Broad-specificity GH131 beta-glucanases are a hallmark of Fungi and Oomycetes that colonise plants

Plant-tissue-colonising fungi fine-tune the deconstruction of plant-cell walls (PCW) using different sets of enzymes according to their lifestyle. However, some of these enzymes are conserved among fungi with dissimilar lifestyles. We identified genes from Glycoside Hydrolase family GH131 as commonly expressed during plant-tissue colonisation by saprobic, pathogenic, and symbiotic fungi. By searching all the publicly available genomes, we found that GH131-coding genes were widely distributed in the Dikarya subkingdom, except in Taphrinomycotina and Saccharomycotina, and in phytopathogenic Oomycetes, but no other eukaryotes nor prokaryotes. The presence of GH131 in a species was correlated with its association with plants as symbiont, pathogen, or saprobe. We propose that GH131-family expansions and horizontal-gene transfers contributed to this adaptation. We analysed the biochemical activities of GH131 enzymes whose genes were up-regulated during plant-tissue colonisation in a saprobe (Pycnoporus sanguineus), a plant symbiont (Laccaria bicolor), and three hemibiotrophic-plant pathogens (Colletotrichum higginsianum, C. graminicola, Zymoseptoria tritici). These enzymes were all active on substrates with beta-1,4, beta-1,3, and mixed beta-1,4/1,3 glucosidic linkages. Combined with a cellobiohydrolase, GH131 enzymes enhanced cellulose degradation. We propose that secreted GH131 enzymes unlock the PCW barrier and allow further deconstruction by other enzymes during plant tissue colonisation by symbionts, pathogens and saprobes. This article is protected by copyright. All rights reserved.

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