Dothideomycete Plant Pathogens Require Specific Virulence Factors for Colonization and Host Plants Have Developed Specific R Genes for Defence

The tomato pathogen Cladosporium fulvum is a Dothideomycete that is most related to the hemi-biotrophic fungal pine pathogen Dothistroma septosporum. We study genomic adaptations in these and related fungi that can explain host plant-specificity. The C. fulvum genomic sequence allowed us to identify and study its complete effector catalogue including three core effectors (Avr4, Ecp2 and Ecp6). The genome of D. septosporum harbors the highest number of homologs of C. fulvum effectors, but some are pseudogenized. Both C. fulvum and D. septosporum contain a large number of genes involved in the production of secondary metabolites. C. fulvum seems to adapt its host plant tomato by down-regulation or pseudogenization of genes involved in the production of toxic secondary metabolites. One example is dothiostromin, a toxin produced by D. septosporum during colonization of pine needle. C. fulvum contains all genes required for the production of this toxin, but a few of these genes are pseudogenized. Apart from new effectors (Avr5) we have also identified new pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) from C. fulvum. Both represent cell-wall degrading enzymes produced by C. fulvum during infection of tomato. We also found that C. fulvum has adapted to grow on tomato by secreting the enzyme a-tomatinase that hydrolyses the antifungal tomato saponin a-tomatine into the non-toxic compounds lycotetraose and tomatidine.