Borisjuk N, Sitailo L, Adler K, Malysheva L, Tewes A, Borisjuk L, Manteuffel R
Institut für Pflanzengenetik und Kulturpflanzenforschung, Gatersleben, Germany.
Planta. 1998 Nov;206(4):504-14. doi: 10.1007/s004250050427.
The tissue-specific expression pattern and the intracellular distribution of the Ca(2+)-binding protein calreticulin at the mRNA and protein levels have been studied during somatic and zygotic embryogenesis of Nicotiana plumbaginifolia Viv. A full-length cDNA sequence encoding calreticulin was isolated from a lembda Zap cDNA library from early developmental stages of somatic embryogenesis. The deduced amino acid sequence of the calreticulin from N. plumbaginifolia shows high homology to the corresponding proteins of tobacco (98.2% identity), maize (80%) and barley (76.5%), and more than 55% homology to animal calreticulins, and the sequence motifs with established functions found in calreticulins of other species were quite conserved. Northern experiments revealed a developmental regulation of the calreticulin transcript with a maximum during the early stages of somatic embryogenesis and an auxin dependence during in-vitro cell culture. alpha-Naphthaleneacetic acid stimulated calreticulin expression whereas 2,4-dichlorophenoxyacetic acid reduced it. Immunohistological analysis of calreticulin distribution in the ovaries during zygotic embryogenesis showed that calreticulin biosynthesis started tissue specifically, with a high abundance in the endothelium of the integument in the ovules, followed by calreticulin accumulation in the embryo proper and in the associated endosperm at the late globular stage of embryogenesis. Using immunogold labeling, calreticulin was intracellularly localized with a high abundance to the Golgi compartment and to patches on the surface of dividing protoplasts. Smaller amounts were found in the endoplasmic reticulum and plasma membranes. The functional role of calreticulin in posttranslational processing and translocation processes, apart from its postulated function in cellular Ca2+ homeostasis, is discussed.
在白花烟草的体细胞胚胎发生和合子胚胎发生过程中，研究了Ca(2+)结合蛋白钙网蛋白在mRNA和蛋白质水平上的组织特异性表达模式及细胞内分布。从体细胞胚胎发生早期阶段的λZap cDNA文库中分离出编码钙网蛋白的全长cDNA序列。白花烟草钙网蛋白的推导氨基酸序列与烟草相应蛋白高度同源（同一性为98.2%），与玉米（80%）和大麦（76.5%）同源，与动物钙网蛋白的同源性超过55%，并且在其他物种钙网蛋白中发现的具有确定功能的序列基序相当保守。Northern实验揭示了钙网蛋白转录本的发育调控，在体细胞胚胎发生早期达到最大值，并且在体外细胞培养中依赖生长素。α-萘乙酸刺激钙网蛋白表达，而2,4-二氯苯氧乙酸则降低其表达。对合子胚胎发生过程中卵巢中钙网蛋白分布的免疫组织学分析表明，钙网蛋白的生物合成在组织特异性启动，在胚珠珠被的内皮中含量很高，随后在胚胎发育的晚期球形阶段，钙网蛋白在胚体和相关胚乳中积累。使用免疫金标记，钙网蛋白在细胞内高度定位于高尔基体区室和分裂原生质体表面的斑块。在内质网和质膜中发现的量较少。除了其在细胞Ca2+稳态中的假定功能外，还讨论了钙网蛋白在翻译后加工和转运过程中的功能作用。
