Role of Phosphorylation in Fungal Spore Germination

Spore germination is a common and fundamental event in fungal development and in many instances an essential phase of fungal infection and dissemination. Spore germination is also critical for hyperparasites to function as biocontrol agents as well as in fermentation proceses. Our common objective is to understand the mechanisms which regulated spore germination and identify factors involved in pathogenicity related prepenetration development. Our approach is to exploit the overall similarity among filamentous fungi using both a plant pathogen (Colletotricum trifolii) and a model system that is genetically sophisticated (Neurospora crassa). The simulataneous use of two organisms has the advantage of the available tools in Neurospora to rapidly advance the functional analysis of genes involved in spore germination and development of an economically important fungal phytopathogen. Towards this we have isolated a protein kinase gene from C. trifolii (TB3) that is maximally expressed during the first hour of conidial germination and prior to any visible gene tube formation. Based on sequence similarities with other organisms, this gene is likely to be involved in the proliferative response in the fungus. In addition, TB3 was able to functionally complement a N. crassa mutant (COT-1). Pharmacological studies indicated the importance of calmodulin in both germination and appressorium differentiation. Using an antisense vector from N. crassa, direct inhibition of calmodulin results in prevention of differentiation as well as pathogenicity. Both cAMP dependent protein kinase (PKA) and protein kinase C (PKC) like genes have been cloned from C. trifolii. Biochemical inhibition of PKA prevents germination; biochemical inhibitors of PKC prevents appressorium differentiation. In order to analyze reversible phosphorylation as a regulatory mechanism, some ser.thr dephosphorylative events have also been analyzed. Type 2A and Type 2B (calcineurin) phosphatases have been identified and structurally and functionally analyzed in N. crassa during this project. Both phosphatases are essential for hyphal growth and maintenance of proper hyphal architecture. In addition, a first novel-type (PPT/PP5-like) ser/thr phosphatase has been identified in a filamentous fungus. The highly collaborative project has improved our understanding of a fundamental process in fungi, and has identified targets which can be used to develop new approaches for control of fungal plant pathogens as well as improve the performance of beneficial fungi in the field and in industry. In addition, the feasibility of molecular technology transfer in comparative mycology has been demonstrated.