Tuesday, August 12, 2008 - 11:00 AM
S57
Genome analysis of the brown-rot wood decay fungus Postia placenta
Randy Berka, Novozymes Biotech Inc, 1445 Drew Ave, Davis, CA 95618, Daniel Cullen, USDA Forest Service - Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI 53726, and Diego A. Martinez, Genomics and Computational Biology, Los Alamos National Laboratory/Joint Genome Institute, PO Box 1663, MS M888, Los Alamos, NM 87545.
In contrast to white-rot fungi which degrade both lignin and polysaccharides in wood, brown-rot fungi degrade only the major polysaccharide components such as cellulose and hemicellulose, leaving behind a modified lignin residue. Despite the economic impact of these organisms, detailed knowledge of the enzymatic and genetic machinery involved in brown-rot wood decay lags behind that of the wood-degrading white rot fungi. Summarizing the concerted efforts of >40 participants worldwide, analysis of the genome sequence of Postia placenta will be presented. This brown-rot basidiomycete contains a unique repertoire of extracellular enzymes, including a constellation of glycoside hydrolases that is markedly different from white-rot and soft-rot fungi. The genome also encodes putative iron reductases and structurally divergent oxidases, enzymes potentially involved in extracellular generation of FeII and peroxide, respectively. Their presence is consistent with Fenton chemistry in which FeII and peroxide spontaneously react to form hydroxyl radical, a highly reactive oxidant capable of depolymerizing cellulose. The availability of the P. placenta genome also offers insight into the phylogeny of lignocellulose-degrading fungi. For example, comparisons between P. placenta and the closely related white rot fungus, Phanerochaete chrysosporium, support an evolutionary shift from white rot to brown rot, during which genes and gene families were lost, including those encoding lignin peroxidases and manganese peroxidases which are involved in lignin depolymerization.