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
Related in: MedlinePlus
Mentions: Our results indicate that SakA is phosphorylated and accumulated in the nucleus not only in response to oxidative stress but also during normal spore development. To provide further support to this, we followed SakA::GFP and AtfA::GFP localization during development. AtfA::GFP showed nuclear localization in intact and germinating spores and throughout mycelial growth and conidiophore development (Fig. 8A, top panels). SakA::GFP showed discrete as well as evenly distributed signals in intact and germinating spores, while fluorescence was homogeneously distributed in growing hyphae (Fig. 8A, bottom panels). In contrast to AtfA::GFP, SakA::GFP signal showed a more uniform localization within the different conidiophore cell types, as well as in some patches (Fig. 8A, bottom panels). SakA localization results are consistent with its phosphorylation in conidia and suggest that SakA becomes partially phosphorylated during conidiophore development. Taking advantage of the fact that the alcA promoter is derepressed during conidiophore formation (Marhoul, 1996), we also used BiFC to evaluate the physical interaction of SakA and AtfA during conidiophore development. Although fluorescence was not detected in every cell, it was possible to clearly detect YFP signal in different conidiophore cell types, including metulae, phialides and developing spores (Fig. 8B). These results suggest that these cell types are under physiological stress and that the SakA–AtfA interaction during conidiophore development is critical in regulating gene expression and the developmental stages that culminate with the formation of viable dormant spores.
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.