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Aspergillus nidulans HOG pathway is activated only by two‐component signalling pathway in response to osmotic stress
Author(s) -
Furukawa Kentaro,
Hoshi Yukiko,
Maeda Tatsuya,
Nakajima Tasuku,
Abe Keietsu
Publication year - 2005
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2005.04605.x
Subject(s) - aspergillus nidulans , biology , saccharomyces cerevisiae , complementation , mutant , yeast , mapk/erk pathway , microbiology and biotechnology , phosphorylation , protein kinase a , osmotic shock , signal transduction , mitogen activated protein kinase , genetics , gene , biochemistry
Summary Genome sequencing analyses revealed that Aspergillus nidulans has orthologous genes to all those of the high‐osmolarity glycerol (HOG) response mitogen‐activated protein kinase (MAPK) pathway of Saccharomyces cerevisiae . A. nidulans mutant strains lacking sskA , sskB , pbsB, or hogA , encoding proteins orthologous to the yeast Ssk1p response regulator, Ssk2p/Ssk22p MAPKKKs, Pbs2p MAPKK and Hog1p MAPK, respectively, showed growth inhibition under high osmolarity, and HogA MAPK in these mutants was not phosphorylated under osmotic or oxidative stress. Thus, activation of the A. nidulans HOG (AnHOG) pathway depends solely on the two‐component signalling system, and MAPKK activation mechanisms in the AnHOG pathway differ from those in the yeast HOG pathway, where Pbs2p is activated by two branches, Sln1p and Sho1p. Expression of pbsB complemented the high‐osmolarity sensitivity of yeast pbs2Δ , and the complementation depended on Ssk2p/Ssk22p, but not on Sho1p. Pbs2p requires its Pro‐rich motif for binding to the Src‐homology3 (SH3) domain of Sho1p, but PbsB lacks a typical Pro‐rich motif. However, a PbsB mutant (PbsB(Pro)) with the yeast Pro‐rich motif was activated by the Sho1p branch in yeast. In contrast, HogA in sskAΔ expressing PbsB(Pro) was not phosphorylated under osmotic stress, suggesting that A. nidulans ShoA, orthologous to yeast Sho1p, is not involved in osmoresponsive activation of the AnHOG pathway. We also found that besides HogA, PbsB can activate another Hog1p MAPK orthologue, MpkC, in A. nidulans , although mpkC is dispensable in osmoadaptation. In this study, we discuss the differences between the AnHOG and the yeast HOG pathways.