Mechanisms of wood decay inferred from recent genome investigations
D. CULLEN (1), D. Floudas (2), D. Hibbett (2). (1) USDA Forest Products Laboratory, Madison, WI, U.S.A.; (2) Clark University, Worcester, MA, U.S.A.
Common inhabitants of woody debris and forest litter, ‘white-rot’ fungi can efficiently mineralize all plant cell wall components including the recalcitrant lignin. The unique physiology these fungi has attracted recent interest, as plant feedstocks are increasingly viewed as a potential source for high value, small molecular weight products. Extracellular oxidative and hydrolytic enzymes of white-rot fungi are thought to be involved in lignin and cellulose degradation, respectively. The model white-rot fungus, <i>Phanerochaete chrysosporium</i>, simultaneously degrades lignin and cellulose, whereas the phylogenetically related polypore, <i>Ceriporiopsis subvermispora</i>, selectively depolymerizes lignin with relatively little cellulose degradation. In contrast, ‘brown-rot’ decay fungi such as <i>Postia placenta</i> rapidly depolymerize cellulose but the lignin remains as a modified polymeric residue. Small molecular weight, diffusible oxidants, such as hydroxyl radical, have been implicated, and the non-enzymatic Fenton reaction (H<sub>2</sub>O<sub>2</sub> + Fe<sup>2+</sup> + H<sup>+</sup> --> H<sub>2</sub>O + Fe<sup>3+</sup> + ×OH), has been repeatedly linked to brown-rot decay. Nevertheless, mechanistic aspects of brown-rot remain obscure. Comparative genome studies of wood decay fungi are being published at an increasing rate. Together with transcriptome and proteome data, these investigations are defining the key genes and processes in lignocellulose degradation. Recent advances will be discussed and areas of uncertainty highlighted.
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