Proteomic and oxi-proteomic response of apple to a compatible (P. expansum) and a non-host (P. digitatum) pathogen
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Despite the current use of chemical fungicides, Penicillium expansum still is one of the most devastating pathogens of pome fruit. In particular, P. expansum enters tissues through wounds causing large economic losses worldwide. To obtain new rational and environmental friendly control alternatives,
it is fundamental to unravel the molecular mechanisms underlying the fruit defence responses and the pathogen virulence factors. The main objective of this work was to examine the protein abundance changes (proteome), as well as the protein carbonylation formed by reactive oxygen species (ROS) (oxi-proteome) in 'Golden Smoothee' apple in response to wounding, P. expansum (compatible) and P. digitatum (non-host) pathogen. In addition, we evaluated the correlation between the transcript and protein abundances of six genes involved in wound and pathogen responses. Our results identified 26 proteins whose abundance changed in response to both abiotic and biotic stress. While many of these changes are constitutively observed in response to abiotic and biotic stresses, other proteins, as Mal d 1.03E and EF-Tu, were specifically induced in response to the non-host pathogen. Using our protein carbonyl detection method based on fluorescent Bodipy, we also identified 27 proteins as sensitive ROS targets (oxidized). In fact, ACC oxidase and two glutamine synthetases showed the highest protein oxidation level in response to P. digitatum infection. Finally, only one of the six studied genes showed a significant correlation at the transcript and protein level: Mal d 1.03E. This result supports the idea that studies only based on transcriptional changes may provide a partial view of the fruit response against external stresses. This methodology gives valuable information on how impaired protein functions affect fruit defense mechanisms.