The authors have engineered plasmid constructs for developmental and constitutive expression of yeast-enhanced green fluorescent protein (yEGFP3) in Candida albicans. The promoter for the hyphae-specific gene Hyphal Wall Protein 1 (HWP1) conferred developmental expression of yEGFP3 in germ tubes and hyphae but not in yeasts or pseudohyphae when targeted to the ENO1 (enolase) locus in single copy. The pHWP1GFP3 construct allows for the easy visualization of HWP1 promoter activity in individual cells expressing true hyphae without having to prepare RNA for analysis. Constitutive expression of yEGFP was seen in all cell morphologies when the HWP1 promoter was replaced with the ENO1 promoter region. The use of the plasmids for expression of genes other than yEGFP3 was examined by substituting the putative C. albicans BCY1 (SRA1) gene, a component of the cAMP signalling pathway involved in yeast to hyphae transitions, for yEGFP3. Strains overexpressing BCY1 from the ENO1 promoter were inhibited in germ tube formation and filamentation in both liquid and solid media, a phenotype consistent with keeping protein kinase A in its inactive form by association with Bcy1p. The plasmids are suitable for studies of germ tube induction or assessing germ tube formation by measuring yEGFP3 expression, for inducible expression of genes concomitant with germ tube formation by the HWP1 promoter, for constitutive expression of genes by the ENO1 promoter, and for expressing yEGFP3 using a promoter of choice.
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