不同启动子控制下Ac转座酶基因的表达对玉米Ds因子在水稻中切离频率的影响

用水稻愈伤组织比较了Ac启动子、35S启动子与Ubi启动子控制下Ac转座酶基因（Ts）的表达对Ds因子切离频率的影响。结果表明Ubi启动子与Ac转座酶编码区嵌合基因（Ubipro-Ts）反式激活Ds因子的切离频率最高，达到了72.9%。通过杂交将Ubipro-Ts基因导入Ds因子转化植株，得到9株Ubipro-Ts基因与Ds因子共存的F1代杂交水稻植株，其中有8株Ds因子发生了切离。用Inverse-PCR的方法从其中一株杂交植株中克隆到Ds因子的旁邻序列，其DNA顺序与亲本中Ds因子原插入位点的序列不同，表明Ds因子转座到了新的基因组位点。

Effects of Different Promoters Controlling Expression of Ac Transposase Gene on Excision Frequency of Maize Ds Element in Rice

Three chimeric genes constructed by fusion of three different promoters, Ac promoter, CaMV 35S promoter and Ubi promoter, to Ac transposase coding region(Fig.1), were each induced into rice calli generated from immature embryo containing Ds element (Fig.2) mediated by Agrobacterium(Fig.3a,b). The effects of Ac transposase (Ts) gene expression directed by these three different promoters on the excision frequency of Ds element were compared in rice calli carrying both Ts gene and Ds element (Fig.3c). The excision frequency of Ds element trans-activated by Ac transposase driven by Ubi promoter was found to be highest(about 72.9%, against 65.0% and 45.7% for the Acpro-Ts and the 35Spro-Ts, respectively)(Table 1). Nine F 1 offsprings which had both the Ubipro-Ts gene and the Ds element were obtained by crossing transgenic plants containing Ubipro-Ts gene (Fig.4) and rice plant strain 87-1 harboring the Ds element. PCR analysis showed that Ds elements in 8 of these F 1 plants were excised from their original insertion sites. A DNA fragment flanking the Ds element from a F 1 plant was cloned using the Inverse-PCR method. Comparison of the nucleotide sequence of this DNA fragment with that at the original site of Ds element in the parent plant strain 87-1 revealed that the Ds element had been excised from the original site and re-integrated into a new genomic site (Fig.5).