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PubMed1997

Nucleotide sequence evidence for the occurrence of three distinct whitefly-transmitted, Sida-infecting bipartite geminiviruses in Central America.

The nucleotide sequences of two Sida-infecting geminiviruses from Honduras were determined. The symptoms of both viruses are identical in Sida rhombifolia but different in Nicotiana benthamiana. An additional symptom of one virus was yellow vein clearing on infected N. benthamiana leaves. Both Sida golden mosaic viruses (SiGMV-Ho and SiGMV-Ho(yv)) have bipartite genomes (DNAs A and B). From the SiGMV-Ho(yv)-infected S. rhombifolia plant two different DNA B molecules were isolated and cloned. They differ in length by 24 nucleotides [SiGMV-Ho(yv) B1 (2593 nt) and B2 (2569 nt)] and at eight nucleotide positions. Both proteins encoded by DNA B (BV1 and BC1) are affected by these substitutions. Computer analysis shows that the bipartite genomes resemble those of other whitefly-transmitted geminiviruses. From homology analyses we conclude that both viruses are closely related but distinct. Comparison with a Sida-infecting virus from Costa Rica (SiGMV-Co) showed that the two viruses from Honduras are more similar to each other than either of them are to SiGMV-Co. Exchange of SiGMV-Ho and SiGMV-Ho(yv) genomic components resulted in viable pseudorecombinant viruses. SiGMV-Ho DNA A was able to produce a viable pseudorecombinant with SiGMV-Co DNA B while the reciprocal exchange was not infectious in N. benthamiana. SiGMV-Ho(yv) DNA A and SiGMV-Co DNA B produced a viable pseudorecombinant virus whereas only pseudorecombination of SiGMV-Co DNA A with SiGMV-Ho(yv) DNA B2, and not with DNA B1, was infectious in N. benthamiana.

Amino Acid Sequence↗

PubMed1995

Nucleotide sequences from tomato leaf curl viruses from different countries: evidence for three geographically separate branches in evolution of the coat protein of whitefly-transmitted geminiviruses.

The coat protein (CP) gene-containing circular DNA molecule of an isolate of tomato leaf curl geminivirus (ITmLCV; 2749 nt) obtained from southern India, and the CP genes of tomato yellow leaf curl geminivirus isolates from Nigeria and two regions of Saudia Arabia were sequenced. ITmLCV DNA had the same arrangement of ORFs, and the same pattern of repeats in the large intergenic region as is found in in DNA-A of other whitefly-transmitted geminivirus (WTGs) from the Old World. However, the sequence of ITmLCV DNA and the sequences of its predicted translation products differed substantially from those of other WTGs, including one isolate obtained from a tomato plant in northern India. Comparison of the four CP sequences deduced here with those of 18 WTGs previously studied indicated that their relationships can be represented by a tree with three branches that are unrelated to plant host species but which contains viruses from the Americas, Africa to the Middle East, and Asia to Australia, respectively. It is suggested that WTG CP evolution has proceeded along different paths in these three main regions, and that WTGs have adapted freely to new hosts in each region. Indeed, the virus isolates causing similar diseases of tomato plants in the different continents are, with few exceptions, not closely related and warrant recognition as separate species.

Amino Acid Sequence↗

PubMed2005

Transgene elimination in genetically modified dry bean and soybean lines.

Transgene elimination is a poorly studied phenomenon in plants. We made genetic and molecular studies of a transgenic dry bean line immune to bean golden mosaic geminivirus and a soybean line. In both lines, the transgenes were stable during the vegetative phase but were eliminated during meiosis. Due to its potential biotechnological value, this transgenic line was micropropagated by grafting and the vegetative copies were studied for more than two years. More than 300 plants of progeny were obtained during this period, demonstrating that the phenomenon of elimination was consistently repeated and offering an opportunity for detailed study of transgene elimination, including the characterization of the integration sites. Cloning and sequencing of the transgenic loci, reciprocal crosses to untransformed plants, genomic DNA blots, and GUS assays were performed in the transgenic lines. Based on the molecular and genetic characterization, possible mechanisms involved in transgene elimination include intrachromosomal recombination, genetic instability resulting from the tissue culture manipulations, and co-elimination of transgenes, triggered by a process of genome defense.

DNA, Plant↗

PubMed2000

Tomato yellow leaf curl geminivirus (TYLCV-Is) is transmitted among whiteflies (Bemisia tabaci) in a sex-related manner.

