|Dawson, William -|
Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 16, 2012
Publication Date: July 11, 2012
Repository URL: http://handle.nal.usda.gov/10113/55923
Citation: Tatineni, S., Dawson, W.O. 2012. Enhancement or attenuation of disease by deletion of genes from Citrus tristeza virus. Journal of Virology. 86: 7850-7857. Interpretive Summary: Citrus tristeza virus (CTV), a phloem limited virus, is the most economically important virus infecting citrus. CTV induces quick decline and stem pitting diseases on Citrus spp. Stem pitting is a common virus-induced phenotype of perennial woody plants that results from interference with stem growth. Although the stem pitting disease phenotype is common in virus-infected perennial woody plants, there is little understanding of the processes that cause the stem pits. The ability to systemically infect certain species of citrus with CTV deletion mutants provided an opportunity to examine the effect of the lack of these genes on the development of stem pits by CTV. In the most susceptible experimental host, Citrus macrophylla, the full-length virus causes only very mild stem pitting symptoms. Surprisingly, certain deletion combinations induced greatly increased stem pitting symptoms while other combinations resulted in reduced stem pitting, suggesting that stem pitting can result from a balance between the expression of different viral genes. We also found the virus in locations outside of the normal ring of phloem in pitted areas and increased stem pitting was not only associated with a prevention of xylem production, but also a proliferation of cells that supported viral replication in the pitted areas.
Technical Abstract: 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.