Epsilon Open Archive

Abstract

This thesis summarizes the results of four studies regarding transcriptional changes of Heterobasidion annosum (Fr.) Bref. sensu lato and conifers in response to their pathogenic interaction. The diversity of expressed genes in H. annosum during the pathogenic interaction with Scots pine seedlings were studied by construction of a cDNA-library and generation of expressed sequence tags. Contig analysis identified 318 unigenes, of which 62 were repeatedly sampled. A putative function was assigned to 223 unigenes (70 %) that showed high or moderate similarity to protein sequences in public databases. The unigenes encoded proteins of metabolic functions with putative involvement in the pathogenic process, such as secondary metabolism, degradation of host material, signal perception and transduction and membrane transport. The transcriptional responses of several genes were studied with realtime-PCR during fungal infection of conifer material. Genes with a putative involvement in secondary metabolism, protection against oxidative stress and degradation/detoxification of host material were shown to be differentially expressed. A cytochrome P450 gene displayed sequence similarities towards genes encoding proteins involved in secondary metabolism and was highly expressed during fungal growth in Norway spruce bark. Up-regulation of a superoxide dismutase gene during early infection of Scots pine seedlings was detected. Transcript profiles of a laccase and two glutathione S-transferase genes showed transient expression during a time-coarse experiment of fungal infection of Norway spruce tissue cultures. A putative arabinase gene was exclusively expressed during infection of Scots pine seedlings. Up-regulation of Norway spruce genes phenylalanine ammonia lyase, peroxidase, glutathione S-transferase and class II and IV chitinases were detected upon fungal colonization of spruce callus tissue.