Molecular response of resistant and susceptible apple genotypes to Erwinia amylovora infection

Abstract

The leaves of apple cultivars resistant (cv. Free Redstar) and susceptible (cv. Idared) to fire blight were infiltrated with Erwinia amylovora. After 24 hours, differential gene expression was analysed using cDNA-AFLP technique. The expression pattern in the resistant cultivar, especially up-regulated genes encoding proteins involved in hypersensitive reaction and controlled cell death (BAX inhibitor and HIR protein), support the hypothesis that hypersensitive reaction is the main mechanism of resistance to fire blight in cv. Free Redstar. An important role in the resistance reaction is also played by proteins involved in signal transduction, especially serine/threonine kinase, which has been shown previously to confer resistance to fungal and bacterial pathogens in a number of plant species. A potential role in the defence against Erwinia amylovora was probably also β-1,3-glucanase (PR-2 protein), which was up-regulated in the resistant cultivar only. One of the proteins known to be involved in plant defense against pathogens – glutamate receptor – was up-regulated in the leaves of cv. Idared. Although the susceptible phenotype of this cultivar shows that expression of glutamate receptor only does not provide substantial resistance, it may be considered in gene pyramiding in apple breeding programmes.