The Arabidopsis translocator protein (AtTSPO) is regulated at multiple levels in response to salt stress and perturbations in tetrapyrrole metabolism.
The Arabidopsis translocator protein (AtTSPO) is regulated at multiple levels in response to salt stress and perturbations in tetrapyrrole metabolism.
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DOI：
10.1186/1471-2229-11-108
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发表时间：
2011-06-20
影响因子：
5.3
通讯作者：
Sachetto-Martins G
中科院分区：
文献类型：
--
作者：
Balsemão-Pires E;Jaillais Y;Olson BJ;Andrade LR;Umen JG;Chory J;Sachetto-Martins G
转运蛋白18kda (TSPO)，以前被称为外周型苯二氮卓受体（PBR），在哺乳动物和细菌的许多细胞功能中起重要作用，如类固醇生物合成、细胞呼吸、细胞增殖、细胞凋亡、免疫调节、卟啉和阴离子的运输。拟南芥含有一个单一的TSPO/ pbr相关基因，与细菌或哺乳动物的同源基因相比，其n端延伸了40个氨基酸，这表明它可能是叶绿体或线粒体定位的。为了测试TSPO n端延伸是否靶向细胞器，我们将TSPO cDNA中的三个潜在翻译起始位点融合到GFP的n端（AtTSPO:eGFP）。发现AtTSPO:eGFP融合蛋白的位置取决于翻译起始位置和植物生长条件。在标准条件下生长的植物中，在内质网和身份未知的囊泡中发现了全长AtTSPO:eGFP融合蛋白。然而，当盐胁迫条件下150 mM NaCl存在时，全长AtTSPO:eGFP定位于叶绿体。相比之下，当AtTSPO:eGFP被截断到氨基酸位置21或42的第二或第三个起始密码子时，融合蛋白在标准条件下与线粒体标记共定位。利用启动子GUS融合、qRT-PCR、荧光蛋白标记和叶绿体分离等方法，研究人员证明，在非生物胁迫条件下，AtTSPO水平在转录、转录后和翻译后水平受到调控。在盐胁迫条件下，与野生型相比，tspo-1敲除突变体的盐反应基因增加，而当AtTSPO过表达时，盐反应基因减少。四吡咯生物合成基因的突变以及叶绿素或类胡萝卜素生物合成抑制剂的应用也会影响AtTSPO的表达。我们的数据表明，AtTSPO在拟南芥对高盐胁迫的反应中起作用。盐胁迫导致AtTSPO通过其n端延伸从内质网重新定位到叶绿体。此外，我们的研究结果表明，AtTSPO在四吡咯生物合成突变体的转录水平上受到调控。因此，我们提出AtTSPO可能在盐胁迫和其他四吡咯代谢受损的条件下运输四吡咯中间体中发挥作用。
The translocator protein 18 kDa (TSPO), previously known as the peripheral-type benzodiazepine receptor (PBR), is important for many cellular functions in mammals and bacteria, such as steroid biosynthesis, cellular respiration, cell proliferation, apoptosis, immunomodulation, transport of porphyrins and anions. Arabidopsis thaliana contains a single TSPO/PBR-related gene with a 40 amino acid N-terminal extension compared to its homologs in bacteria or mammals suggesting it might be chloroplast or mitochondrial localized. To test if the TSPO N-terminal extension targets it to organelles, we fused three potential translational start sites in the TSPO cDNA to the N-terminus of GFP (AtTSPO:eGFP). The location of the AtTSPO:eGFP fusion protein was found to depend on the translational start position and the conditions under which plants were grown. Full-length AtTSPO:eGFP fusion protein was found in the endoplasmic reticulum and in vesicles of unknown identity when plants were grown in standard conditions. However, full length AtTSPO:eGFP localized to chloroplasts when grown in the presence of 150 mM NaCl, conditions of salt stress. In contrast, when AtTSPO:eGFP was truncated to the second or third start codon at amino acid position 21 or 42, the fusion protein co-localized with a mitochondrial marker in standard conditions. Using promoter GUS fusions, qRT-PCR, fluorescent protein tagging, and chloroplast fractionation approaches, we demonstrate that AtTSPO levels are regulated at the transcriptional, post-transcriptional and post-translational levels in response to abiotic stress conditions. Salt-responsive genes are increased in a tspo-1 knock-down mutant compared to wild type under conditions of salt stress, while they are decreased when AtTSPO is overexpressed. Mutations in tetrapyrrole biosynthesis genes and the application of chlorophyll or carotenoid biosynthesis inhibitors also affect AtTSPO expression. Our data suggest that AtTSPO plays a role in the response of Arabidopsis to high salt stress. Salt stress leads to re-localization of the AtTSPO from the ER to chloroplasts through its N-terminal extension. In addition, our results show that AtTSPO is regulated at the transcriptional level in tetrapyrrole biosynthetic mutants. Thus, we propose that AtTSPO may play a role in transporting tetrapyrrole intermediates during salt stress and other conditions in which tetrapyrrole metabolism is compromised.
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