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

赤霉素（giberellins, GAs）是植物生长发育过程中必不可少的内源性调节剂。伦巴第杨（Populus nigra）的GA活性形态为GA_1、GA_3和GA_4。通过对GA_3处理后伦巴第杨枝长、干物质产量、木材解剖结构、细胞壁成分、净光合速率和色素水平的测定，发现GA_3处理对陆生部分生物量产量有积极影响。我们还分离到了ga生物合成酶ga20氧化酶和ga3 β-羟化酶的两个基因，以及ga失活酶ga2 β-羟化酶的7个基因。GA_3处理时，ga20氧化酶和ga3 β-羟化酶基因表达均下调，而ga2 β-羟化酶基因表达上调。事实上，GA_3处理后，内部GA_3水平显著升高，GA_1、GA_4、GA_5、GA_9和GA_<20>水平显著降低。因此，这些基因的表达水平与内源GAs水平的变化高度相关。此外，我们还建立了一种简单可靠的转基因杨树再生方法，即选择除草剂bialaphos和抗生素hygromycin B。利用这些转化体系，在花菜花叶病毒35S启动子的控制下，将ga20氧化酶基因和参与赤霉素低浓度信号转导的水稻异三聚体G蛋白α-亚基基因分别导入到lombardy杨树和水稻中。我们研究了人造光下植物加速器中获得的变形体的生长特性。综上所述，可能通过上调ga20氧化酶和ga3 β-羟化酶基因或下调ga2 β-羟化酶基因来控制其生长。

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.