Cell wall localization of Red clover necrotic mosaic virus movement protein is required for cell-to-cell movement

Abstract

The Red clover necrotic mosaic virus movement protein (MP) is essential for cell-to-cell movement. Eight previously characterized alanine-scanning mutants of the MP were fused to the green fluorescent protein (GFP) and expressed from viral infectious transcripts. Inoculated plants were assayed for movement and intracellular accumulation of MP by confocal laser-scanning microscopy. A strict correlation was observed between the targeting to the cell wall (presumably the plasmodesmata) and cell-to-cell movement. Complementation of dysfunctional MP mutants with either wild-type MP or other null mutants in some cases rescued intracellular targeting and movement. The data suggest the presence of distinct domains in the MP for virus movement (near residues 27-31), complementarity (near residues 122 and 128), and intracellular localization (near residue 161). These data support a model of MP interacting cooperatively with itself to bind viral RNA, localize to and modify plasmodesmata and effect virus movement.

The Red clover necrotic mosaic virus RNA-2 encoded movement protein is a second suppressor of RNA silencing

“…It was found that the three mutants identified in this current study that suppress RNA silencing also localized to the cell wall. Alanine substitutions around amino acids 27 and 277 both consistently localized to the cell wall in those studies while 122 localized to the cell wall approximately 10% of the time (Tremblay et al, 2005). Of the three MP alanine mutants that did not suppress silencing in this current study, mutants 128 and 161 exhibited no localization to the cell wall in the previous study, while mutant 144 did.…”

“…MP might instead work intercellularly to disrupt the RNA silencing cascade by disrupting the spread of the silencing signal. MP is known to target to the cell wall of plant cells, presumably the plasmodesmata, a logical location for the interception of the spreading signal adding support for this argument (Osman and Buck, 1991; Tremblay et al, 2005). Indeed, earlier work in characterizing the MP alanine-scanning mutants used in these studies suggests that the intracellular location of MP directly correlates with the ability of MP to suppress RNA silencing.…”

“…Much work has been done examining the cell-to-cell movement capabilities of MP, including the generation of a series of alanine-scanning mutants (Giesman-Cookmeyer and Lommel, 1993). Some of these alanine-scanning mutants abolish the cell-to-cell movement function of RCNMV, serving as ideal candidates for the potential uncoupling of VSR activity from cell-to-cell movement activity (Giesman-Cookmeyer and Lommel, 1993; Tremblay et al, 2005). …”

“…Of these, three had been shown to retain cell-to-cell movement activity (MPAla27, MPAla144, and MPAla277), while the other three mutants were shown to have lost their cell-to-cell movement function (MPAla122, MPAla128, and MPAla161; Tremblay et al, 2005). Each mutant was cloned into pPZP212 and transformed into A. tumeafaciens (PZP-MPAlaXXX).…”

Capsid protein gene and the type of host plant differentially modulate cell-to-cell movement of cowpea chlorotic mottle virus

“…In the CP-independent mechanism, MP alone mediates cell-to-cell movement by modifying the size exclusion limits of the plasmodesmata and transporting themselves and viral genomic RNA as ribonucleoprotein complexes. The cell-to-cell movement process of members of the tobamovirus and dianthovirus genera are CP-independent [2,9] whereas that of members of the genera Comovirus, Closterovirus, Cucumovirus, Bromovirus, Nepovirus, Potyvirus and Potexviruses is CPdependent [1,5,8,10,11]. In addition to MP and CP, in some viruses replicase genes are implicated in local and systemic infection [1,12,13].…”