Transgenic Rice Plants Containing a Chlorsulfuron Resistance Gene, a Hygromycin Resistance Gene and the Maizeactivator Transposable Element.

A mutant Arabidopsis acetolactate synthase (ALS) gene csr-1-1, conferring chlorsulfuron resistance, was tested in transgenic rice to develop an alternative selectable marker for rice transformation. Up to a 200-fold increase in chlorsulfuron resistance was detected in transgenic rice calli expressing the mutant ALS gene under control of the CaMV 35S promoter. Efficient selection of resistant protoplast colonies was achieved by using 10 to 50 nM of chlorsulfuron after transformation with the 35S/ALS gene. Fertile transgenic rice plants were successfully recovered from 35S/ALS-containing transformants. These results demonstrated that the 35S/ALS gene could be used as a selectable marker gene in rice transformation. Progeny of protoplast-derived nontransformed rice plants and transgenic rice plants containing the hygromycin phosphotransferase (hph) gene and the maize activator (Ac) transposable element were investigated in a field experiment. Comparison with seed-derived plants for six major agronomic traits indicated that nontransformed protoplast-derived plants were essentially indistinguishable from the parent cultivar, suggesting that somaclonal variation in these plants was not significant. Hph-containing transgenic plants were relatively normal. The generally low fertility in these plants may have been caused by the hygromycin selection procedure. In the majority of transgenic rice plants, the hph gene was inherited as a single dominant locus. Transferred DNA was maintained stably in the rice genome through the third generation of selfing. Ac-containing transgenic plants produced a significantly higher frequency of phenotypic variations than protoplast-derived nontransformed plants and transgenic plants containing the hph gene. In some varied traits such as sterility and albinism were segregated as a single locus among transgenic progeny and may have been associated with the presence of an active Ac element. This field experiment enabled us to assess the traits of transgenic rice plants for transposon tagging and obtain useful mutant materials.