Development of an infectious clone and replicon system of norovirus GII.4.

Human norovirus (HuNoV) is one of the main causes of acute gastroenteritis worldwide and is responsible for at least 20% of all cases. The detailed molecular mechanism of this norovirus remains unknown due to the lack of a suitable in vitro culturing system. An infectious clone of HuNoV would be a useful tool for elucidating the processes of viral infection and the mechanisms of replication. We developed an infectious cDNA clone of HuNoV using the rapid technique of Gibson Assembly. The complete genome of the HuNoV GII.4 Sydney subtype was cloned into a previously modified pcDNA3.1-based plasmid vector downstream from a cytomegaloviral promoter. We monitored the viral infection in vitro by inserting the reporter gene of the green fluorescent protein (GFP) between the NTPase and p22 genes, also by Gibson Assembly, to construct a HuNoV-GFP replicon. Human Caco-2 cells were transfected with the full-length genomic clone and the replicon containing GFP. The gene encoding the VP1/VP2 capsid protein was expressed, which was indirect evidence of the synthesis of subgenomic RNAs and thus the negative strand of the genome. We successfully constructed the infectious clone and its replicon containing GFP for the HuNoV GII.4 Sydney subtype, a valuable tool that will help the study of noroviral infection and replication.

The complete genome of the tospovirus Zucchini lethal chlorosis virus.

BACKGROUND: Zucchini lethal chlorosis virus (ZLCV) causes significant losses in the production of cucurbits in Brazil. This virus belongs to the genus Tospovirus (family Bunyaviridae) and seems to be exclusively transmitted by Frankliniella zucchini (Thysanoptera). Tospoviruses have a tripartite and single-stranded RNA genome classified as S (Small), M (Medium) and L (Large) RNAS. Although ZLCV was identified as a member of the genus Tospovirus in 1999, its complete genome had not been sequenced until now. FINDINGS: We sequenced the full-length genome of two ZLCV isolates named ZLCV-SP and ZLCV-DF. The phylogenetic analysis showed that ZLCV-SP and ZLCV-DF clustered with the previously reported isolate ZLCV-BR09. Their proteins were closely related, except the non-structural protein (NSm), which was highly divergent (approximately 90 % identity). All viral proteins clustered similarly in our phylogenetic analysis, excluding that these ZLCV isolates have originated from reassortment events of different tospovirus species. CONCLUSION: Here we report for the first time the complete genome of two ZLCV isolates that were found in the field infecting zucchini and cucumber.

Transreplication of a Tomato yellow leaf curl Thailand virus DNA-B and replication of a DNAbeta component by Tomato leaf curl Vietnam virus and Tomato yellow leaf curl Vietnam virus.

The genomes of two tomato-infecting begomoviruses from Vietnam were cloned and sequenced. A new variant of Tomato leaf curl Vietnam virus (ToLCVV) consisting of a DNA-A component and associated with a DNAbeta molecule as well as an additional begomovirus tentatively named Tomato yellow leaf curl Vietnam virus (TYLCVV) consisting also of a DNA-A component were identified. To verify if monopartite viruses occurring in Vietnam and Thailand are able to transreplicate the DNA-B component of Tomato yellow leaf curl Thailand virus-[Asian Institute of Technology] (TYLCTHV-[AIT]) infectivity assays were performed via agroinoculation and mechanically. As result, the DNA-B component of TYLCTHV-[AIT] was transreplicated by different DNA-A components of viruses from Vietnam and Thailand in Nicotiana benthamiana and Solanum lycopersicum. Moreover, the TYLCTHV-[AIT] DNA-B component facilitated the mechanical transmission of monopartite viruses by rub-inoculation as well as by particle bombardment in N. benthamiana and tomato plants. Finally, defective DNAs ranging from 735 to 1457 nucleotides were generated in N. benthamiana from those combinations containing TYLCTHV-[AIT] DNA-B component.

Molecular characterization and detection of Vicia cryptic virus in different Vicia faba cultivars.

After extraction of double-stranded (ds) RNAs from Vicia faba, dsRNA1 and dsRNA2 of Vicia cryptic virus (VCV), a member of the genus Alphacryptovirus (family Partitiviridae), were detected in six out of seven different cultivars by agarose gel electrophoresis. In attempts to sequence the complete VCV genome, the dsRNA1 and dsRNA2 sequences from a total of five different V. faba cultivars were determined. Analysis of these sequences indicated that V. faba cultivars contain almost indistinguishable VCV sequences. The larger dsRNA1 was 2012 bp in length and contained a major open reading frame (ORF) encoding a putative RNA-dependent RNA polymerase (RdRp). The smaller dsRNA2 was 1779 bp in length and comprised a single ORF on its plus-strand encoding the coat protein (CP). The sequences of the dsRNA1 and dsRNA2 ORFs shared highest amino acid sequence identities (84 and 56%, respectively) with the corresponding gene products of the alphacryptovirus white clover cryptic virus 1 (WCCV-1). The 5'-terminal untranslated regions of dsRNA1 and dsRNA2 of VCV were highly conserved and were strikingly similar to the corresponding regions of WCCV-1. RdRp amino acid sequence alignments revealed conserved motifs, which correlate with the phylogenetic clustering of the family Partitiviridae.

The complete nucleotide sequence of a capsicum chlorosis virus isolate from Lycopersicum esculentum in Thailand.

The complete nucleotide sequence of a tospovirus isolated from Lycopersicum esculentum in Thailand was determined. The L RNA comprises of 8912 nt and codes for the RNA-dependent RNA-polymerase (RdRp) (2877 aa). Two ORFs are located on the M RNA (4823 nt) encoding the non-structural (NSm) protein (308 aa) and the viral glycoprotein precursors (Gn/Gc) (1121 aa) separated by an intergenic region of 433 nt. ORFs coding for the non-structural (NSs) and nucleocapsid (N) protein, 439 aa and 275 aa, respectively, were identified on the S RNA (3477 nt) separated by an intergenic region of 1202 nt. The N protein of the Thailand isolate was most closely related to that of capsicum chlorosis virus (CaCV), sharing an amino acid sequence identity of 92.7%. Additionally, multiple sequence analyses revealed significant similarities to tospoviruses of the species Watermelon silver mottle virus and to several putative tospovirus entries in GenBank. Based on these alignments it is proposed to refer to all these different viruses as isolates of CaCV.