Only members of the crucifer family are susceptible to CaMV. Plants can be stunted. The primary source is infected brassica crops and cruciferous weeds. The virus gets transmitted to the crop by many species of aphids, like the cabbage aphid, the false cabbage aphid and the green peach aphid.
2. Plant viruses
• Plant viruses are those viruses that affects the plants.
• They are pathogenic to higher plants.
• Most plant viruses are rod shaped and do not have an envelope.
• They usually have RNA genome that is single stranded and small.
• To transmit from one plant to another, they use vectors.
• Example for vector- insects.
4. CAULIFLOWER MOSAIC VIRUS
• Genus: Caulimovirus
• Family: Cauliflower mosaic virus
• First mosaic virus to have dsDNA.
• Infects mostly plants of the family Brassicaceae.
• Some strains affects plants of family Solanaceae.
• Identified by leaves discoloration and mottling.
• Transmission: Myzus spp.
• Inhibits growth and structure of host.
5. STRUCTURE
• Icosahedral.
• 52nm in diameter.
• 420 capsid proteins.
• Circular, dsDNA with 8.0 kb.
• dsDNA gets interrupted by nicks that results from action of RNAse H.
• Nicks arise from tRNA and two RNA primers.
• ssDNA in viral DNA gets repaired and forms a supercoiled structure.
• This DNA transcribes to form into full length
• 1. 35S RNA
• 2. 19S RNA
6. GENOME
• 35S RNA promoter- responsible for transcription.
• CaMV 35S promoter is widely used general purpose promoter.
• Chua and et al., in1980’s.
• Has highly structured 600 nucleotide sequence.
• With 6 short ORFs, followed by 7 and 8 longer ORFs.
• These 7,8 ORFs encodes for all viral proteins.
9. Viral DNA enters the nucleus where the discontinuation gets
filled in.
Viral DNA associates with host’s histones and forms
minichromosome.
Host DNA dependent RNA polymerase transcribes the 35S
promoter.
Viral particles enter the plant cell.
Three fragments of viral DNA gets assembled into genome
with 3 gaps.
10. Viral RNAs pass into cytoplasm of host and gets transcribed.
3’ end of tRNA anneals to D1 near 5’ end.
tRNA prime synthesis by viral RT and gets encoded by ORF
VI.
RNAse H removes RNA from DNA-RNA bond, leaving behind
DNA.
New DNA binds to promoter at 3’end of RNA template and
synthesis of α-strand of DNA continues.
RNAse H continues it degradation work.
11. Synthesis of alpha strand completes.
RNAse H activity exposes purine rich region D3 that primers
synthesis of γ- DNA strand.
RNAse activity exposes purine rich region at D2 that primes
synthesis of β-DNA strand.
Newly synthesized α-strand
Reaches 5’end of new α-strand and recreates
discontinuous D1.
Reaches 5’end of new β-strand and recreates
discontinuous D2 by displacing primers.
12. New β-strand
Reaches 5’end of new α-strand displacing primer that results in
recreating D3.
At this stage, new viral genomes can be packed into capsids.
Releases from the cell or is transported by new proteins into
nearby uninfected cells in the plant host cell.
13.
14. TRANSMISSION
• Aphids are most common source of infection.
• Needle like mouthpiece.
• Ingests plant nutrients and sap.
• It leaves saliva behind in the part of the plant.
• Myzus periscae- 1.5-2mm (mature).
• Appears during warmer seasons.
• Generation rate within 10-12 days.
15. IMMUNITY AND PREVENTION
• Plants depend on natural defense mechanism.
• Rely on own immune system.
• Prevention-
• Transmission by aphids- any pesticide (ex: nicotine) can be used.
• Silver-grey netting can be done.
• Disinfecting tools and equipment's reduces the infection if harboured.
• Keep weeds away.
• Remove infected plants to stop spreading of infection.
• 20:2:1 (water:vinegar:brown sugar) spray can be used to trap adults.
• Chemical control- Abamectin, methylamine, imidaclopid can be used.
16. REFRENCES
1. Cauliflower mosaic virus - microbewiki (kenyon.edu)
2. Myzus persicae – Wikipedia
3. Cauliflower mosaic virus – Wikipedia
4. Handbook of Proteolytic Enzymes | ScienceDirect
5. Caulimoviruses: Molecular Biology – ScienceDirect
6. Encyclopedia of Virology | ScienceDirect
7. Cauliflower mosaic virus: still in the news (wiley.com)
8. cauliflower mosaic virus - Bing images
