Identification of genes differentially expressed during interaction of resistant and susceptible apple cultivars (Malus × domestica) with Erwinia amylovora

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.

dHPLC efficiency for semi-automated cDNA-AFLP analyses and fragment collection in the apple scab-resistance gene model

“…In fact, a good correspondence between intensities of detected peaks upon dHPLC analysis and levels of expression of identified genes after qRT-PCR was found for 81.3% of selected TDFs. This result is comparable to that obtained by Baldo et al (2010) who reported that the expression profile observed by AFLP was confirmed by qRT-PCR on the same cDNA in 79% of 28 ESTs under examination. According to these results, it can be assumed that the modulation of about 81% of the collected TDF is confirmed.…”

“…With respect to the microarray technology (based on known genes spotted on the slide/chip), the transcriptional profiling obtained by cDNA-AFLP makes it possible to cover the whole transcriptome using different combinations of restriction enzymes and primers. This approach has already been successfully used in apple to define the rootstock effect on gene expression patterns in tree scions (Jensen et al 2003), the interaction between (Baldo et al 2010).…”

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

“…However, since the cultivar studied is susceptible to fire blight, most likely the majority of these differentially-expressed genes are linked to disease development rather than to disease resistance. Baldo et al (2010) analysed transcriptomes of resistant (G.41 rootstock) and susceptible (M.26 rootstock) apple genotypes challenged with E. amylovora using a cDNA-AFLP technique. Two genes which were up-regulated in the resistant genotype, 176.2-G41-48I encoding putative disease resistance protein and 137.1-G41-48I encoding protein similar to Rubredoxin-type Fe(Cys)4 protein from Oryza sativa, were considered as good candidates conferring resistance to fire blight.…”

Closely-related Xanthomonas citri subsp. citri isolates trigger distinct histological and transcriptional responses in Citrus limon

“…Baldo et al (2010) also found a TDF homologue to MYB 11 in Malus domestica, which was overexpressed in susceptible cultivars after inoculation with Erwinia amylovora. In the same way, two MYB genes in Arabidopsis thaliana were specifically induced by Type 3 effector proteins, and they negatively regulated phenylpropanoid metabolism (Preston et al, 2004).…”

“…It has been shown that the PSII system plays an important role in preventing the accumulation of reactive oxygen species (ROS) (Asada, 1999), and it also seems to participate in both compatible and incompatible plant pathogen interactions (Baldo et al, 2010).…”