pH Regulates Endoglucanase Expression and Virulence of Alternaria alternata in Persimmon Fruit

The phytopathogenic fungus Alternaria alternata produces one endo-1,4-β-glucanase, AaK1, which is an important factor in disease development in persimmon fruit. During growth of A. alternata in media containing acidified yeast extract or cell walls from persimmon fruit, the fungus secreted ammonia and raised the medium pH. A rise in media pH from 3.8 to 6.0 in the presence of cell walls induced the expression of AaK1, whereas a glucose-induced decline in pH to 2.5 repressed transcription and enzymatic production. Treatments with buffered solutions at pH 6.0 during growth of A. alternata in the presence of glucose derepressed AaK1 expression and endo-1,4-β-glucanase production and enhanced decay development on the fruit. The results suggest that conditions affecting environmental pH modulate gene expression of AaK1 and virulence of A. alternata in persimmon fruit.