Plant viruses Flashcards
Baltimore classification of most plant viruses
56% are + sense RNA (IV)
Structure of plant viral ss+ RNA genome
ORF1: Replication (polymerase, helicase, methyl transferase)
ORF2: Movement (movement protein)
ORF3: Encapsidation
What do the 5’ and 3’ ends consists of
5’ end: capped end or Vpg (Viral protein genome linked)
3’ end: poly A tail or tRNA-like folded RNA structure
Virus translational tricks
- Segmentation of the genome
- Translation of subgenomic mRNAs
- Read-through translation (leaky termination)
- Frame Shifting (ribosomal shift)
- Polyprotein processing (requires a viral protease)
Structure of Cucumber mosaic virus
three RNA’s (RNA-1/2/3). ORF1a, ORF2a/b, ORF3a/b.
translation strategy: genome segmentation and subgenomic mRNA.
proteome of CMV: 5 multifunctional proteins
1a: methyltransferase and RNA helicase domain: 5’ capping and RNA synthesis
2a: RdRp : RNA synthesis
2b: long-distance movement: suppression of RNA silencing
3a: movement protein: cell-to-cell and long distance movement.
Coat protein: encapsidation
how does read-through translation work
A stop codon is “leaky” where it is not recognized because of suppression of the amber UAG stopcodon by tRNA of host
how do polyproteins work
all proteins are translated in one go. It contains a protease that will cut out the different parts. Potato virus Y has this.
how does frameshift work
ribosome slips back -1 nucleotide and reads a compelte new reading frame
how does subgenomic messenger work
when transcribing from a ss- RNA it will skip some of the ORFs so that only a secondary ORF is taken
Infection cycle (6 steps)
- virus entry
- Co-translational and disassembly
- Genome replication and translation
- Assembly of new virions and accumulation in cytoplasm
- Local movement of RNA or virions to neighboring cells and further systemic spread.
- Vectored transmission
Virus entry of plants
Pore-mediated penetration
major steps in ss+ RNA genome replication
- replication factors are translated, modified and complex is assembled on the membrane.
- template RNA is recognized, translation inhibited and recruitment to replication complex is activated.
- ss- RNA synthesis, ss+ RNA synthesis created progeny RNA
location of replication +RNA strands
cytoplasm
Movement of plant viurses through plasmodesmata
MP of plant viruses modifies size exclusion limit of PD for viral RNA and forms tubule in PD to transport virions
