HYPHAL DEVELOPMENT IN NEUROSPORA-CRASSA - INVOLVEMENT OF A 2-COMPONENT HISTIDINE KINASE

Two-component signal transduction systems are most often found in prok aryotic organisms where they are responsible for mediating the cellula r responses to many environmental stimuli, These systems are composed of an autophosphorylating histidine kinase and a response regulator, W e have found evidence for the existence of two-component histidine kin ases in the eukaryotic filamentous fungus Neurospora crassa based on s creening with degenerate primers to conserved regions of these signali ng proteins, Subsequent cloning and sequencing of one member of this n ewly discovered group, nik-1(+), shows that the predicted protein sequ ence shares homology with both the kinase and response regulator modul es of two-component signaling proteins, In addition, the N-terminal re gion of the protein has a novel repeating 90-amino acid motif, Deletio n of the nik-1(+) gene in N. crassa results in an organism that displa ys aberrant hyphal structure, which is enhanced under conditions of hi gh osmostress, Increased osmotic pressure during growth on solid mediu m leads to restricted colonial growth, loss of aerial hyphae formation , and no subsequent conidiophore development, This finding may have im plications for mechanisms of fungal colonization and pathogenicity.