Early-Stage Infection-Specific Heterobasidion annosum (Fr.) Bref. Transcripts in H. annosum–Pinus sylvestris L. Pathosystem

Transcriptomes from stem-inoculated Scots pine saplings were analyzed to identify unique and enriched <i>H. annosum</i> transcripts in the early stages of infection. Comparing different time points since inoculation identified 131 differentially expressed <i>H. annosum</i> genes with <i>p</i>-values of ≤0.01. Our research supports the results of previous studies on the Norway spruce-<i>Heterobasidion annosum s.l.</i> pathosystem, indicating the role of carbohydrate and lignin degradation genes in pathogenesis at different time points post-inoculation and the role of lipid metabolism genes (including but not limited to the delta-12 fatty acid desaturase gene previously reported to be an important factor). The results of this study indicate that the malic enzyme could be a potential gene of interest in the context of <i>H. annosum</i> virulence. During this study, difficulties related to incomplete reference material of the host plant species and a low proportion of <i>H. annosum</i> transcripts in the RNA pool were encountered. In addition, <i>H. annosum</i> transcripts are currently not well annotated. Improvements in sequencing technologies (including sequencing depth) or bioinformatics focusing on small subpopulations of RNA would be welcome.