Complete Genome Sequence Analysis of Guangdong Isolates of Cymbidium Mosaic Virus

[Objectives]The paper was to explore the genetic information and evolution of CymMV,and to provide an important scientific basis for monitoring and early warning of orchid virus disease and anti-virus genetic engineering of orchid in Guangdong Province.[Methods]RT-PCR and DASELISA were used to detect and identify CymMV from leaves with suspected virus disease of Cymbidium sinense collected from Guangzhou area.The genome sequence assembly,annotation,phylogeny and selection pressure analysis of CymMV isolates were performed with related molecular biology software.[Results]Two CymMV isolates(GZV013 and ZC29)were found in Guangdong Province for the first time in this study.The genome of both GZV013 and ZC29 were 6227 nt in length,encoding 5 functional proteins.The similarity analysis of the full sequence showed that the nucleotide sequence identity of GZV013 and Taiwan isolate M2 was 97.03% and that of ZC29 and Nanjing isolate NJ-1 was 97.11%.The complete genome sequence identity among CymMV isolates ranged from 86.85% to 98.31%,and the differentiation of diverse populations was closely related to host species and geographical isolation.Each region of CymMV genome was affected by negative selection and conformed to the neutral evolution model.The genes encoding RdRp,TGB1 and TGB2 had the highest mutation rates in the genome.[Conclusions]GZV013 was most closely related to Taiwan isolate M2,and ZC29 was most closely related to Nanjing isolate NJ-1,belonging to the same branch of a family.

Quantitative detection of Cymbidium mosaic virus by real time PCR

The technique of SYBR Green-based quantitative real-time reverse transcription polymerase chain reaction(real-time RT-PCR)was applied to quantitative detect a 764 bp nucleotide sequence containing total coat protein(cp)gene of Cymbidium mosaic virus(CyMV).The plasmid containing the target sequence was constructed to prepare the standard curve and detect the sensitivity.The standard curve was drawn based on the linear relationship between the logarithm(base 10)of the quantity of target sequence and cycle threshold[C(T)].While the concentration of plasmid DNA falling within the range of 2.6×10^(7)to 2.6×10^(2)copies per tube established a regression equation,y=-0.3583x+10.32,and related coefficient:r^(2)=0.995.The real-time RT-PCR assay for CyMV had a minimum detectable quantity of two copies per tube.The naturally infected samples of Phalaenopsis sp.and the artificially inoculated samples of Arachnis sp.with trace CyMV were quantitatively detected using this method.CyMVin the positive samples of Phalaenopsis sp.and Arachnis sp.was confirmed by DNA sequencing and cp gene homeology blast.The results showed that CyMV extracted from the leaves of orchid in Hangzhou,Zhejiang Province,China,could be derived from Kunming city(KM),Yunnan Province,China.This method characterized by high sensitivity,specificity,and precision is suitable for early diagnosis and quantitative detection of CyMV.