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The expression of b-glucuronidase (GUS) under the control of a 940 bp rice b-glucanase 9 (Gns9) gene promoter was developmentally regulated and could only be detected in rice calli but not in leaves, roots or seeds. To prevent the accumulation of a selectable marker gene product in transgenic rice seeds, the Gns9 promoter was then fused to the gene encoding hygromycin B phosphotransferase (hpt) and the resulting plasmid, pAPI76, was used to transform rice. A new method for selecting and regenerating transgenic rice based on pAPI76 was developed. Over 96% of the transgenic rice plants selected using pAPI76 were found to contain the uidA gene. Southern blot analysis confirmed that both genes were integrated into the rice genome and segregated in the R1 progenies in a classic Mendelian fashion. Enzymatic assays of seed extracts from transgenic rice detected no hygromycin B phosphotransferase (HPT) activity. We conclude that tightly regulated promoters like the Gns9 promoter can be used to target the expression of transgenes like hpt, to specific tissues and to specific developmental stages of rice. In the case of the hpt gene, transgenic rice seeds free of HPT were generated. © 2001 Elsevier Science Ireland Ltd. All rights reserved.
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