Verticillium albo-atrum is a vascular wilt pathogen capable of infecting many important dicotyledonous plant species. Fungal isolates from hop differ in aggressiveness, causing either mild or lethal symptoms in infected plants. As in other plant pathogenic fungi, extracellular
proteins, such as cell wall-degrading
enzymes and effectors, are thought to be crucial in the pathogenesis process. In this study, mild and lethal isolates from three countries were grown in simulated xylem medium and secretome analysis by 2D-DIGE showed low qualitative and high quantitative variability among the isolates. Functional classification of 194 identified
proteins representing 100 unique
protein accessions revealed an arsenal of cell wall-degrading
enzymes and potential effectors. The set of
proteins that were more abundant in at least two lethal isolates included
enzymes acetylcholinesterases, lipases, polygalacturonases,
pectate lyase, rhamnogalacturonan acetylesterases,
acetylxylan esterase,
endoglucanase, xylanases,
mannosidases, and a
protein similar to
alginate lyase and also potential effectors
necrosis- and
ethylene-inducing
protein, small basic 14 kDa hypothetical
protein and 79 kDa hypothetical
proteins. Other
proteins associated with virulence showed different expression profiles between mild and lethal isolates. The results suggest that the increased virulence of lethal isolates has little background shared by all three lethal isolates and that upregulation of isolate specific sets of
proteins may be most important.