Xylella fastidiosa strain CoDiRO and olive: a transcriptome view of the interactions

A strain of Xylella fastidiosa is ravaging the olive trees of Southern Apulia, Italy (Saponari et
al., 2013). The bacterium causes the Olive Quick Decline Syndrome (OQDS), a disease
showing symptoms of apical and marginal leaf scorching, extensive branch and twig dieback
and death of the trees (Martelli et al., 2016). Transmission tests demonstrated that the
Xylella fastidiosa-olive infecting strain is transmitted by the xylem-feeding meadow
froghopper Philaenus spumarius (Saponari et al., 2014) whereas genome studies proved that
it belongs to the subspecies pauca, sequence type 53 (Giampetruzzi et al., 2015). Field
observations allowed to identify a possible source of resistance in the olive cv Leccino, which
reacts with milder symptoms, and hosts a much lower bacterial concentration of bacterial
cells than the locally grown cv Ogliarola salentina. A global transcriptome profiling revealed
that a higher number of genes is altered upon Xylella fastidiosa infection in the susceptible
cv Ogliarola salentina compared to the resistant cv Leccino, with respect to the healthy
plants of the same cultivars (Giampetruzzi et al., 2016). Gene expression analysis showed
that both cultivars perceive the presence of the bacterium with the involvement of
membrane signaling receptors, whose characterization is ongoing. Analysis of altered genes
of the susceptible cv Ogliarola salentina (expansin, early-late inducible proteins, late
embryogenesis abundant proteins and involvement of the abscissic acid pathway) indicated
that plants are subjected to a intense water stress. A further transcriptome analysis of the
recently discovered Xylella-resistant olive cv FS17® is in process. Results of these studies will
be presented.