Abstract: GA20-oxidase (GA20ox) is a key rate-limiting enzyme in the synthesis of gibberellic acid (GA). In order to study the function of GA20ox gene in Medicago truncatula, the amino acid sequence alignment of GA20ox of Arabidopsis thaliana and Medicago truncatula was carried out by bioinformatics methods, and the phylogenetic tree of the families was constructed. The results showed that there were three MtGA20ox, which were MtGA20ox1, MtGA20ox7 and MtGA20ox8, respectively. They had highly homologous to AtGA20ox, and each of them contained a conserved 20G-FeⅡ_Oxy domain. Further, the results of transcript analysis indicated that the expressions of MtGA20ox1, MtGA20ox7 and MtGA20ox8 were tissue specific. Meanwhile, the result of subcellular localization indicated that MtGA20ox1, MtGA20ox7 and MtGA20ox8 proteins were probably localized in nucleus and cytoplasm. In order to comprehend the function of MtGA20ox, two mutants with retrotransposon Tnt1 inserted in MtGA20ox7 and one mutant with retrotransposon Tnt1 inserted in MtGA20ox8 were obtained. The phenotypic observations and data statistics of the three mutants manifested that there were no significant changes in the plant height compared with the wild type. This might be due to the functional redundancy of the three MtGA20ox genes. Results of this study had a certain reference value for studying the function of GA20ox and the regulation of gibberellin on plant height in Medicago truncatula.

Key words: GA20-oxidase, plant height, Medicago truncatula, gibberellic acid

摘要： GA20-氧化酶（GA20-oxidase，GA20ox）是赤霉素（gibberellic acid，GA）合成过程中的关键限速酶。为了对蒺藜苜蓿（Medicago truncatula）中GA20ox基因的功能进行研究，利用生物信息学的方法对蒺藜苜蓿和拟南芥（Arabidopsis thaliana）的GA20ox家族成员进行氨基酸序列比对并构建系统进化树。结果表明，与拟南芥AtGA20ox高度同源的蒺藜苜蓿MtGA20ox有3个，分别为MtGA20ox1、MtGA20ox7和MtGA20ox8，均含有保守的2OG-FeⅡ_Oxy结构域。进一步通过RT-PCR检测MtGA20ox1、MtGA20ox7和MtGA20ox8在不同组织中的表达，结果显示它们的表达都具有组织特异性。同时，亚细胞定位结果表明MtGA20ox1、MtGA20ox7和MtGA20ox8蛋白定位于细胞核和细胞质。为了对MtGA20ox的功能进行深入解析，筛选获得了逆转座子Tnt1插入MtGA20ox7的2个突变体和插入MtGA20ox8的1个突变体，并分别对3个插入突变体进行表型观察和数据统计，发现其与野生型相比株高无明显变化，这可能是由于这3个MtGA20ox基因存在功能冗余。研究结果对深入研究苜蓿中GA20ox的功能以及进一步研究赤霉素对株高的调控具有一定的参考价值。

关键词: GA20-氧化酶, 株高, 蒺藜苜蓿, 赤霉素