Kuwano Mio, Mimura Tetsuro, Takaiwa Fumio, Yoshida Kaoru T
Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
Plant Biotechnol J. 2009 Jan;7(1):96-105. doi: 10.1111/j.1467-7652.2008.00375.x. Epub 2008 Sep 30.
Phytic acid acts as the major storage form of phosphorus in plant seeds and is poorly digested by monogastric animals. The degradation of phytic acid in animal diets is necessary to overcome both environmental and nutritional issues. The enzyme 1D-myo-inositol 3-phosphate [Ins(3)P(1)] synthase (EC 5.5.1.4) catalyses the first step of myo-inositol biosynthesis and directs phytic acid biosynthesis in seeds. The rice Ins(3)P(1) synthase gene (RINO1) is highly expressed in developing seed embryos and in the aleurone layer, where phytic acid is synthesized and stored. In rice seeds, 18-kDa oleosin (Ole18) is expressed in a seed-specific manner, and its transcripts are restricted to the embryo and the aleurone layer. Therefore, to effectively suppress phytic acid biosynthesis, antisense RINO1 cDNA was expressed under the control of the Ole18 promoter, directing the same spatial pattern in seeds as RINO1 in transgenic rice plants. The generated transgenic rice plants showed strong 'low phytic acid' (lpa) phenotypes, in which seed phytic acid was reduced by 68% and free available phosphate was concomitantly increased. No negative effects on seed weight, germination or plant growth were observed. The available phosphate levels of the stable transgenic plants surpassed those of currently available rice lpa mutants.
植酸是植物种子中磷的主要储存形式，单胃动物对其消化能力较差。降解动物饲料中的植酸对于解决环境和营养问题都很有必要。1D-肌醇3-磷酸[Ins(3)P(1)]合酶（EC 5.5.1.4）催化肌醇生物合成的第一步，并指导种子中植酸的生物合成。水稻Ins(3)P(1)合酶基因（RINO1）在发育中的种子胚和糊粉层中高度表达，植酸在这些部位合成并储存。在水稻种子中，18 kDa油质蛋白（Ole18）以种子特异性方式表达，其转录本局限于胚和糊粉层。因此，为了有效抑制植酸生物合成，反义RINO1 cDNA在Ole18启动子的控制下表达，在转基因水稻植株种子中指导与RINO1相同的空间模式。所产生的转基因水稻植株表现出强烈的“低植酸”（lpa）表型，其中种子植酸减少了68%，同时游离有效磷增加。未观察到对种子重量、发芽或植株生长的负面影响。稳定转基因植株的有效磷水平超过了目前已有的水稻lpa突变体。
