PR genes of apple: identification and expression in response to elicitors and inoculation with Erwinia amylovora.

BACKGROUND: In the past decade, much work has been done to dissect the molecular basis of the defence signalling pathway in plants known as Systemic Acquired Resistance (SAR). Most of the work has been carried out in model species such as Arabidopsis, with little attention paid to woody plants. However within the range of species examined, components of the pathway seem to be highly conserved. In this study, we attempted to identify downstream components of the SAR pathway in apple to serve as markers for its activation. RESULTS: We identified three pathogenesis related (PR) genes from apple, PR-2, PR-5 and PR-8, which are induced in response to inoculation with the apple pathogen, Erwinia amylovora, but they are not induced in young apple shoots by treatment with known elicitors of SAR in herbaceous plants. We also identified three PR-1-like genes from apple, PR-1a, PR-1b and PR-1c, based solely on sequence similarity to known PR-1 genes of model (intensively researched) herbaceous plants. The PR-1-like genes were not induced in response to inoculation with E. amylovora or by treatment with elicitors; however, each showed a distinct pattern of expression. CONCLUSION: Four PR genes from apple were partially characterized. PR-1a, PR-2, PR-5 and PR-8 from apple are not markers for SAR in young apple shoots. Two additional PR-1-like genes were identified through in-silico analysis of apple ESTs deposited in GenBank. PR-1a, PR-1b and PR-1c are not involved in defence response or SAR in young apple shoots; this conclusion differs from that reported previously for young apple seedlings.