Zhou Yijun Puzuqin
It belongs to double-stranded deoxyribonucleic acid, non-enveloped, spherical genome virus. Shepherd et al. (1968) first proved that the genome of cauliflower mosaic virus (CaMV) is dsDNA. According to B.D. Harrison (1971), the genomes of cauliflower mosaic virus, dahlia mosaic virus (DaMV) and carnation ete hedge virus (CERV) are all dsDNA, with the same particle morphology and virus vector, and have serological correlation with each other. 1976 was officially named cauliflower mosaic virus in the second report of the International Committee on Virus Classification. This group name comes from the abbreviation of cauliflower mosaic virus. The typical member is cauliflower mosaic virus. The coding program of cauliflower mosaic virus group is D/2∶45/ 16∶S/S∶S/Ve/Ap.
Viral characteristics
The particles are spherical with a diameter of 45 ~ 50 nm. The thickness of protein shell is 6.5 nm, and DNA is attached to the inner wall of protein shell. There are few or no protein and DNA in electron density centers. The sedimentation coefficient (S20 w) is 208, and the buoyancy density in cesium chloride is 1.37 g/cm3. The molecular weight of the nucleic acid genome is 5.0× 106, 7.8 ~ 8.0 kilobase pairs, accounting for 17% of the particle weight. The melting temperature (Tm) in 0. 15mol/L sodium chloride or 0.025mol/L sodium citrate is 87.2℃, and the buoyancy density in cesium chloride is 6544. Protein has a molecular weight of 35 ~ 42× 103 and is a phosphorylated glycoprotein.
Its in vitro properties are relatively stable, the passivation temperature is 80 ~ 90℃, the survival time at room temperature is 7 days, and the dilution limit is 10-3.
Genome and replication
The DNA molecules of most members of this group have two forms: circular and linear. Ring is a natural state existing in particles, and linear may be caused by physical damage or enzymatic cracking during extraction. Only circular DNA is contagious. DNA molecules are relatively loose, with 3 ~ 4 gaps, one gap is on the α chain and the others are on the β chain. Restriction endonuclease analysis showed that these gaps were located in fixed positions. The 5' end of each gap in cauliflower mosaic virus DNA is in a fixed nucleotide position, and a part of the 3' end overlaps with the variable overlapping interval of the 5' end. The DNA of cauliflower mosaic virus has 80 16 ~ 803 1 base pair and 6 ~ 8 reading frames (putative genes). DNA can replicate in the nucleus, accumulate in inclusion bodies, and assemble into complete virus particles in inclusion bodies. The small DNA strand of cauliflower mosaic virus is transcribed in the nucleus. 19S and 35S have two major polyadenylation transcripts (namely mRNA). The mRNA of 19S was partially transcribed from ⅵ gene and translated into inclusion body protein with molecular weight of 62000. 35S mRNA may be the template of viral DNA replication controlled by reverse transcriptase.
Distribution and harm
The distribution of viruses is often related to the distribution of their hosts. Cauliflower mosaic virus, Dahlia mosaic virus and Dianthus etching ringspot virus are widely distributed, and cauliflower mosaic virus is also harmful in Xinjiang, China. Scrophularia mosaic virus (FMV) and Mirabilis jalapa mosaic virus (MMV) are mainly distributed in North America. Thistle mosaic virus (ThMV) and Petunia vein clearing virus (PVCV) are mainly distributed in Europe. Soybean chlorotic mottle virus is distributed in Japan. The virus can infect the host systematically, showing symptoms such as whole body mosaic, mottling, dwarfing, necrosis, and even the whole plant dies. Viruses can spread from sap to viruses. Under natural conditions, aphids spread in a semi-continuous way. When aphids spread cauliflower mosaic virus, they need the help of protein (molecular weight 18000) cofactor encoded by the virus. The host range of the virus is narrow, generally limited to 1 ~ 2 family, and some members even only infect 1 family 1 ~ 3 genus.
Relationship between virus and host cell
Virus particles exist in inclusion bodies, sometimes in cytoplasm, and occasionally in enlarged plasmodesmata. Inclusion bodies are round or oval, with a diameter of 5 ~ 20 microns, no outer membrane and surrounded by ribosomes. In the early stage of infection, the smaller inclusions are scattered throughout the cell, often close to the nucleus, and gradually fuse to form larger inclusions of 1 ~ 2 in the later stage of infection. Inclusion bodies are places where virus particles are stored and assembled. Inclusion exists in mesophyll cells, parenchyma cells and epidermal cells, and sometimes in sieve tubes and tracheids of phloem. This unique inclusion is one of the main characteristics of cauliflower mosaic virus group.
The relationship between virus members
There is serological correlation between cauliflower mosaic virus and horseradish latent virus (HrLV), carnation ring erosion virus, Dahlia mosaic virus and strawberry vein virus (SVBV), but there is no correlation between cauliflower mosaic virus and blueberry red ring spot virus (BRRV), but there is correlation between carnation ring erosion virus and Dahlia. Caution should be taken when interpreting the results of serum reaction among members of cauliflower mosaic virus group, because the hydrolysis of coat protein will affect the detection results. Hybridization with DNA molecules can accurately reflect the relationship between virus members. For example, cauliflower mosaic virus has high homology with wasabi latent virus, but has no homology with Dahlia leaf, Scrophularia leaf and Dianthus caryophyllus ring erosion virus.