MFS-transporter Flr1 is a major drug-efflux transporter in Saccharomyces cerevisiae ascospores.

In fungi, spores represent a highly resilient stage of the life cycle, characterized by low metabolic activity that confers resistance to xenobiotics. However, as soon as spores start germination, they become vulnerable to low-molecular-weight toxins. We hypothesized that during sporulation fungi presynthesize spore-specific drug-efflux transporters to mitigate this vulnerability. To test this hypothesis, we compared the repertoire of ATP-binding cassette- and major facilitator superfamily (MFS)- transporters involved in multidrug resistance (MDR) between spores and proliferating cells of yeast Saccharomyces cerevisiae. Using a set of strains in which MDR-transporters are tagged with a GFP, we showed that in spores the major efflux pump is MFS transporter Flr1, whereas in proliferating vegetative cells it is Pdr5p. In the presence of xenobiotics, deletion of the FLR1 gene reduced the growth rate of microcolonies originating from spores but did not affect growth from vegetative cells. We propose that Pdr5p's basal ATPase activity may be disadvantageous for spores, as it could be detrimental during prolonged dormancy.