The relevance of tomatinase activity in pathogens of tomato:: disruption of the β2-tomatinase gene in Colletotrichum coccodes and Septoria lycopersici and heterologous expression of the Septoria lycopersici β2-tomatinase in Nectria haematococca, a pathogen of tomato fruit

Many fungal pathogens of tomato have the ability to enzymatically detoxify the toxic steroidal glyco alkaloid alpha -tomatine, synthesized by Lycopersicon and some Solanum species. However, it is unclear whether detoxification of this phytoanticipin is involved in the ability of these fungi to parasitize tomato. We have taken two approaches to address this question. For one approach, we have reduced or eliminated this enzymatic function by transformation-mediated disruption of the gene encoding beta (2)-tomatinase in Colletotrichum coccodes and Septoria lycopersici. Gene disruption of the S. lycopersici beta (2)-tomatinase gene in an albino strain resulted in both a loss of beta (2)-tomatinase activity and a loss of tolerance to a-tomatine. The results of pathogenicity tests with this mutant were inconclusive due to the lack of pathogenicity of the albino mutant. Disruption of the beta (2)-tomatinase gene in C. coccodes resulted in a loss of beta (2)-tomatinase activity but these mutants retained their tolerance to cc-tomatine and their abilities to degrade a-tomatine via other enzyme(s). The gene-disrupted mutants were as pathogenic as wild type isolates on green tomato fruit, an organ containing high levels of cc-tomatine. For our other approach, we have expressed the S. lycopersici beta (2)-tomatinase gene in a tomatine tolerant mutant of Nectria haematococca MPVI, a fungus that normally can infect ripe but not green tomato fruit. Expression of beta (2)-tomatinase in this N. haematococca mutant enabled it to detoxify alpha -tomatine and resulted in its ability to parasitize green tomato fruit. (C) 2001 Academic Press.