Doctoral thesis, 2010
Heterobasidion - conifer pathosystemLundén, Karl
AbstractIn this thesis the Heterobasidion – conifer pathosystem is discussed in a symbiosis context. Heterobasidion annosum (Fr.)Bref. s.l. is a species complex with closely related species with partly overlapping host range. There are three European Heterobasidion species, H. annosum, H. abietinum and H. parviporum. In the first study it was shown that cDNA arrays printed for one species can be used to study gene expression in the other species. H. annosum can grow both as a saprotroph on dead wood or kill its conifer host as a necrotroph. This possibility to switch nutritional mode has impact on forest management as H. annosum can prevail in old wood for decades until infecting the next generation of trees. Gene expression patterns during the transition from saprotrophic to necrotrophic growth were studied in a nutrient limited microcosm system with dead and living Pinus sylvestris seedlings connected by a common mycelium. These results were compared with gene expression patterns of H. annosum, Phanerochaete chrysosporium (saprotroph) and Paxillus involutus (mutualist) growing in nutrient rich systems. In the nutrient rich comparison a higher correlation was found, than between the saprotrophic and necrotrophic growth of H. annosum where no differentially expressed genes were identified. However differences were found when the genes were annotated into functional categories by KOG groups. This suggests that differences between the two growth modes might depend on the magnitude of gene expression rather than distinct qualitative differences. The specificity of two mycorrhiza-associated Pinus genes (similar to Clavata 1 and MtN21) in comparison to known auxin-induced and defence genes through early signalling and ECM development with and without the auxin transport inhibitor TIBA was further investigated. The Clv-1-like gene seems to be associated with lateral root formation since expression was detected in root primordia during lateral root formation and in mycorrhizal roots.
Keywordsheterobasidion annosum; pinophyta; symbiosis; saprophytes; growth; genes; gene expression; pinus sylvestris; auxins; mycorrhizae
Published inActa Universitatis Agriculturae Sueciae
2010, number: 2010:19
Publisher: Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences