The Role of Lytic Polysaccharide Monooxygenases in Wood Rotting Basidiomycetes

The group of filamentous fungi called wood rotting fungi comprises the main decomposers of woody biomass in forest ecosystems. These wood rotting fungi secrete various extracellular enzymes, such as cellulases and lytic polysaccharide monooxygenases (LPMOs) to degrade cellulose in wood cell walls. Interestingly, one particular group of wood-rotting fungi, called brown-rot fungi, lacks key cellulases for degrading crystalline cellulose, namely cellobiohydrolases (CBHs), with only a few exceptions. On the other hand, genes encoding LPMOs are widely conserved among brown-rot fungi, suggesting the importance of these enzymes in the brown-rot system. In this paper, after reviewing the wood degradation process by wood rotting fungi, we describe the history of the discovery of LPMOs and then review current knowledge on the characteristics of these enzymes. We then review our research on LPMOs derived from a brown-rot fungus and discuss possible physiological roles of LPMOs in the brown-rot system. Finally, we address the significance of LPMOs in the evolution of brown rot system.