Integrated pararetroviral sequences define a unique class of dispersed repetitive DNA in plants.
Although integration of viral DNA into host chromosomes occurs regularly in bacteria and animals, there are few reported cases in plants, and these involve insertion at only one or a few sites. Here, we report that pararetrovirus-like sequences have integrated repeatedly into tobacco chromosomes, attaining a copy number of approximately 10(3). Insertion apparently occurred by illegitimate recombination. From the sequences of 22 independent insertions recovered from a healthy plant, an 8-kilobase genome encoding a previously uncharacterized pararetrovirus that does not contain an integrase function could be assembled. Preferred boundaries of the viral inserts may correspond to recombinogenic gaps in open circular viral DNA. An unusual feature of the integrated viral sequences is a variable tandem repeat cluster, which might reflect defective genomes that preferentially recombine into plant DNA. The recurrent invasion of pararetroviral DNA into tobacco chromosomes demonstrates that viral sequences can contribute significantly to plant genome evolution.
Jakowitsch
J
J
Institute of Molecular Biology, Austrian Academy of Sciences, Billrothstrasse 11 A-5020 Salzburg, Austria.
Mette
M F
MF
van Der Winden
J
J
Matzke
M A
MA
Matzke
A J
AJ
D001483:Base Sequence; D003001:Cloning, Molecular; D018744:DNA, Plant / Q000235:genetics*; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D010947:Plants, Toxic; D012091:Repetitive Sequences, Nucleic Acid; D012190:Retroviridae / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D014026:Nicotiana / Q000235:genetics*; D016662:Virus Integration
D018744:DNA, Plant