Characterization and expression analysis of a serine acetyltransferase gene family involved in a key step of the sulfur assimilation pathway in Arabidopsis
Characterization and expression analysis of a serine acetyltransferase gene family involved in a key step of the sulfur assimilation pathway in Arabidopsis
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DOI：
10.1104/pp.104.045377
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发表时间：
2005-01-01
期刊：
影响因子：
7.4
通讯作者：
Saito, K
中科院分区：
文献类型：
--
作者：
Kawashima, CG;Berkowitz, O;Saito, K
丝氨酸乙酰转移酶(SATase；EC 2.3.1.30)催化L丝氨酸和乙酰辅酶A生成O-乙酰-丝氨酸，进而合成半胱氨酸。根据SATase在硫同化途径和氨基酸代谢途径中的决定性结合点位置，SATase受到控制半胱氨酸合成通量的调控机制的影响。在拟南芥中，有5个基因编码类SATase蛋白。对两种异构体Serat3；1和Serat3；2的酶学性质、L-半胱氨酸的反馈抑制作用和亚细胞定位进行了研究。Serat3；1和Serat3；2的功能同源性是通过对大肠杆菌SATase缺陷突变体的互补而建立的。通过与绿色荧光蛋白的融合构建，证实了Serat3；1和Serat3；2的胞浆定位。重组的Serat3；1不受L-半胱氨酸的抑制，而Serat3，2是强反馈抑制的异构体。表达谱定量分析表明，Serat2；1在所研究的大多数组织中是主要的表达形式，其次是Serat1；1和Serat2；2。虽然Serat3；1和Serat3；2在大多数组织中都有微弱的表达，但Serat3；2在缺硫和镉胁迫下以及在生殖发育阶段都有显著的诱导表达，这意味着当植物受到不同的条件时，Serat3；1和Serat3；2具有特定的作用。在5个启动子控制下表达绿色荧光蛋白的转基因拟南芥植株表明，在所有的SERAT基因中，该表达主要定位于维管系统，尤其是韧皮部。这些结果表明，拟南芥利用一系列具有不同酶性质和表达模式的区室特异性SATase亚型来确保半胱氨酸的供应，以响应发育和环境的变化。
Ser acetyltransferase (SATase; EC 2.3.1.30) catalyzes the formation of O-acetyl-Ser from L-Ser and acetyl-CoA, leading to synthesis of Cys. According to its position at the decisive junction of the pathways of sulfur assimilation and amino acid metabolism, SATases are subject to regulatory mechanisms to control the flux of Cys synthesis. In Arabidopsis (Arabidopsis thaliana) there are five genes encoding SATase-like proteins. Two isoforms, Serat3;1 and Serat3;2, were characterized with respect to their enzymatic properties, feedback inhibition by L-Cys, and subcellular localization. Functional identity of Serat3;1 and Serat3;2 was established by complementation of a SATase-deficient mutant of Escherichia coli. Cytosolic localization of Serat3;1 and Serat3;2 was confirmed by using fusion construct with the green fluorescent protein. Recombinant Serat3;1 was not inhibited by L-CYS, while Serat3,2 was a strongly feedback-inhibited isoform. Quantification of expression patterns indicated that Serat2;1 is the dominant form expressed in most tissues examined, followed by Serat1;1 and Serat2;2. Although Serat3;1 and Serat3;2 were expressed weakly in most tissues, Serat3;2 expression was significantly induced under sulfur deficiency and cadmium stress as well as during generative developmental stages, implying that Serat3;1 and Serat3;2 have specific roles when plants are subjected to distinct conditions. Transgenic Arabidopsis plants expressing the green fluorescent protein under the control of the five promoters indicated that, in all Serat genes, the expression was predominantly localized in the vascular system, notably in the phloem. These results demonstrate that Arabidopsis employs a complex array of compartment-specific SATase isoforms with distinct enzymatic properties and expression patterns to ensure the provision of Cys in response to developmental and environmental changes.