Saponin detoxification enzymes from pathogenic fungi are involved in the 
infection process of their host plants. Fusarium oxysporum f. sp lycopersici, a 
tomato pathogen, produces the tomatinase enzyme Tom1, which degrades 
alpha-tomatine to less toxic derivates. To study the role of the tom1 gene in 
the virulence of F. oxysporum, we performed targeted disruption and 
overexpression of the gene. The infection process of tomato plants inoculated 
with transformants constitutively producing Tom1 resulted in an increase of 
symptom development. By contrast, tomato plants infected with the knockout 
mutants showed a delay in the disease process, indicating that Tom1, although 
not essential for pathogenicity, is required for the full virulence of F. 
oxysporum. Total tomatinase activity in the disrupted strains was reduced only 
25%, leading to beta(2)-tomatine as the main hydrolysis product of the saponin 
in vitro. In silico analysis of the F. oxysporum genome revealed the existence 
of four additional putative tomatinase genes with identities to tomatinases from 
family 3 of glycosyl hydrolases. These might be responsible for the remaining 
tomatinase activity in the Deltatom1 mutants. Our results indicate that 
detoxification of alpha-tomatine in F. oxysporum is carried out by several 
tomatinase activities, suggesting the importance of these enzymes during the 
infection process.