水稻ABA生物合成基因OsNCED3响应干旱胁迫

9-顺-环氧类胡萝卜素双加氧酶(NCED)是植物内源脱落酸(ABA)生物合成的限速酶，由NCED基因家族编码，水稻中响应干旱胁迫并以此调节ABA水平的OsNCED基因尚见未报道。本研究发现在水稻已报道的5个OsNCED基因中，OsNCED3的表达受干旱胁迫诱导，复水处理后其表达快速下调，其表达模式与此过程中内源ABA含量变化趋势一致。OsNCED3的RNAi转基因植株表现为干旱敏感，且生物量下降；而过量表达OsNCED3基因增加了水稻的抗旱性。干旱胁迫下过量表达OsNCED3的转基因株系有较高的ABA水平，同时其抗氧化酶超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性，以及逆境响应基因脱水素蛋白(Dehydrin)和胚胎发育晚期丰富蛋白(LEA)转录表达均高于野生型。下调表达OsNCED3的转基因株系则呈现相反的变化趋势。因此，OsNCED3是水稻干旱胁迫响应基因，调节了干旱环境下ABA水平和抗逆性。

ABA Biosynthesis Gene OsNCED3 Confers Drought Stress Tolerance in Rice

NCED (9-cis-epoxycarotenoid dioxygenase), encoded by NCED gene family, is a rate limited enzyme responsible for the ABA biosynthesis in plants. It remains unknown whether OsNCED genes are responsible for controlling ABA levels during drought stress in rice. Among the five OsNCED genes, we found that OsNCED3 mRNA level was promptly induced by PEG-mimic drought stress and decreased by re-watering, with a tendency of well consistent with the variation of ABA content. Down-regulating of OsNCED3 gene expression in RNA interference (RNAi)-transgenic plants decreased the total biomass and showed a hypersensitive phenotype subjecting to drought stress, while the overexpression (OE)-transgenic seedlings increased the drought stress tolerance compared with the wild-type (WT). ABA contents in OsNCED3-OE leaves were higher than those in WT, meanwhile, OsNCED3-OE lines also increased the activities of anti-oxidative enzyme including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and expressions of stress/drought-related genes, i.e. dehydrin protein, LEA protein under drought stress. OsNCED3-RNAi lines showed an opposite tendency with the OsNCED3-OE plants. We therefore conclude that OsNCED3 gene plays an important role in controlling ABA level and drought stress resistance in rice.