Characterization of the glycoside hydrolase family 15 glucoamylase gene from the ectomycorrhizal basidiomycete Tricholoma matsutake

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The gene encoding the glycoside hydrolase family 15 glucoamylase (TmGlu1) in the ectomycorrhizal fungus Tricholoma matsutake was cloned and characterized. After the culture of T. matsutake mycelia in media containing different forms of starch as a carbon source, increased extracellular glucoamylase activity in the culture medium and a correspondingly higher transcriptional level of TmGlu1 in mycelia were detected, particularly in amylose- supplemented medium, when compared with those in the glucose medium. These results suggest that starch, especially amylose, affects the transcription of TmGlu1 and downstream glucoamylase activity, which is directly related to starch utilization. Similar results were obtained when compound forms of starch were used to culture mycelia. Glucoamylase genes from saprophytic and ectomycorrhizal fungi formed a single clade. The observed inducibility of TmGlu1 and lack of distinct phylogenetic differences among glucoamylase genes of saprophytic and ectomycorrhizal fungi suggest that glucoamylase may relate to some common functions in these two types of fungi.