Que Q., Wang H. Y., English J. J., Jorgensen R. A.
Environmental Horticulture, University of California, Davis, California 95616-8587.
Plant Cell. 1997 Aug;9(8):1357-1368. doi: 10.1105/tpc.9.8.1357.
By comparing the effects of strong and weak promoters that drive sense chalcone synthase (Chs) transgenes in large populations of independently transformed plants, we show here that a strong transgene promoter is required for high-frequency cosuppression of Chs genes and for production of the full range of cosuppression phenotypes. In addition, sense Chs transgenes driven by a cauliflower mosaic virus 35S promoter possessing a single copy of the upstream activator region (UAR) were found to produce a significantly lower degree of cosuppression than they did when the transgene promoter possessed two or four copies of the UAR. It has been shown elsewhere that 35S promoter strength increases with increasing UAR copy number. Frameshift mutations producing early nonsense codons in the Chs transgene were found to reduce the frequency and the degree of cosuppression. These results suggest that promoter strength and transcript stability determine the degree of cosuppression, supporting the hypothesis that sense cosuppression is a response to the accumulation of transcripts at high concentrations. This conclusion was shown to apply to single-copy transgenes but not necessarily to inversely repeated transgenes. The results presented here also have significance for efficient engineering of cosuppression phenotypes for use in research and agriculture.
通过比较在大量独立转化植株中驱动正义查尔酮合酶（Chs）转基因的强启动子和弱启动子的作用，我们在此表明，Chs基因的高频共抑制以及产生完整范围的共抑制表型需要一个强转基因启动子。此外，发现由具有单个上游激活区（UAR）拷贝的花椰菜花叶病毒35S启动子驱动的正义Chs转基因产生的共抑制程度明显低于转基因启动子具有两个或四个UAR拷贝时的情况。在其他地方已经表明，35S启动子强度随着UAR拷贝数的增加而增强。发现在Chs转基因中产生早期无义密码子的移码突变会降低共抑制的频率和程度。这些结果表明启动子强度和转录本稳定性决定了共抑制的程度，支持了正义共抑制是对高浓度转录本积累的一种反应这一假说。这一结论适用于单拷贝转基因，但不一定适用于反向重复转基因。这里呈现的结果对于高效构建用于研究和农业的共抑制表型也具有重要意义。
