Identification of photorespiratory glutamate:glyoxylate aminotransferase (GGAT) gene in Arabidopsis
Identification of photorespiratory glutamate:glyoxylate aminotransferase (GGAT) gene in Arabidopsis
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DOI：
10.1046/j.1365-313x.2003.01688.x
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发表时间：
2003-03-01
期刊：
影响因子：
7.2
通讯作者：
Ohsumi, C
中科院分区：
文献类型：
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作者：
Igarashi, D;Miwa, T;Ohsumi, C
在光呼吸过程中，谷氨酸乙醛转氨酶(GGAT)催化谷氨酸和乙醛生成2-氧戊二酸和甘氨酸。虽然GGAT被认为在光呼吸碳循环的转氨化过程中起着重要作用，但编码GGAT的基因还没有被确定。在这里，我们报告了一个类似丙氨酸：2-氧代戊二酸氨基转移酶(AOAT)的蛋白在过氧化酶体中作为GGAT发挥功能。拟南芥有四个编码AOAT类蛋白的基因，其中两个(即AOAT1和AOAT2)含有过氧化体靶向信号1(PTS1)。对编码AOATs和EST信息的mRNA的表达分析表明，AOAT1是绿叶中的主要蛋白质。当AOAT1与绿色荧光蛋白(GFP)融合在BY-2细胞中表达时，发现其定位于依赖于PTS1的过氧体。通过对拟南芥T-DNA插入系的筛选，获得了一个AOAT1基因敲除系(aoat1-1)。AOAT1-1地上部组织中GGAT和丙氨酸乙醛转氨酶(AGAT)活性显著降低，AOAT和谷丙转氨酶(GPAT)活性也降低。在野生型中检测到过氧化物体GGAT，而在aoat1-1中未检测到。在高辐射和无糖条件下生长的AoAT1-1的生长速率受到抑制，而在低辐射、高CO2(0.3%)或高糖(3%蔗糖)条件下生长的Aoat1-1的生长速度略有不同。这些表型与光呼吸缺陷突变体的表型相似。在正常空气条件下生长的AOAT1-1，谷氨酸水平升高，丝氨酸水平下降。这些结果表明，AOAT1是以过氧化物体为靶标的，作为一种光呼吸GGAT，在植物生长和氨基酸代谢中发挥着重要的作用。
In the photorespiratory process, peroxisomal glutamate:glyoxylate aminotransferase (GGAT) catalyzes the reaction of glutamate and glyoxylate to 2-oxoglutarate and glycine. Although GGAT has been assumed to play important roles for the transamination in photorespiratory carbon cycles, the gene encoding GGAT has not been identified. Here, we report that an alanine:2-oxoglutarate aminotransferase (AOAT)-like protein functions as GGAT in peroxisomes. Arabidopsis has four genes encoding AOAT-like proteins and two of them (namely AOAT1 and AOAT2 ) contain peroxisomal targeting signal 1 (PTS1). The expression analysis of mRNA encoding AOATs and EST information suggested that AOAT1 was the major protein in green leaves. When AOAT1 fused to green fluorescent protein (GFP) was expressed in BY-2 cells, it was found to be localized to peroxisomes depending on PTS1. By screening of Arabidopsis T-DNA insertion lines, an AOAT1 knockout line (aoat1-1 ) was isolated. The activity of GGAT and alanine:glyoxylate aminotransferase (AGAT) in the above-ground tissues of aoat1-1 was reduced drastically and, AOAT and glutamate:pyruvate aminotransferase (GPAT) activity also decreased. Peroxisomal GGAT was detected in the wild type but not in aoat1-1 . The growth rate was repressed in aoat1-1 grown under high irradiation or without sugar, though differences were slight in aoat1-1 grown under low irradiation, high-CO2 (0.3%) or high-sugar (3% sucrose) conditions. These phenotypes resembled those of photorespiration-deficient mutants. Glutamate levels increased and serine levels decreased in aoat1-1 grown in normal air conditions. Based on these results, it was concluded that AOAT1 is targeted to peroxisomes, functions as a photorespiratory GGAT, plays a markedly important role for plant growth and the metabolism of amino acids.