Abstract
BackgroundThe recent Xylella fastidiosa subsp. pauca (Xfp) outbreak in olive (Olea europaea) groves in southern Italy is causing a destructive disease denoted Olive Quick Decline Syndrome (OQDS). Field observations disclosed that Xfp-infected plants of cv. Leccino show much milder symptoms, than the more widely grown and highly susceptible cv. Ogliarola salentina. To determine whether these field observations underlie a tolerant condition of cv. Leccino, which could be exploited for lessening the economic impact of the disease on the local olive industry, transcriptional changes occurring in plants of the two cultivars affected by Xfp were investigated.ResultsA global quantitative transcriptome profiling comparing susceptible (Ogliarola salentina) and tolerant (Leccino) olive cultivars, infected or not by Xfp, was done on messenger RNA (mRNAs) extracted from xylem tissues. The study revealed that 659 and 447 genes were differentially regulated in cvs Leccino and Ogliarola upon Xfp infection, respectively, whereas 512 genes were altered when the transcriptome of both infected cultivars was compared. Analysis of these differentially expressed genes (DEGs) shows that the presence of Xfp is perceived by the plants of both cultivars, in which it triggers a differential response strongly involving the cell wall. Up-regulation of genes encoding receptor-like kinases (RLK) and receptor-like proteins (RLP) is the predominant response of cv. Leccino, which is missing in cv. Ogliarola salentina. Moreover, both cultivars react with a strong re-modelling of cell wall proteins. These data suggest that Xfp elicits a different transcriptome response in the two cultivars, which determines a lower pathogen concentration in cv. Leccino and indicates that this cultivar may harbor genetic constituents and/or regulatory elements which counteract Xfp infection.ConclusionsCollectively these findings suggest that cv. Leccino is endowed with an intrinsic tolerance to Xfp, which makes it eligible for further studies aiming at investigating molecular basis and pathways modulating its different defense response.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2833-9) contains supplementary material, which is available to authorized users.
Highlights
The recent Xylella fastidiosa subsp. pauca (Xfp) outbreak in olive (Olea europaea) groves in southern Italy is causing a destructive disease denoted Olive Quick Decline Syndrome (OQDS)
To confirm these findings a calibration curve was constructed correlating known amounts of Xfp cells (CFU/ml) to their corresponding Cqs obtained by quantitative Polymerase Chain Reaction (qPCR) assays
Since in olive the bacterial titer was evaluated in xylem tissues of the stem, we suggest that the multiplication of Xfp "Complesso del Disseccamento Rapido dell’Olivo" (CoDiRO) is impaired in this cv
Summary
The recent Xylella fastidiosa subsp. pauca (Xfp) outbreak in olive (Olea europaea) groves in southern Italy is causing a destructive disease denoted Olive Quick Decline Syndrome (OQDS). Xylella fastidiosa (Xf ) is a polyphagous bacterium causing important diseases of a wide number of crops [1, 2], to which olive (Olea europaea) has recently been added. In this last species a strain of Xf subsp. In several species, Xf multiplies and colonizes the host without inducing symptoms, whereas in other, a classical leaf scorching recalling water deficit occurs Hypotheses behind these symptoms rely on the occlusion of xylem vessels by bacterial colonies aggregated in a biofilm envelope and a plant defense response consisting in the production of tyloses and gums. Because of all the above the current view retains that a disease occurs when the bacterium spreads and multiplies exceeding a certain threshold level and/or finds physiological conditions that make it shifting from a commensalistic relationship to disease induction [5]
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