Shi L, Olszewski N E
Department of Plant Biology, University of Minnesota, St. Paul 55108, USA.
Plant Mol Biol. 1998 Dec;38(6):1053-60. doi: 10.1023/a:1006007315718.
Both gibberellic acid (GA3) and abscisic acid (ABA) regulate the expression of the GAST1 gene of tomato. Treatment with GA3 increases the abundance of GAST1 RNA while treatment with ABA blocks this effect. In this study, the effects of GA3 and ABA on the rate of transcription of the GAST1 gene and the stability of GAST1 RNA were examined. Nuclear run-on analyses detected an increase in transcription of the GAST1 gene 1 h after GA3 treatment with transcription increasing to a maximum at 9 h after treatment. The half-life of GAST1 RNA in GA3-treated leaves was similar to that in control leaves. In addition, the extent of overexpression of GAST1 RNA in transgenic tomato plants containing the CaMV 35S promoter driving the expression of the GAST1 transcribed region was largely unaffected by GA3. These results suggest that GA3 stimulates the expression of the GAST1 gene by acting only at the level of transcription. ABA treatment dramatically reduced the abundance of GAST1 RNA in gib1 shoots through an effect at the level of transcription and did not appear to affect the stability of this RNA. Midcourse ABA addition to the GA3-incubated shoots reversed the GA3-mediated increase in the transcription of GAST1 gene within 15 min. Transgenic plants that either overexpressed or underexpressed GAST1 RNA exhibited no phenotypic differences from wild type.
赤霉素（GA3）和脱落酸（ABA）均调控番茄GAST1基因的表达。用GA3处理可增加GAST1 RNA的丰度，而用ABA处理则会阻断这种效应。在本研究中，检测了GA3和ABA对GAST1基因转录速率以及GAST1 RNA稳定性的影响。核转录分析检测到，GA3处理1小时后GAST1基因的转录增加，处理9小时后转录增加到最大值。GA3处理叶片中GAST1 RNA的半衰期与对照叶片中的相似。此外，在含有驱动GAST1转录区表达的CaMV 35S启动子的转基因番茄植株中，GA3对GAST1 RNA的过表达程度影响不大。这些结果表明，GA3仅通过作用于转录水平来刺激GAST1基因的表达。ABA处理通过在转录水平上起作用，显著降低了gib1芽中GAST1 RNA的丰度，并且似乎不影响该RNA的稳定性。在GA3处理的芽中添加中期ABA，可在15分钟内逆转GA3介导的GAST1基因转录增加。过表达或低表达GAST1 RNA的转基因植株与野生型没有表型差异。
