ABSTRACT
The aim of this study was to investigate differential expression profiles of the brown rot fungus Rhodonia placenta (previously Postia placenta) harvested at several time points when grown on Pinus radiata (radiata pine) and P. radiata with three different levels of modification by furfuryl alcohol, an environmentally benign commercial wood protection system. For the first time the entire gene expression pattern of a decay fungus is followed in untreated and modified wood from initial to advanced stages of decay. Results support the current model of a two-step decay mechanism, with an initial oxidative depolymerization followed by hydrolysis of cell-wall polysaccharides. The wood decay process is finished, and the fungus goes into starvation mode after five weeks when grown on unmodified P. radiata wood. The pattern of repression of oxidative processes and oxalate synthesis found in P. radiata at later stages of decay is not mirrored for the high furfurylation treatment. The high treatment level provided a more unpredictable expression pattern throughout the entire incubation period. Furfurylation does not seem to directly influence the expression of core plant cell wall hydrolyzing enzymes, as a delayed and prolonged, but similar pattern was observed in the P. radiata and the modified experiments. This indicates that the fungus starts a common decay process in the modified wood, but proceeds at a slower pace as access to the plant cell wall polysaccharides is restricted. This is further supported by the downregulation of hydrolytic enzymes for the high treatment level at the last harvest point (mass loss 14%). Moreover, the mass loss does not increase the last weeks. Collectively, this indicates a potential threshold for lower mass loss for highly modified wood.
IMPORTANCE Fungi are important decomposers of woody biomass in natural habitats. Investigation of the mechanisms employed by decay fungi in their attempt to degrade wood is important for both the basic scientific understanding of ecology and carbon cycling in nature, and for applied uses of woody materials. For wooden building materials long service life and carbon storage is essential, but decay fungi are responsible for massive losses of wood in service. Thus, optimizing durable wood products for the future are of major importance. In this study we have investigated the fungal genetic response to furfurylated wood, a commercial environmentally benign wood modification approach, that improves service life of wood in outdoor applications. Our results show that there is a delayed wood decay by the fungus as a response to furfurylated wood and new knowledge about the mechanisms behind the delay is provided.
