Behavior of a modified Dissociation element in barley: a tool for genetic studies and for breeding transgenic barley

Maize-derived sequences from the transposable elements Activator (Ac) and Dissociation (Ds) have enabled studies of gene function via transposon tagging. The characteristics of modified, transgene-containing Ds elements constructed for some of these studies have demonstrated their ability to resolve complex loci, separate transgenes from marker genes and vector sequences, and to support high and heritable levels of transgene expression. To most efficiently design breeding schemes for developing transgenic populations via Ds-mediated transposition, detailed knowledge of the dynamics and characteristics of transposition in barley is necessary. Examination of a barley transposon tagging population (n = 4,954) derived from crosses of lines containing Ds-bar insertions to lines expressing Ac transposase showed that the frequencies of transposition from eight original Ds-bar loci ranged from 5 to 41 % among F₂ individuals. Sequence analysis of Ds-bar terminal sequences and of flanking genomic sequences for 107 F₂ and F₃ individuals indicated precise integrations. Analysis of 173 flanking sequences derived from these populations and from previously produced populations, primarily using sequence-based methods, enabled the mapping of 159 to a specific chromosome and 136 to specific map locations. Of the 156 DsT loci that could be located to specific contigs, most were located in gene-rich areas and approximately 40 % were either in or near (within 1 kb) expressed sequences or predicted proteins. These data will enable the design of optimal breeding schemes for developing and using Ds-based systems for transposon tagging and for transgene delivery that are specific to barley.