Redox Regulation of an AP-1-Like Transcription Factor, YapA, in the Fungal Symbiont Epichloë festucae

Abstract

One of the central regulators of oxidative stress in Saccharomyces cerevisiae is 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 symbiont Epichloë festucae and shown to complement an S. cerevisiae ⌬yap1 mutant. Hyphae of the E. festucae ⌬yapA strain were sensitive to menadione and diamide but resistant to H 2 O 2 , KO 2 , and tert-butyl hydroperoxide (t-BOOH). In contrast, conidia of the ⌬yapA strain were very sensitive to H 2 O 2 and failed to germinate. Using a PcatA-eGFP degron-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 ⌬yapA strain compared to the wild-type strain. Homologs of the S. cerevisiae and Schizosaccharomyces pombe redox-sensing proteins (Gpx3 and Tpx1, respectively) did not act as redox sensors for YapA in E. festucae. In response to oxidative stress, YapA-EGFP localized to the nuclei of E. festucae ⌬gpxC, ⌬tpxA, and ⌬gpxC ⌬tpxA cells to the same degree as that in wild-type cells. These results show that E. festucae has a robust system for countering oxidative stress in culture and in planta but that Gpx3-or Tpx1-like thiol peroxidases are dispensable for activation of YapA.

NapA Mediates a Redox Regulation of the Antioxidant Response, Carbon Utilization and Development in Aspergillus nidulans

“…For example and in contrast to our results, yapA deletion in symbiotic fungus Epichloë festucae causes sensitivity to H 2 O 2 and t -BOOH in conidia but not in mycelia and YapA, instead of AtfA, is required for expression of the spore-specific catalase CatA (Cartwright and Scott, 2013). Neurospora crassa mutants lacking the NapA homolog NcAp-1 were reported as showing no sensitivity to osmotic stress and only a slight sensitivity to H 2 O 2 (Takahashi et al, 2010), although recent work showed that mutants were sensitive to osmotic stress, cadmium and H 2 O 2 (Tian et al, 2011).…”

“…We found that none of these peroxiredoxins was required for H 2 O 2 or menadione resistance and therefore are unnecessary for NapA activation. This is consistent with results in E. festucae , where peroxiredoxins Gpx3 (GpxA) and Tpx1 (TpxA) were not needed for YapA H 2 O 2 -induced nuclear accumulation (Cartwright and Scott, 2013). On the contrary, M. oryzae mutants lacking Gpx3 functional homolog MoHYR1 are sensitive to H 2 O 2 , fail to express several genes related to the antioxidant response and show reduced virulence.…”

“…Unrelated protein AN8863, putatively involved in nucleosome assembly, was later also referred to as NapA (Araújo-Bazan et al, 2008). Here we keep using NapA to name the A. nidulans Yap1/Pap1 homolog (AN7513) because it has been used this way in other publications (Lessing et al, 2007; Thön et al, 2010), and because the name “ap” preceded by the first letter of the species name (i.e., n idulans ap A) has been widely used in many other filamentous fungi, where the role of Yap1/Pap1 homologs in oxidative stress resistance has been demonstrated (Lessing et al, 2007; Qiao et al, 2008; Temme and Tudzynski, 2009; Tian et al, 2011; Cartwright and Scott, 2013). Notably, in several plant pathogens Yap1/Pap1 homologs are involved not only in regulation of the antioxidant response but also in plant virulence (Molina and Kahmann, 2007; Guo et al, 2011; Huang et al, 2011).…”

Reactive oxygen species metabolism and plant-fungal interactions

“…E. festucae is an endophyte that intercellularly colonizes the aerial tissue of its perennial ryegrass host, Lolium perenne. In ΔyapA mutant strains of E. festucae, conidia were hypersensitive to H 2 O 2 while hyphae were not (Cartwright and Scott, 2013). However, unlike UmAp1, YapA was not required for plant infection.…”

Functional analysis of the role of glutathione peroxidase (GPx) in the ROS signaling pathway, hyphal branching and the regulation of ganoderic acid biosynthesis in Ganoderma lucidum

“…nih.gov/Blast.cgi) (Cartwright and Scott, 2013). The corresponding gene was identified in the G. lucidum genome database G. lucidum G.260125-1 (taxid: 1077286) (GL25996-R1) (Chen et al, 2012).…”