Does the genome of Sarcoleotia globosa encode a rich carbohydrate-active enzyme gene repertoire?

Abstract

The lifestyles of the order Geoglossales (Geoglossomycetes, Ascomycota) remain largely unknown. Recent observations support ericoid mycorrhizal lifestyles, especially in cultured Sarcoleotia-related species. However, the currently known genomes of geoglossoid fungi encode fewer carbohydrate-active enzymes (CAZymes) in Pezizomycotina, in contrast to the abundant CAZyme repertoires found in well-known ericoid mycorrhizal fungi. The absence of assembled genomes for cultured geoglossoid fungi hinders our understanding of the genomic features related to their lifestyles. We hypothesize that the genome of Sarcoleotia globosa, a putative ericoid mycorrhizal fungus, encodes abundant CAZymes, consistent with its culturability. General features, such as smaller genome size and smaller number of genes, are shared between the genome of S. globosa strain NBRC 116039 and other geoglossalean genomes. However, the former had the most extensive CAZyme repertoire, with several enzyme families involved in plant cell wall degradation. Some of these CAZymes are not found in Geoglossales and closely related lineages. Nonetheless, the number of CAZymes from S. globosa was notably smaller than that previously reported in ericoid mycorrhizal fungi. This inconsistency may highlight not only ecophysiological variation among ericoid root mycobionts but also the specific evolution of lifestyles in Geoglossales.