Calcium- and Calmodulin-mediated Protein Synthesis and Protein Phosphorylation during Germination, Growth and Protease Production by Metarhizium anisopliae

Protein synthesis and phosphorylation were studied in Metarhizium anisopliae. Calmodulin (CaM) and CaM-target proteins were found in conidia and germlings of M. anisopliae. Conidial uptake of [35S]methionine and [32P]orthophosphate and their incorporation into protein was massively reduced by known antagonists of CaM, depletion of intracellular Ca2+ by ionophoresis or antagonism of Ca2+ with La3+, agents which prevented nuclear division and germination. Inhibitors of C-kinase (H-7) and cyclic-nucleotide-dependent kinase (H-8) selectively repressed phosphorylation of a 27 kDa protein but did not affect the profile of protein synthesis nor change germination frequency and mode of growth. By contrast, inhibitor and ionophoresis studies on mycelia showed that extracellular secretion of proteins but not protein synthesis was Ca2+-dependent. Protein phosphorylation in mycelia was also Ca2+-dependent/ CaM-independent. CaM antagonists stimulated phosphorylation of 17 and 33 kDa polypeptides. Most proteins in mycelia were phosphorylated at serine and threonine residues. However, immunoblotting with anti-phosphotyrosine serum revealed prominent bands at 34·5 and 38 kDa. The 38 kDa protein was detectable on isolated plasma membranes. Our results suggest that M. anisopliae possesses stimulus transduction pathways similar to those known in plant and animal systems.