Quantitative variation of Revolver transposon-like genes in synthetic wheat and their structural relationship with the LARD element

Abstract

Revolver is a multi-gene family dispersed through Triticeae genomes like transposons. Revolver is similar to class II transposable elements and shows considerable quantitative variation in wheat and its relatives. The highest copy number of Revolver is found in Secale cereale (RR) and the lowest in hexaploid wheat Triticum aestivum (AABBDD). In this study, Revolver copy numbers were determined in synthetic hexaploid wheat lines from crosses between Aegilops tauschii (DD) and T. turgidum tetraploid wheat species (T. dicoccoides, T. dicoccum, T. carthlicum and T. durum, AABB). Eight out of 18 lines showed significantly lower copies than the sum of their parents and seven lines were equal to the sum, suggesting that polyploidy caused loss of Revolver. Members of the Revolver family also showed structural variation in the 5′ region, especially in length. Revolver did not share any similarity with autonomous transposable elements. However, the long terminal repeats (LTRs) of the non-autonomous large retrotransposon derivative (LARD) in barley, showed 60% homology to both 5′ and 3′ ends of some variants of Revolver. LARD LTRs lack the Revolver region from the first exon to the middle of the first intron resulting in non-coding sequences. Evolutionary relationships between Revolver and LARD are discussed.