FREQUENCY AND DISTANCE OF TRANSPOSITION OF A MODIFIED DISSOCIATION ELEMENT IN TRANSGENIC TOBACCO

Effective transposon tagging with the Ac/Ds system in heterologous pla nt species relies on the accomplishment of a potentially high transpos on-induced mutation frequency. The primary parameters that determine t he mutation frequency include the transposition frequency and the tran sposition distance. In addition, the development of a generally applic able transposon tagging strategy requires predictable transposition be haviour. We systematically analysed Ds transposition frequencies and D s transposition distances in tobacco. An artificial Ds element was eng ineered with reporter genes that allowed transposon excision and integ ration to be monitored visually. To analyse the variability of Ds tran sposition between different tobacco lines, eight single copy T-DNA tra nsformants were selected. For trans-activation of the Ds elements, dif ferent Ac lines were used carrying an unmodified Ac+ element, an immob ilized sAc element and a stable Ac element under the control of a hete rologous chalcone synthase (chsA) promoter. With all Ac elements, each Ds line showed characteristic and heritable variegation patterns at t he seedling level. Similar Ds line-specificity was observed for the fr equency by which Ds transpositions were-germinally transmitted, well a s for the distances of the Ds transpositions. The sAc element induced transposition of Ds late in plant development, resulting in low germin al transposition Frequencies (0.37%) and high incidences of independen t transposition (83%). The majority-of these Ds elements (58%) transpo sed to genetically closed linked sites (less than or equal to 10 cM).