A novel signal transduction pathway involved in regulation of development and mycotoxin production in the filamentous fungus Aspergillus nidulans
Cell Biology
Final Report Abstract
Initial experiments performed during this project failed to demonstrate that ImeB is directly involved in light-regulation of fungal development. In particular, in vitro kinase assay did not provide hints that components of the velvet complex, a key factor for light control in the nucleus, is phosphorylated by the ImeB protein kinase. TAP purifications assays did not result in the identification of other putative substrates of ImeB. However, it could be shown that the velvet component VeA is phosphorylated by another protein kinase, the MAP kinase MpkB. This kinase is the homolog to the yeast Fus3 of the pheromone response pathway. These findings with MpkB (AnFus3) prompted me to study this signal transduction pathway in detail. It was shown that MpkB (AnFus3) mediated phosphorylation of VeA promotes assembly of the velvet complex. MkkB (AnSte7) and SteC (AnSte11) were identified as kinases acting upstream of MpkB (AnFus3) in the MAP kinase module. These kinases were found to be associated with each other, as well as with SteD (AnSte50), which acts an adaptor for membrane localization. Mutants lacking any of these factors are impaired in sexual development and secondary metabolism. In summary, this part of the project demonstrated that the pheromone response pathway acts upstream of the velvet complex in regulating development and secondary metabolism. Furthermore, genetic experiments revealed further hints regarding regulation of the velvet complex. The light response defect of laeA deletions was efficiently restored by a single mutation. This mutation in the veA gene results in the production of a truncated VeA protein, which cannot be imported into the nucleus. This part of the projects provides compelling evidence that inactivating VeA in the nucleus is the crucial function of LaeA in the light response pathway.
Publications
- (2011) The Ime2 protein kinase family in fungi: More duties than just meiosis. Mol. Microbiology, 80: 1-13
Irniger S
- (2012) The Aspergillus nidulans MAPK module AnSte11-Ste50-Ste7-Fus3 controls development and secondary metabolism. PLoS Genet 8: e1002816
Bayram O, Bayram OS, Ahmed YL, Maruyama J, Valerius O, Rizzoli SO, Ficner R, Irniger S, Braus GH
(See online at https://doi.org/10.1371/journal.pgen.1002816)
