Hallmarks of basidiomycete soft- and white-rot in wood-decay -omics data of Armillaria

Abstract

The genus Armillaria spp. (Fungi, Basidiomycota) includes devastating pathogens of temperate forests and saprotrophs that decay wood. Pathogenic and saprotrophic Armillaria species can efficiently colonize and decay woody substrates, however, mechanisms of wood penetration and colonization are poorly known. We assayed the colonization and decay of autoclaved spruce roots using the conifer-specialists Armillaria ostoyae and A. cepistipes using transcriptomic and proteomic data. Transcript and protein levels were altered more extensively in the saprotrophic A. cepistipes than in the pathogenic A. ostoyae and in invasive mycelia of both species compared to their rhizomorphs. Diverse suites of carbohydrate-active enzyme genes (CAZymes), in particular pectinolytic ones and expansins, were upregulated in both species, whereas ligninolytic genes were mostly downregulated. Our gene expression data, together with previous comparative genomic and decay-chemistry analyses suggest that wood decay by Armillaria differs from that of typical white-rot fungi and shows features resembling soft rot. We propose that Armillaria species have modified the ancestral white-rot machinery so that it allows for selective ligninolysis based on environmental conditions and/or host types.