Biomedical subjects

C M Fauquet

Publications and source records attributed to C M Fauquet.

40 records · Page 3Linked to original sources

PubMed1995

Tomato leaf curl geminivirus from India has a bipartite genome and coat protein is not essential for infectivity.

Genomes of two isolates of tomato leaf curl geminivirus from India (ToLCV-India) have been sequenced. ToLCV-India contains A and B components, both of which are required for systemic movement and symptom development. The two isolates have 94% sequence identify but one isolate gave mild symptoms in Nicotiana benthamiana and tomato. The genome organization of ToLCV-India is similar to other whitefly-transmitted geminiviruses (WTGs) with bipartite genomes. However, it contains an additional ORF, AV3, that has not been reported for other WTGs. Its coat protein (CP) sequence is highly homologous to that of Indian cassava mosaic virus (90%). Two mutations that truncated the CP after amino acids 65 or 172 did not affect systemic movement and symptom development in either N. benthamiana or tomato. However, the symptoms caused by mutant viruses were different from those in plants infected with unmodified viruses, and plants infected with the mutants had markedly reduced amounts of single-stranded viral DNA. Comparison of sequences and other biological features of ToLCV-India with other geminiviruses showed that ToLCV-India is a distinct virus and is related to the WTGs from the Old World. It is similar to African cassava mosaic virus in its requirement for B component and dispensability of coat protein for symptom development, unlike other geminiviruses that infect tomato in the Old World. It is proposed that ToLCV-India evolved more recently as compared to other geminiviruses that infect tomato in the Old World.

Base Sequence↗

PubMed1995

Classification and identification of geminiviruses using sequence comparisons.

The genomes and ORFs of 36 geminiviruses were compared to obtain phylogenetic trees and frequency distributions of all possible pairwise comparisons with an objective to classify geminiviruses. Such comparisons show that geminiviruses form two distinct clusters of leafhopper-transmitted viruses that infect monocots (subgroup I) and whitefly-transmitted viruses that infect dicots (subgroup III), irrespective of the part of the genome considered. Of the two leafhopper-transmitted viruses that infect dicots, tobacco yellow dwarf virus has a sequence most similar to subgroup I viruses, and that of beet curly top virus differed depending upon the ORF considered. The distributions of identities within subgroups are significantly different suggesting that the taxonomic status of a particular isolate within a subgroup can be quantified. All the recognized strains of any one virus have greater than 90% sequence identity. It was observed that the 200 nucleotide intercistronic regions of geminiviruses are more variable than the remainder of the genome. The amino acid sequences of the coat protein (CP) of subgroup III viruses are more conserved than the remainder of the genome. However, a short N-terminal region (60-70 amino acids) of the CP is more variable than the rest of the CP sequence and is a close representation of the genome. PCR primers based on conserved sequences can be used to clone and sequence the N-terminal sequences of the CP of the geminiviruses; this sequence is sufficient to classify a virus isolate. A possible taxonomic structure for geminiviruses is proposed after considering the sequence comparisons and biological properties.

Amino Acid Sequence↗

PubMed1994

Complete nucleotide sequence of the geminivirus tomato yellow leaf curl virus, Thailand isolate.

The complete genome of a Thailand isolate of the geminivirus tomato yellow leaf curl virus (TYLCV-Th) has been cloned and the nucleotide sequence determined. The genome consists of two DNAs each slightly greater than 2700 nucleotides in length and designated A-DNA and B-DNA. The A-DNA contains six open reading frames (ORFs) capable of encoding proteins with M(r)s greater than 10K; two ORFs were located on the B-DNA. The predicted ORFs were found at positions on the genome similar to those identified in other geminiviruses. Based upon computer-assisted sequence comparisons with other geminiviruses, TYLCV-Th maintained the greatest degree of similarity with a tomato pathogen isolated in Australia, tomato leaf curl virus. Furthermore, sequence comparisons with a large number of geminiviruses confirm further divisions of the geminiviruses based upon geographical proximity of the viruses. Agroinoculation of Nicotiana benthamiana with a TYLCV-Th A-DNA clone containing a mutation in the capsid protein ORF demonstrated that the coat protein is not essential for TYLCV-Th infection but enhances the progression of the disease.

Base Sequence↗

PubMed1993

Geminivirus nomenclature: the need to set taxonomic standards.

The geminiviruses are plant viruses of significant economic impact. Different nomenclature has been used in various studies in descriptions of their genomes. We propose in this communication a uniform nomenclature to be used in future studies.

Plant Viruses↗