Comparative analysis for transcription start sites of enolase genes in Aspergillus oryzae and Aspergillus nidulans

Aspergillus oryzae is a domesticated filamentous fungus used for Japanese fermentation industries and has been well known for its high ability of starch assimilation. In A. oryzae, transcription of glycolytic genes is induced at high level in the presence of fermentable carbon sources such as glucose. This feature would be important for the growth in industrial culture conditions of A. oryzae. However, it has not been evaluated whether or not the transcriptional induction of glycolytic genes is a specific feature to A. oryzae compared with the related species existing in natural environments such as Aspergillus nidulans.

Our previous studies in A. oryzae uncovered that the enolase gene (AoenoA), one of the most strongly expressing glycolytic genes, has two alternative transcription start sites (TSSs) dependent on the difference of two types of carbon source; the TSS located at -510 nt upstream of the start codon (+1) is strictly used under condition with nonfermentable carbon sources and another TSS located at -36 nt is used under condition with fermentable carbon sources.

To elucidate the conservation of alternative TSSs in enoA among the genus Aspergillus, we investigated the TSS usage of A. nidulans enoA (AnenoA) under glucose or acetate culture condition. Although 5′ RACE analysis revealed that AnenoA had also two TSSs located at around -440 nt and -19 ~ -67 nt, transcription from the downstream TSS was not preferentially observed under glucose condition unlike in AoenoA. In addition, Northern blot and qRT-PCR analyses showed that the induction levels of the transcript from the downstream TSS in the presence of glucose were approx. 18-fold in AnenoA and approx. 100-fold in AoenoA compared those in the presence of acetate. These results indicated that transcription from the downstream TSS under glucose condition is markedly upregulated in AoenoA compared to that in AnenoA.