title: Cotton leaf curl Gezira virus-satellite DNAs represent a divergent, geographically isolated Nile Basin lineage: predictive identification of a satDNA REP-binding motif.
abstract: Cotton leaf curl Gezira virus (CLCuGV), a species of the genus Begomovirus (family Geminiviridae), was recently cloned from cotton, okra, and Sida alba plants exhibiting leaf-curling and vein-thickening symptoms in Sudan. Here, we describe a previously unknown lineage of single-stranded DNA satellite (satDNA) molecules, which are associated with CLCuGV, and are required for development of characteristic disease symptoms. Co-inoculation of cotton and Nicotiana benthamiana plants with satDNAs cloned from cotton, okra, and S. alba, together with CLCuGV as the 'helper virus' resulted in the development of characteristic leaf-curling and vein-thickening symptoms in both hosts. An anatomical study of symptomatic, virus-infected cotton leaves revealed that spongy parenchyma cells had developed instead of collenchyma cells at the sites of vein thickening. Phylogenetically, the CLCuGV-associated satDNAs from Sudan, together with their closest relatives from Egypt, form a new satDNA lineage comprising only satDNAs from the Upper and Lower Nile Basins. Analysis of satellites and their helper virus sequences identified a predicted REP-binding site consisting of the directly repeated sequence, 'CGGTACTCA', and an inverted repeated sequence, 'TGAGTACCG', which occur in the context of a 17-nucleotide motif. The conserved REP-binding motif identified herein, together with strict geographic isolation, and apparent host-restriction, may be the collective hallmark of these new satDNA-begomovirus lineages, extant in the Nile Basin.
authors.affiliation: Department of Plant Sciences, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Idris
authors.forename: Rob W
authors.initials: RW
authors.lastname: Briddon
authors.forename: Simon E
authors.initials: SE
authors.lastname: Bull
authors.forename: J K
authors.initials: JK
authors.lastname: Brown
mesh_terms: D001665:Binding Sites / Q000235:genetics; D017124:Conserved Sequence; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification*; D004534:Egypt; D017791:Geminiviridae / Q000235:genetics* / Q000302:isolation & purification*; D003368:Gossypium / Q000821:virology; D008969:Molecular Sequence Data; D010802:Phylogeny; D010935:Plant Diseases / Q000821:virology; D012091:Repetitive Sequences, Nucleic Acid; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D013397:Sudan; D014026:Nicotiana / Q000821:virology
chemical_list: D004277:DNA, Single-Stranded; D004279:DNA, Viral