Sakamoto T, Kobayashi M, Itoh H, Tagiri A, Kayano T, Tanaka H, Iwahori S, Matsuoka M
Institute of Agriculture and Forestry, University of Tsukuba, Tsukuba 305-8572, Japan.
Plant Physiol. 2001 Mar;125(3):1508-16. doi: 10.1104/pp.125.3.1508.
A major catabolic pathway for gibberellin (GA) is initiated by 2beta-hydroxylation, a reaction catalyzed by GA 2-oxidase. We have isolated and characterized a cDNA, designated Oryza sativa GA 2-oxidase 1 (OsGA2ox1) from rice (Oryza sativa L. cv Nipponbare) that encodes a GA 2-oxidase. The encoded protein, produced by heterologous expression in Escherichia coli, converted GA(1), GA(4), GA(9), GA(20), and GA(44) to the corresponding 2beta-hydroxylated products GA(8), GA(34), GA(51), GA(29), and GA(98), respectively. Ectopic expression of the OsGA2ox1 cDNA in transgenic rice inhibited stem elongation and the development of reproductive organs. These transgenic plants were deficient in endogenous GA(1). These results indicate that OsGA2ox1 encodes a GA 2-oxidase, which is functional not only in vitro but also in vivo. OsGA2ox1 was expressed in shoot apex and roots but not in leaves and stems. In situ hybridization analysis revealed that OsGA2ox1 mRNA was localized in a ring at the basal region of leaf primordia and young leaves. This ring-shaped expression around the shoot apex was drastically decreased after the phase transition from vegetative to reproductive growth. It was absent in the floral meristem, but it was still present in the lateral meristem that remained in the vegetative phase. These observations suggest that OsGA2ox1 controls the level of bioactive GAs in the shoot apical meristem; therefore, reduction in its expression may contribute to the early development of the inflorescence meristem.
赤霉素（GA）的主要分解代谢途径由2β-羟基化起始，该反应由GA 2-氧化酶催化。我们从水稻（Oryza sativa L. cv Nipponbare）中分离并鉴定了一个名为水稻GA 2-氧化酶1（OsGA2ox1）的cDNA，其编码一种GA 2-氧化酶。在大肠杆菌中异源表达产生的编码蛋白分别将GA(1)、GA(4)、GA(9)、GA(20)和GA(44)转化为相应的2β-羟基化产物GA(8)、GA(34)、GA(51)、GA(29)和GA(98)。OsGA2ox1 cDNA在转基因水稻中的异位表达抑制了茎的伸长和生殖器官的发育。这些转基因植物内源性GA(1)缺乏。这些结果表明，OsGA2ox1编码一种GA 2-氧化酶，其不仅在体外而且在体内均具有功能。OsGA2ox1在茎尖和根中表达，但在叶和茎中不表达。原位杂交分析显示，OsGA2ox1 mRNA定位于叶原基和幼叶基部区域的一个环中。从营养生长向生殖生长的阶段转变后，茎尖周围这种环状表达急剧下降。它在花分生组织中不存在，但仍存在于处于营养阶段的侧生分生组织中。这些观察结果表明，OsGA2ox1控制茎尖分生组织中生物活性GA的水平；因此，其表达的降低可能有助于花序分生组织的早期发育。
