ANALYSIS OF THE FREQUENCY OF INHERITANCE OF TRANSPOSED DS ELEMENTS INARABIDOPSIS AFTER ACTIVATION BY A CAMV 35S PROMOTER FUSION TO THE AC TRANSPOSASE GENE

The Ac/Ds transposon system of maize shows low activity in Arabidopsis . However, fusion of the CaMV 35S promoter to the transposase gene (35 S::TPase) increases the abundance of the single Ac mRNA encoded by Ac and increases the frequency of Ds excision. In the experiments reporte d here it is examined whether this high excision frequency is associat ed with efficient re-insertion of the transposon. This was measured by using a Ds that carried a hygromycin resistance gene (HPT) and was in serted within a streptomycin resistance gene (SPT). Excision of Ds the refore gives rise to streptomycin resistance, while hygromycin resista nce is associated with the presence of a transposed Ds or with retenti on of the element at its original location. Self-fertilisation of most individuals heterozygous for Ds and 35S::TPase produced many streptom ycin-resistant (strep(r)) progeny, but in many of these families a sma ll proportion of strep(r) seedlings were also resistant to hygromycin (hyg(r)). Nevertheless, 70% of families tested did give rise to at lea st one strep(r), hyg(r) seedling, and over 90% of these individuals ca rried a transposed Ds. In contrast, the Ac promoter fusion to the tran sposase gene (Ac::TPase) produced fewer strep(r)hyg(r) progeny, and on ly 53% of these carried a transposed Ds. However, a higher proportion of the strep(r) seedlings were also hyg(r) than after activation by 35 S::TPase:. We also examined the genotype of strep(r), hyg(r) seedlings and demonstrated that after activation by 35S::TPase: many of these w ere homozygous for the transposed Ds, while this did not occur after a ctivation by Ac::TPase. From these and other data we conclude that exc isions driven by 35S::TPase usually occur prior to floral development, and that although a low proportion of strep(r) progeny plants inherit a transposed Ds, those that do can be efficiently selected with an an tibiotic resistance gene contained within the element. Our data have i mportant implications for transposon tagging strategies in transgenic plants and these are discussed.