Transcriptional profile of AvrRpt2EA-mediated resistance and susceptibility response to Erwinia amylovora in apple

Abstract

Most of the commercial apple cultivars are highly susceptible to fire blight, which is the most devastating bacterial disease affecting pome fruits. Resistance to fire blight is described especially in wild Malus accessions such as M. × robusta 5 (Mr5), but the molecular basis of host resistance response to the pathogen Erwinia amylovora is still largely unknown. The bacterial effector protein AvrRpt2EA was found to be the key determinant of resistance response in Mr5. A wild type E. amylovora strain and the corresponding avrRpt2EA deletion mutant were used for inoculation of Mr5 to induce resistance or susceptible response, respectively. By comparison of the transcriptome of both responses, 211 differentially expressed genes (DEGs) were identified. We found that heat-shock response including heat-shock proteins (HSPs) and heat-shock transcription factors (HSFs) are activated in apple specifically in the susceptible response, independent of AvrRpt2EA. Further analysis on the expression progress of 81 DEGs by high-throughput real-time qPCR resulted in the identification of genes that were activated after inoculation with E. amylovora. Hence, a potential role of these genes in the resistance to the pathogen is postulated, including genes coding for enzymes involved in formation of flavonoids and terpenoids, ribosome-inactivating enzymes (RIPs) and a squamosa promoter binding-like (SPL) transcription factor.

A complete twelve-gene deletion null mutant reveals that cyclic di-GMP is a global regulator of phase-transition and host colonization in Erwinia amylovora

“…amylovora and the heat shock response of the pathogen is a target for AvrRpt2 mediated resistance to E . amylovora in apple [ 56 – 59 ]. While the link between heat shock response and c-di-GMP has not been studied in E .…”

“…The overexpression of edcC and edcE resulted in the increased expression of heat shock related proteins including ibpA, dnaK and hspQ. Lon and CsrA have been linked to heat shock response regulation in E. amylovora and the heat shock response of the pathogen is a target for AvrRpt2 mediated resistance to E. amylovora in apple [56][57][58][59]. While the link between heat shock response and c-di-GMP has not been studied in E. amylovora, in V. cholerae, Lon was identified as a cdi-GMP receptor that could regulate the stability of TfoY leading to downstream effects on the heat shock response of the pathogen [60].…”