Submit Article |Resources | Link to us | Sitemap | Search | Language
Back to Home
Home >> Plant Viral Vectors >> Caulimoviruses
Back to Home

Caulimoviruses - The caulimoviruses group consists of 6-19 viruses, each of which has a relatively limited host range; the commonest. The best known member, cauliflower mosaic virus (CaMV), infects many members of Cruciferae (cabbage, cauliflower, turnips, brussel sprouts, rapeseed, Arabidopsis, etc.) and Datura stramonium.

Virulence of different CaMV strains varies from very mild (essentially latent) to lethal. The virus is readily transmitted mechanically and by aphids; there is no evidence for seed transmission.Caulimoviruses are similar in particle size, in vivo behavior and several are serologically related.

They are confined to a few closely related plants in nature. There appears to be little, if any, overlap between the host ranges of the individual viruses within the group, in spite of some of the close serological affinities.

CaMV is experimentally transmissible to a few plants outside the Cruciferae family. Caulimoviruses are widely distributed throughout the temperate regions of the world and are responsible for a number of economically important diseases of cultivated crops.

The impetus for development of CaMV as a vector stems from study of the virus itself, as a consequence of its pathogenic activities on susceptible plants. Symptoms of infection vary, depending on the virus isolate, time of inoculation and condition of the plant, from mild vein clearing to more severe leaf stunting.

The virus is transmitted by aphids in a nonpersistent or style borne manner. Successful transfer of CaMV by aphids requires the presence of a transmission factor in infected cells. This factor is not part of the virus particle but must be synthesized in response to infection since two non transmissible isolates of CaMV have been identified.

However, one of the main attractions is that both the virus and the isolated DNA are infectious and readily transmitted by abrasion of the leaves. In laboratory experiments virus particles (or the DNA isolated from them) have infected a plant when rubbed on the surface of a leaf in the presence of a small amount of abrasive compound.

Upon infection, the virus particles reproduce in the plant cells. Their DNA genomes serve as templates for the synthesis of new DNA and for the transcription of messenger RNA, which encodes for coat protein and other proteins that might be needed for the maturation and spread of the virus.

In an infected plant virus particles move through the phloem into the expanding leaves, where they disturb leaf development. These leaves have a mosaic or mottled appearance, with vein clearing and dark green islands in the midst of more normally colored regions.

Differences in the expansion rates of different leaf regions lead to a crinkled and stunted leaf appearance. How the virus produces changes in leaf morphology is itself an interesting problem but since the same symptoms are caused by many other viruses, it is unlikely that unravelling the specific characteristics of GaMV will help much in solving this problem.

In infected cells GaMV particles accumulate in cytoplasmic inclusion bodies. Early labeling studies showed that radioactivity accumulates rapidly in these inclusion bodies, suggesting that viral replication occurs there. How ever, recent evidence from several labs shows that replication and transcription of CaMV probably occur in the nucleus.

Transcription of GaMV in isolated nuclei is 8-amanitin sensitive, suggesting that RNA polymerase If transcribes the genome. Isolated nuclei from infected plants can incorporate a radioactive label into viral DNA.

A covalently closed form of GaMV without gaps can be isolated from infected cells; probably this molecule is packaged in nucleosomes. The host range and other biological properties of CaMV suggest that it is not likely to become an economically important vector in future.

However, as a DNA virus whose genome is known to be packaged in nucleosomes and transcribed by RNA polymerase II, it is presently more suited than, any other plant virus for exploitation as an experimental tool, in the same way as SV40 and polyoma have been used in mammalian systems. The knowledge gained from a GaMV model system should contribute to the development of other types of plant vectors.

Submit Article |Resources | Link to us | Sitemap | Search | Language
English|Français|Español|Deutsch|Italiano|Portugues|Japanese|Korean|Sim-Chinese| Language