The black mold Alternaria alternata causes dramatic losses in agriculture due to postharvest colonization and mycotoxin formation and is a weak pathogen on living plants. Fungal signaling processes are crucial for successful colonization of a host plant. Because the mitogen-activated protein kinase HogA is important for the expression of stress-associated genes, we tested a ∆hogA-deletion strain for pathogenicity. When conidia were used as inoculum, the ∆hogA-deletion strain was largely impaired in colonizing tomato and apple. In comparison, hyphae as inoculum colonized the fruit very well. Hence, HogA appears to be important only in the initial stages of plant colonization. A similar difference between conidial inoculum and hyphal inoculum was observed on artificial medium in the presence of different stress agents. Whereas wild-type conidia adapted well to different stresses, the ∆hogA-deletion strain failed to grow under the same conditions. With hyphae as inoculum, the wild type and the ∆hogA-deletion strain grew in a very similar way. At the molecular level, we observed upregulation of several catalase (catA, -B, and -D) and superoxide dismutase (sodA, -B, and -E) genes in germlings but not in hyphae after exposure to 4 mM hydrogen peroxide. The upregulation required the high osmolarity glycerol (HOG) pathway. In contrast, in mycelia, catD, sodA, sodB, and sodE were upregulated upon stress in the absence of HogA. Several other stress-related genes behaved in a similar way.

黑霉菌链格孢由于收获后的定居和霉菌毒素的形成而在农业上造成巨大损失，并且是活植物上的弱病原体。真菌信号传导过程对于成功定植寄主植物至关重要。由于丝裂原激活的蛋白激酶HogA对应激相关基因的表达很重要，因此我们测试了ΔhogA缺失菌株的致病性。当分生孢子用作接种物时，ΔhogA-缺失菌株在定殖的番茄和苹果中大大受损。相比之下，菌丝作为接种物很好地定居在果实上。因此，HogA似乎仅在植物定植的初始阶段才重要。在存在不同压力的情况下，在人工培养基上观察到分生孢子接种物和菌丝接种物之间存在相似的差异。野生型分生孢子能很好地适应不同的压力，而ΔhogA缺失菌株在相同条件下无法生长。以菌丝为接种物，野生型和ΔhogA-缺失菌株以非常相似的方式生长。在分子水平上，我们观察到几种过氧化氢酶（catA，-B和-D）和超氧化物歧化酶（sodA，-B和-E）基因在幼苗中，但在暴露于4 mM过氧化氢中的菌丝中没有。上调需要高渗透压甘油（HOG）途径。相反，在菌丝体中，在没有HogA的情况下，catD，sodA，sodB和sodE在压力作用下会上调。其他几个与压力有关的基因也有类似的表现。