TRANSPOSITION OF MAIZE TRANSPOSABLE ELEMENT ACTIVATOR IN RICE

To explore the possibility of using the maize (Zea mays L.) transposable element Activator (Ac) as a mutagen and gene tag in rice cells, we have introduced plasmid pKU3, a derivative of an Ac constructed by Baker, into protoplasts of Oryza sativa L. subsp. japonica by the polyethylene glycol method. Several lines of evidence are presented for the transposition of the Ac element in transformed calli. (1) In the pKU3 plasmid, the Ac element was inserted in the untranslated leader sequence of the neomycin phosphotransferase II (NPT II) gene. This construction allowed us to follow the excision of Ac by reconstruction of NPT II gene activity. For this, we have obtained 12 Km(r) calli selected from about 10(6) pKU3 DNA-treated protoplasts. The NPT II enzyme activity could be detected in most of the selected calli. (2) Southern blot analysis confirmed the presence of the Ac element in genomic DNA from transformed Km(r) calli. (3) A probe comprising leader sequence P1' of the NPT II gene hybridized to the EcoRI-HindIII digested genomic DNA from transformed Km(r) calli to produce a 3.0-kb fragment which indicates that the interrupted NPT II gene had been reconstructed. These facts, taken together, show that the maize Ac element was introduced into some transformed rice cells. In some transformed cells, this element had been excised from its original location in the NPT II gene had moved elsewhere in the transformed rice genome.