Capsid protein heterogeneity in turnip mosaic virus

Biological, Physical, and Molecular Properties of a Papaya lethal yellowing virus Isolate

Papaya (Carica papaya) is an important tropical fruit crop in northeastern Brazil. Lethal yellowing is a disease caused by Papaya lethal yellowing virus (PLYV) that occurs only in northeastern Brazil. The symptoms are characterized by progressive leaf yellowing and greenish circular spots on the fruits. The virus has isometric particles (30 nm), genomic single-stranded (ss)RNA (1.6 × 10⁶ Da), and a coat protein with a single component (35 kDa). Although no biological vector has been confirmed, the virus is spreading every year. In the present study, an isolate of the virus was characterized biologically, serologically, physically, and molecularly, and its survival in dried tissue was evaluated. Approximately 309.5 mg of virus was purified per kilogram of infected papaya leaves, and a high-titer polyclonal antiserum (1:1,024,000) was obtained from an immunized rabbit. The virus was detected in dried roots and leaves maintained up to 120 days. Its physical properties were thermal inactivation point (80°C), longevity in vitro (60 days), and dilution end point (10^-6). The virus was inactivated in leaves and roots eradicated from infected plants when they were submitted to a solarization period of 12 days, but maintained its infectivity when leaves and roots were maintained over the soil at natural conditions for 32 days. Among 58 plant species from 13 botanical families, the PLYV isolate infected only C. papaya, Jacaratia heterophylla, J. spinosa, Vasconcella cauliflora, V. quercifolia, and V. monoica, all from the family Caricaceae. A fragment of 1,098 nt of the virus isolate, corresponding to the 3' replicase (RdRp) and 5' coat protein (CP) cistron, was cloned and sequenced. Phylogenetic analysis of the RdRp nucleotide sequences indicated some similarity of PLYV with members of the genus Sobemovirus.

Characterization of a New Potyvirus Naturally Infecting Chickpea

During the 1999 to 2001 growing seasons, symptoms consisting of mosaic, stunting, yellowing, wilting, shortening of internodes, and phloem discoloration were observed in chickpea (Cicer arietinum) grown in the Department of Chuquisaca in southern Bolivia. In some fields, approximately 10% of the plants exhibited viruslike symptoms and suffered greatly reduced seed yields. Lentil (Lens culinaris) was also observed to be infected but not pea (Pisum sativum) or faba bean (Vicia faba) growing in nearby fields. Infected chickpea tissue reacted positively to the potyvirus group-specific monoclonal antibody (MAb), but there was no serological reaction with antisera to the potyviruses Bean yellow mosaic virus, Clover yellow vein virus, Cowpea aphid-borne mosaic virus, Pea seedborne mosaic virus, Bean common mosaic virus, or Bean common mosaic necrosis virus. Western blots of total protein extracts probed with the potyvirus MAb revealed a single band ca. 32 kDa. Comparative sequence analysis of cDNA clones generated from the putative coat protein gene consisted of 282 amino acids (31.9 kDa) and showed moderate identities of 67, 66, 63, 63, and 61% with the coat proteins of potyviruses Pepper severe mosaic virus, Pepper yellow mosaic virus, Potato virus Y, Plum pox virus, and Pepper mottle virus, respectively. Phylogenetic analysis of the coat protein amino acid sequence revealed that this virus is a unique member of the family Potyviridae and is phylogenetically most closely related to a group of Solanaceae-infecting potyviruses rather than to other legumeinfecting potyviruses. The proposed name for the new causal agent is Chickpea yellow mosaic virus.

Genetic mapping of turnip mosaic virus resistance in Lactuca sativa

Presence of the dominant Tu gene in Lactuca sativa is sufficient to confer resistance to infection by turnip mosaic virus (TuMV). In order to obtain an immunological assay for the presence of TuMV in inoculated plants, the TuMV coat protein (CP) gene was cloned by amplification of a cDNA corresponding to the viral genome using degenerate primers designed from conserved potyvirus CP sequences. The TuMV CP was overexpressed in Escherichia coli, and polyclonal antibodies were produced. To locate Tu on the L. sativa genetic map, F3 families from a cross between cvs "Cobbham Green" (resistant to TuMV) and "Calmar" (susceptible) were genotyped for Tu. Families known to be recombinant in the region containing Tu were infected with TuMV and tested by the indirect enzyme-linked immunosorbent assay (ELISA) using the anti-CP serum. This assay placed Tu between two random amplified polymorphic DNA (RAPD) markers and 3.2 cM from Dm5/8 (which confers resistance to Bremia lactucae). Also, bulked segregant analysis was used to screen for additional RAPD markers tightly linked to the Tu locus. Five new markers linked to Tu were identified in this region, and their location on the genetic map was determined using informative recombinants in the region. Six markers were identified as being linked within 2.5 cM of Tu.