Differential regulation of genes encoding manganese peroxidase (MnP) in the basidiomycete Ceriporiopsis subvermispora

We previously identified and characterized three mnp genes coding for manganese peroxidase (MnP) in the white rot fungus Ceriporiopsis subvermispora. In this work, we assessed transcript levels of mnp genes in liquid cultures of this fungus grown under various conditions. In the absence of Mn²⁺, mnp1 and mnp2 mRNA were detected by Northern hybridization, irrespective of the lack of extracellular MnP activity. Addition of Mn²⁺ to the cultures led to a marked increase in both transcripts, the highest titers being observed at 10 μM Mn²⁺. mnp1 mRNA was not detected at Mn²⁺ concentrations above 80 μM, whereas mnp2 mRNA was still observed at 320 μM Mn²⁺. Differential regulation of these genes was confirmed by the addition of Cu²⁺, Zn²⁺, Ag⁺ and Cd²⁺. These metal ions dramatically elevated both transcripts and also allowed the detection of the mnp3 transcript. In most cases, the increase in mRNA levels was partially abolished by the simultaneous presence of Mn²⁺, although the latter was strictly required to detect extracellular MnP activity. However, the lignin-related compound syringic acid specifically increased the mnp1 transcript, although only in the absence of Mn²⁺. These results indicate that there is no clear correlation between mnp mRNA levels and MnP activity. In addition, they strongly suggest that Mn²⁺ plays a post-transcriptional role which is essential for the presence of active MnP in the extracellular fluid.