Browsing by Author "Gordon, Donald T."

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    Reciprocal exchanges involving virion and complementary sense genes, the LIR and SIR between the two clones of maize streak mastrevirus result in ameliorated symptoms in maize
    (Research Square, 2022) Edema, Richard; Gordon, Donald T.
    A genetic analysis of maize streak mastrevirus (MSV) virulence was conducted using two infectious DNA clones derived from isolates collected in Kenya. Virulence was tested on the susceptible Pioneer hybrid 3379 using vascular puncture inoculation of kernels. Marked differences in the severity of chlorotic streaks and stunting of seedlings were associated with mild [pMSV-KL (mild)] and severe [pMSVKm( severe)] parental infectious MSV DNA clones. To identify determinants conditioning these differences, chimeric clones were constructed from parental clones employing restriction endonuclease fragments. Clone identities were confirmed by restriction mapping. Putative virulence determinants were identified for genomic fragments encoding the replication initiator (Rep and RepA), movement (MP) and coat (CP) protein ORFs and for those containing non-coding long (LIR) and short intergenic regions (SIR). Recombinant clones containing LIRs plus the 5'–terminus of Rep/RepA (first 189 nt) ORFs from pMSVKm( Severe) and pMSV-KL(Mild) reciprocally exchanged displayed intermediate symptoms. Complementary replacement of the Rep/RepA ORF resulted in symptoms indistinguishable from those of parental clones. The recombinant clone constructed with LIR, Rep and RepA genome sequences from pMSV-Km(Severe) and MP, CP and SIR sequences from pMSV-KL(Mild) showed significantly more severe symptoms and accumulated higher concentrations than pMSV-Km(Severe). In contrast, the reciprocal clone showed significantly milder symptoms and lower viral titers than pMSV-KL(Mild). Viral accumulation was correlated with the intensity of leaf chlorosis and the degree of plant stunting. These data support the hypothesis that MSV virulence is a polymorphic trait involving virion and complementary sense genes (LIR and SIR).
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    Transmission of viral RNA and DNA to maize kernels by vascular puncture inoculation
    (Journal of virological methods, 2001) Redinbaugh, Margaret G.; Louie, Raymond; Ngwira, Patricia; Edema, Richard; Gordon, Donald T.; Bisaro, David M.
    Vascular puncture inoculation (VPI) is an effective technique for transmission of maize viruses without using arthropods or other biological vectors. It involves using a jeweler’s engraving tool to push minuten pins through a droplet of virus inoculum toward the major vascular bundle in the scutellum of germinating kernels. Here, VPI is shown to be useful for introducing RNA and DNA viral genomes into maize. Maize dwarf mosaic potyvirus (MDMV) virions, MDMV genomic RNA, foxtail mosaic potexvirus (FoMV) genomic RNA and maize streak geminivirus (MSV) DNA were introduced into kernels by VPI, and infection rates determined. At high concentrations, both MDMV virion and genomic RNA preparations produced 100% infection of susceptible maize. However, MDMV genomic RNA was transmitted with about 100-fold lower efficiency than virions. FoMV genomic RNA and MSV DNA were transmitted at lower efficiency than the MDMV RNA, and the highest transmission rates were about 50%. Ribonuclease A pretreatment prevented genomic MDMV and FoMV RNA transmission, but not MDMV virion transmission indicating the viral RNA was the infectious entity. Proteinase K (ProK) pretreatment reduced transmission of MDMV RNA suggesting that integrity of the viral genomic protein bound covalently to the viral RNA may be important for efficient transmission