|Albiach-Marti, Maria -|
|Robertson, Cecile -|
|Gowda, Siddarame -|
|Belliure, Belen -|
|Garnsey, Stephen -|
|Folimonova, Svetlana -|
|Moreno, Pedro -|
|Dawson, William -|
Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 2, 2009
Publication Date: January 1, 2010
Citation: Albiach-Marti, M.R., Robertson, C., Gowda, S., Tatineni, S., Belliure, B., Garnsey, S.M., Folimonova, S.Y., Moreno, P., Dawson, W.O. 2010. The Pathogenicity Determinant of Citrus Tristeza Virus Causing the Seedling Yellows Syndrome is Located at the 3’-Terminal Region of the Viral Genome. Molecular Plant Pathology, Volume 11 (1), pages 55-67. Interpretive Summary: The T36 isolate of Citrus tristeza virus (CTV) in Florida induces seedling yellows (SY) symptoms in sour orange, lemon, and grapefruit seedlings, while the T30 isolate, a widely distributed mild isolate, failed to induce SY. In this study, we identified viral determinants that induce SY symptoms by creating hybrid viruses between SY inducing T36 isolate and non-SY inducing T30 isolate. Among several T36-T30 hybrid viruses, a hybrid T36 virus containing the p23 ORF and 3’ nontranslated region from T30 isolate failed to induce SY syndrome in sour orange and grapefruit seedlings, suggesting that the SY symptom determinant is located in p23-3’NTR region of T36 isolate. Furthermore, the non-SY hybrid virus (T36 with p23-3’NTR from T30) effectively cross protected citrus seedlings from the SY when challenged by the parent T36 virus, suggesting that the engineered mild strains of T36 virus could potentially use to cross protect from a severe CTV isolate, T36.
Technical Abstract: Citrus tristeza virus (CTV) (genus Closterovirus, family Closteroviridae) causes some of the more important viral diseases of citrus worldwide. The ability to map disease-inducing determinants of CTV is needed to develop better diagnostic and disease control procedures. A distinctive phenotype of some isolates of CTV is the ability to induce seedling yellows (SY) in sour orange, lemon and grapefruit seedlings. In Florida, the decline isolate of CTV, T36, induces SY, while a widely distributed mild isolate, T30, does not. To delimit the viral sequences associated with the SY syndrome, we created a number of T36/T30 hybrids by substituting T30 sequences into different regions of the 3’ half of the genome of an infectious cDNA of T36. Eleven T36/T30 hybrids replicated in Nicotiana benthamiana protoplasts. Five of these hybrids formed viable virions that were mechanically transmitted to Citrus macrophylla, a permissive host for CTV. All of them induced systemic infections, similar to that of the parental T36 clone. Tissues from these C. macrophylla source plants were then used to graft-inoculate sour orange and grapefruit seedlings. Inoculation with three of the T30/T36 hybrid constructs induced SY symptoms identical to those of T36, however, two hybrids with T30 substitutions in the p23-3´non translated region (NTR) region (nts 18394-19296) failed to induce SY. Sour orange seedlings infected with a recombinant non-SY P23-3’NTR hybrid also remained symptomless when challenged with the parental virus (T36) and demonstrated the potential feasibility of using engineered constructs of CTV for mitigating disease.