SummaryWe investigated whether termination of transcripts with a self-cleaving ribozyme can enhance nuclear retention and serve as a tool to decrease speci®c plant gene expression. Nuclear retention was ®rst monitored in tobacco using the b-glucuronidase gene terminated with either the 35S CaMV 3¢ untranslated sequence (UTR) or a cis-acting ribozyme. Northern blot analysis of nuclear RNA and total RNA, and in situ hybridizations showed that the ribozyme-terminated transcripts were preferentially retained in the nucleus of transgenic tobacco. Ribozyme-terminated transcripts were subsequently tested as a gene down-regulation strategy in soybean. The embryo-speci®c D-12 fatty acid desaturase FAD2-1 gene was targeted because its down-regulation elevates oleic acid content of seed storage lipids. Both ribozyme-terminated antisense and standard antisense constructs were capable of gene downregulation, producing over 57% oleic acid compared with less than 18% in wild-type seed. Ribozyme termination cassettes were also constructed to evaluate sense transcripts for single gene downregulation and the simultaneous down-regulation of two embryo-speci®c genes in soybean using a single promoter. Eight independent soybean transformants were screened that harboured standard plus sense or ribozyme terminated FAD2-1 cassette. Two of the eight ribozyme terminated transformants displayed oleic acids levels in the seed storage lipids of over 75%, while none of the standard plus sense FAD2-1 lines showed elevated oleic acid phenotypes. The dual constructs targeted FAD2-1 and the FatB gene encoding a palmitoyl-thioesterase. Five transgenic soybean lines harbouring the dual constructs had oleic acid levels, greater than 85%, and saturated fatty acids levels, less than 6%. Thus, ribozyme termination of transcripts can be utilized to speci®cally down-regulate endogenous gene expression in soybean.