Illumination of the transmission mechanism of Soil-borne wheat mosaic virus by its vector, Polymyxa graminis and identification of novel resistance factors in barley

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Polymyxa graminis-transmitted soil-borne viruses cause severe losses in cereals worldwide. As the viruses remain infectious inside polymyxa resting spores for decades, cereal cultivation on contaminated soil is only economic by growing resistant cultivars. Unfortunately, resistances to these viruses are readily overcome by the viruses, thus necessitating innovative resistance strategies. One way to identify novel resistance strategies is the illumination of the molecular mechanisms underlying the interaction between polymyxa-transmitted soil-borne viruses, thereby identifying candidates for virus control by the targeted modulation of host processes involved in infection. Therefore, the objective of the proposed work is the identification of key factors determining the P. graminis - Soil-borne wheat mosaic virus (SBWMV) – barley interaction. As virus transmission and movement are key processes influencing infection, the work specifically elucidates the function and interaction network of the SBWMV transmission factor CP-RT and the SBWMV movement protein (MP). The previewed work includes a detailed analysis of the virus transmission process and virus movement between root cells. In particular, we will investigate interaction between P. graminis and barley root cells by high-resolution in vivo fluorescence microscopy with specific attention on membrane and cytoskeletal rearrangements occurring during the infection process and during virus transmission. Moreover, we will uncover the intra- and intercellular transport pathways the viral MP and CP-RT proteins use to transport viral infectious RNA across the plasmodium membrane and between root cells. Finally, we will use life cell microscopy and immunolocalization in combination with methods for virus quantification to investigate whether virions or viral components are present inside the vector and whether the virus is able to replicate inside polymyxa zoospores. In parallel to these cell biological approaches, we will identify and functionally characterize MP- and CP-RT-interacting host factors in regard to a role in antiviral resistance. Candidate host factors interacting with SBWMV MP and CP-RT proteins will be identified by co-immunoprecipitation followed by mass spectroscopy and a role of the candidate host factors in virus infection will be determined by quantification of vector and virus levels in plants with reduced candidate gene expression. The proposed work will significantly advance our understanding of the molecular mechanisms underlying the interaction between P. graminis, SBWMV and barley in particular and the transmission and infection mechanisms of polymyxa-transmitted soil borne viruses in general. By identifying novel resistance factors in the natural SBWMV host barley, the project will directly contribute to the development of sustainable solutions for agriculture by allowing direct inclusion of the identified resistance factors into resistance breeding programs.