TheCladosporium fulvumVirulence Protein Avr2 Inhibits Host Proteases Required for Basal Defense  

Abstract

Cladosporium fulvum (syn. Passalora fulva) is a biotrophic fungal pathogen that causes leaf mold of tomato (Solanum lycopersicum). During growth in the apoplast, the fungus establishes disease by secreting effector proteins, 10 of which have been characterized. We have previously shown that the Avr2 effector interacts with the apoplastic tomato Cys protease Rcr3, which is required for Cf-2-mediated immunity. We now show that Avr2 is a genuine virulence factor of C. fulvum. Heterologous expression of Avr2 in Arabidopsis thaliana causes enhanced susceptibility toward extracellular fungal pathogens, including Botrytis cinerea and Verticillium dahliae, and microarray analysis showed that Avr2 expression triggers a global transcriptome reflecting pathogen challenge. Cys protease activity profiling showed that Avr2 inhibits multiple extracellular Arabidopsis Cys proteases. In tomato, Avr2 expression caused enhanced susceptibility toward Avr2-defective C. fulvum strains and also toward B. cinerea and V. dahliae. Cys protease activity profiling in tomato revealed that, in this plant also, Avr2 inhibits multiple extracellular Cys proteases, including Rcr3 and its close relative Pip1. Finally, silencing of Avr2 significantly compromised C. fulvum virulence on tomato. We conclude that Avr2 is a genuine virulence factor of C. fulvum that inhibits several Cys proteases required for plant basal defense.

Chitin and chitin-related compounds in plant–fungal interactions

“…In C. fulvum mutants deleted in CfWor1 , which is a global transcriptional regulator (Okmen et al 2014), expression of Avr2, Avr4, Ecp6 genes were all highly reduced, particularly during the early stage of infection. Avr2 is an inhibitor of several plant Cys proteases that are required for a basal response but is recognised by the extracellular Cf-2 immune receptor (Rooney et al 2005; Van Esse et al 2008). Avr4 is a chitin-binding protein that protects the fungus from plant chitinases, and it is recognised by the Hcr9-4D LRR-RLP gene located at the Cf-4 locus (Thomas et al 1997; Van Den Burg et al 2006).…”

Effector Biology of Plant-Associated Organisms: Concepts and Perspectives

“…1A). Classic examples include the effectors of the dothidiomycete leaf mold fungus Cladosporium fulvum Avr2, Avr4, and ECP6, which target various extracellular processes of the host plant tomato (van den Burg et al 2006;Bolton et al 2008;van Esse et al 2008). Whereas Avr2 is an inhibitor of tomato apoplastic cysteine proteases, ECP6 interferes with the perception of C. fulvum cell wall chitin by tomato cell surface immune receptors (de Jonge et al 2010).…”

An Effector-Targeted Protease Contributes to Defense against Phytophthora infestans and Is under Diversifying Selection in Natural Hosts

“…ABPP of PLCPs is based on the use of DCG-04, which is a biotinylated derivative of the PLCP inhibitor E-64 that irreversibly reacts with the active site Cys residue in a mechanism-dependent manner (Greenbaum et al, 2000). This technique was used to show that AVR2 inhibits RCR3 and PIP1 (Rooney et al, 2005;Shabab et al, 2008;van Esse et al, 2008), EPIC1 inhibits RCR3 (Song et al, 2009), and EPIC2B inhibits PIP1 and RCR3 (Tian et al, 2007;Song et al, 2009). The advantage of using ABPP is that proteases can be produced in planta and tested without purification, allowing us to test for selectivity in the presence of other proteases.…”

“…C. fulvum secretes AVR2, which mainly inhibits the tomato-secreted PLCPs PIP1 and RCR3 (Rooney et al, 2005;Shabab et al, 2008;van Esse et al, 2008). P. infestans secretes cystatin-like EPIC1 and EPIC2B proteins.…”

“…RCR3 contributes to resistance to C. fulvum and P. infestans (Dixon et al, 2000;Song et al, 2009). Furthermore, constitutive expression of the protease inhibitor AVR2 in transgenic Arabidopsis (Arabidopsis thaliana) and tomato results in plants that are more susceptible to a broad range of pathogens (van Esse et al, 2008).…”