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 pat hway during conidial germination and appressorial differentiation, enz ymatic levels of cAMP-dependent protein kinase were measured from coni dia, germinating conidia, appressoria and mycelia. Highest levels of a ctivity were found in germinating conidia, intermediate levels in coni dia, and only basal levels of activity in appressoria and mycelia. Usi ng a specific inhibitor of cAMP-dependent protein kinase, KT5720, both conidial germination and appressorial differentiation were impaired w hen conidia and germinating conidia were treated, respectively. Endoge nous cAMP levels were also measured. Highest cAMP levels were found in conidia. Germinating conidia contained 70% less cAMP and the lowest l evel of cAMP was found in mycelia. Using a pharmacological approach, i ncluding 8-Br-cAMP, sodium fluoride and 3-isobutyl-1-methylxanthine, a ll of which increase endogenous cAMP levels, we showed induction of ap pressorial 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) 199 7 Academic Press Limited.