Immobilized copies with a nearly intact structure of the transposon Tam3 in Antirrhinum majus: implications for the cis-element related to the transposition

Abstract

In this study we have focused on two copies of the transposon Tam3 isolated from an Antirrhinum majus plant which has flower variegation due to the excision of Tam3 from the nivea locus. These two copies possess a high homology, over 95%, to an active Tam3 element found in the nivearecurrence:Tam3 allele. Although somatic excision of the Tam3 copy from the nivea locus can be detected at 15°C by Southern blotting, neither of the two copies showed any sign of the excision. Both of the immobilized copies were also found in five varieties from different A. majus sources, all of which contain common fragments. The results suggest that the two copies have been fixed in the genomes of many A. majus varieties. Structural differences between these immobilized copies and the known active copy were mainly observed in the subterminal regions, including the terminal inverted repeats. The immobility of the two Tam3 copies might be due to mutations within the end regions of essential cis-elements in Tam3 transposition, as reported for Ac and En/Spm.