A mitogen-activated protein kinase (MAPK) signaling pathway regulates specialized cellular responses to external stimuli. In Bipolaris maydis, a Chk1 MAPK orthologous to Fus3/Kss1 MAPKs of Saccharomyces cerevisiae is known to regulate various developmental processes, including the formation of appressoria. However, upstream factors that regulate the Chk1 cascade have not been well clarified. In this study, we identified and characterized the BmSte50 gene, an ortholog of the yeast Ste50 in B. maydis. Our yeast two-hybrid assay indicated that BmSte50 interacts with a MAPK kinase kinase BmSte11, a component of the Chk1 cascade. ΔBmSte50 strains exhibited a loss of pathogenicity due to a lack of appressorial formation. The mutants also showed a reduction in melanization, conidial production, and aerial-mycelial and sexual development. Such phenotypes of the mutants were consistent with those of the Chk1 cascade gene mutants previously reported. In addition, ΔBmSte50 strains indicated lower conidial germination efficiency than the wild type. Notably, a significant number of ΔBmSte50 conidia could be germinated, while the Chk1 cascade gene mutants were reported to lack conidial germination ability. Our results suggested that BmSte50 may act as an adaptor protein for the Chk1 cascade and is involved in the regulation of various cellular processes.

丝裂原激活的蛋白激酶（MAPK）信号通路调节对外部刺激的专门细胞反应。在双极可能中，已知与酿酒酵母的Fus3 / Kss1 MAPKs同源的Chk1 MAPK调节各种发育过程，包括食欲的形成。但是，尚不清楚调控Chk1级联反应的上游因素。在这项研究中，我们鉴定并鉴定了BmSte50基因，即B. maydis中酵母Ste50的直系同源基因。我们的酵母双杂交检测表明BmSte50与MAPK激酶激酶BmSte11（Chk1级联的一个成分）相互作用。Δ BmSte50由于缺乏附生形成，这些菌株表现出致病性的损失。突变体还显示出黑色素化，分生孢子产生以及气生菌丝和性发育减少。突变体的这种表型与先前报道的Chk1级联基因突变体的表型一致。另外，ΔBmSte50菌株显示出比野生型更低的分生孢子萌发效率。值得注意的是，大量的ΔBmSte50分生孢子可以发芽，而据报道Chk1级联基因突变体没有分生孢子萌发能力。我们的结果表明BmSte50可能充当Chk1级联的衔接蛋白，并参与各种细胞过程的调控。