Mitogen-activated protein kinase (MAPK) cascades are broadly conserved and play essential roles in multiple cellular processes, including fungal development, pathogenicity, and secondary metabolism. Their function, however, also exhibits species and strain specificity. Penicillium oxalicum secretes plant-biomass-degrading enzymes (PBDEs) that contribute to the carbon cycle in the natural environment and to utilization of lignocellulose in industrial processes. However, knowledge of the MAPK pathway in P. oxalicum has been relatively limited. In this study, comparative transcriptomic analysis of P. oxalicum, cultured on different carbon sources, found ten putative kinase genes with significantly modified transcriptional levels. Six of these putative kinase genes were knocked out in the parental strain ∆PoxKu70, and deletion of the gene, Fus3/Kss1-like PoxMK1 (POX00158), resulted in the largest reduction (91.1%) in filter paper cellulase production. Further tests revealed that the mutant ∆PoxMK1 lost 37.1 to 92.2% of PBDE production, under both submerged- and solid-state fermentation conditions, compared with ∆PoxKu70. In addition, the mutant ∆PoxMK1 had reduced vegetative growth and increased pigment biosynthesis. Comparative transcriptomic analysis showed that PoxMK1 deletion from P. oxalicum downregulated the expression of major PBDE genes and known regulatory genes such as PoxClrB and PoxCxrB, whereas the transcription of pigment biosynthesis-related genes was upregulated. Comparative phosphoproteomic analysis revealed that PoxMK1 deletion considerably modified phosphorylation of key transcription- and signal transduction-associated proteins, including transcription factors Mcm1 and Atf1, RNA polymerase II subunits Rpb1 and Rpb9, MAPK-associated Hog1 and Ste7, and cyclin-dependent kinase Kin28. These findings provide novel insights into understanding signal transduction and regulation of PBDE gene expression in fungi.

Key points

• PoxMK1 is involved in expression of PBDE- and pigment synthesis-related genes.

• PoxMK1 is required for vegetative growth of P. oxalicum.

• PoxMK1 is involved in phosphorylation of key TFs, kinases, and RNA polymerase II.

丝裂原活化的蛋白激酶（MAPK）级联是广泛保守的，并在包括真菌发育，致病性和次级代谢在内的多个细胞过程中起重要作用。然而，它们的功能还表现出物种和菌株特异性。草酸青霉分泌的植物生物质降解酶（PBDEs）有助于自然环境中的碳循环，并有助于工业过程中木质纤维素的利用。但是，对草酸青霉中MAPK途径的了解相对有限。在这项研究中，草酸假单胞菌的比较转录组学分析在不同的碳源上进行培养，发现了十个推定的激酶基因，它们的转录水平明显改变。在亲本菌株∆ PoxKu70中敲除了这些推定的激酶基因中的六个，并且删除了基因Fus3 / Kss1样PoxMK1（POX00158），导致滤纸纤维素酶生产的下降幅度最大（91.1％）。进一步试验表明，该突变体Δ PoxMK1丢失37.1至PBDE生产的92.2％，两者submerged-和固态发酵条件下，与Δ相比PoxKu70。此外，突变体△ PoxMK1减少了营养生长，增加了色素的生物合成。对比转录组分析显示， 从草假单胞菌中 删除PoxMK1可以下调主要PBDE基因和已知调控基因（如PoxClrB和PoxCxrB）的表达，而色素生物合成相关基因的转录则被上调。比较磷酸化蛋白质组学分析显示 PoxMK1 缺失显着修饰了关键转录和信号转导相关蛋白的磷酸化，包括转录因子Mcm1和Atf1，RNA聚合酶II亚基Rpb1和Rpb9，MAPK相关Hog1和Ste7，以及细胞周期蛋白依赖性激酶Kin28。这些发现为了解真菌中信号转导和PBDE基因表达的调控提供了新颖的见解。

关键点

•PoxMK1与PBDE和色素合成相关基因的表达有关。

•PoxMK1是草假对虾营养生长所需的。

•PoxMK1参与了关键TF，激酶和RNA聚合酶II的磷酸化。