|Robertson, Cecile -|
|Garnsey, Stephen -|
|Dawson, William -|
Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 23, 2011
Publication Date: October 18, 2011
Repository URL: http://handle.nal.usda.gov/10113/55921
Citation: Tatineni, S., Robertson, C.J., Garnsey, S.M., Dawson, W.O. 2011. A plant virus evolved by acquiring multiple non-conserved genes to extend its host range. Proceedings of the National Academy of Sciences. 108:42:17366-17371. Interpretive Summary: Plant viruses have evolved as combinations of genes that interact with host factors to produce progeny virus throughout the plants and in most cases to interact with a vector to be moved to other plants. Viral genes that involve in replication and virion assembly tend to be relatively conserved while other genes appear to be completely unrelated. The less conserved genes tend to be those that have evolved for interactions with the specific host for movement and to counter host defense systems. Citrus tristeza virus (CTV), the most economically important virus of citrus, possesses nine conserved genes that involve in replication, virions assembly, virus movement, and suppressors of RNA silencing. Additionally, CTV contains three nonconserved genes, which are dispensable for systemic infection of susceptible citrus species. In this study, we demonstrated that the three nonconserved genes in different combinations involved in infecting additional citrus species. Our results revealed that CTV evolved by progressively acquiring multiple nonconserved genes to interact with host proteins, thus extending its ability to infect additional citrus species. We demonstrated for the first time that a plant virus extended its ability to infect additional hosts by acquiring nonconserved genes.
Technical Abstract: Viruses have evolved as combinations of genes that interact with cellular components to produce progeny virus throughout the plants. Some viral genes, particularly those that are involved in replication and assembly, tend to be relatively conserved, while other genes that have evolved for interactions with the specific host for movement and to counter host defense systems tend to be less conserved. Closteroviridae encode 1 to 5 non-conserved open reading frames (ORFs). Citrus tristeza virus (CTV), a Closterovirus, possesses non-conserved p33, p18 and p13 genes that are expendable for systemic infection of the two major laboratory hosts, Citrus macrophylla and Mexican lime. In this study, we show that the extended host range of CTV does require these non-conserved genes. The p33 ORF was required to systemically infect sour orange and lemon trees, while either the p33 or the p18 gene was sufficient for systemic infection of grapefruit trees and the p33 or the p13 gene was sufficient for systemic infection of calamondin plants. Thus, these three genes are required for systemic infection of the full host range of CTV, but different genes were specific for different hosts. Remarkably, either of two genes was sufficient for infection of some citrus hybrids. These findings suggest that CTV acquired multiple non-conserved genes (p33, p18 and p13) to extend its ability to interact with multiple hosts, thus extending its host range during the course of evolution. These results greatly extend the complexity of known virus plant interactions.