Abstract
Steccherinum ochraceum is a white rot basidiomycete with wide ecological amplitude. It occurs in different regions of Russia and throughout the world, occupying different climatic zones. S. ochraceum colonizes stumps, trunks, and branches of various deciduous (seldom coniferous) trees. As a secondary colonizing fungus, S. ochraceum is mainly observed at the late decay stages. Here, we present the de novo assembly and annotation of the genome of S. ochraceum, LE-BIN 3174. This is the 8th published genome of fungus from the residual polyporoid clade and the first from the Steccherinaceae family. The obtained genome provides a first glimpse into the genetic and enzymatic mechanisms governing adaptation of S. ochraceum to an ecological niche of pre-degraded wood. It is proposed that increased number of carbohydrate-active enzymes (CAZymes) belonging to the AA superfamily and decreased number of CAZymes belonging to the GH superfamily reflects substrate preferences of S. ochraceum. This proposition is further substantiated by the results of the biochemical plate tests and exoproteomic study, which demonstrates that S. ochraceum assumes the intermediate position between typical primary colonizing fungi and litter decomposers or humus saprotrophs. Phylogenetic analysis of S. ochraceum laccase and class II peroxidase genes revealed the distinct evolutional origin of these genes in the Steccherinaceae family.
Highlights
IntroductionA land mass covered in trees, are major ecological units existing on our planet
Forest ecosystems, a land mass covered in trees, are major ecological units existing on our planet
The genome of S. ochraceum announced in this article, strain LE-BIN 3174, together with the data from the biochemical plate tests and exoproteomic study allowed us to gain the first glimpse into the fungal adaptation to the advanced stages of wood decomposition
Summary
A land mass covered in trees, are major ecological units existing on our planet. Given the different physicochemical properties of the substrate occurring at the different stages of wood degradation and SOM decomposition, it is not surprising that fungi operating at these stages adopted different decomposition strategies These strategies can be distinguished based on the profile of lignocellulolytic enzymes (carbohydrate-active enzymes—CAZymes) secreted by fungi during the decomposition process, and many previously published studies demonstrated a strong relationship between the CAZyme content of fungal genomes with their degradation ability [4,12,13,14,15]. Based on the sequenced genomes, the CAZymes repertoire of S. ochraceum LE-BIN 3174 was inferred, compared and contrasted with those of the 8 fungi belonging to the Polyporales and Agaricales orders and occupying different ecological niches and trophic groups—primary and secondary colonizer saprotrophs on lignum, folia dejecta, stramentum, and humus. Genome-based findings regarding the intermediate position of S. ochraceum LE-BIN 3174 in terms of CAZymes repertoire and the peculiar evolutionary history of its laccases and ligninolytic peroxidases were further substantiated by a series of standard biochemical tests and study of the exoproteome obtained after the cultivation in the presence of wood sawdust
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