This dissertation investigates the function of the phosphorelay system containing the response regulator (RR) protein RRG-1 in the filamentous fungus Neurospora crassa. RRG-1 functions as a response regulator (RR) in a multi-component signaling pathway, in which a hybrid histidine kinase (HHK) senses environmental conditions and initiates a phosphorelay through a histidine phosphotransferase (HPT) protein to the response regulator protein (RR). RRG-1 was found to be involved in a number of processes, including spore formation and integrity, female fertility, resistance to hyperosmotic and oxidative stresses and exposure to dicarboximide and phenylpyrrole fungicides. We show that the RR RRG-1 acts upstream of the osmosensing OS-2 mitogen activated protein kinase (MAPK) cascade, which is homologous to the mammalian p38 stress response pathway, in response to hyperosmotic conditions and fungicide treatment. Results indicate that it is the non-phosphorylated form of RRG-1 that activates OS-2 in response to osmotic stress. The N-terminal region of RRG-1, which has high homology to other RR proteins in filamentous fungi but not to the corresponding proteins in yeasts, appears to play a role in regulating the levels of phosphorylated OS-2 induced by salt and fungicide treatment. Results from analysis of RNA and protein levels for RRG-1 suggest that multiple isoforms are produced, with differential abilities to control regulated processes. The function of the eleven HHKs from N. crassa was also investigated. Several phenotypes were observed for various Δhhk mutants including tolerance to oxidative stress, abnormal hyphal morphology and a slower growth rate. The Δos-1 mutant had the most severe phenotype observed for any Δhhk mutant; the defects were similar to those of the Δrrg-1 and os-2 MAPK cascade mutants, including female sterility, impaired conidial integrity, fungicide resistance and osmotic sensitivity. The results suggest that the RR RRG-1 is regulated by the HHK OS-1, which may act as a phosphatase during high osmotic conditions and fungicide treatment.
|School:||University of California, Riverside|
|School Location:||United States -- California|
|Source:||DAI-B 69/10, Dissertation Abstracts International|
|Subjects:||Molecular biology, Genetics, Plant sciences|
|Keywords:||Filamentous fungus, Fungicide resistance, Neurospora crassa, Osmotic sensitivity, Response regulator|
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