Attempts to develop sustainable biocontrol strategies of Xylella fastidiosa infections in olive

X. fastidiosa is a plant pathogenic bacterium, which is causing the ‘Olive Quick Decline
Syndrome’ (OQDS), on olive trees in the southern part of Apulia region. The knowledge of
mechanisms regulating olive- X. fastidiosa interactions is fundamental to develop biocontrol strategies.
In Pierce’s Disease (PD) the pathogen virulence relies on a fine balance between motile cells, which
move and proliferate in xylem vessels, and sticky cells forming a biofilm and responsible for vessels
blockage and insect acquisition. This different behaviour is regulated by diffusible signalling factors
(DSF), synthesised by a bacterial rpfF-gene, that regulate genes inducing biofilm formation. DSFs
produced by the olive-infecting strain (CoDiRO) of X. fastidiosa were analysed by Gas
Chromatography-Mass Spectrometry analysis. Preliminary results showed that a family of unsaturated
fatty acids, with a chain length of 12-18 carbon atoms, is produced. They will be further characterised
by nuclear magnetic resonance (NMR). These studies may be applied in a “pathogen confusion”
strategy for mitigating X. fastidiosa-infections by altering DSFs level in planta. Pursuing this approach,
a plant viral-based vector has been engineered to induce rpfF transient expression. This approach
would make X. fastidiosa cells less motile and more sticky in xylem vessels, thus lowering their
virulence. A model system is being evaluated to verify the DSF expression and accumulation directed
by a viral-rpfF recombinant vector.

Bibliography
Chatterjee et al., 2008. Cell-to-cell signaling in Xylella fastidiosa suppresses movement and xylem vessel colonization in grape. Molecular Plant-Microbe Interactions, 21(10), 1309-1315.
Newman et al., 2004. Cell-cell signaling controls Xylella fastidiosa interactions with both insects and plants. Proceedings of the National Academy of Sciences of the United States of America, 101(6), 1737-1742.
Lindow et al., 2013. Production of Xylella fastidiosa diffusible signal factor in transgenic grape causes pathogen confusion and reduction in severity of Pierce's disease. Molecular Plant-Microbe Interactions, 27(3), 244-254.