Type II myosin is required for cytokinesis/septation in yeast and filamentous fungi, including Fusarium graminearum, a prevalent cause of Fusarium head blight in China. A type II myosin gene from the Chinese F. graminearum strain 5035, isolated from infected wheat spikes, was identified by screening a mutant library generated by restriction enzyme-mediated integration. Disruption of the Myo2 gene reduced mycelial growth by 50% and conidiation by 76-fold, and abolished sexual reproduction on wheat kernels. The Δmyo2 mutants also had a 97% decrease in their pathogenicity on wheat, and mycotoxin production fell to just 3.4% of the normal level. The distribution of nuclei and septa was abnormal in the mutants, and the septal ultrastructure appeared disorganized. Time-lapse imaging of septation provided direct evidence that Myo2 is required for septum initiation and formation, and revealed the dynamic behavior of GFP-tagged Myo2 during hyphal and macroconidia development, particularly in the delimiting septum of phialides and macroconidial spores. Microarray analysis identified many genes with altered expression profiles in the Δmyo2 mutant, indicating that Myo2 is required for several F. graminearum developmental processes and biological activities.
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