Aspergillus nidulans transcription factor AtfA interacts with the MAPK SakA to regulate general stress responses, development and spore functions.
Bottom Line: Constitutive phosphorylation of SakA induced by the fungicide fludioxonil prevents both, germ tube formation and nuclear division.Similarly, Neurospora crassa SakA orthologue OS-2 is phosphorylated in intact conidia and gets dephosphorylated during germination.We propose that SakA-AtfA interaction regulates gene expression during stress and conidiophore development and that SAPK phosphorylation is a conserved mechanism to regulate transitions between non-growing (spore) and growing (mycelia) states.
Affiliation: Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-242, 04510, México, D.F., México.Show MeSH
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Mentions: To evaluate atfA functions and possible connections to the SakA MAPK pathway, we first generated strains carrying complete deletions in either gene, as confirmed by Southern blot analysis (Figs S2 and S3A and B). ΔatfA and ΔsakA mutants were indistinguishable from the wild-type strain under high-temperature (42°C) or high-osmolarity (1 M NaCl or 1.2 M sorbitol) stress conditions (not shown). To test the mutant response to different types of oxidative stress, we incubated ΔatfA and ΔsakA strains in the presence of the redox-cycling compounds menadione and paraquat, the glutathione-depleting compound methylglyoxal and inorganic (H2O2) as well as organic (t-butylhydroperoxide; t-BOOH) peroxides. As shown in Fig. 1A, wild-type, ΔatfA and ΔsakA strains were similarly resistant to menadione and paraquat. In contrast, ΔatfA and ΔsakA mutants were hypersensitive to both t-butylhydroperoxide (Fig. 1A) and hydrogen peroxide (Fig. 1B), showing a slight sensitivity to methylglyoxal (Fig. 1A). Notably, ΔatfA and ΔsakA mutants were as sensitive to H2O2 as the ΔcatA mutant, which lacks the spore-specific catalase CatA (Navarro et al., 1996; Navarro and Aguirre, 1998). On the contrary, a mutant lacking the mycelial inducible catalase CatB (Kawasaki et al., 1997) showed a H2O2 resistance only slightly lower than the wild type (Fig. 1B). This and the fact that conidia from sakA mutants show decreased CatA activity (Kawasaki et al., 2002) suggested that under these conditions, mutant sensitivity to H2O2 could reflect low CatA activity in conidia. To explore this, we carried out similar oxidative stress plate assays but using mycelial plugs instead of conidia. As shown in Fig. 1C, mycelia from ΔatfA and ΔsakA mutants was resistant up to 6 mM H2O2 but resulted hypersensitive to t-BOOH. Notably, under these conditions, mycelia from ΔcatA, ΔcatB and wild-type strains showed similar resistance to H2O2 and t-BOOH. Compared with the wild-type, ΔatfA, ΔsakA and ΔcatB mutants were somewhat more sensitive to menadione. While all strains presented similar growth in paraquat, a brownish pigmentation and decreased conidiation was observed in ΔatfA and ΔsakA mutants (Fig. 1C). Results published during the course of this work show that conidia from ΔatfA (ΔsakA was not analysed) mutants were sensitive to 50 mM H2O2 (t-BOOH was not tested), while ΔatfA mycelia was resistant to 1.2 mM t-BOOH (Hagiwara et al., 2008). In agreement with our results, a more recent report shows that ΔatfA mycelium is indeed sensitive to t-BOOH (Balazs et al., 2010).
Affiliation: Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-242, 04510, México, D.F., México.