MORPHOGENIC REGULATION OF PATHOTOXIN SYNTHESIS IN COCHLIOBOLUS-CARBONUM

The fungus Cochliobolus carbonum causes leaf spot disease of maize, Hi ghly virulent isolates of the pathogen produce a host-selective, pepti de toxin that is active against susceptible genotypes of maize, Prior to infection, spores must germinate and differentiate appressoria, str uctures specialized for leaf penetration, Analysis of spore germinatio n fluids by plasma desorption mass spectrometry, which allowed detecti on of as little as 0.5 ng toxin, revealed that spores induced to form appressoria in vitro synthesized and released the toxin at a time coin cident with maturation of appressoria, Spores incubated under conditio ns that did not induce appressorium formation failed to produce toxin, These observations indicate that synthesis of the host-selective toxi n, which is essential for successful pathogenesis of maize by C. carbo num, is regulated by infection-related morphogenesis. (C) 1996 Academi c Press, Inc.