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Contributions to understanding the genetics and functions of melanin in Ophiostomatoid fungi Tanguay, Philippe

Abstract

The forest products industry plays a critical role in the Canadian economy. In order to remain competitive and profitable, the industry relies on the production of high quality products. However, the aesthetic quality of wood is often compromised by sapstain wood-inhabiting fungi that produce a blue to black discoloration that reduces its value. To develop efficient and environmentally sound control methods, the fundamental nature of the fungal stain has to be deciphered. In this thesis, we examined which genetic factors affected pigmentation and determined one biological function of melanin in the sapstaining Ophiostomatoid fungi. The screening of an insertional mutant library identified 30 Ophiostoma piceae mutants with pigmentation or growth defects. Four pigmentation mutants were further characterized. One mutation in the polyketide synthase gene (PKS1), which encodes an enzyme specific to the melanin biosynthesis pathway, caused albinism while mutations in three other genes only reduced the pigmentation. In the latter, mutations happened in genes that appeared to be involved in the transcriptional regulation of melanin production. These genes were predicted to encode a protein from a MAP kinase signaling pathway, a transcription factor (PIG1), and a protein with unknown function. Additionally, we characterized a spontaneous Ceratocystis resinifera albino mutant (Kasper). Molecular work revealed that the albino phenotype resulted from a single point mutation in the PKS1 gene of the melanin pathway. The results from O. piceae and C. resinifera showed that even if multiple genes are involved in melanin production, a single mutation in the PKS1 gene was enough to induce albinism. Using the mutants described in this study, we found that melanin was involved in the maturation of sexual fruiting bodies. The perithecia from O. piceae and C. resinifera PKS1 mutants had incomplete necks and contained no ascospores. Finally, we assessed the efficiency of Kasper in preventing spruce sapstain in a field trial performed across Canada. Kasper reduced sapstain and was more efficient than Cartapip97, the only sapstain biocontrol agent available commercially. It is anticipated that this information will help both researchers and the forest products industry to develop safe and effective means for controlling sapstain.

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