State Key Laboratory of Agrobiotechnology, China Agricultural University, Yuanmingyan West Road 2, Beijing 100193, China.
Mol Plant Microbe Interact. 2013 Feb;26(2):227-39. doi: 10.1094/MPMI-05-12-0138-R.
Gibberellin (GA) 20-oxidase (GA20ox) catalyses consecutive steps of oxidation in the late part of the GA biosynthetic pathway. A T-DNA insertion mutant (17S-14) in rice, with an elongated phenotype, was isolated. Analysis of the flanking sequences of the T-DNA insertion site revealed that an incomplete T-DNA integration resulted in enhanced constitutively expression of downstream OsGA20ox3 in the mutant. The accumulation of bioactive GA(1) and GA(4) were increased in the mutant in comparison with the wild-type plant. Transgenic plants overexpressing OsGA20ox3 showed phenotypes similar to those of the 17S-14 mutant, and the RNA interference (RNAi) lines that had decreased OsGA20ox3 expression exhibited a semidwarf phenotype. Expression of OsGA20ox3 was detected in the leaves and roots of young seedlings, immature panicles, anthers, and pollens, based on β-glucuronidase (GUS) activity staining in transgenic plants expressing the OsGA20ox3 promoter fused to the GUS gene. The OsGA20ox3 RNAi lines showed enhanced resistance against rice pathogens Magnaporthe oryzae (causing rice blast) and Xanthomonas oryzae pv. oryzae (causing bacterial blight) and increased expression of defense-related genes. Conversely, OsGA20ox3-overexpressing plants were more susceptible to these pathogens comparing with the wild-type plants. The susceptibility of wild-type plants to X. oryzae pv. oryzae was increased by exogenous application of GA(3) and decreased by S-3307 treatment. Together, the results provide direct evidence for a critical role of OsGA20ox3 in regulating not only plant stature but also disease resistance in rice.
赤霉素（GA）20-氧化酶（GA20ox）催化 GA 生物合成途径后期的连续氧化步骤。从水稻中分离到一个具有伸长表型的 T-DNA 插入突变体（17S-14）。T-DNA 插入位点侧翼序列的分析表明，不完全的 T-DNA 整合导致突变体中 OsGA20ox3 的下游组成型表达增强。与野生型植物相比，突变体中生物活性 GA(1)和 GA(4)的积累增加。过表达 OsGA20ox3 的转基因植物表现出与 17S-14 突变体相似的表型，而 OsGA20ox3 表达降低的 RNA 干扰（RNAi）系表现出半矮化表型。基于在表达 OsGA20ox3 启动子与 GUS 基因融合的转基因植物中β-葡萄糖醛酸酶（GUS）活性染色，在幼苗叶片和根、未成熟的小穗、花药和花粉中检测到 OsGA20ox3 的表达。OsGA20ox3 RNAi 系对水稻病原体稻瘟病菌（引起稻瘟病）和稻黄单胞菌 pv.oryzae（引起细菌性条斑病）表现出增强的抗性，并增加了防御相关基因的表达。相反，与野生型植物相比，OsGA20ox3 过表达植物对这些病原体更敏感。外源 GA(3)的应用增加了野生型植物对稻黄单胞菌 pv.oryzae 的敏感性，而 S-3307 处理则降低了这种敏感性。总的来说，这些结果为 OsGA20ox3 在调节水稻不仅株高而且抗病性方面的关键作用提供了直接证据。
