In optimization of modified wood, it is important to understand the mode of action of the wood modification and how the fungi response to it. The aim of this study was to investigate the expression of cellulases during the first two weeks of Postia placenta exposure in acetylated, DMDHEU-treated and thermally modified as well as in untreated wood. Using real-time PCR, the gene expression patterns of the P. placenta endoglucanase Ppl103675 and β-glucosidase Ppl112501 during 56 days of decay was analyzed. Preliminary data indicate that both genes are expressed at higher values in untreated wood at 56 days of exposure (56% mass loss) than at 14 days. We also saw high values for both genes at ten days of exposure for both untreated (11% mass loss) and modified woods (all 0% mass loss). We conclude that the high values at 10 and 56 days in untreated wood may be due to that monosaccharides and by-products from the cellulose degradation process, known to induce cellulase expression, have been released from the wood cell wall. Furthermore, the high values at ten days in the modified woods may be the result of an unknown regulatory mechanism. In addition, we found that the expression patterns for the P. placenta endoglucanase Ppl103675 and β-glucosidase Ppl112501 are very similar in the three modified woods investigated, but different from the patterns in untreated wood. This might be an indication that all the herein studied wood modifications affect fungi in the same way, i.e. they have the same mode of action.

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