A 200-bp constructed inducible PR-1a promoter fusion to the Ac transposase gene drives higher transposition of a Ds element than the native PR-1a promoter fusion drives

Abstract

An inducible transposon tagging technique in plants with a large genome was accessed. The open reading frame coding for the transposase gene of the maize transposon Activator ( Ac) was expressed in transgenic tobacco plants under the control of the promoter of the inducible gene for pathogenesis-related protein 1a (PR-1a). Based on the native PR-1a promoter, several inducible promoters were constructed in order to induce variability of the Ac transposase expression level. Excision of a non-autonomous transposable element ( Ds) from the chimeric β-glucuronidase gene construct was employed to analyze the induction of the Ac transposase by salicylic acid (SA). Applying the β-glucuronidase histochemical assay, Ds excision efficiency was determined in the regeneration calli after treatment of a tobacco leaf disc with SA. A 111-bp regulatory element, located between nucleotides −699 to −588 of the PR-1a promoter, was fused to the 89-bp CaMV35S core promoter to serve as the inducible promoter, PRΔD. When the PRΔD promoter was fused with the Ac transposase gene and induced by SA, it triggered a 26-fold higher Ds excision efficiency than the native PR-1a promoter fusion. Furthermore, Ds excision events occurred mainly in the regeneration calli at day 8 after induction with SA. Because Ds excision events could be induced in such a short period, an alternative gene tagging strategy is suggested.