The antisense promoter of AtRE1, a retrotransposon in Arabidopsis thaliana, is activated in pollens and calluses

The AtRE1retrotransposon of Arabidopsis thaliana is transcribed in both directions and the amount of sense RNA is much less than that of antisense RNA. The characterization of one cDNA derived from an antisense transcript showed that the antisense RNA is complementary to one half of the open reading frame and 5′-LTR. In order to study the function of this antisense RNA, we characterized the promoter activity for the antisense transcript. Primer extension analysis indicated that the antisense RNA is produced from an internal promoter and indicated the possibility of a plural initiation site of transcription. Promoter analysis using β-glucuronidase (GUS) gene as a reporter gene showed that the promoter sequence is localized within an approximately 200 bp region upstream from initiation sites of antisense RNA. However, no typical promoter sequences were detected in this region. Histochemical staining of GUS activity indicated that antisense RNAs are transcribed in pollens and actively proliferative regions of calluses. This result suggests that the expression of AtRE1 is repressed by antisense RNA but this mechanism functions in only limited organs.