Heterologous expression of laccase genes in Pichia pastoris. Data from the transcriptome analysis indicated that Lacc5 and Lacc12 were the main laccases active during fruiting body maturation and primordiation stages, respectively, whereas Lacc2, Lacc8, and Lacc11 were not expressed at any stage (Fig. 2C); in addition, Lacc2 and Lacc11 contained unusual active site arrangements (Fig.2A). Lacc6, which was ubiquitously expressed, is the most studied laccase in P. ostreatus [31]. Moreover, these laccases were scattered among the three phylogenetic groups: Lacc4, Lacc6, and Lacc11 in group I; Lacc12 in group II; and Lacc2 and Lacc5 in group III. Therefore, theses laccases were selected for further characterization. We constructed laccase expression vectors by cloning the six synthesized laccase genes adjacent to the AOX1 promoter in the Pichia expression vector pPICHOLI-2. Next, culture conditions for the production of laccase protein in P. pastoris GS115, using Lacc6 as a model gene, were investigated. In this system, methanol serves as the carbon source for yeast cell growth, as well as the inducer for gene expression. However, the methanol concentration needed to be optimized, as methanol exerts toxic effects on the cells on reaching a critical concentration in the culture medium.