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Enhancement or Attenuation of Disease by Deletion of Genes from Citrus Tristeza Virus

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Stem pitting is a common virus-induced disease of perennial woody plants induced by a range of different viruses. The phenotype results from sporadic areas in which normal xylem and phloem development is prevented during growth of stems. These alterations interfere with carbohydrate transport resulting in reduced plant growth and yield. Citrus tristeza virus (CTV), a phloem-limited Closterovirus, induces economically important stem-pitting diseases of citrus. CTV has three non-conserved genes (p33, p18, and p13) that are not required for systemic infection of some species of citrus, which allowed us to examine the effect of deletions of these genes on symptom phenotypes. In the most susceptible experimental host, Citrus macrophylla, the full-length virus causes only very mild stem pitting symptoms. Surprisingly, we found that certain deletion combinations (p33 and p18 and/or p13) induced greatly increased stem pitting symptoms, while other combinations (p13 or p13 plus p18) resulted in reduced stem pitting. These results suggest that the stem-pitting phenotype, which is one of more economically important disease phenotypes, can result, not from a specific sequence or protein, but from a balance between the expression of different viral genes. Unexpectedly, using GFP-tagged full-length virus and deletion mutants (CTV9'p33 and CTV9'p33'p18'p13), the virus was found at pitted areas in abnormal locations outside of the normal ring of phloem. Thus, increased stem pitting was not only associated with a prevention of xylem production, but also a proliferation of cells that supported viral replication, suggesting that at random areas of stems the virus can elicit changes in cellular differentiation and development.
Satyanarayana Tatineni , William O. Dawson
Citrus macrophylla , Citrus tristeza virus , amino acid sequences , carbohydrates , cell proliferation , gene deletion , gene expression , genes , hosts , mutants , perennials , phenotype , phloem , plant diseases and disorders , plant viruses , stem elongation , stems , virus replication , xylem
Journal of Virology 2012 v.86 no.15
Journal Articles, USDA Authors, Peer-Reviewed
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