Plant viruses and viroids have unique functional associations with their hosts, exploiting cellular pathways to transport their genomes between cell compartments and to accomplish entry into neighbouring cells, and into the vascular system for long-distance movement. Viruses use special non-structural proteins, and both viruses and viroids utilize either direct or indirect interactions with various host nucleic-binding proteins to perform many functions during viral replication, silencing and transport. Directed nucleic acid transport coupled with replication, translation and integrity control is a crucial mechanism to target the pathogen genome within the host cell or tissues. Usually, genomic nucleic acids bind virus and/or host proteins to form nucleoprotein complexes; microtubules, microfilaments, and their motors then transport these complexes to different membrane compartments including organelles and plasmodesmata. At the present time, however, knowledge of the diversity of the proteins involved in the formation of genome-containing complexes is limited to a few viruses and viroids.
In this Research Topic, our current understanding of the non-structural viral and host nucleic acid-binding proteins that bring virus and viroid genomes to membranes and assist their intracellular trafficking and transport in plant tissues will be highlighted. Different potential classes of such proteins and innovative technologies to reveal them will be considered in the experimental papers, reviews and mini-reviews.

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