Cytological and molecular analyses of non-host resistance of Arabidopsis thaliana to Alternaria alternata

When challenged with the necrotrophic fungal pathogen Alternaria alternata Japanese pear pathotype, all tested ecotypes of Arabidopsis plants failed to show hypersensitive cell death, accumulation of detectable levels of reactive oxygen species or accumulation of phytoalexin. We operationally define A. alternata as a non-host pathogen for Arabidopsis plants and show that the protection against A. alternata demonstrated in this study is a non-host penetration resistance. To characterize non-host penetration resistance, we examined the expression patterns of c. 7000 genes by cDNA microarray analysis in Arabidopsis Col-0 plants after inoculation with A. alternata. After inoculation with A. alternata, the transcript levels of 48 genes increased in Col-0 plants. The expression of genes associated with hypersensitive reaction was induced in the non-host penetration resistance to A. alternata, despite the fact that A. alternata had no visible effect on the plants. The non-host penetration resistance to A. alternata was clearly associated with activation of the jasmonate- and ethylene-signalling pathways. In addition, analysis using histochemical staining of GUS activity suggests that defence reactions in non-host penetration resistance are activated locally. The characterization of non-host pathosystem involving Arabidopsis and A. alternata offers an overview of non-host penetration resistance.