NONAUTONOMOUS INVERTED REPEAT ALIEN TRANSPOSABLE ELEMENTS ARE ASSOCIATED WITH GENES OF BOTH MONOCOTYLEDONOUS AND DICOTYLEDONOUS PLANTS

Alien are highly repeated plant transposable elements characterized by their small size (approx. 400 bp), high A+T content, target site spec ificity, potential to form stable secondary structures and possession of a conserved 28-bp terminal inverted repeat (TIR). Besides the TIR, they contain subterminal inverted repeat motifs (SIRM), as well as the 5'-CATGCAT domain which has been reported to be a cis-acting regulato ry element of gene expression in some plant species. Although they wer e first identified in the intron of the bell pepper (Capsicum annuum) Sn-2 gene and in the promoter region of the potato starch phosphorylas e-encoding gene, Alien arranged in tandem are present in the promoter of patatin class-II genes. PCR on the bell pepper genomic DNA using th e Alien TIR consensus sequence as primer yielded DNA fragments of near ly 400 bp. These fragments have characteristics of transposable elemen ts and contain numerous motifs reminiscent of Alien elements. Importan tly, PCR on genomic DNA extracts from various monocotyledonous and dic otyledonous plants using the TIR consensus sequence as primer and subs equent hybridization with different Alien probes revealed that these e lements are ubiquitously present and highly repeated in the genomes of higher plants.