Genome Sequence Determination And Analysis Of A Chinese Virulent Strain, LMS Of Marek’s Disease Virus Serotype-1

Marek’s disease (MD) is a lymphoproliferative disease of chickens. The agent of MD is Marek’sdisease virus serotype1(MDV1), which is also called Gallid herpesvirus type2(GaHV-2). MDV1is amember of the Mardivirus genus in the family Herpesviridae.MD is a worldwide disease, which causes great economic losses. Although vaccination has beenused widely in China, MD still occurs frequently. Some molecular epidemiologic studies have shownthat Chinese MDV1isolates seem to constitute a separate clade from strains isolated from other regions.However, all researches above were based on such special genes as meq or pp38, and no genomeinformation for the Chinese virulent strains of MDV1was available.In2007, a virulent MDV1field strain, named LMS, was isolated from diseased chicken flocks inthe southwest of China. Challenge tests indicated that LMS has similar pathogenicity with Md5. Growthdynamics experiments also showed that LMS had strong replicative ability. In order to further evaluatethe genetic properties of LMS, the genomic sequence of LMS was investigated.In this experiment,72pairs of primers were used to amplify the whole genome of LMS isolate(genebank accession: JQ314003). Genetic analysis, predicting open reading frame (ORF), SNP analysisand identifying intergenic differences of LMS genome were performed using many local and web-basedbio-information tools including DNASTAR, Bioedit, Mega and Emboss. A total of25MDV1(10completed and15partial) strains from different period and regions was used for the bio-informationanalysis.The genome of LMS is177,526bp long, and the genome was organized similar to other class Ealphaherpesviruses with six genomic regions. A total of197ORFs were predicted. Of the197ORFs,90ORFs have low sequence identity with homologous ORFs of reference strains (identity<98%). Grossgenetic alterations (insertions, deletions and frame mutations) were identified in a haploid gene,MDV086.4, and five diploid genes: MDV001/MDV080, MDV003.6/MDV078.2,MDV005.5/MDV077.91, MDV081.5/MDV102.5, and MDV086.2/MDV97.6. Oncogenic genes andvirulent genes in LMS genome didn’t great altered compared with reference strains. There are22uniquenonsynonymous mutations in LMS genome. Possible transcription start sites (29bp long) of LATs arenaturally deleted in LMS. Two copies of novel tandem repeats were found in the α like region.Evolutionary analysis demonstrated that LMS has a larger phylogenetic distance from most Americanisolated strains but a closer relationship with648Ap80and the European pC12/130strain. LMS sharedthe high nucleotide similarities (identity>94%) with other foreign virulent strains, which reflectedMDV1strains from different regions were conservative on evolution.In this research the genome sequence of a Chinese virulent strain of MDV1was determined andanalyzed for the first time. The characterised genome of LMS provides further insight into the geneticsof the Chinese MDV1field strains, which is useful for the control of MD in China.