EXPRESSION OF THE TOBACCO TNT1 RETROTRANSPOSON PROMOTER IN HETEROLOGOUS SPECIES

The expression of the tobacco (Nicotiana tabacum) retrotransposon Tnt1 has previously been shown to be strongly regulated and driven from th e 5' long terminal repeat (LTR). We report here that the Tnt1 LTR can promote activity of the beta-glucuronidase (GUS) reporter gene in two heterologous species of the Brassicaceae family, namely rapeseed (Bras sica napus) and Arabidopsis thaliana. The translational LTR-GUS fusion was active in transient expression studies performed with tobacco and rapeseed protoplasts, indicating that the LTR sequences are recognize d in heterologous species. Our results also showed that Tnt1 LTR-promo ted GUS expression in transgenic Arabidopsis is strongly regulated, an d that, in contrast to tobacco, hormonal activation plays a significan t role in the expression of the Tnt1 LTR in Arabidopsis. LTR sequences were shown to be more effective than the CaMV 35S enhancer region in transient expression studies performed with tobacco or rapeseed protop lasts, and substitution of the LTR sequences upstream from the major t ranscriptional start with the CaMV 35S enhancer region gave high level s of expression in transgenic tobacco and Arabidopsis leaves, suggesti ng that a Tnt1 element with similar substitutions in its 5' LTR might be suited for gene-tagging experiments in heterologous species.