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A novel begomovirus isolated from a Sida rhombifolia plant collected in Sinaloa, Mexico, was characterized. The genomic components of sida mosaic Sinaloa virus (SiMSinV) shared highest sequence identity with DNA-A and DNA-B components of chino del tomate virus (CdTV), suggesting a vertical evolutionary relationship between these viruses. However, recombination analysis indicated that a short segment of SiMSinV DNA-A encompassing the plus-strand replication origin and the 5´-proximal 43 codons of the Rep gene was derived from tomato mottle Taino virus (ToMoTV). Accordingly, the putative cis- and trans-acting replication specificity determinants of SiMSinV were identical to those of ToMoTV but differed from those of CdTV. Modeling of the SiMSinV and CdTV Rep proteins revealed significant differences in the region comprising the small β1/β5 sheet element, where five putative DNA-binding specificity determinants (SPDs) of Rep (i.e., amino acid residues 5, 8, 10, 69 and 71) were previously identified. Computer-assisted searches of public databases led to identification of 33 begomoviruses from three continents encoding proteins with SPDs identical to those of the Rep encoded by SiMSinV. Sequence analysis of the replication origins demonstrated that all 33 begomoviruses harbor potential Rep-binding sites identical to those of SiMSinV. These data support the hypothesis that the Rep β1/β5 sheet region determines specificity of this protein for DNA replication origin sequences.

Rhynchosia minima (L.) DC. (Fabaceae) plants exhibiting bright golden mosaic symptoms were previously associated with begomovirus infection in Yucatan, México [1]. To characterize the begomovirus infecting these plants, the complete bipartite genome was cloned and sequenced. Sequence comparisons indicated that the virus was distinct from all other begomoviruses known to date, including those previously identified from symptomatic R. minima, and the name Rhynchosia yellow mosaic Yucatan virus (RhYMYuV) is proposed. Pairwise comparisons indicated that RhYMYuV DNA-A [2,597 nt, (EU021216)] and DNA-B [2,542 nt, (FJ792608)] components shared the highest nt sequence identity with Cabbage leaf curl virus (CaLCuV), 87% for component A and 71% for component B. Phylogenetic analysis indicated that both components of RhYMYuV are most closely related to other New World begomoviruses, having as closest relatives immediate outliers to the major Squash leaf curl virus (SLCV) clade. Recombination analysis of the RhYMYuV genome indicated that the DNA-A component has arisen through intermolecular recombination. R. minima plants inoculated with the monomeric clones developed a bright yellow mosaic similar to symptoms observed in naturally infected plants, confirming that the clones were infectious. Nicotiana benthamiana plants biolistically inoculated with monomeric clones developed curling and chlorosis in the newly emerging leaves. RhYMYuV was also detected in symptomatic Desmodium sect. Scorpiurus Benth. (Fabaceae) that were collected near the RhYMYuV-infected plants.