidipes (formerly A. ostoyae), a causal agent of Armillaria root disease, is a virulent primary pathogen with a broad host range of woody plants across the Northern Hemisphere. This white-rot pathogen grows between trees as rhizomorphs and attacks sapwood as mycelial fans under the bark. Armillaria root disease is responsible for reduced forest productivity due to direct tree mortality and non-lethal infections that impact growth. Here, we characterize a transcriptome of a widespread, virulent genet (vegetative clone) of A. solidipes isolated from a mycelial fan on a natural grand fi r( Abies grandis) sapling in northern Idaho, USA. cDNA from polyA + -purified total RNA was sequenced using a singleend read approach on the Illumina GAIIx platform which generated 24 170 384 reads. A BLASTx search against the NCBI nr database using 39 943 de novo assembled contigs resulted in 24 442 sequences with significant hits (e-value < 1e 3 ), predominantly to fungi (85%). A filtered data set of 20 882 assembled transcripts that encoded putative homologous fungal proteins was created and used for all subsequent analyses. Signal P identified 10 668 putative signal peptides from these fungal transcripts, and 14 360 were annotated with gene ontology terms. Several sequences showed strong homology to annotated genes with functions in pathogenesis, specifically those involved in plant cell wall degradation and response to the post-infection host environment. This transcriptome contributes to the growing body of resources for studies on fungal pathogens of woody plants, and our results provide useful insights towards identifying specific genes with potential roles associated with pathogenesis and other metabolic functions.