INVOLVEMENT OF PROTEIN-PHOSPHORYLATION IN THE INDUCTION OF APPRESSORIUM FORMATION IN COLLETOTRICHUM-GLOEOSPORIOIDES BY ITS HOST SURFACE WAX AND ETHYLENE

Avocado surface wax and the ripening hormone ethylene induce conidial germination and appressorium formation in the avocado pathogen, Colletotrichum gloeosporioides. Both the host surface wax and ethylene induced phosphorylation of mainly 29 kDa and 43 kDa proteins and enhanced phosphorylation of proteins at 18 kDa. Protein kinase inhibitors H-7 and genistein inhibited ethylene-induced appressorium formation and phosphorylation of the proteins. However, wax-induced appressorium formation and protein phosphorylation were hardly affected by H-7. In yeast extract that allows spore germination, calyculin A, a potent inhibitor of protein phosphatases, induced appressorium formation and phosphorylation of the same 29 and 43 kDa proteins as did ethylene and avocado wax. Calyculin A also caused abnormal differentiation such as the formation of an additional appressorium directly from the initial appressorium and at higher concentrations the formation of unusual structures. These results indicate that protein phosphorylation may be involved in the induction of appressorium formation by the two host signals. (C) 1995 Academic Press Limited