Development of a promoter shutoff system in <i>Aspergillus oryzae</i> using a sorbitol-sensitive promoter

<p>Promoter shutoff is a general method for analyzing essential genes, but in the fungus <i>Aspergillus oryzae</i>, no tightly repressed promoters have been reported. To overcome the current limitations of conditional promoters, we examined sorbitol- and galactose-responsive genes using microarrays to identify regulatable genes with only minor physiological and genetic effects. We identified two sorbitol-induced genes (designated as <i>sorA</i> and <i>sorB</i>), cloned their promoters, and built a regulated <i>egfp</i> and <i>brlA</i> expression system. Growth medium-dependent enhanced green fluorescence protein (EGFP) fluorescence and conidiation were confirmed for <i>egfp</i> and <i>brlA</i> under the control of their respective promoters. We also used this shutoff system to regulate the essential <i>rhoA</i>, which demonstrated the expected growth inhibition under repressed growth conditions. Our new sorbitol promoter shutoff system developed can serve as a valuable new tool for essential gene analyses of filamentous fungi.</p> <p>A sorbitol-responsive promoter shutoff system was evaluated for <i>egfp</i> and essential <i>rhoA</i> expression controlled with P<i>sorA</i> and P<i>sorB</i> in <i>A. oryzae</i>.</p