A stretch of 11 amino acids in the betaB-betaC loop of the coat protein of grapevine fanleaf virus is essential for transmission by the nematode Xiphinema index.
Grapevine fanleaf virus (GFLV) and Arabis mosaic virus (ArMV) from the genus Nepovirus, family Secoviridae, cause a severe degeneration of grapevines. GFLV and ArMV have a bipartite RNA genome and are transmitted specifically by the ectoparasitic nematodes Xiphinema index and Xiphinema diversicaudatum, respectively. The transmission specificity of both viruses maps to their respective RNA2-encoded coat protein (CP). To further delineate the GFLV CP determinants of transmission specificity, three-dimensional (3D) homology structure models of virions and CP subunits were constructed based on the crystal structure of Tobacco ringspot virus, the type member of the genus Nepovirus. The 3D models were examined to predict amino acids that are exposed at the external virion surface, highly conserved among GFLV isolates but divergent between GFLV and ArMV. Five short amino acid stretches that matched these topographical and sequence conservation criteria were selected and substituted in single and multiple combinations by their ArMV counterparts in a GFLV RNA2 cDNA clone. Among the 21 chimeric RNA2 molecules engineered, transcripts of only three of them induced systemic plant infection in the presence of GFLV RNA1. Nematode transmission assays of the three viable recombinant viruses showed that swapping a stretch of (i) 11 residues in the betaB-betaC loop near the icosahedral 3-fold axis abolished transmission by X. index but was insufficient to restore transmission by X. diversicaudatum and (ii) 7 residues in the betaE-alphaB loop did not interfere with transmission by the two Xiphinema species. This study provides new insights into GFLV CP determinants of nematode transmission.
Schellenberger
Pascale
P
Institut National de la Recherche Agronomique, UMR 1131 INRA/Université de Strasbourg, 28 Rue de Herrlisheim, 68021 Colmar, France.
Andret-Link
Peggy
P
Schmitt-Keichinger
Corinne
C
Bergdoll
Marc
M
Marmonier
Aurélie
A
Vigne
Emmanuelle
E
Lemaire
Olivier
O
Fuchs
Marc
M
Demangeat
Gérard
G
Ritzenthaler
Christophe
C
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000235:genetics; D000818:Animals; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D004199:Disease Vectors; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009348:Nematoda / Q000821:virology*; D017860:Nepovirus / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D010935:Plant Diseases / Q000821:virology*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011995:Recombination, Genetic; D016415:Sequence Alignment; D027843:Vitis / Q000821:virology
D000596:Amino Acids; D036022:Capsid Proteins