Abstract
BackgroundThe necrogenic enterobacterium, Erwinia amylovora is the causal agent of the fire blight (FB) disease in many Rosaceaespecies, including apple and pear. During the infection process, the bacteria induce an oxidative stress response with kinetics similar to those induced in an incompatible bacteria-plant interaction. No resistance mechanism to E. amylovora in host plants has yet been characterized, recent work has identified some molecular events which occur in resistant and/or susceptible host interaction with E. amylovora: In order to understand the mechanisms that characterize responses to FB, differentially expressed genes were identified by cDNA-AFLP analysis in resistant and susceptible apple genotypes after inoculation with E. amylovora.ResultscDNA were isolated from M.26 (susceptible) and G.41 (resistant) apple tissues collected 2 h and 48 h after challenge with a virulent E. amylovora strain or mock (buffer) inoculated. To identify differentially expressed transcripts, electrophoretic banding patterns were obtained from cDNAs. In the AFLP experiments, M.26 and G.41 showed different patterns of expression, including genes specifically induced, not induced, or repressed by E. amylovora. In total, 190 ESTs differentially expressed between M.26 and G.41 were identified using 42 pairs of AFLP primers. cDNA-AFLP analysis of global EST expression in a resistant and a susceptible apple genotype identified different major classes of genes. EST sequencing data showed that genes linked to resistance, encoding proteins involved in recognition, signaling, defense and apoptosis, were modulated by E. amylovora in its host plant. The expression time course of some of these ESTs selected via a bioinformatic analysis has been characterized.ConclusionThese data are being used to develop hypotheses of resistance or susceptibility mechanisms in Malus to E. amylovora and provide an initial categorization of genes possibly involved in recognition events, early signaling responses the subsequent development of resistance or susceptibility. These data also provided potential candidates for improving apple resistance to fire blight either by marker-assisted selection or genetic engineering.
Highlights
The necrogenic enterobacterium, Erwinia amylovora is the causal agent of the fire blight (FB) disease in many Rosaceaespecies, including apple and pear
E. amylovora, a comparison of gene expression patterns between the resistant apple rootstock ‘G.41’ and the susceptible ‘M.26’ was carried out using cDNA-AFLP-analysis at 2 and 48 hpi. These time points were selected based upon previous analysis of the temporal transcriptional response of Malus to E. amylovora [23]which indicated that basal defense to pathogen associated molecular patterns (PAMPs) occurred within 1-2 hpi whereas expression of PR proteins occurred 24-48 hpi
CDNA templates were prepared from leaves inoculated with E. amylovora, and from control leaves treated with buffer for both apple cultivars
Summary
The necrogenic enterobacterium, Erwinia amylovora is the causal agent of the fire blight (FB) disease in many Rosaceaespecies, including apple and pear. Various defense responses are induced when a pathogen attempts to invade a non-host plant or resistant host The ability of some gram negative bacterial pathogens, such as Erwinia, Pseudomonas, Xanthomonas and Ralstonia strains, to cause disease in susceptible plants and elicit HR in resistant or non-host plants is governed by the hrp(hypersensitive reaction and pathogenicity) gene cluster [7,8]. These genes encode components of a type
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