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Trichaptum abietinum by Otto Miettinen

Trichaptum abietinum

Within the framework of the CSP project 'Metatranscriptomics of Forest Soil Ecosystems', we are aiming to explore the interaction of forest trees with communities of soil fungi, including ectomycorrhizal symbionts that dramatically affect bioenergy-relevant plant growth, and saprotrophic soil fungi impacting carbon sequestration in forests. We are sequencing the metatranscriptome of soil fungi in ecosystems representative of major Earth ecosystems, the boreal, temperate and mediterranean forests. We are also sequencing the genome of the most abundant fungal species harvested on studied sites to serve as the foundation for a reference database for metagenomics of fungi and for a comprehensive survey of the potential soil fungal metabolome.

This species is one of the most powerful white rotters in temperate forest ecosystems. It grows on dead wood of various conifer species and degrades the wood material quickly to a soft fibrous material, decomposing both the lignin and the cellulose polymers (hence, white rot). Though previously assigned to the order Polyporales, more recent molecular phylogenies have placed it in the Hymenochaetales. Using other fungal genomes previously sequenced at JGI, it has been reported that lignin degrading enzyme families have been expanded in copy number in white rot species, as compared with brown rot and mycorrhizal ones, however, what makes a white rot species more or less powerful remained an open question. This and other emerging fungal genomes will enable us to test whether the strength of wood decay is conferred by copy number variation in important gene families or sequence-level evolution of specific genes.

The genus Trichaptum produces hundreds of perennial fruiting bodies, with attractive violet colors when young. The fruiting bodies start as a crust/like covering of the wood surface, then they produce caps with irregular pores on the underside (hymenophore), on which the spores mature. This irregular hymenophore is transitional between poroid and lamellar structures; with age it often splits up appearing more like a toothed fungus. Because of this transitional hymenophore type, Trichaptum abietinum will provide information on the evolution of hymenophore types. The primary purpose of structured hymenophores is to increase the surface for spore production. Fungi have evolved several different solutions, ranging from small excrescences on a smooth surface to teeth, pores or lamellae, several of these evolved multiple times independently in several clades, however, the genetic bases for these transitions are unknown.