Characterization of rice tryptophan decarboxylases and their direct involvement in serotonin biosynthesis in transgenic rice
Characterization of rice tryptophan decarboxylases and their direct involvement in serotonin biosynthesis in transgenic rice
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DOI：
10.1007/s00425-007-0614-z
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发表时间：
2007-12-01
期刊：
影响因子：
4.3
通讯作者：
Back, Kyoungwhan
中科院分区：
文献类型：
--
作者：
Kang, So;Kang, Kiyoon;Back, Kyoungwhan
色氨酸脱羧酶（TDC）和酪氨酸脱羧酶（TYDC）属于芳香族L-氨基酸脱羧酶家族，分别催化色氨酸和酪氨酸转化为色胺和酪胺。水稻基因组中含有7个TDC或TYDC样基因。其中三个基因的cDNA克隆是可用的，其特征在于分配其功能，使用异源表达在大肠杆菌和水稻（水稻品种。Dongjin）。其中两个基因的纯化产物在E.在大肠杆菌中表达，其中TDC基因具有活性，而其余基因不能在大肠杆菌中表达。杆菌具有最大TDC活性的重组TDC蛋白对色氨酸显示出0.9 mM的K，，，并且其活性不被苯丙氨酸或酪氨酸抑制，表明对色氨酸具有高水平的底物特异性。这三个cDNA克隆在水稻中的异位表达导致了编码酶酪胺和色胺产物的大量产生。TYDC的过量生产导致生长发育不良，并且由于酪胺积累而导致种子产量不足，酪胺积累随着植物衰老而增加。相反，产生TDC的转基因植物表现出正常的表型，并且在叶和种子中分别含有比野生型植物高25倍和11倍的5-羟色胺。酪胺或5-羟色胺的过量产生与酪胺或5-羟色胺衍生物的合成增强没有强烈关系，如阿魏酰酪胺和阿魏酰5-羟色胺，它们是植物中作为植物抗毒素的次级代谢产物。
L-Tryptophan decarboxylase (TDC) and L-tyrosine decarboxylase (TYDC) belong to a family of aromatic L-amino acid decarboxylases and catalyze the conversion of tryptophan and tyrosine into tryptamine and tyramine, respectively. The rice genome has been shown to contain Seven TDC or TYDC-like genes. Three of these genes for which cDNA clones were available were characterized to assign their functions using heterologous expression in Escherichia coli and rice (Oryza sativa cv. Dongjin). The purified products of two of the genes were expressed in E. coli and exhibited TDC activity, whereas the remaining gene could not be expressed in E. coli. The recombinant TDC protein with the greatest TDC activity showed a K,,, of 0.9 mM for tryptophan, and its activity was not inhibited by phenylalanine or tyrosine, indicating a high level of substrate specificity toward tryptophan. The ectopic expression of the three cDNA clones in rice led to the abundant production of the products of the encoded enzymes, tyramine and tryptamine. The overproduction of TYDC resulted in stunted growth and a lack of seed production due to tyramine accumulation, which increased as the plant aged. In contrast, transgenic plants that produced TDC showed a normal phenotype and contained 25-fold and I I-fold higher serotonin in the leaves and seeds, respectively, than the wild-type plants. The overproduction of either tyramine or serotonin was not strongly related to the enhanced synthesis of tyramine or serotonin derivatives, such as feruloyltyramine and feruloylserotonin, which are secondary metabolites that act as phytoalexins in plants.