Molecular and Biological Characterization of Distinct Strains of Jatropha mosaic virus from the Dominican Republic Reveal a Potential to Infect Crop Plants

Mixed infection of a new begomovirus, Jatropha leaf curl Guntur virus and recombinant/chimeric jatropha leaf curl Gujarat virus in Jatropha gossypiifolia

The Jatropha gossypiifolia plant showing the severe leaf curl symptom grown in the borders of chilli fields in Guntur, Andhra Pradesh, India was collected. The infection of begomovirus was detected using the degenerate primers followed by rolling circle amplification (RCA). The RCA products digested with KpnI and EcoRI showing the unit length of begomovirus genome was cloned in pUC19 and sequenced to obtain the complete begomoviral genome. The sequence information of DNA-A of the two clones GuWC10 contained 2794 nt (MZ217773) and an incomplete genome GuWC3 with 2337 nt (MZ217772). The BLAST analysis of GuWC3 and GuWC10 sequences showed 85.57% identity with jatropha leaf curl Gujarat virus (JLCGV) and 82.68% identity with croton yellow vein mosaic virus (CroYVMV) respectively. The sequence analysis also showed that the GuWC10 clone had a 177 bp recombinant/chimeric sequence of JLCGV while the other region containing 2611 bp showed 92.63% identity with papaya leaf curl virus (PaLCuV/PK). However, the global alignment of GuWC10 sequence showed a maximum of 80.60% identity with croton yellow vein virus (CroYVV) (FN645902), CroYVMV (JN817516) and PaLCuV/PK (KY978407). The second clone GuWC3 although shorter in length had recombinant sequences of JLCGV, jatropha leaf curl virus (JLCuV/ND) and okra enation leaf curl virus (OELCuV). The nucleotide sequence identity among the GuWC10 and GuWC3 was 71.9%. The phylogenetic analysis placed both the viral strains in a same clade located between PaLCuV/PK and JLCuV clades. According to the ICTV species demarcation criteria of 91% DNA-A sequence identity, the present isolate was considered as a new species of begomovirus and the name Jatropha leaf curl Guntur virus was proposed. This is the first report of a new begomovirus species infecting Jatropha gossypiifolia and the study also reports a mixed infection of Jatropha leaf curl Guntur virus with a recombinant/chimeric JLCGV in the host Jatropha gossypiifolia. Present study suggests the role of weed Jatropha in harboring begomoviruses and probable source for viral recombination.

Weed-infecting viruses in a tropical agroecosystem present different threats to crops and evolutionary histories

In the Caribbean Basin, malvaceous weeds commonly show striking golden/yellow mosaic symptoms. Leaf samples from Malachra sp. and Abutilon sp. plants with these symptoms were collected in Hispaniola from 2014 to 2020. PCR tests with degenerate primers revealed that all samples were infected with a bipartite begomovirus, and sequence analyses showed that Malachra sp. plants were infected with tobacco leaf curl Cuba virus (TbLCuCV), whereas the Abutilon sp. plants were infected with a new bipartite begomovirus, tentatively named Abutilon golden yellow mosaic virus (AbGYMV). Phylogenetic analyses showed that TbLCuCV and AbGYMV are distinct but closely related species, which are most closely related to bipartite begomoviruses infecting weeds in the Caribbean Basin. Infectious cloned DNA-A and DNA-B components were used to fulfilled Koch's postulates for these diseases of Malachra sp. and Abutilon sp. In host range studies, TbLCuCV also induced severe symptoms in Nicotiana benthamiana, tobacco and common bean plants; whereas AbGYMV induced few or no symptoms in plants of these species. Pseudorecombinants generated with the infectious clones of these viruses were highly infectious and induced severe symptoms in N. benthamiana and Malachra sp., and both viruses coinfected Malachra sp., and possibly facilitating virus evolution via recombination and pseudorecombination. Together, our results suggest that TbLCuCV primarily infects Malachra sp. in the Caribbean Basin, and occasionally spills over to infect and cause disease in crops; whereas AbGYMV is well-adapted to an Abutilon sp. in the Dominican Republic and has not been reported infecting crops.

