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: The H2O2 sensitivity observed in ΔatfA and ΔsakA mutants suggested that AtfA and SakA could play a role in the regulation of catalase genes catA and catB, as well as in the regulation of other genes specifically involved in the response to oxidative stress caused by t-BOOH. To determine if sensitivity to H2O2 was related to catalase gene expression, we first examined catalase activity in conidial samples from wild-type, ΔatfA and ΔsakA strains. Consistent with previous findings (Kawasaki et al., 2002; Vargas-Perez et al., 2007), CatA activity levels in ΔsakA conidia were lower than in wild-type conidia. This situation was more severe in the ΔatfA mutant, as no CatA activity was detected in ΔatfA conidia (Fig. 2A), a result consistent with the absence of catA mRNA in ΔatfA conidia (Hagiwara et al., 2008). However, as catA mRNA accumulates in response to different types of stress, some of which induce conidiation (Navarro and Aguirre, 1998), we examined catA mRNA levels under nutrient starvation conditions. As shown in Fig. 2B, catA mRNA did not accumulate when mycelia grown for 12 h was transferred to regular media for another 3 h. In contrast, catA mRNA accumulated in response to nutrient starvation and the lack of sakA or atfA had negative effects on catA mRNA levels. While sakA and atfA were partially required for high catA mRNA levels in response to carbon starvation, either gene was essential for increased catA mRNA levels under nitrogen starvation. These results indicate that AtfA and SakA function in the same pathway to regulate catA expression during development and in response to stress, and show that the SakA pathway is involved in transducing carbon and nitrogen starvation signals.
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.