Structural Insights into Viral Determinants of Nematode Mediated Grapevine fanleaf virus Transmission

Abstract

Many animal and plant viruses rely on vectors for their transmission from host to host. Grapevine fanleaf virus (GFLV), a picorna-like virus from plants, is transmitted specifically by the ectoparasitic nematode Xiphinema index. The icosahedral capsid of GFLV, which consists of 60 identical coat protein subunits (CP), carries the determinants of this specificity. Here, we provide novel insight into GFLV transmission by nematodes through a comparative structural and functional analysis of two GFLV variants. We isolated a mutant GFLV strain (GFLV-TD) poorly transmissible by nematodes, and showed that the transmission defect is due to a glycine to aspartate mutation at position 297 (Gly297Asp) in the CP. We next determined the crystal structures of the wild-type GFLV strain F13 at 3.0 Å and of GFLV-TD at 2.7 Å resolution. The Gly297Asp mutation mapped to an exposed loop at the outer surface of the capsid and did not affect the conformation of the assembled capsid, nor of individual CP molecules. The loop is part of a positively charged pocket that includes a previously identified determinant of transmission. We propose that this pocket is a ligand-binding site with essential function in GFLV transmission by X. index. Our data suggest that perturbation of the electrostatic landscape of this pocket affects the interaction of the virion with specific receptors of the nematode's feeding apparatus, and thereby severely diminishes its transmission efficiency. These data provide a first structural insight into the interactions between a plant virus and a nematode vector.

Plant to Plant Movement

“…The determinant has been further identified in GFLV and ArMV as a stretch of 11 amino acids on the surface of the GFLV CP (Schellenberger et al, 2010). The transmission defect in a poorly transmissible mutant strain of GFLV is due to a glycine to aspartate mutation at position 297 in the CP which is in an exposed loop on the outer surface of the capsid (Schellenberger et al, 2011). This loop forms part of a positively charged pocket (Figure 12.20) which is suggested to be a ligand-binding site associated with binding to specific receptor(s) in X. index feeding apparatus.…”

Multiple functions of capsid proteins in (+) stranded RNA viruses during plant–virus interactions

“…A poorly transmissible GFLV strain (GFLV-TD) carries the debilitating glycine-to-aspartate mutation at position 297 (Gly297Asp) within the CP (Schellenberger et al, 2011). The mutation was carried within an exposed loop as part of a positively charged pocket in the virion structure.…”

Bacterial Diseases of Crops

“…This appears to be the case particularly with stressed plants, which are susceptible to multiple infections by opportunistic pathogens such as P. syringae and Xanthomonas arboricola (Lamichhane, 2014). Many complex associations between nematodeepathogen (bacteria, fungi, and virus) disease complexes reported on a variety of crop species suggest the frequent occurrence of complex disease phenomena in the field (Back et al, 2000;Bertrand et al, 2000;Brown et al, 1995;Cao et al, 2006;Schellenberger et al, 2011). Experiments conducted under carefully controlled conditions also confirmed such associations.…”