Tomato yellow leaf curl virus (TYLCV) is the name given to a complex of geminiviruses infecting tomato cultures worldwide. TYLCV is transmitted by a single insect species, the whitefly Bemisia tabaci. Herein we show that a TYLCV isolate from Israel (TYLCV-Is) can be transmitted among whiteflies in a sex-dependent manner, in the absence of any other source of virus. TYLCV was transmitted from viruliferous males to females and from viruliferous females to males but not among insects of the same sex. Transmission took place when insects were caged in groups or in couples, in a feeding chamber or on cotton plants, a TYLCV nonhost. The recipient insects were able to efficiently inoculate tomato test plants. Insect-to-insect virus transmission was instrumental in increasing the number of whiteflies capable of infecting tomato test plants in a whitefly population. TYLCV was present in the hemolymph of whiteflies caged with viruliferous insects of the other sex; therefore, the virus follows, at least in part, the circulative pathway associated with acquisition from infected plants. Taken as a whole, these results imply that a plant virus can be sexually transmitted from insect to insect.

Animals↗

PubMed1992

Mechanism of Ds1 excision from the genome of maize streak virus.

We have previously shown that the maize transposable element Ds1 introduced into maize plants by agroinfection can be excised from the genome of geminivirus maize streak virus (MSV). Excision depended strictly on the presence of an active Ac element in the plants. In this study, the excision products or "footprints" left in the MSV genome after Ds1 excision were extensively characterized and the effects of flanking sequences on Ds1 excision were analysed. Most types of footprints obtained were comparable to those described for Ds1 excision in the maize genome, and could be explained by the models proposed for excision of plant transposable elements. In two revertants, however, some terminal sequences of the Ds1 element were found to have been left behind at the excision site. The finding of this novel type of Ds1 footprint indicated that gene conversion events occurred during and/or after Ds1 excision from the MSV genome. A partial deletion of one copy of the 8 bp duplications flanking the Ds1 element had no effect on the frequency or on the types of footprints of Ds1 excision from the MSV genome. Thus, the duplicated 8 bp sequences flanking the transposable element are not involved in Ds1 excision. These results, as well as a statistical analysis of the modifications of the bases flanking the Ds1 element after excision, are discussed in terms of excision models.

Base Sequence↗

PubMed1999

A GroEL homologue from endosymbiotic bacteria of the whitefly Bemisia tabaci is implicated in the circulative transmission of tomato yellow leaf curl virus.

Evidence for the involvement of a Bemisia tabaci GroEL homologue in the transmission of tomato yellow leaf curl geminivirus (TYLCV) is presented. A approximately 63-kDa protein was identified in B. tabaci whole-body extracts using an antiserum raised against aphid Buchnera GroEL. The GroEL homologue was immunolocalized to a coccoid-shaped whitefly endosymbiont. The 30 N-terminal amino acids of the whitefly GroEL homologue showed 80% homology with that from different aphid species and GroEL from Escherichia coli. Purified GroEL from B. tabaci exhibited ultrastructural similarities to that of the endosymbiont from aphids and E. coli. In vitro ligand assays showed that tomato yellow leaf curl virus (TYLCV) particles displayed a specific affinity for the B. tabaci 63-kDa GroEL homologue. Feeding whiteflies anti-Buchnera GroEL antiserum before the acquisition of virions reduced TYLCV transmission to tomato test plants by >80%. In the haemolymph of these whiteflies, TYLCV DNA was reduced to amounts below the threshold of detection by Southern blot hybridization. Active antibodies were recovered from the insect haemolymph suggesting that by complexing the GoEL homologue, the antibody disturbed interaction with TYLCV, leading to degradation of the virus. We propose that GroEL of B. tabaci protects the virus from destruction during its passage through the haemolymph.

Amino Acid Sequence↗

PubMed1994

Whitefly transmission and efficient ssDNA accumulation of bean golden mosaic geminivirus require functional coat protein.

Bean golden mosaic geminivirus (BGMV) has a bipartite genome composed of two circular ssDNA components (DNA-A and DNA-B) and is transmitted by the whitefly, Bemisia tabaci. DNA-A encodes the viral replication proteins and the coat protein. To determine the role of BGMV coat protein systemic infection and whitefly transmission, two deletions and a restriction fragment inversion were introduced into the BGMV coat protein gene. All three coat protein mutants produced systemic infections when coinoculated with DNA-B onto Phaseolus vulgaris using electric discharge particle acceleration "particle gun." However, they were not sap transmissible and coat protein was not detected in mutant-infected plants. In addition, none of the mutants were transmitted by whiteflies. With all three mutants, ssDNA accumulation of DNA-A and DNA-B was reduced 25- to 50-fold and 3- to 10-fold, respectively, as compared to that of wild-type DNA. No effect on dsDNA-A accumulation was detected and there was 2- to 5-fold increase in dsDNA-B accumulation. Recombinants between the mutated DNA-A and DNA-B forms were identified when the inoculated coat protein mutant was linearized in the common region.

Animals↗