Characterization of a highly active promoter, PBbgpd, in Beauveria bassiana

The promoter of glyceraldehyde-3-phosphate dehydrogenase (gpd) gene from Aspergillus nidulans (PgpdA) is widely used to direct expression of target genes constitutively in fungi. However, in some species, a heterogeneous promoter is found to be of low efficiency. To obtain a high-efficiency promoter for transformation of Beauveria bassiana, an entomopathogenic fungus widely used as an mycoinsecticide, a glyceraldehyde-3-phosphate dehydrogenase gene (Bbgpd) promoter, was cloned and characterized. Four deletion constructs (-2118, -1153, -726, and -354) of the 5'-upstream sequence of Bbgpd linked to a bar::gus fusion gene (phosphinothricin-resistance::beta-glucuronidase fused gene), which were used as selected marker gene and report gene, respectively, were generated. GUS activities of transgenic strains harboring -726, -1153, and -2118 deletion constructs were much stronger than that of the promoter of Aspergillus nidulans gpdA (PgpdA), with a twofold to threefold increase over that in the PgpdA construct. The -726 fragment was necessary to direct GUS expression in B. bassiana. No -354 transgenic progenies were obtained, possibly because it failed to initiate the transcription of bar::gus fusion gene. A remarkable increase of GUS activity was found between the -1153 and -726 constructs, indicating that some active transcriptional elements were located in this region. With a high expression level and relatively short sequence, PBbgpd can be used to drive target genes in B. bassiana transgenic research.