Fungal Adaptation to the Advanced Stages of Wood Decomposition: Insights from the Steccherinum ochraceum

Abstract

<i>Steccherinum ochraceum</i> is a white rot basidiomycete with wide ecological amplitude. It occurs in different regions of Russia and throughout the world, occupying different climatic zones. <i>S. ochraceum</i> colonizes stumps, trunks, and branches of various deciduous (seldom coniferous) trees. As a secondary colonizing fungus, <i>S. ochraceum</i> is mainly observed at the late decay stages. Here, we present the <i>de novo</i> assembly and annotation of the genome of <i>S. ochraceum</i>, LE-BIN 3174. This is the 8th published genome of fungus from the residual polyporoid clade and the first from the <i>Steccherinaceae</i> family. The obtained genome provides a first glimpse into the genetic and enzymatic mechanisms governing adaptation of <i>S. ochraceum</i> 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 <i>S. ochraceum</i>. This proposition is further substantiated by the results of the biochemical plate tests and exoproteomic study, which demonstrates that <i>S. ochraceum</i> assumes the intermediate position between typical primary colonizing fungi and litter decomposers or humus saprotrophs. Phylogenetic analysis of <i>S. ochraceum</i> laccase and class II peroxidase genes revealed the distinct evolutional origin of these genes in the <i>Steccherinaceae</i> family.