| Aspartate aminotransferase(AAT) is a key enzyme in the synthesis of amino acids.It plays an important role in regulation of carbon and nitrogen metabolism in almost all organisms.In this study,we over-expressed in rice separately all three AAT genes from rice(OsAAT1～3) and one AAT gene from Escherichia coli(EcAAT). Over-expression was driven by the CaMV 35S promoter and transformed into rice by Agrobacterium tumefaciens-mediated transformation.Compared with control plants, the genetically engineered transformant plants showed significantly increased leaf AAT activity and seed amino acid and protein contents despite the lack of observed phenotypical changes.The total leaf AAT activities in OsAAT1,OsAAT2 and EcAAT over-expressed plants were 26.6,23.6 and 19.6 A/mg/min,which were significantly higher than that in the wild type control(17.7 A/mg/min).The amino acid content in seeds of transgenic plants over-expressing OsAAT1,OsAAT2,and EcAAT was 119.36 mg/g,102.84 mg/g and 113.72 mg/g,respectively,which were 16.1%,12.0%and 5.4%higher,respectively,than that in the control plants.The transgenic plants over-expressing OsAAT1,OsAAT2,and EcAAT had significantly higher protein contents(increased 22.2%,21.1%,and 11.1%,respectively) than wild type plants.No significant changes were found in leaf AAT activity,seed amino acid content or protein content in OsAAT3 over-expressed plants.The expression patterns of the three OsAAT genes and their different functions are also discussed.We do some RT-PCR and real-time PCR to check the expression of AAT genes. As result shows that OsAAT1 and OsAAT2's expression level are higher than OsAAT3, and when over-expressing EcAAT gene in transfer rice,it would result in higher expression of OsAAT1 and OsAAT2,but OsAAT3 expression level is lower.Except OsAAT1 gene has higher expression level in OsAAT2 transgenic rice,over-expressing one of OsAAT genes,it couldn't induce other OsAAT genes changed their expression.
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