Knowledge of the molecular basis of plant resistance to pathogens in species other than Arabidopsis is limited. The function of Fa WRKY1, the first WRKY gene isolated from strawberry (Fragaria x ananassa), an important agronomical fruit crop, has been investigated here. Fa WRKY1 encodes a IIc WRKY transcription factor and is up-regulated in strawberry following Colletotrichum acutatum infection, treatments with elicitors, and wounding. Its Arabidopsis sequence homologue, At WRKY75, has been described as playing a role in regulating phosphate starvation responses. However, using T-DNA insertion mutants, a role for the At WRKY75 and Fa WRKY1 in the activation of basal and R-mediated resistance in Arabidopsis is demonstrated. At wrky75 mutants are more susceptible to virulent and avirulent isolates of Pseudomonas syringae. Overexpression of Fa WRKY1 in At wrky75 mutant and wild type reverts the enhanced susceptible phenotype of the mutant, and even increases resistance to avirulent strains of P. syringae. The resistance phenotype is uncoupled to PATHOGENESIS-RELATED (PR) gene expression, but it is associated with a strong oxidative burst and glutathione-S-transferase (GST) induction. Taken together, these results indicate that At WRKY75 and Fa WRKY1 act as positive regulators of defence during compatible and incompatible interactions in Arabidopsis and, very likely, Fa WRKY1 is an important element mediating defence responses to C. acutatum in strawberry. Moreover, these results provide evidence that Arabidopsis can be a useful model for functional studies in Rosacea species like strawberry.

Important losses in strawberry production are caused by species of the fungus Colletotrichum, the causal agent of anthracnose. However, very limited studies at molecular level exist of the mechanisms related to strawberry susceptibility against this pathogen. We have analysed a moderately resistant cultivar (cv. Andana) together with a very susceptible one (cv. Camarosa) during the process of infection with Colletotrichum acutatum at a molecular level. To gain insight into this interaction we have identified a large number of strawberry genes involved in signalling, transcriptional control, defence and many genes with unknown function with altered expression in response to C. acutatum infection. Spatial and temporal gene expression profiles after infection showed that the response was dependant on the tissue and cultivar analysed and also quicker and/or stronger in the moderately resistant cultivar (cv. Andana) than in the susceptible one (cv. Camarosa). Interestingly, we found that genes described as being induced during pathogen infection such as g-thionins, peroxidases, chitinases and b-1-3-glucanases were downregulated in fruit and/ or crown tissues of the very susceptible cultivar. Our results yielded a first insight on some of the genes responding to this plant-pathogen interaction at molecular level and suggest that pathogen progression can be dependent upon a reduction of the active defences of strawberry and this is genotype and tissue dependent.

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