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<div>The P6 protein of <i>Cauliflower mosaic virus</i> (CaMV) is a 66 kDa protein that forms the matrix for the electron dense, amorphous inclusion bodies (IBs) that accumulate in the cytoplasm. Early electron micrographs revealed that host ribosomes were found in association with the P6 IBs, and nearly all of the icosahedral CaMV virions accumulate and are retained within the P6 IBs. Subsequent studies provided an explanation for the association of P6 IBs and host ribosomes; the P6 protein physically interacts with host ribosomes to reprogram them for expression of all CaMV proteins on the polycistronic 35S mRNA, a process called translational transactivation. For many years, translational transactivation was thought to be the primary function of the P6 protein. However, several recent studies have expanded our understanding of the true impact of the P6 protein on CaMV infections, as the P6 protein has been shown to mediate intracellular movement, elicit defenses in hypersensitive hosts or symptoms in susceptible hosts, modulate SA- and JA-mediated host defenses, and suppress antiviral gene silencing. Furthermore, the P6 protein interacts with at least 14 host and virus proteins, of which distinct subsets are associated with individual functions. This presentation will illustrate how newly identified virus-host protein interactome maps complemented with subcellular localization studies can be used to further define the role of the P6 protein in the CaMV disease cycle.</div>