Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2009
Publication Date: 3/27/2009
Citation: Hu, X., Meacham, T., Ewing, L., Gray, S.M., Karasev, A.V. 2009. A novel recombinant strain of Potato virus Y allows identification of a new viral genetic determinant of vein necrosis in tobacco. Virus Genes. 143(1):68-76. Interpretive Summary: Potato virus Y is the most economically important disease affecting the US seed potato industry. In recent years several new strains of the virus have been discovered in the US and they cause necrosis in tobacco and potato tubers. There is interest by the industry and regulatory agencies to eliminate these strains. The problem is there is no quick way to distinguish the necrotic strains from the ordinary strains that are commonly found in potato production areas. The research reported here is the first step in developing a new diagnostic test. We have identified the virus gene that is important for the necrotic disease expression and furthermore have identified specific sequences in that gene that are partially responsible for the necrosis. Knowing the sequences that are important will allow the development of a specific diagnostic test that can identify these sequences and distinguish the necrotic isolates from the ordinary isolates. This will allow the seed certification agencies to quickly identify the necrotic isolates in seed lots and prevent these lots from being planted.
Technical Abstract: A novel Potato virus Y (PVY) isolate, L26, recovered from a Frontier potato line was initially typed as a PVYNTN strain using multiplex RT-PCR and serological assays. However, L26 induced mosaic and mild vein clearing symptoms in tobacco rather than vein necrosis characteristic of the PVY NTN strain. The whole genome sequence was determined for L26 and two other PVYNTN isolates, HR1 and N4, from Idaho that did induce vein necrosis in tobacco. The sequence of all three isolates was similar to typical European PVYNTN isolates that contain three recombination junctions in their genome. The sequence of the L26 genome was nearly identical to the genomes HR1, N4, and to a previously characterized PVYNTN isolate, 423-3, differing by only five nucleotides in the entire ca. 9.7-kb genome, only one resulting in a corresponding amino acid change, D-205 to G-205 in the central region of HC-Pro. Two “signature” amino acid residues, thought involved in induction of the vein necrosis syndrome in tobacco, K-400 and E-419, were present in the C-terminal region of HC-Pro of all three isolates. Multiple alignments of the whole genome sequences of L26 and other PVYNTN isolates whose phenotype in tobacco has been reported, suggests that the single amino acid change (D-205 to G-205) in the HC-Pro cistron of L26 correlates with the loss of the vein necrosis phenotype in tobacco. Secondary structure modeling of the HC-Pro protein predicts the G-205 residue, and the previously identified residues K-400 and E-419, would all be located on the exposed surface of the protein. Taken together, these data suggest that the vein necrosis genetic determinant of PVY in tobacco is complex and includes other element(s), in addition to the C-terminal fragment of HC-Pro.