Department of Plant Molecular Biology, University of Delhi South Campus, New Delhi-110021, India.
BMC Genomics. 2010 Feb 8;11:95. doi: 10.1186/1471-2164-11-95.
ClpB-cyt/HSP100 protein acts as chaperone, mediating disaggregation of denatured proteins. Previous studies have shown that ClpB-cyt/HSP100 gene belongs to the group class I Clp ATPase proteins and ClpB-cyt/HSP100 transcript is regulated by heat stress and developmental cues.
Nine ORFs were noted to constitute rice class I Clp ATPases in the following manner: 3 ClpB proteins (ClpB-cyt, Os05g44340; ClpB-m, Os02g08490; ClpB-c, Os03g31300), 4 ClpC proteins (ClpC1, Os04g32560; ClpC2, Os12g12580; ClpC3, Os11g16590; ClpC4, Os11g16770) and 2 ClpD proteins (ClpD1, Os02g32520; ClpD2, Os04g33210). Using the respective signal sequences cloned upstream to GFP/CFP reporter proteins and transient expression studies with onion epidermal cells, evidence is provided that rice ClpB-m and Clp-c proteins are indeed localized to their respective cell locations mitochondria and chloroplasts, respectively. Associated with their diverse cell locations, domain structures of OsClpB-c, OsClpB-m and OsClpB-cyt proteins are noted to possess a high-level conservation. OsClpB-cyt transcript is shown to be enriched at milk and dough stages of seed development. While expression of OsClpB-m was significantly less as compared to its cytoplasmic and chloroplastic counterparts in different tissues, this transcript showed highest heat-induced expression amongst the 3 ClpB proteins. OsClpC1 and OsClpC2 are predicted to be chloroplast-localized as is the case with all known plant ClpC proteins. However, the fact that OsClpC3 protein appears mitochondrial/chloroplastic with equal probability and OsClpC4 a plasma membrane protein reflects functional diversity of this class. Different class I Clp ATPase transcripts were noted to be cross-induced by a host of different abiotic stress conditions. Complementation assays of Deltahsp104 mutant yeast cells showed that OsClpB-cyt, OsClpB-m, OsClpC1 and OsClpD1 have significantly positive effects. Remarkably, OsClpD1 gene imparted appreciably high level tolerance to the mutant yeast cells.
Rice class I Clp ATPase gene family is constituted of 9 members. Of these 9, only 3 belonging to ClpB group are heat stress regulated. Distribution of ClpB proteins to different cell organelles indicates that their functioning might be critical in different cell locations. From the complementation assays, OsClpD1 appears to be more effective than OsClpB-cyt protein in rescuing the thermosensitive defect of the yeast ScDeltahsp104 mutant cells.
ClpB-cyt/HSP100 蛋白作为伴侣蛋白，介导变性蛋白的解聚。先前的研究表明，ClpB-cyt/HSP100 基因属于 I 类 Clp ATPase 蛋白，ClpB-cyt/HSP100 转录本受热应激和发育线索的调节。
注意到 9 个 ORF 以以下方式构成水稻 I 类 Clp ATPase：3 个 ClpB 蛋白（ClpB-cyt、Os05g44340；ClpB-m、Os02g08490；ClpB-c、Os03g31300）、4 个 ClpC 蛋白（ClpC1、Os04g32560；ClpC2、Os12g12580；ClpC3、Os11g16590；ClpC4、Os11g16770）和 2 个 ClpD 蛋白（ClpD1、Os02g32520；ClpD2、Os04g33210）。使用分别克隆在上游的信号序列到 GFP/CFP 报告蛋白上，并通过洋葱表皮细胞进行瞬时表达研究，提供了证据表明，水稻 ClpB-m 和 Clp-c 蛋白确实分别定位于它们各自的细胞位置线粒体和叶绿体。与它们不同的细胞位置相关，OsClpB-c、OsClpB-m 和 OsClpB-cyt 蛋白的结构域结构被注意到具有高度的保守性。OsClpB-cyt 转录本在种子发育的牛奶和面团阶段丰富。虽然 OsClpB-m 的表达与细胞质和叶绿体对应物相比显著较少，但在 3 个 ClpB 蛋白中，该转录本表现出最高的热诱导表达。OsClpC1 和 OsClpC2 被预测为定位于叶绿体，就像所有已知的植物 ClpC 蛋白一样。然而，OsClpC3 蛋白似乎具有相等的线粒体/叶绿体概率，而 OsClpC4 蛋白是质膜蛋白，这反映了该类别的功能多样性。不同的 I 类 Clp ATPase 转录本被注意到受到多种不同非生物胁迫条件的交叉诱导。Deltahsp104 突变酵母细胞的互补测定表明，OsClpB-cyt、OsClpB-m、OsClpC1 和 OsClpD1 具有显著的正效应。值得注意的是，OsClpD1 基因赋予突变酵母细胞相当高的耐受力。
水稻 I 类 Clp ATPase 基因家族由 9 个成员组成。在这 9 个成员中，只有属于 ClpB 组的 3 个受到热应激的调节。ClpB 蛋白在不同细胞器官中的分布表明，它们的功能在不同的细胞位置可能是关键的。从互补测定来看，OsClpD1 似乎比 OsClpB-cyt 蛋白更有效地挽救酵母 ScDeltahsp104 突变细胞的热敏缺陷。
