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: Our results above suggest a model in which the MAPK SakA regulates putative transcription factor AtfA, in response to different stress signals. To examine AtfA and SakA localization we generated strains TFL3 and TFL6, which carry atfA::gfp or sakA::gfp alleles replacing the wild-type genes respectively (confirmed by Southern blot analysis; not shown). As shown in Fig. S5, conidia from strains TFL3 and TFL6 were not sensitive to H2O2, indicating that GFP tagging did not interfere with AtfA or SakA functions. In addition, the atfA::gfp allele was introduced into a ΔsakA genetic background by sexual crosses, to generate strain CFL9, and the presence of both mutant alleles was confirmed by Southern analysis (not shown). When these strains were used to detect GFP localization, we found AtfA::GFP in the nucleus even in the absence of any experimentally induced stress. Furthermore, such nuclear localization was largely unaffected by the absence of the MAPK SakA (Fig. 4A). In contrast, SakA::GFP fluorescence was not restricted to DAPI-stained nuclei, showing a more uniform distribution in hyphae (Fig. 4A, right panels). These results supported AtfA function as transcription factor and suggested that to regulate AtfA, SakA would need to be translocated to the nucleus. Indeed, treatment with H2O2 induced a re-distribution of SakA::GFP fluorescence consistent with the nuclear localization of SakA in response to oxidative stress (Fig. 4B).
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.