New chimeric promoter useful for expression of selectable marker genes in rice transformation

We developed a new chimeric promoter to express a selectable marker gene specifically at the selection stage during transformation of rice (Oryza sativa L.). The promoter consists of a 135-bp upstream sequence of the rice RezA gene and 4 or 8 copies of an enhancer fragment of the CaMV35S promoter. The β-glucuronidase (GUS) reporter gene under the control of this promoter was strongly expressed in transgenic rice calli but not in endosperm, the edible tissue in rice grains. When the hygromycin B phosphotransferase gene was fused with this chimeric promoter and introduced into rice, we were able to select transgenic plants. We demonstrated that the chimeric promoter did not influence expression of the endogenous RezA gene in the transgenic calli. These results indicate that this chimeric promoter could be useful for the selection of transgenic rice free of marker gene products in the edible tissue.