Begomovirus, the largest genus of plant viruses with >440 species, has caused severe economic losses by infecting many crops worldwide. Homologous recombination has been implicated as one of the major courses for generating novel begomoviruses, but the underlying mechanisms are not entirely clear, especially with regard to the role of their insect vectors. A team of scientists have identified that a new begomovirus, called tomato yellow leaf curl Shuangbai virus (TYLCSbV) has acquired high pathogenicity from one of the two parent viruses with vector transmission specificity from the other parent virus. This novel feature endows the recombinant virus a vector-associated selective advantage to evolve under changing environmental conditions.
Viruses are known to evolve rapidly for adaptation to environments. Recombination plays an important role in virus evolution and seems highly frequent in members of Begomovirus (family Geminiviridae). Begomoviruses are exclusively transmitted by whiteflies of the Bemisia tabaci cryptic complex (Hemiptera: Aleyrodoidea). Different whitefly species of this cryptic complex, such as the two invasive species called MEAM1 and MED, have disparate transmission efficiencies for a given begomovirus, and different begomoviruses may be transmitted by a given whitefly species with varying efficiencies. Some studies have explored the ecological significance of pathogenicity associated with recombinant begomoviruses. However, experimental studies seem lacking to characterize both pathogenicity and transmissibility of begomoviruses, thus illustrating how a recombination event may facilitate adaptation to host plants and shift of vector populations in the field.
In a recent article, a group of researchers have identified a new begomovirus called TYLCSbV, likely originated from a recombination between two parent viruses, i.e., Ageratum yellow vein China virus (AYVCNV) and tobacco curl shoot virus (TbCSV). TYLCSbV and AYVCNV exhibit similar levels of infectivity but contrasted specificities of vector transmission: TYLCSbV is efficiently transmitted by MED but not by MEAM1, whereas AYVCNV is more efficiently transmitted by MEAM1. The combined feature of pathogenicity and vector specificity of TYLCSbV is associated with the genomic combination of the various genome segments from two parent viruses (AYVCNV and TbCSV, see Title image). Field surveys indicate that MED had displaced MEAM1 in some regions where TYLCSbV was collected. Viral competition assays indicate that TYLCSbV outcompeted AYVCNV when the transmission was done by MED, while the outcome of competition between the two viruses reversed when the transmission was done by MEAM1. These findings suggest that the recombination event has resulted in a shift of vector specificity that could provide TYLCSbV with a potential selective transmission advantage, and the population shift of whitefly cryptic species potentially could have influenced the virus evolution towards an extended trajectory of transmission.
Yun-Yun Fan, Yu-Wei Zhong, Li-Long Pan, Xiao-Wei Wang, Ming Ding and Shu-Sheng Liu published this study in Molecular Plant Pathology:
TITLE IMAGE: Diagram depicting how various genome segments from two parent viruses (AYVCNV and TbCSV) combine to generate a new recombinant virus TYLCSbV with new adaptive potential. TYLCSbV contains C2 and C4 genes (pathogenicity determinants) from AYVCNV and the V1 gene (determinant of whitefly transmission specificity) from TbCSV. All images used with permission of the author.