2 research outputs found
From a movement-deficient grapevine fanleaf virus to the identification of a new viral determinant of nematode transmission
Grapevine fanleaf virus (GFLV) and arabis mosaic virus (ArMV) are nepoviruses responsible
for grapevine degeneration. They are specifically transmitted from grapevine to grapevine by two
distinct ectoparasitic dagger nematodes of the genus Xiphinema. GFLV and ArMV move from cell to
cell as virions through tubules formed into plasmodesmata by the self-assembly of the viral movement
protein. Five surface-exposed regions in the coat protein called R1 to R5, which differ between the
two viruses, were previously defined and exchanged to test their involvement in virus transmission,
leading to the identification of region R2 as a transmission determinant. Region R4 (amino acids
258 to 264) could not be tested in transmission due to its requirement for plant systemic infection.
Here, we present a fine-tuning mutagenesis of the GFLV coat protein in and around region R4 that
restored the virus movement and allowed its evaluation in transmission. We show that residues
T258, M260, D261, and R301 play a crucial role in virus transmission, thus representing a new viral
determinant of nematode transmission
Structural Insights into Viral Determinants of Nematode Mediated Grapevine fanleaf virus Transmission
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 Ã… and of
GFLV-TD at 2.7 Ã… 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