Aspergillus oryzae has an ability to produce copious amounts of amylolytic enzymes, production of which is repressed in the presence of glucose. Glucose repression in filamentous fungi is mediated by the transcriptional repressor CreA. In Aspergillus nidulans, it has been proposed that ubiquitination and deubiquitination of CreA play a key role in regulating glucose repression, and that HECT ubiquitin ligase HulA is involved in ubiquitination of CreA. Since yeast ortholog (Rsp5) of HulA is an essential factor for cell viability, we speculated that HulA is also essential for cell viability in filamentous fungi. In addition, it has been known that deletion of creA has a detrimental effect on growth, although CreA is not essential for cell viability. Thus, we generated the conditional expression strains for CreA and HulA in A. oryzae to investigate the mechanism of glucose repression. The conditional expression strains were generated by using the promoter of nmtA, expression of which is repressed considerably in the presence of thiamine. The resultant conditional HulA expression strain was defective in conidial formation in thiamine8208;containing medium, suggesting that HulA is essential for conidiation or cell viability. On the other hand, the growth defect of CreA conditional expression strain in thiamine8208;containing medium was leaky as compared with the creA null mutant. Northern blot analysis of α 8208;amylase gene showed that glucose repression was relieved in the CreA conditional expression strain. These results suggested that suppression of CreA expression level is highly effective in relieving the glucose repression without growth defect.
Full conference title:
11 th European Conference on Fungal Genetics
- ECFG 11th (2012)