Project number		Stand-alone Projects  P24201
Title		Plant Signaling and Phytoplasma Response
Principal investigator		BRADER Günter
Approval date		03.10.2011
University / Research institution		Department of Health and Environment Bioresources Unit, Austrian Institute of Technology
Scientific field(s)
Keywords		Plant-Microbe interaction, Induced resistance, Stolbur, Bacterial effectors, Bois Noir, Gene expression
Homepage		http://www.ait.ac.at/departments/health-environment

Candidatus Phytoplasma is a genus of small wall-less, phloem-dwelling bacteria associated with more than 100 plant diseases world-wide. Phytoplasmas are transmitted by phloem sucking hemipterous insects belonging to Auchenorrhyncha and Psyllidae. The most problematic phytoplasma diseases in Europe are affecting fruit trees of the rose family and grapevines. These grapevine yellows diseases are associated with distinct phytoplasma species causing flavescence dorée (FD) and bois noir (BN; caused by stolbur phytoplasma). Due to the phloem restriction and bacterial nature, control of phytoplasma diseases is challenging. Also the management of the reservoir-hosts such as bindweed and the partly unknown vectors is a difficult task. However, grapevines might recover from phytoplasma symptoms for unclear reasons. Previous contacts to pathogens, to beneficial microorganism and chemicals acting as elicitors and secondary messengers can induce resistance in plants. In this state, plants respond to subsequent infections of a wide array of pathogens by enhanced defense responses leading to reduction of symptoms and milder infections. Very little is known, if induced resistance and treatment with beneficial microorganisms are also effective against phytoplasmas. Also, it is unclear, which plant defense pathways are involved in resistance to phytoplasmas and in the phenomenon of recovery.
In the current project proposal we plan to investigate if inducing resistance in plants will lead to conditions limiting phytoplasma growth and proliferation. To test the hypothesis, plants will be treated with resistance inducing chemicals or beneficial bacteria and graft-inoculated with phytoplasma infected scions. Samples taken in time series will allow the determination of phytoplasma DNA content with quantitative PCR in various distances of the graft junction. The involvement of different pathways contributing to plant defense responses will be also established using tomato mutants impaired in defense and hormone signaling. These investigations should help to enlighten the role of active plant defense in phytoplasma infections. Closely related but distinct stolbur phytoplasma strains occur in different herbaceous host and with distinct geographic distribution. Genome sequencing and comparison of these strains should give valuable information of phytoplasma genes and sequence elements involved in host specifications and specific virulence. Phytoplasma gene expression studies of these genes and genes with signaling sequences encoding for excreted proteins will allow evaluation of potential effectors necessary for the establishment of phytoplasma in host and vector interactions.