Modes of transmission of the Cherry leaf roll virus: genetic basis of seed transmissibility and investigation of possible arthropod vectors

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Cherry leaf roll virus is a worldwide spread Nepovirus that infects a wide range of woody hosts. The virus is reported to spread in nature mainly vertically by seed, but also horizontally by pollen. Although transmission through seed is a critical epidemic feature of many plant viruses, the underlying mechanisms of seed infection are not specified. After transmission experiments of CLRV on birch and Arabidopsis thaliana seedlings, evidence has been obtained that the vertical spread of the virus is achieved due to the presence of the virus in the embryo rather than due to contamination of the seed coat. The embryo invasion is believed to occur through invasion of the gametes before fertilization (indirect embryo invasion). To investigate virus-plant interactions involved in meristem invasion and seed transmission, we intent to apply the yeast two-hybrid system method on the model system CLRV/A. thaliana. The aim of our investigation is to determine host and viral factors responsible for the seed transmission, to confirm the virus invasion of the floral meristems in our model system and to localize the virus in plant tissues of natural hosts. In regard to further epidemiological studies on CLRV, we intent to investigate possible transmission through arthropod vectors on birch forests and elderberry plantations in Germany and Finland. Transmission of CLRV through aphids and mites is speculated; this may constitute one factor potentially responsible for the recent broad CLRV epidemics in north European birch forests.