Journal
MOLECULAR PLANT-MICROBE INTERACTIONS
Volume 33, Issue 12, Pages 1405-1410Publisher
AMER PHYTOPATHOLOGICAL SOC
DOI: 10.1094/MPMI-06-20-0165-R
Keywords
Alternaria; fungal development; fungus-plant interactions; hyphae; mechanisms of pathogenicity; oxidative stress
Funding
- German Science Foundation [DFG Fi 459-19]
- Chinese Scholar Council (CSC)
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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 Delta hogA-deletion strain for pathogenicity. When conidia were used as inoculum, the Delta 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 Delta hogA-deletion strain failed to grow under the same conditions. With hyphae as inoculum, the wild type and the Delta 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.
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