Molecular analysis of the essential and nonessential genetic elements in the genome of peanut chlorotic streak caulimovirus.
The DNA genome of caulimoviruses contains a set of essential genes: I (movement gene), IV (major capsid protein gene), V (reverse transcriptase gene), and VI (gene coding for a post-transcriptional activator of the expression of other virus genes). In peanut chlorotic streak caulimovirus (PCISV), three ORFs, A, B, and C, are located between genes I and IV. They are dissimilar to other caulimovirus ORFs. ORF VII of PCISV is a homolog of ORF VII of soybean chlorotic mottle caulimovirus (SoCMV), but is not similar to the nonconserved ORF VII in other caulimoviruses. The sequence complementary to a portion of tRNA(Met), thought to be essential for the priming of minus-strand DNA synthesis in caulimoviruses, is located within the coding sequence of ORF A. To explore the functional significance of ORFs VII, A, B, and C, various mutations were engineered into an infectious DNA clone of PCISV. ORFs VII and B are shown to be dispensable, while ORFs A and C are essential. ORF C is a possible functional equivalent of gene III in other caulimoviruses. Sequences within ORF A that are required for efficient priming of minus-strand synthesis are likely to extend beyond the 12-bp tRNA-binding site. Complete deletion of ORF VII was correlated with severe symptoms, notably with the necrosis of apical meristems. Significance of these observations for the understanding of replication and pathogenesis of plant pararetroviruses and for the improvement of caulimovirus-based expression vectors is discussed.
Mushegian
A R
AR
Department of Plant Pathology, University of Kentucky, Lexington 40546-0091.
Wolff
J A
JA
Richins
R D
RD
Shepherd
R J
RJ
D010367:Arachis / Q000821:virology*; D001483:Base Sequence; D002213:Capsid / Q000235:genetics; D017796:Caulimovirus / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D003001:Cloning, Molecular; D017931:DNA Primers; D004279:DNA, Viral / Q000235:genetics / Q000302:isolation & purification; D005804:Genes, Lethal; D016679:Genome, Viral; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016254:Mutagenesis, Insertional; D016366:Open Reading Frames; D010935:Plant Diseases; D010957:Plasmids; D016133:Polymerase Chain Reaction; D012194:RNA-Directed DNA Polymerase / Q000235:genetics; D015183:Restriction Mapping; D017384:Sequence Deletion; D015534:Trans-Activators / Q000235:genetics; D014771:Virion / Q000235:genetics
D017931:DNA Primers; D004279:DNA, Viral; D015534:Trans-Activators; D012194:RNA-Directed DNA Polymerase