Cloning and characteristic analysis of a novel aspartic protease gene Asp55 from Trichoderma asperellum ACCC30536

Proteases secreted by fungi belonging to the genus Trichoderma play important roles in biocontrol. In this study, the coding sequence and promoter region of the novel aspartic protease gene Asp55 were cloned from strain Trichoderma asperellum ACCC30536. Many cis-elements involved in phytopathogenic and environmental stress responses were identified in the Asp55 promoter region and may be recognized by MYB or WRKY transcription factors. The expression pattern of Asp55 under eight culture conditions was investigated by RT-qPCR. The expression level of Asp55 was up-regulated by poplar stem powder, Alternaria alternata cell wall fragments and A. alternata fermentation liquid, while it was down-regulated by carbon and nitrogen source starvation, and by powdered poplar leaves and roots. Additionally, the expression patterns of 15 genes encoding MYB transcription factors (Myb1 to Myb15) were also analyzed by RT-qPCR. Myb2 showed the most similar expression pattern with Asp55. The cDNA of Asp55 was expressed in Escherichia coli BL21, and recombinant ASP55 (rASP55) was purified. The purified rASP55 was evaluated for enzymatic activity and showed inhibitory effect on phytopathogenic A. alternata.