A pandemic, very aggressive population of Pseudomonas syringae pv. actinidiae is currently causing severe economic losses to kiwifruit crops worldwide. Upon leaf attack, this Gram-negative bacterium systemically reaches the plant shoot in a week period. In this study, combined 2-DE and nanoLC-ESI-LIT-MS/MS procedures were used to describe major proteomic changes in Actinidia chinensis shoot following bacterial inoculation in host leaf. A total of 117 differentially represented protein spots were identified in infected and control shoots. Protein species associated with plant defence, including type-members of the plant basal defence, pathogenesis, oxidative stress and heat shock, or with transport and signalling events, were the most represented category of induced components. Proteins involved in carbohydrate metabolism and photosynthesis were also augmented upon infection. In parallel, a bacterial outer membrane polypeptide component was identified in shoot tissues, whose homologues were already linked to bacterial virulence in other eukaryotes. Semiquantitative RT-PCR analysis confirmed expression data for all selected plant gene products. All these data suggest a general reprogramming of shoot metabolism following pathogen systemic infection, highlighting organ-specific differences within the context of a general similarity with respect to other pathosystems. In addition to present preliminary information on the molecular mechanisms regulating this specific plant-microbe interaction, our results will foster future proteomic studies aimed at characterizing the very early events of host colonization, thus promoting the development of novel bioassays for pathogen detection in kiwifruit material.
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