Inspirations on Virus Replication and Cell-to-Cell Movement from Studies Examining the Cytopathology Induced by Lettuce infectious yellows virus in Plant Cells

Abstract

Lettuce infectious yellows virus (LIYV) is the type member of the genus Crinivirus in the family Closteroviridae. Like many other positive-strand RNA viruses, LIYV infections induce a number of cytopathic changes in plant cells, of which the two most characteristic are: Beet yellows virus-type inclusion bodies composed of vesicles derived from cytoplasmic membranes; and conical plasmalemma deposits (PLDs) located at the plasmalemma over plasmodesmata pit fields. The former are not only found in various closterovirus infections, but similar structures are known as ‘viral factories’ or viroplasms in cells infected with diverse types of animal and plant viruses. These are generally sites of virus replication, virion assembly and in some cases are involved in cell-to-cell transport. By contrast, PLDs induced by the LIYV-encoded P26 non-virion protein are not involved in replication but are speculated to have roles in virus intercellular movement. These deposits often harbor LIYV virions arranged to be perpendicular to the plasma membrane over plasmodesmata, and our recent studies show that P26 is required for LIYV systemic plant infection. The functional mechanism of how LIYV P26 facilitates intercellular movement remains unclear, however, research on other plant viruses provides some insights on the possible ways of viral intercellular movement through targeting and modifying plasmodesmata via interactions between plant cellular components and viral-encoded factors. In summary, beginning with LIYV, we review the studies that have uncovered the biological determinants giving rise to these cytopathological effects and their importance in viral replication, virion assembly and intercellular movement during the plant infection by closteroviruses, and compare these findings with those for other positive-strand RNA viruses.

Efficient Protein Expression and Virus-Induced Gene Silencing in Plants Using a Crinivirus-Derived Vector

“…However, until the present work no crinivirus-derived vector has yet been available. Criniviruses have genomes that are bipartite in contrast to the monopartite genome of viruses in other genera of the family Closteroviridae [ 47 ]. The genomic RNAs are separately encapsidated into virions approximately half the length of the virions seen for monopartite viruses of the genus Closterovirus .…”

Two Crinivirus-Conserved Small Proteins, P5 and P9, Are Indispensable for Efficient Lettuce infectious yellows virus Infectivity in Plants

“…LIYV P5 is an ER-localizing protein. Positive-strand RNA viruses are known to recruit endomembranes for the formation of spherules and vesicles, which provide protective environments and enlarged surfaces for not only viral genome replication, translation and particle assembly, but also for intracellular and cell-to-cell movement [ 38 , 39 , 40 ]. The movement proteins of several plant viruses were found in tight association with the ER and behaved as integral membrane proteins to support viral movement, as exemplified by BYV P6 (a LIYV P5 ortholog), TuMV 6K2 and MNSV P7B [ 3 , 6 , 7 , 15 ], which share a similar protein topology with LIYV P5.…”

Killing two birds with one stone: How do Plant Viruses Break Down Plant Defenses and Manipulate Cellular Processes to Replicate Themselves?

“…Besides, the tight regulation of NPC mediated transport consists of an important and effective antiviral response. Nevertheless, viruses might cheat this regulation of nucleus-cytoplasmic pathways and access nuclear functions crucial for its replication (Qiao et al 2017;Walker et al 2017;Li et al 2018).…”