Transport of protein—nucleic acid complexes within and between plant cells

In eukaryotic organisms, nucleic acid molecules are constantly transported between the nucleus and the cytoplasm. This transport includes nuclear export and import of RNAs and nuclear import of retrotransposable elements and invading viruses. Higher plants have an additional nucleic acid transport system that allows infectious viral genomes to be transported between adjacent host cells. Nuclear import and plasmodesmal transport of nucleic acids in plants exhibit several structural and functional similarities. This chapter focuses on two processes of nucleic acid transport in plants: (1) the transport of Agrobacterium single-stranded (ss) DNA through nuclear pores and (2) the movement of tobacco mosaic virus (TMV) genomic RNA through plant intercellular connections, the plasmodesmata. Both processes involve single-stranded nucleic acids that are transported as complexes with specialized transport proteins. These proteins bind ssDNA and RNA, producing thin unfolded filaments of protein–nucleic acid transport complexes. In addition to shaping nucleic acid molecules in a transferable form, the transport proteins also provide specific signals for targeting and interaction with the nuclear pores or plasmodesmal channels.