Molecular and Biological Characterization of a New World Mono-/Bipartite Begomovirus/Deltasatellite Complex Infecting Corchorus siliquosus

The genus Begomovirus (family Geminiviridae) is the largest genus in the entire virosphere, with more than 400 species recognized. Begomoviruses are single-stranded DNA plant viruses transmitted by whiteflies of the Bemisia tabaci complex and are considered one of the most important groups of emerging plant viruses in tropical and subtropical regions. Several types of DNA satellites have been described to be associated with begomoviruses: betasatellites, alphasatellites, and deltasatellites. Recently, a family of single-stranded DNA satellites associated with begomoviruses has been created, Tolecusatellitidae, including the genera Betasatellite and Deltasatellite. In this work, we analyzed the population of begomoviruses and associated DNA satellites present in Corchorus siliquosus, a malvaceous plant growing wild in Central America, southeastern North America and the Caribbean, collected in Cuba. The genomes of isolates of two New World begomoviruses [(Desmodium leaf distortion virus (DesLDV) and Corchorus yellow vein Cuba virus (CoYVCUV)] and two deltasatellites [tomato yellow leaf distortion deltasatellite 2 (TYLDD2) and Desmodium leaf distortion deltasatellite (DesLDD)] have been cloned and sequenced from plants showing yellow vein symptoms. Isolates of one of the begomoviruses, CoYVCUV, and one of the deltasatellites, DesLDD, represent novel species. Experiments with infectious clones showed the monopartite nature of CoYVCUV and that DesLDD utilizes the bipartite DesLDV as helper virus, but not the monopartite CoYVCUV. Also, CoYVCUV was shown to infect common bean in addition to Nicotiana benthamiana. This is the first time that (i) a monopartite New World begomovirus is found in a host other than tomato and (ii) deltasatellites have been found in C. siliquosus, thus extending the host and helper virus ranges of this recently recognized class of DNA satellites.

Characterization of a New Monopartite Begomovirus with a Betasatellite Associated with Leaf Curl, Yellow Vein, and Vein Enation in Hibiscus rosa-sinensis

A new begomovirus, tentatively named hibiscus yellow vein leaf curl virus (HYVLCV), was identified in Hibiscus rosa-sinensis plants showing symptoms of leaf curl, yellow vein, and vein enation on the undersides of the leaf in Taiwan. Sequence analysis of the full-length HYVLCV genome from the rolling cycle amplicon revealed a genome of 2,740 nucleotides that contains six open reading frames and a conserved sequence (5'-TAATATTAC-3') commonly found in geminiviral genomes. HYVLCV shares the highest nucleotide identity (88.8%) with cotton leaf curl Multan virus (CLCuMuV) genome, which is lower than the criteria (91%) set for species demarcation in the genus Begomovirus. No begomoviral DNA-B was detected; however, a begomovirus-associated DNA betasatellite (DNA-β) was detected. The DNA-β (1,355 nucleotides) shares the highest nucleotide identity (78.6%) with malvastrum yellow vein betasatellite (MaYVB). Because the identity is slightly higher than the criteria (78%) set for the species demarcation threshold for a distinct DNA-β species, the DNA-β of HYVLCV reported in this study is considered the same species of MaYVB and tentatively named MaYVB-Hib. An expected 1,498-bp fragment was amplified with two HYVLCV-specific primers from 10 of 11 field-collected samples. Four independent amplicons were sequenced, revealing 100% nucleotide identity with the HYVLCV genome. Agroinoculation of a dimer of the infectious monopartite genome alone to Nicotiana benthamiana resulted in mild symptoms at 28 days postinoculation (dpi); coagroinoculation with the DNA-β satellite resulted in severe symptoms at 12 dpi. HYVLCV could be transmitted to healthy H. rosa-sinensis by grafting, resulting in yellow vein symptoms at 30 dpi.

