Regulation of cAMP and cAMP dependent protein kinase during conidial germination and appressorium formation in Colletotrichum trifolii

Colletotrichum trifolii is the causal agent of alfalfa anthracnose. To investigate the involvement of cAMP/cAMP-dependent protein kinase pathway during conidial germination and appressorial differentiation, enzymatic levels of cAMP-dependent protein kinase were measured from conidia, germinating conidia, appressoria and mycelia. Highest levels of activity were found in germinating conidia, intermediate levels in conidia, and only basal levels of activity in appressoria and mycelia. Using a specific inhibitor of cAMP-dependent protein kinase, KT5720, both conidial germination and appressorial differentiation were impaired when conidia and germinating conidia were treated, respectively. Endogenous cAMP levels were also measured. Highest cAMP levels were found in conidia. Germinating conidia contained 70% less cAMP and the lowest level of cAMP was found in mycelia. Using a pharmacological approach, including 8-Br-cAMP, sodium fluoride and 3-isobutyl-1-methylxanthine, all of which increase endogenous cAMP levels, we showed induction of appressorial differentiation on a non-inductive surface (1.5% water agar). These data strongly suggest that cAMP/cAMP-dependent protein kinase pathway plays a key role during morphogenesis of C. trifolii. (C) 1997 Academic Press Limited.