Figure 6. Pseudorevertants induce hyphal morphology and gene expression in response to many inducers, but not CO₂.

Strains carrying the HWP1-GFP reporter gene were incubated under the indicated hyphal inducing conditions and then photographed using light microscopy to detect cell morphology and fluorescence microscopy to determine if GFP was produced. As expected, all of the inducers stimulated the wild type control strain to form hyphae and produce GFP, whereas the cyr1Δ strain showed no detectable hyphae or GFP. In contrast, the pseudorevertant strain PR3 showed induction of filamentous cells and GFP levels similar to the wild type under all conditions except for CO₂. All inductions were performed at 37°C. GlcNAc induction was performed using SC-URA medium with 100 mM GlcNAc and was visualized at 90 min. Serum induction was performed in SC-URA plus 100 mM dextrose and 30% bovine calf serum and was visualized after 90 min. Hyphal induction with alkaline pH was performed by culturing cells overnight in SC medium buffered to pH 8 with 150 mM HEPES. CO₂ induction was performed by culturing cells overnight in a chamber with 5% CO₂.