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Eukaryotic Cell, September 2007, p. 1570-1583, Vol. 6, No. 9
1535-9778/07/$08.00+0     doi:10.1128/EC.00085-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Response Regulators SrrA and SskA Are Central Components of a Phosphorelay System Involved in Stress Signal Transduction and Asexual Sporulation in Aspergillus nidulans{triangledown} ,{dagger}

Itzel Vargas-Pérez, Olivia Sánchez, Laura Kawasaki, Dimitris Georgellis, and Jesús Aguirre*

Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-242, 04510, México, D.F., México

Received 16 March 2007/ Accepted 6 July 2007

Among eukaryotes, only slime molds, fungi, and plants contain signal transduction phosphorelay systems. In filamentous fungi, multiple sensor kinases appear to use a single histidine-containing phosphotransfer (HPt) protein to relay signals to two response regulators (RR). In Aspergillus nidulans, the RR SskA mediates activation of the mitogen-activated protein kinase SakA in response to osmotic and oxidative stress, whereas the functions of the RR SrrA were unknown. We used a genetic approach to characterize the srrA gene as a new member of the skn7/prr1 family and to analyze the roles of SrrA in the phosphorelay system composed of the RR SskA, the HPt protein YpdA, and the sensor kinase NikA. While mutants lacking the HPt protein YpdA are unviable, mutants lacking SskA ({Delta}sskA), SrrA ({Delta}srrA), or both RR ({Delta}srrA {Delta}sskA) are viable and differentially affected in osmotic and oxidative stress responses. Both RR are involved in osmostress resistance, but {Delta}sskA mutants are more sensitive to this stress, and only SrrA is required for H2O2 resistance and H2O2-mediated induction of catalase CatB. In contrast, both RR are individually required for fungicide sensitivity and calcofluor resistance and for normal sporulation and conidiospore viability. The {Delta}srrA and {Delta}sskA sporulation defects appear to be related to decreased mRNA levels of the key sporulation gene brlA. In contrast, conidiospore viability defects do not correlate with the activity of the spore-specific catalase CatA. Our results support a model in which NikA acts upstream of SrrA and SskA to transmit fungicide signals and to regulate asexual sporulation and conidiospore viability. In contrast, NikA appears dispensable for osmotic and oxidative stress signaling. These results highlight important differences in stress signal transmission among fungi and define a phosphorelay system involved in oxidative and osmotic stress, cell wall maintenance, fungicide sensitivity, asexual reproduction, and spore viability.

* Corresponding author. Mailing address: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-242, 04510, México, D.F., México. Phone: (5255) 5622 5651. Fax: (5255) 5622 5630. E-mail: jaguirre{at}ifc.unam.mx

{triangledown} Published ahead of print on 13 July 2007.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

Eukaryotic Cell, September 2007, p. 1570-1583, Vol. 6, No. 9
1535-9778/07/$08.00+0     doi:10.1128/EC.00085-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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  • Bahn, Y.-S. (2008). Master and Commander in Fungal Pathogens: the Two-Component System and the HOG Signaling Pathway. Eukaryot Cell 7: 2017-2036 [Full Text]  


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