Plant-Polysaccharide-Degrading Enzymes from Basidiomycetes

Abstract

SUMMARY Basidiomycete fungi subsist on various types of plant material in diverse environments, from living and dead trees and forest litter to crops and grasses and to decaying plant matter in soils. Due to the variation in their natural carbon sources, basidiomycetes have highly varied plant-polysaccharide-degrading capabilities. This topic is not as well studied for basidiomycetes as for ascomycete fungi, which are the main sources of knowledge on fungal plant polysaccharide degradation. Research on plant-biomass-decaying fungi has focused on isolating enzymes for current and future applications, such as for the production of fuels, the food industry, and waste treatment. More recently, genomic studies of basidiomycete fungi have provided a profound view of the plant-biomass-degrading potential of wood-rotting, litter-decomposing, plant-pathogenic, and ectomycorrhizal (ECM) basidiomycetes. This review summarizes the current knowledge on plant polysaccharide depolymerization by basidiomycete species from diverse habitats. In addition, these data are compared to those for the most broadly studied ascomycete genus, Aspergillus , to provide insight into specific features of basidiomycetes with respect to plant polysaccharide degradation.

Comparative study of genome-wide plant biomass-degrading CAZymes in white rot, brown rot and soft rot fungi

“…Cellulose, hemicellulose and pectin are the most important and major polysaccharides of the plant cell walls. The presence of lignin (heterophenolic aromatic polymer) along with these components make the plant cell wall recalcitrant (Rytioja et al 2014). Structurally and functionally plant cell walls are unique, and they can be divided into (a) middle lamella, (b) primary cell wall and (c) secondary cell wall.…”

“…Primary cell walls of renewable energy crops (monocots, grasses, etc.) contain cellulose and hemicellulose similarly secondary cell walls contains higher amounts of cellulose, varied compositions of hemicellulose and substantial amounts of lignin (Vogel 2008; Rytioja et al 2014). Where as in dicots primary cell walls contain low xylan, high xyloglucan and mannan, secondary cell walls contain cellulose, hemicellulose and lignin, in dicot plant cell walls pectin is considerably higher (Vogel 2008; Rytioja et al 2014).…”

“…Cellulose is made up of β (1→4) linear chains of d -glucose repeating units linked through hydrogen bonds, wherein the ratio of crystalline to amorphous regions differs between the layers of primary and secondary cell walls and also among the plant species (Harris and Stone 2008; Sjostrom 2013). Hemicellulose constitutes to 20–30% dry weight of the plant biomass; it is mainly composed of xylan (β (1→4) d -xylose units), xyloglucan, β-glucans (β (1→3) (1→4) d -glucose) and mannan (β 1→4 d -mannose); it also contains oligomers of galactose, xylose, arabinose, fucose and glucuronic acid (Sjostrom 2013; Rytioja et al 2014). The hemicellulose occurs in close association with cellulose, by supporting the microfibrillar structure of cellulose.…”

“…In plant cell walls, pectin occurs as homogalacturonan (α (1→4) d -galacturonic acid), xylogalacturonan (galacturonan and β (1→3) d -xylose), rhamnogalacturonan-I and rhamnogalacturonan-II. Thus, pectin is the non-cellulosic plant polysaccharide which occurs in intricate associations with other plant cell wall components (Sjostrom 2013; Rytioja et al 2014). Fungi secrete an array of CAZymes and lignin-degrading enzymes (which includes aromatic compound-degrading and -detoxifying enzymes) for the degradation of lignocellulose (Rytioja et al 2014) (Figure 1).…”

“…Thus, pectin is the non-cellulosic plant polysaccharide which occurs in intricate associations with other plant cell wall components (Sjostrom 2013; Rytioja et al 2014). Fungi secrete an array of CAZymes and lignin-degrading enzymes (which includes aromatic compound-degrading and -detoxifying enzymes) for the degradation of lignocellulose (Rytioja et al 2014) (Figure 1).

10.1080/21501203.2017.1419296-F0001Figure 1.Tentative network of CAZymes involved in depolymerisation of lignin, cellulose, pectin and hemicellulose observed in selected popular white rot, brown rot and soft rot fungi.

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