Constitutive BiP protein accumulation in Arabidopsis mutants defective in a gene encoding chloroplast-resident stearoyl-acyl carrier protein desaturase
Constitutive BiP protein accumulation in Arabidopsis mutants defective in a gene encoding chloroplast-resident stearoyl-acyl carrier protein desaturase
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DOI：
10.1111/gtc.12585
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发表时间：
2018-06-01
期刊：
影响因子：
2.1
通讯作者：
Koizumi, Nozomu
中科院分区：
文献类型：
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作者：
Iwata, Yuji;Iida, Tsukasa;Koizumi, Nozomu
未折叠蛋白质反应（UPR）发生在内质网（ER）中蛋白质折叠和成熟受到干扰时。在UPR过程中，包括编码ER驻留分子伴侣的基因在内的许多基因被诱导。在拟南芥中，BiP 3已被用作UPR标记基因，其表达响应于ER胁迫而被强烈诱导。在这项研究中，我们诱变拟南芥植物表达β-葡萄糖醛酸酶（GUS）基因的BiP 3启动子的控制下，并分离出一个突变体，表现出较强的GUS活性，而不与ER应激诱导剂处理。通过全基因组测序，我们在突变体中鉴定出一个致病基因为水杨酸不敏感性的供应者2（SSI 2），其编码硬脂酰酰基载体蛋白去饱和酶，该酶在叶绿体中将硬脂酸转化为油酸。除了GUS蛋白，ssi 2突变体积累内源性BiP 3蛋白，而无需任何应激试剂处理。有趣的是，虽然内源性BiP 3蛋白质积累的程度在ssi 2突变体是可比的，在野生型植物与ER应激诱导剂衣霉素处理，少得多的BiP 3转录检测到的ssi 2突变体相比，衣霉素处理的野生型植物。我们的发现表明叶绿体中的脂肪酸代谢和ER功能之间存在遗传联系。
The unfolded protein response (UPR) occurs when protein folding and maturation are disturbed in the endoplasmic reticulum (ER). During the UPR, a number of genes including those encoding ER-resident molecular chaperones are induced. In Arabidopsis, BiP3 has been used as a UPR marker gene whose expression is strongly induced in response to ER stress. In this study, we mutagenized Arabidopsis plants expressing -glucuronidase (GUS) gene under the control of BiP3 promoter and isolated a mutant that exhibits strong GUS activity without treatment with ER stress inducers. By whole genome sequencing, we identified a causal gene in the mutant as SUPPRESSOR OF SALICYLIC ACID INSENSITIVITY2 (SSI2), which encodes stearoyl-acyl carrier protein desaturase that converts stearic acids to oleic acids in the chloroplasts. In addition to GUS proteins, the ssi2 mutant accumulates endogenous BiP3 proteins without treatment by any stress reagents. Interestingly, although the degree of endogenous BiP3 protein accumulation in the ssi2 mutant was comparable to that in wild-type plants treated with the ER stress inducer tunicamycin, much less BiP3 transcripts were detected in the ssi2 mutant compared to tunicamycin-treated wild-type plants. Our finding suggests a genetic link between fatty acid metabolism in the chloroplasts and ER functions.