Redox Regulation of an AP-1-Like Transcription Factor, YapA, in the Fungal Symbiont Epichloë festucae
ABSTRACTOne of the central regulators of oxidative stress inSaccharomyces cerevisiaeis Yap1, a bZIP transcription factor of the AP-1 family. In unstressed cells, Yap1 is reduced and cytoplasmic, but in response to oxidative stress, it becomes oxidized and accumulates in the nucleus. To date, there have been no reports on the role of AP-1-like transcription factors in symbiotic fungi. An ortholog of Yap1, named YapA, was identified in the genome of the grass symbiontEpichloë festucaeand shown to complement anS. cerevisiaeΔyap1mutant. Hyphae of theE. festucaeΔyapAstrain were sensitive to menadione and diamide but resistant to H2O2, KO2, andtert-butyl hydroperoxide (t-BOOH). In contrast, conidia of the ΔyapAstrain were very sensitive to H2O2and failed to germinate. Using a PcatA-eGFPdegron-tagged reporter, YapA was shown to be required for expression of a spore-specific catalase gene,catA. Although YapA-EGFP localized to the nucleus in response to host reactive oxygen species during seedling infection, there was no difference in whole-plant and cellular phenotypes of plants infected with the ΔyapAstrain compared to the wild-type strain. Homologs of theS. cerevisiaeandSchizosaccharomyces pomberedox-sensing proteins (Gpx3 and Tpx1, respectively) did not act as redox sensors for YapA inE. festucae. In response to oxidative stress, YapA-EGFP localized to the nuclei ofE. festucaeΔgpxC, ΔtpxA, and ΔgpxCΔtpxAcells to the same degree as that in wild-type cells. These results show thatE. festucaehas a robust system for countering oxidative stress in culture andin plantabut that Gpx3- or Tpx1-like thiol peroxidases are dispensable for activation of YapA.