Integration of viral DNA into the host nuclear genome, although not unusual in bacterial and animal systems, has surprisingly not been reported for plants. We have discovered geminivirus-related DNA (GRD) sequences, in the form of distinct sets of multiple direct repeats comprising three related repeat classes, situated in a unique locus in the Nicotiana tabacum (tobacco) nuclear genome. The organization of these sequences is similar or identical in eight different tobacco cultivars we have examined. DNA sequence analysis reveals that each repeat has sequences most resembling those of the New World geminiviral DNA replication origin plus the adjacent AL1 gene, encoding the viral replication protein. We believe these GRD sequences originated quite recently in Nicotiana evolution through integration of geminiviral DNA by some combination of the processes of illegitimate recombination, amplification, deletions, and rearrangements. These events must have occurred in plant tissue that was subsequently able to contribute to meristematic tissue yielding gametes. GRD may have been retained in tobacco by selection or by random fixation in a small evolving population. Although we cannot detect transcription of these sequences, this does not exclude the possibility that they may originally have been expressed.

* Present address: Unidad de Genética, Departamento de Biología Celular y Genética, Facultad de Ciencias, Campus Universitario de Teatinos 29017, Málaga, Spain.
Present address: School of Biological Sciences, Queen Mary and Westfield College, Mile End Road, London E1 4NS, United Kingdom.

** NOTICE: In accordance with Title 17 U.S.C. Section 107, this material is distributed for research and educational purposes only. **