Stress & Granules : regulation of Cauliflower mosaic virus disease in Arabidopsis thaliana

Viruses exist in intimate relationships with the organisms they are infecting and are just as dependent on compatibility with their host’s cellular components as they are on subverting them. During any virus infection, the cells are flooded with foreign nucleic acids (DNA and/or RNA) and have learned to recognize, disarm, or eliminate them. In turn, viruses have evolved to use the cellular transcription and RNA regulatory machinery for their own benefit. Cytoplasmic RNA granules, namely Processing bodies (PBs) and Stress granules (SGs) are at the forefront of RNA regulation as they contain and store untranslated RNA and are responsive in number, size, and composition to various stresses, including virus infection. For this thesis, we have explored the role of Arabidopsis thaliana RNA granules during infection with the pararetrovirus Cauliflower mosaic virus (CaMV). We show that PB components aid virus accumulation through shielding of the viral RNA from the antiviral RNA silencing machinery (Paper I). In addition, we find that the cytoplasmic viral replication factory contains several RNA granule proteins during infection, including both, PB components and SG components. Opposite to PBs, SGs are likely antiviral and CaMV subverts their biogenesis through its multifunctional protein P6 (Paper II). In an effort to uncover novel disease determinants, we explore the variation of CaMV disease in naturally occurring populations of Arabidopsis thaliana and uncover the importance of the plant hormone abscisic acid and its homeostasis for CaMV infection, as well as a novel CaMV susceptibility factor, the ABA synthesis gene NCED9 (Paper III).