Abstract
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.
Highlights
Capsid proteins (CPs) protect the genome of plant viruses, but are often crucial in a variety of other functions including vector transmission, replication, translation, cell-to-cell and long distance movements, pathogenicity, inactivation of plant antiviral defenses, or host range determination [1].CPs of plant viruses bear the determinants of essential interactions with vector and host factors or even with other virus proteins
Regions R3, R4, and R5 located in the jelly-roll domain B of the 2CCP protein were initially predicted to be exposed at the outer in the jelly‐roll domain B of the 2CCP protein were initially predicted to be exposed at the outer surface surface of the Grapevine fanleaf virus (GFLV) capsid from a GFLV 3D homology model derived from TRSV [27]
We showed that a limited GFLV cell-to-cell movement is possible even when capsids are improperly formed, efficient tubule-guided cell-to-cell movement depends on the quality of the assembled particles
Summary
CPs of plant viruses bear the determinants of essential interactions with vector and host factors or even with other virus proteins. CP determinants have been implicated in the interaction with the C-terminus of movement proteins (MPs) belonging to the 30K superfamily to ensure specific virus transport [2]. Such CP determinants are involved in virus transmission, as exemplified with potyviruses [3,4] or cucumber mosaic virus (CMV) [5,6]. Conserved negatively charged residues of the outer surface exposed βH-βI loop of the CMV capsid were shown to be essential for virus transmission by a given aphid species [6]. Residues involved in quaternary interactions of the CMV particle at the Viruses 2019, 11, 1146; doi:10.3390/v11121146 www.mdpi.com/journal/viruses
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