Reversible pseudohyphal growth in haploid Saccharomyces cerevisiae is an aerobic process

Pseudohyphal growth in Saccharomyces cerevisiae has been postulated to be an adaptation to foraging for nitrogen during nitrogen starvation. This process was described as a strictly diploid phenomenon which did not occur in haploid yeast cells and was under the genetic control of both the mating-type locus and a group of five genes, the BUD genes, regulating bud formation. We have also observed a dimorphic growth pattern in yeast growing on various nitrogen-limiting synthetic media. However, and in contrast to a previous report, we find that pseudohyphal growth is not precluded in haploid cells. We demonstrate that haploid pseudohyphal growth is strictly oxygen-dependent and is rapidly reversible, defining pseudohyphal growth as a reversible developmental pathway in yeast.