Complete sequence of a new bipartite begomovirus infecting Sida sp. in Northeastern Brazil

In Brazil, non-cultivated plants, especially weeds, are infected with a diversity of begomoviruses and often show striking golden mosaic symptoms. In the present study, leaves showing these symptoms were collected from Sida sp. plants in Guadalupe, Piaui State, Northeastern Brazil, in 2015 and 2016. PCR tests with degenerate primers revealed the presence of begomovirus DNA-A and DNA-B components. Restriction enzyme digestion of rolling circle-amplified DNA revealed fragments totaling ~5.2 kb, indicating infection by a bipartite begomovirus. The DNA-A and DNA-B components have a genome organization typical of New World (NW) bipartite begomoviruses and a common region of 220 nucleotides (nt) with 96% identity, indicating these are cognate components. Comparisons performed with the DNA-A sequence revealed the highest nt sequence identity (84%) with that of sida angular mosaic virus (SiAMV), whereas those performed with the DNA-B sequence revealed highest identity (77%) with that of sida chlorotic vein virus (SiCVV). In phylogenetic analyses, the DNA-A sequence was placed in a strongly supported clade with SiAMV and SiCVV from Piaui, whereas the DNA-B sequence was placed in a clade with SiCVV and corchorus mottle virus. Based on the current ICTV criteria for the demarcation of begomovirus species (<91% nt sequence identity for the DNA-A component), this is a member of a new species for which the name "Sida yellow golden mosaic virus" is proposed.

A Bipartite Begomovirus Infecting Boerhavia erecta (Family Nyctaginaceae) in the Dominican Republic Represents a Distinct Phylogenetic Lineage and has a High Degree of Host Specificity

Boerhavia erecta plants in and around agricultural fields in the Azua Valley of the southeastern Dominican Republic often show striking golden mosaic symptoms. Leaf samples from B. erecta plants showing these symptoms were collected in 2012 and 2013, and PCR tests with degenerate primers revealed begomovirus DNA-A and DNA-B components. The complete sequences of the DNA-A and DNA-B components of four isolates show a high degree of sequence identity (>96%) and a genome organization typical of New World (NW) bipartite begomoviruses. Sequence comparisons and phylogenetic analyses revealed that these isolates composed a new phylogenetic lineage of NW bipartite begomoviruses. The most closely related begomovirus is Merremia mosaic virus, a weed-infecting species from Puerto Rico. Because DNA-A sequence identities are well below the 91% threshold, these isolates represent a new begomovirus species, for which the name Boerhavia golden mosaic virus (BoGMV) is proposed. Infectious cloned BoGMV DNA-A and DNA-B components induced golden mosaic symptoms in agroinoculated B. erecta plants, thereby fulfilling Koch's postulates for this disease. Agroinoculation and mechanical transmission experiments revealed that BoGMV has an unusually narrow host range, limited to members of the family Nyctaginaceae and not including the permissive host Nicotiana benthamiana. The inability of BoGMV to infect N. benthamiana was due to a deficiency in cell-to-cell movement but not to a unique amino acid residue in the movement protein.

Tomato Yellow Leaf Curl Sardinia Virus, a Begomovirus Species Evolving by Mutation and Recombination: A Challenge for Virus Control

The tomato leaf curl disease (TYLCD) is associated with infections of several species of begomoviruses (genus Begomovirus, family Geminiviridae) and causes severe damage to tomatoes throughout tropical and sub-tropical regions of the world. Among others, the Tomato yellow leaf curl Sardinia virus (TYLCSV) species causes damage in the Mediterranean Basin since early outbreaks occurred. Nevertheless, scarce information is available about the diversity of TYLCSV. Here, we study this aspect based on the sequence information accessible in databases. Isolates of two taxonomically differentiated TYLCSV strains can be found in natural epidemics. Their evolution is mostly associated with mutation combined with selection and random genetic drift and also with inter-species recombination which is frequent in begomoviruses. Moreover, a novel putative inter-strain recombinant is reported. Although no significantly new biological behaviour was observed for this latter recombinant, its occurrence supports that as shown for other related begomoviruses, recombination continues to play a central role in the evolution of TYLCD-associated viruses and the dynamism of their populations. The confrontation of resistant tomatoes with isolates of different TYLCD-associated viruses including the novel recombinant demonstrates the existence of a variable virus x plant genotype interaction. This has already been observed for other TYLCD-associated viruses and is a challenge for the control of their impact on tomato production.