Gene expression in apple in response to inoculation with Erwinia amylovora

Two cDNA phagmid libraries were constructed from RNA isolated from young Buckeye Gala apple leaves. One library represents the transcriptome of apple inoculated with Erwinia amylovora strain Ea273. This library was prepared from a pool of RNAs collected at nine intervals from 3 h to 6 days post inoculation. A second library was prepared from RNA isolated from non-inoculated apple leaves. 99 random clones from the inoculated library were sequenced and the sequences were analyzed by Blast searches. Sixty percent of the sequenced clones are similar to known genes of other plants. In addition, the apple genes PR-5, PR-10 and ACC synthase, which are known to be induced by pathogen attack, were found among the clones. Differential expression analysis and subtraction hybridization are being used to study the time-course of gene expression following inoculation with E. amylovora. Genes that are induced rapidly and strongly, shortly after inoculation are likely to be involved in the interaction with initial bacterial gene products and may help elucidate the interaction of the plant and pathogen on a molecular basis. Preliminary evaluations of the two approaches to define the time course of expression of apple genes following inoculation with E. amylovora indicates the subtraction technique is much more likely to facilitate meeting our goal. Further characterization of genes identified through subtraction is in progress.