Abstract
Transposable elements Activator (Ac) was first discovered in maize by Barbara McClintock (1947). She found that Ac transposed autonomously between genes and trans-activated another non-autonomous element Dissociation (Ds). Ac-Ds was cloned and sequenced by Starlinger (1984). Further studies showed that: (1) Ac is 4565 bp long and codes for a single product, the transposase. (2) generally, Ds elements are internal deletion derivatives of Ac (3) A fully active minimal Ds element may contain only 300 bp of each end of Ac element. Gene tagging technique using the transposable element as an insertional mutagen for the isolation of important plant genes has been proven to be a useful tool.A curious aspect of Ac transposon is that the accumulation of high levels of the Ac transposase may inhibit subsequent transposon excision, which termed as “inverse dosage effect”. This effect was saw in maize, tobacco and tomato but not Arabidopsis. It was hypothesized that high level of the transposase might aggregate on the nuclear membrane. As a result of this, the transposase cannot transport into the nuclear to perform the transposition events. In this study, a classical nuclear localization signal (NLS) was fused with the transposase gene under the control of promoter of the inducible gene for pathogenesis-related protein 1a (PR-1a). The purpose of the NLS fusion is to help the entrance of the transposase into the nucleus for the subsequent transposition events. Excision of non-autonomous transposable element(Ds) from luciferase(LUC) and β-glucu- ronidase(GUS) reporter gene constructs was employed to analyze the induction of the Ac transposase containing NLS. Spontaneous excision has been primarily identified by polymerase chain reaction in 56 out of 72 independent transgenic tobacco plants. This result suggested that transposase could be transported into the nucleus immediately by induction of the internal salicylic acid stimuli. An alternative inducible transposon strategy for functional genomic is suggested.