Pathogen-inducible cDNAs from the interaction of the root rot fungus Heterobasidion annosum with Scots pine (Pinus sylvestris L.)

Subtractive hybridization was used to select cDNAs representing genes that are differentially expressed during interaction of the necrotroph Heterobasidion annosum and its conifer host (Pinus sylvestris). We obtained 966 ESTs from the subtraction cDNA library, which included 509 singletons and 147 contigs. The sequences of 492 clones (51%) significantly matched National Centre for Biotechnology Information Database entries. Four hundred and seventy-four ESTs (49%) had not been previously described. The ESTs with moderate to high similarity scores based on BlastX were organized into categories based on their putative function. Among the genes identified, 16% were associated with metabolism and other cellular functions, 14% with cell rescue and defence and 39% were classified as unknown. Seven of the genes shared significant homology to fungal genes. A cDNA encoding an antimicrobial peptide (AMP) was the most abundant transcript representing 2% of the total sequenced clones. The expression pattern of five ESTs (peroxidase, anti-microbial peptide, resistance gene analogue, unknown protein, thaumatin) were analysed by virtual Northern blot, and confirmed elevated levels of the gene transcripts upon pathogen infection. These ESTs provide insight into the host-pathogen interaction and also represent a resource for future research on H. annosum-conifer pathosystems.