Copper-tolerant brown-rot decay fungi exploit intricate mechanisms to neutralize the efficacy of copper-containing preservative formulations. The production and accumulation of oxalate is the most widely recognized theory regarding the mechanism of copper-tolerance in these fungi. The role of oxalate, however, may be only one part of a series of necessary components required for this complex mechanism. Annotation of the Fibroporia radiculosa genes involved in copper-tolerance characterized a subset of proteins, three copper-transporting ATPase pumps, which regulate copper concentrations inside the fungal cell by exporting excess copper ions. The goal of this study was to determine the relevance of copper-transporting ATPase pumps in the mechanism of F. radiculosa copper-tolerance. Southern pine test blocks were pressure-treated with 0.6%, 1.2%, and 2.4% ammoniacal copper citrate and subjected to a copper-tolerant strain of F. radiculosa and a copper-sensitive strain of Gloeophyllum trabeum in decay tests over a four week period. Untreated Southern pine test blocks subjected to both test fungi served as controls. Expression levels of three copper-transporting ATPase pumps were evaluated each week by qRT-PCR. F. radiculosa showed up-regulation of all three ATPase pumps when exposed to the copper treatments over the course of this study. G. trabeum showed down-regulation of ATPase1 and ATPase2 and no expression of ATPase3 when exposed to the copper treatments over the course of this study. Up-regulation of the three ATPase pumps can be correlated to the ability of F. radiculosa to decay copper-treated wood (12% weight loss at week 4). Down-regulation of ATPase1 and ATPase2 and lack of ATPase3 expression can be correlated to the inability of G. trabeum to decay copper-treated wood (1% weight loss at week 4). Preliminary results indicate these three ATPase pumps function as an essential component of the complex mechanism of copper-tolerance utilized by F. radiculosa.

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