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Tobamovirusis a large group of positive-sense, single-stranded RNA viruses that cause diseases in a broad range of plant species, including many agronomically important crops. The number of knownTobamovirusspecies has been on the rise in recent years, and currently, this genus includes 47 viruses. Tobamoviruses are transmitted mainly by mechanical contact, such as physical touching by hands or agricultural tools; and some are also transmitted on seeds, or through pollinator insects. The tobamoviral genome encodes proteins that have evolved to fulfill the main conceptual task of the viral infection cycle - the spread of the invading virus throughout the host plant cells, tissues, and organs. Here, we discuss this aspect of the infection cycle of tobamoviruses, focusing on the advances in our understanding of the local, i.e., cell-to-cell, and systemic, i.e., organ-to-organ, virus movement, and the viral and host plant determinants of these processes. Specifically, we spotlight two viral proteins—the movement protein (MP) and the coat protein (CP), which are directly involved in the local and systemic spread of tobamoviruses—with respect to their phylogeny, activities during viral movement, and interactions with the host determinants of the movement process. 

Several species of the Agrobacterium genus represent unique bacterial pathogens able to genetically transform plants, by transferring and integrating a segment of their own DNA (T-DNA, transferred DNA) in their host genome. Whereas in nature this process results in uncontrolled growth of the infected plant cells (“tumors”), this capability of Agrobacterium has been widely used as a crucial tool to generate transgenic plants, for research and biotechnology. The virulence of Agrobacterium relies on a series of virulence genes, mostly encoded on a large plasmid (Ti-plasmid, tumor inducing plasmid), involved in the different steps of the DNA transfer to the host cell genome: activation of bacterial virulence, synthesis and export of the T-DNA and its associated proteins, intracellular trafficking of the T-DNA and effector proteins in the host cell, and integration of the T-DNA in the host genomic DNA. Multiple interactions between these bacterial encoded proteins and host factors occur during the infection process, which determine the outcome of the infection. Here, we review our current knowledge of the mechanisms by which bacterial and plant factors control Agrobacterium virulence and host plant susceptibility.