Growth control of woody plants by genetic engineering with genes for gibberellin-biosynthetic enzymes.

赤霉素（GAs）是植物生长发育过程中必不可少的内源调节因子。白杨（Populusnigra）的GA活性形式为GA_1、GA_3和GA_4。通过对赤霉素（GA_3）处理后的伦巴第白杨地上部生物量、干物质生产、木材解剖、细胞壁成分、净光合速率和色素含量的测定，发现GA_3处理对陆地部分生物量生产有促进作用。我们还分离了GA生物合成酶中的GA 20-氧化酶和GA 3 β-羟化酶的两个基因，以及GA失活酶中的GA 2 β-羟化酶的七个基因。在GA_3处理过程中，GA 20-氧化酶和GA 3 β-羟化酶基因的表达均下调，而GA 2 β-羟化酶基因的表达上调。事实上，GA_3处理后内部GA_3水平明显增加，GA_1、GA_4、GA_5、GA_9和GA_3处理后GA_1、GA_4、GA_5、GA_9和GA_3水平<20>明显下降。因此，这些基因的表达水平与内源GAs水平的变化密切相关。此外，我们还建立了一套简单可靠的转基因白杨再生体系，并利用除草剂双丙氨膦和抗生素潮霉素B进行筛选。利用这些转化系统，我们将GA 20氧化酶基因导入伦巴第白杨，并将水稻异源三聚体G蛋白α亚基基因导入花椰菜花叶病毒35 S启动子控制下，该基因参与低浓度赤霉素的信号传导。我们已经检查了获得的转化体在人工气候室人工光下的生长特性。因此，可能通过上调GA 20-氧化酶和GA 3 β-羟化酶基因或下调GA 2 β-羟化酶基因来调控生长。

Gibberellins (GAs) are essential endogenous regulators of growth and developmental processes throughout the plant life cycle. Lombardy poplar (Populus nigra) has GA_1, GA_3 and GA_4 as the active form of GA. We examined the shoot elongation, the dry-matter production, the wood anatomy, the cell wall components, the net photosynthetic rate and the levels of pigments of lombardy poplar after treatment with GA_3, and found that the GA_3 treatments have positive effects on the biomass production of terrestrial parts. We also isolated the two genes for GA20-oxidase and GA3β-hydroxylase of GA-biosynthetic enzymes, and the seven genes for GA2β-hydroxylase which is one of GA-deactivation enzymes. During the treatment with GA_3, the expression of both genes for GA20-oxidase and GA3β-hydroxylase was down-regulated while that of the genes for GA2β-hydroxylase was up-regulated. In fact, the internal level of GA_3 increased markedly after the treatments, and the levels of GA_1, GA_4, GA_5, GA_9 and GA_<20> significantly decreased after the GA_3 treatments. Thus, the levels of expression of these genes were highly related to the changes of the levels of endogenous GAs. Furthermore, we established the simple and reliable procedure for the regeneration of transgenic poplar using selection of herbicide 'bialaphos' and antibiotic ‘hygromycin B'. With these transformation systems, we introduced the gene for GA20-oxidase into lombardy poplar, and the gene for the α-subunit of the rice heterotrimeric G proteins which participate in signaling of gibberellin at low concentrations, under control of the cauliflower mosaic virus 35S promoter. We have examined the growth characteristics of obtained transformants in a phytotron under artificial-light. In conclusion, it may be possible to control the growth by up-regulation of the genes for GA20-oxidase and GA3β-hydroxylase or down-regulation of the genes for GA2β-hydroxylase.