Rieu Ivo, Ruiz-Rivero Omar, Fernandez-Garcia Nieves, Griffiths Jayne, Powers Stephen J, Gong Fan, Linhartova Terezie, Eriksson Sven, Nilsson Ove, Thomas Stephen G, Phillips Andrew L, Hedden Peter
Plant Science Department, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK.
Plant J. 2008 Feb;53(3):488-504. doi: 10.1111/j.1365-313X.2007.03356.x. Epub 2007 Dec 6.
The activity of the gibberellin (GA) biosynthetic enzymes GA 20-oxidases (GA20ox) is of particular importance in determining GA concentration in many plant species. In Arabidopsis these enzymes are encoded by a family of five genes: AtGA20ox1-AtGA20ox5. Transcript analysis indicated that they have different expression patterns and may thus participate differentially in GA-regulated developmental processes. We have used reverse genetics to determine the physiological roles of AtGA20ox1 and AtGA20ox2, the most highly expressed GA20ox genes during vegetative and early reproductive development. AtGA20ox1 and AtGA20ox2 act redundantly to promote hypocotyl and internode elongation, flowering time, elongation of anther filaments, the number of seeds that develop per silique and elongation of siliques, with AtGA20ox1 making the greater contribution to internode and filament elongation, and AtGA20ox2 making the greater contribution to flowering time and silique length. Pollination of the double mutant with wild-type pollen indicated that the GA promoting silique elongation is of maternal origin. The ga20ox2 phenotype revealed that GA promotes the number of stem internodes that elongate upon bolting, and does so independently of its effect on internode elongation. Comparison of the phenotype of the double mutant with that of the highly GA-deficient ga1-3 mutant indicates that other GA20ox genes contribute to all the developmental processes examined, and, in some cases such as root growth and leaf expansion, make major contributions, as these processes were unaffected in the double mutant. In addition, the effects of the mutations are mitigated by the homeostatic mechanism that acts on expression of other GA dioxygenase and GID1 receptor genes.
赤霉素（GA）生物合成酶GA 20-氧化酶（GA20ox）的活性在决定许多植物物种中的GA浓度方面尤为重要。在拟南芥中，这些酶由五个基因家族编码：AtGA20ox1-AtGA20ox5。转录本分析表明它们具有不同的表达模式，因此可能在GA调控的发育过程中发挥不同的作用。我们利用反向遗传学来确定AtGA20ox1和AtGA20ox2的生理作用，这两个基因是营养生长和早期生殖发育过程中表达量最高的GA20ox基因。AtGA20ox1和AtGA20ox2在促进下胚轴和节间伸长、开花时间、花药花丝伸长、每角果发育的种子数量以及角果伸长方面发挥冗余作用，其中AtGA20ox1对节间和花丝伸长贡献更大，而AtGA20ox2对开花时间和角果长度贡献更大。用野生型花粉对双突变体进行授粉表明，促进角果伸长的GA来自母本。ga20ox2突变体表型表明，GA促进抽薹时伸长的茎节间数量增加，且这一作用独立于其对节间伸长的影响。将双突变体的表型与高度GA缺陷的ga1-3突变体的表型进行比较表明，其他GA20ox基因对所有检测的发育过程都有贡献，在某些情况下，如根生长和叶片扩展，这些基因起主要作用，因为在双突变体中这些过程不受影响。此外，作用于其他GA双加氧酶和GID1受体基因表达的稳态机制减轻了突变的影响。
