Transposable elements in plants have been extremely useful for a variety of applications, including gene tagging and transgene delivery. For many years the use of maize transposable elements as molecular tools was restricted to their natural host or to those dicot species, which could be routinely transformed with Agrobacterium tumefaciens. The development of efficient transformation systems for cereals has made possible the introduction of transposons into agronomically important monocots. We established in barley an efficient maize transposon system that utilizes an immobilized, trans-active Activator (Ac) transposase gene linked to a negative selectable marker codA and an unlinked cis-responsive Dissosiation (Ds) element carrying the selectable marker gene bar as an insert. Ac activity assays demonstrated frequent excisions of Ds when the non-autonomous element was introduced transiently into Ac transposase expressing immature embryos by bombardment. Crosses between stably transformed Ac-positive plants expressing transposase either under transcriptional control of the putative Ac promoter or the promoter and first intron from the maize ubiquitin gene and Ds-containing plants resulted in low somatic and germinal transposition frequencies in F1 plants. F2 progeny derived from selfed F1 plants exhibited high transposition frequencies with up to 70% of the plants exhibiting new bands in DNA hybridization analysis using a Ds-specific probe. Further analysis of F3 plants showed that about 75% of the transposed Ds elements reinserted into linked locations, 25% into unlinked locations. Transposed Ds elements of plants, that are negative for Ac can be reactivated to move to a new site by crossing with plants expressing transposase, making this transposon system useful for targeted gene tagging and gene delivery.

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** International Centre for Brewing and Distilling, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, Scotland, United Kingdom