CERATO-ULMIN, A HYDROPHOBIN SECRETED BY THE CAUSAL AGENTS OF DUTCH ELM DISEASE, IS A PARASITIC FITNESS FACTOR

Dutch elm disease is caused by the aggressive Ophiostoma novo-ulmi and the nonaggressive O. ulmi, Both secrete the protein cerato-ulmin (CU) , To determine what role CU plays in the pathology of Dutch elm diseas e, we constructed a CU overexpression mutant of the nonaggressive O. u lmi H5, Stable integration of a single copy of the cu gene from the ag gressive O. novo-ulmi into the genome of the nonaggressive isolate res ulted in increased secretion of CU protein, Trials with American elm, Ulmus americana, suggested no alteration of virulence of this overexpr essing transformant, Using aggressive and nonaggressive wild types, th e cu overexpressing mutant, and our cu(-) mutant (Bowden et al., 1996) , we have demonstrated that CU production is correlated with an altere d phenotype and more hydrophobic and adherent yeast-like cells, Our re sults also demonstrate that CU has a role in protecting infectious pro pagules from desiccation. These biological roles for CU would affect t ransmission of Dutch elm disease, and we therefore propose that this h ydrophobin acts as a parasitic fitness factor. (C) 1997 Academic Press .