THE BARE-1 RETROTRANSPOSON IS TRANSCRIBED IN BARLEY FROM AN LTR PROMOTER ACTIVE IN TRANSIENT ASSAYS

The BARE-1 retrotransposon occurs in more than 10(4) copies in the bar ley genome. The element is bounded by long terminal repeats (LTRs, 182 9 bp) containing motifs typical of retrotransposon promoters. These, t he presence of predicted priming sites for reverse transcription, and the high conservation for all key functional domains of the coding reg ion suggest that copies within the genome could be active retrotranspo sons. In view of this, we looked for transcription of BARE-1 within ba rley tissues and examined the promoter function of the BARE-1 LTR. We demonstrate here that BARE-1-like elements are transcribed in barley t issues, and that the transcripts begin within the BARE-1 LTR downstrea m of TATA boxes. The LTR can drive expression of reporter genes in tra nsiently transformed barley protoplasts. This is dependent on the pres ence of a TATA box functional in planta as well. Furthermore, we ident ify regions within the LTR responsible for expression within protoplas ts by deletion analyses of LTR-luc constructs. Similarities between pr omoter regulatory motifs and regions of the LTR were identified by com parisons to sequence libraries. The activity of the LTR as a promoter, combined with the abundance of BARE-1 in the genome, suggests that BA RE-1 may retain the potential for propagation in the barley genome.