ANALYSIS OF THE FUNCTIONAL-ACTIVITY OF THE 1.4-KB 5'-REGION OF THE RICE ACTIN 1 GENE IN STABLE TRANSGENIC PLANTS OF MAIZE (ZEA-MAYS L)

The activity of the 5'-region of the rice actin 1 gene (Act1), coverin g a region 1,4 kb upstream of the Act1 translation initiation codon, w as extensively analyzed in transgenic maize plants. The 5'-region of A ct1 fused to the beta-glucuronidase (GUS) gene (gas) coding region was co-transformed to maize with the phosphinothricin acetyltransferase g ene (bar) and the potato proteinase inhibitor II gene (pin2). One and 29 independent transformation events with expression of both bar and g us were recovered from bombardment of immature embryo-derived embryoge nic callus of Hi-II derivative and bombardment of shoot tips of Honey N Pearl and Illinois Golden Extra Sweet, respectively. Expression of g us in tissues of transgenic plants was examined by histochemical assay , immunoblot analysis, and fluorometric GUS specific activity assay. A constitutive expression of the introduced gus was observed throughout the developmental stages of the vegetative and reproductive organs in transgenic maize plants. Quantitative analysis of GUS in transgenic p lants showed that GUS, as percent of total soluble protein, was as muc h as 3.1% in leaves and 2.8% in roots, The functional activity of the 5'-region of Act1 was inherited to transgenic progeny. The results ind icate that the 1.4-kb 5'-region of Act1 is an efficient and strong pro moter for gene expression in stable transgenic maize plants.