STRUCTURAL INSTABILITY OF A TRANSGENE LOCUS IN TOBACCO IS ASSOCIATED WITH ANEUPLOIDY

This paper describes molecular and cytogenetic evidence for the instab ility of a transgene locus that is present on the triplicated chromoso me in an aneuploid tobacco line. This instability was manifested in se veral ways in trisomics including a major chromosome rearrangement tha t was detectable cytogenetically, smaller scale DNA rearrangements tha t occurred both germinally and somatically, and methylation/epigenetic silencing. In a deletion derivative of the locus, DNA breakpoints wer e found in AT-rich regions. One of these regions binds to nuclear scaf folds in vitro, suggesting a possible role for aberrant topoisomerase II cleavage in destabilization of the locus. The implications of incre ased chromosome instability in aneuploids for plant karyotype evolutio n and human carcinogenesis are discussed.