Abstract
Xanthomonas arboricola pv. pruni is a quarantine bacterial pathogen that threatens peach production by causing necrotic spots on leaves and fruits, thus with the potential of severely reducing yields. The current understanding of the host plant defense responses to the pathogen is very limited. Using whole transcriptome sequencing, differential gene expression was analyzed at two time points, 2 h and 12 h post inoculation (hpi), by comparing the inoculated samples to their respective controls. On the total of 19,781 known peach genes that were expressed in all time points and conditions, 34 and 263 were differentially expressed at 2 and 12 hpi, respectively. Of those, 82% and 40% were up-regulated, respectively; and 18% and 60% were down-regulated, respectively. The functional annotation based on gene ontology (GO) analysis highlighted that genes involved in metabolic process and response to stress were particularly represented at 2 hpi whereas at 12 hpi cellular and metabolic processes were the categories with the highest number of genes differentially expressed. Of particular interest among the differentially expressed genes identified were several pathogen-associated molecular pattern (PAMP) receptors, disease resistance genes including several RPM1-like and pathogenesis related thaumatin encoding genes. Other genes involved in photosynthesis, in cell wall reorganization, in hormone signaling pathways or encoding cytochrome were also differentially expressed. In addition, novel transcripts were identified, providing another basis for further characterization of plant defense-related genes. Overall, this study gives a first insight of the peach defense mechanisms during the very early stages of infection with a bacterial disease in the case of a compatible interaction.
Highlights
Bacterial spot of stone fruits, caused by Xanthomonas arboricola pv. pruni, is a severe disease that threaten the most economically important Prunus crops, including peach, apricot, nectarine and plum
This hypothesis is further supported by the fact that reads obtained from X. arboricola pv. pruni from in vitro culture mapped to the P. persica genome
Subsets of 5 to 40 million reads were randomly selected from the total pool of reads of each sample at each time point in order to check the effect of sampling depth on gene expression
Summary
Bacterial spot of stone fruits, caused by Xanthomonas arboricola pv. pruni, is a severe disease that threaten the most economically important Prunus crops, including peach, apricot, nectarine and plum. Bacterial spot of stone fruits, caused by Xanthomonas arboricola pv. Pruni, is a severe disease that threaten the most economically important Prunus crops, including peach, apricot, nectarine and plum. The pathogen uses wounds or stomata to access the intercellular spaces where it degrades the cell wall components [3]. This causes necrotic lesions on both leaves and fruits, leading to severe defoliations and yield losses. Pruni relies on a large repertoire of 21 type III effectors (T3Es) which can be delivered directly into the host cells via the type III secretion system [5]. T3Es are known to promote bacterial growth in the host plant by suppressing plant defenses [6]
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