| Summary: | The ability to adapt to changing environmental conditions is crucial for living organisms, as it enables them to successfully compete in natural niches, a process which generally depends upon protein phosphorylation-mediated signaling transduction. In the present study, protein kinase PoxMKK1, an ortholog of mitogen-activated protein kinase kinase Ste7 in <i>Saccharomyces cerevisiae</i>, was identified and characterized in the filamentous fungus <i>Penicillium oxalicum</i>. Deletion of <i>PoxMKK1</i> in <i>P. oxalicum</i> Δ<i>PoxKu70</i> led the fungus to lose 64.4–88.6% and 38.0–86.1% of its plant-polysaccharide-degrading enzyme (PPDE) production on day 4 after a shift under submerged- and solid-state fermentation, respectively, compared with the control strain Δ<i>PoxKu70</i>. In addition, PoxMKK1 affected hypha growth and sporulation, though this was dependent on culture formats and carbon sources. Comparative transcriptomics and real-time quantitative reverse transcription PCR assay revealed that PoxMKK1 activated the expression of genes encoding major PPDEs, known regulatory genes (i.e., <i>PoxClrB</i> and <i>PoxCxrB</i>) and cellodextrin transporter genes (i.e., <i>PoxCdtD</i> and <i>PoxCdtC</i>), while it inhibited the essential conidiation-regulating genes, including <i>PoxBrlA</i>, <i>PoxAbaA</i> and <i>PoxFlbD</i>. Notably, regulons modulated by PoxMKK1 and its downstream mitogen-activated protein kinase PoxMK1 co-shared 611 differential expression genes, including 29 PPDE genes, 23 regulatory genes, and 16 sugar-transporter genes. Collectively, these data broaden our insights into the diverse functions of Ste7-like protein kinase, especially regulation of PPDE biosynthesis, in filamentous fungi.
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