Identification of genes differentially expressed during interaction of resistant and susceptible apple cultivars (Malus x domestica) with Erwinia amylovora.
BACKGROUND
The necrogenic enterobacterium, Erwinia amylovora is the causal agent of the fire blight (FB) disease in many Rosaceae species, 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.


RESULTS
cDNA 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.


CONCLUSIONS
These 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.
Baldo
Angela
A
FEM-IASMA Research Centre, Via E. Mach 1, San Michele all'Adige, TN, Italy.
Norelli
Jay L
JL
Farrell
Robert E
RE
Bassett
Carole L
CL
Aldwinckle
Herb S
HS
Malnoy
Malnoy
M
D054458:Amplified Fragment Length Polymorphism Analysis; D018076:DNA, Complementary / Q000235:genetics; D044084:Erwinia amylovora / Q000472:pathogenicity*; D020224:Expressed Sequence Tags; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D054884:Host-Pathogen Interactions; D007113:Immunity, Innate; D027845:Malus / Q000235:genetics* / Q000276:immunology / Q000382:microbiology; D010935:Plant Diseases / Q000235:genetics*; D018749:RNA, Plant / Q000235:genetics
D018076:DNA, Complementary; D018749:RNA, Plant