Identification of bacterial protein markers and enolase as a plant response protein in the infection of Olea europaea subsp. europaea by Pseudomonas savastanoi pv. savastanoi

Olive knot disease is characterised by the development of galls on Olea europaea stems as a result of infection by Pseudomonas savastanoi pv. savastanoi. Protein differential accumulation during the first week of infection was studied using two-dimensional gel electrophoresis and MALDI-TOF mass spectrometry to investigate the biochemical changes occurring in infected tissues and to understand the factors involved in bacteria pathogenesis and plant response to infection. Common infection symptoms were obtained in 1 year-old plants of two Portuguese cultivars, ‘Galega’ and ‘Cordovil de Serpa’ using the strain NCPPB 2327. The comparison of protein patterns of non-inoculated stem tissues, stem tissues inoculated with water or with the strain NCPPB 2327 led to the detection of differentially expressed infection-related proteins. Moreover a distinct protein pattern was obtained between cultivars in response to infection. The differential protein expression was characterised by qualitative and quantitative variation. Among the differentially expressed proteins were the bacterial P. savastanoi orthologues of outer membrane porin F, the tellurium resistance protein, aconitate hydratase 2 and a hypothetical protein with unknown function. From O. europaea, protein orthologues of enolase and calcium-dependent protein kinase were found to be differentially expressed. Results are discussed in the context of the molecular basis of plant–pathogen interactions in the search for markers for the presence of the bacterium in plant tissues.