Potato virus X RNA-mediated assembly of single-tailed ternary ‘coat protein–RNA–movement protein’ complexes

Abstract

Different models have been proposed for the nature of the potexvirus transport form that moves from cell to cell over the infected plant: (i) genomic RNA moves as native virions; or (ii) in vitro-assembled non-virion ribonucleoprotein (RNP) complexes consisting of viral RNA, coat protein (CP) and movement protein (MP), termed TGBp1, serve as the transport form in vivo. As the structure of these RNPs has not been elucidated, the products assembled in vitro from potato virus X (PVX) RNA, CP and TGBp1 were characterized. The complexes appeared as single-tailed particles (STPs) with a helical, head-like structure composed of CP subunits located at the 59-proximal region of PVX RNA; the TGBp1 was bound to the terminal CP molecules of the head. Remarkably, no particular non-virion RNP complexes were observed. These data suggest that the CP-RNA interactions resulting in head formation prevailed over TGBp1-RNA binding upon STP assembly from RNA, CP and TGBp1. STPs could be assembled from the 59 end of PVX RNA and CP in the absence of TGBp1. The translational ability of STPs was characterized in a cell-free translation system. STPs lacking TGBp1 were entirely non-translatable; however, they were rendered translatable by binding of TGBp1 to the end of the head. It is suggested that the RNA-mediated assembly of STPs proceeds via two steps. Firstly, non-translatable CP-RNA STPs are produced, due to encapsidation of the 59-terminal region. Secondly, the TGBp1 molecules bind to the end of a polar head, resulting in conversion of the STPs into a translatable form.

Molecular characterization and field survey of Iranian potato virus X isolates

“…The TGB proteins are highly conserved in members of the genera Potexvirus, Hordeivirus, Benyvirus and Carlavirus [6,15,23]. ORF5 encodes the capsid protein (CP) with an estimated molecular mass of 25 kDa and plays an significant role in cell-to-cell movement of PVX particles and translational regulation of the PVX RNA genome [10,14]. The CP gene is widely used for identification and classification of PVX isolates [3,25,26].…”

Nucleocytoplasmic Distribution Is Required for Activation of Resistance by the Potato NB-LRR Receptor Rx1 and Is Balanced by Its Functional Domains

“…Thus, the CP localization by itself does not exclude the nucleus as the compartment where recognition could take place. It is tempting to speculate that the roles the CP fulfills in PVX replication and cell-cell movement of viral RNA Fedorkin et al, 2001;Karpova et al, 2006;Bamunusinghe et al, 2009), which have been associated with the endomembrane system and plasmodesmata, form the ground for its recognition in the cytoplasm.…”

Population genetic analysis of potato virus X based on the CP gene sequence

“…Previous studies have shown that the PVX isolates can be classified into two lineages, Eurasia and America, which correspond to their geographical origin [22,24,44,45]. PVX is well-known as a model for understanding pathogen-host interaction [4,14,20] and efforts in recent years have established good knowledge about genetic basis of resistance and the genetic system controlling behavior of the pathogen [2,21,32].…”