THE IN PLANTA-PRODUCED EXTRACELLULAR PROTEINS ECP1 AND ECP2 OF CLADOSPORIUM-FULVUM ARE VIRULENCE FACTORS

The two extracellular proteins ECP1 and ECP2 are abundantly secreted b y the plant-pathogenic fungus Cladosporium fulvum during colonization of the intercellular space of tomato leaves. We examined the involveme nt of both proteins in pathogenicity and virulence of this fungus. ECP 1-deficient, ECP2-deficient, and ECP1/ECP2-deficient isogenic C. fulvu m strains were created by targeted gene replacement. Upon inoculation onto susceptible 6-week-old tomato plants, all three mutants showed re duced virulence, Deficiency in ECP2 resulted in a strain that poorly c olonized the leaf tissue and secreted lower amounts of the in planta-p roduced ECP3, AVR4, and AVR9 proteins than the wild-type strain, The E CP2-deficient strain produced little emerging mycelium and few conidia . Deficiency in ECP1 did not significantly modify colonization of the leaf tissue, but reduced secretion of in planta-produced proteins. The ECP1-deficient strain emerged from stomata of the lower epidermis, bu t failed to sporulate as abundantly as the wild-type strain. A strain deficient in both ECP1 and ECP2 proteins had a phenotype similar to th at of the ECP2-deficient strain, Accumulation of pathogenesis-related proteins and induction of late responses, such as leaf desiccation and abscission, occurred more quickly and more severely in tomato after i noculation with the ECP1-, ECP2-, and ECP1/ECP2-deficient strains than after inoculation with the wild-type strain. Moreover, partial collap se of stomatal guard cells occurred at emergence of the ECP2-deficient strain. These results indicate that the ECP1 and ECP2 proteins play a role in virulence of C. fulvum on tomato and suggest that both are in volved in suppression of host defense responses.