Polarity-dependent expression and localization of secretory glucoamylase mRNA in filamentous fungal cells

In multinuclear and multicellular filamentous fungi little is known about how mRNAs encoding secreted enzymes are transcribed and localized spatiotemporally. To better understand this process we visualized mRNA encoding GlaA, a glucoamylase secreted in large amounts by the industrial filamentous fungus Aspergillus oryzae, in living cells by the MS2 system. We found that glaA mRNA was significantly transcribed and localized near the hyphal tip and septum, which are the sites of protein secretion. We also revealed that glaA mRNA exhibits long-range dynamics in the vicinity of the endoplasmic reticulum (ER) in a manner that is dependent on the microtubule motor proteins kinesin-1 and kinesin-3, but independent of early endosomes. Moreover, we elucidated that the regulatory mechanisms of glaA mRNA by stress granules and processing bodies were different under high temperature and ER stress. Collectively, this study uncovers a dynamic regulatory mechanism of mRNA encoding a secretory enzyme in filamentous fungi.