State Agricultural Biotechnology Centre, Murdoch University, & Western Australian Department of Agriculture & Food, Murdoch, WA 6150, Australia.
BMC Plant Biol. 2010 Sep 27;10:212. doi: 10.1186/1471-2229-10-212.
Isoprenylcysteine methylesterases (ICME) demethylate prenylated protein in eukaryotic cell. Until now, knowledge about their molecular information, localization and expression pattern is largely unavailable in plant species. One ICME in Arabidopsis, encoded by At5g15860, has been identified recently. Over-expression of At5g15860 caused an ABA hypersensitive phenotype in transgenic Arabidopsis plants, indicating that it functions as a positive regulator of ABA signaling. Moreover, ABA induced the expression of this gene in Arabidopsis seedlings. The current study extends these findings by examining the sub-cellular localization, expression profiling, and physiological functions of ICME and two other ICME-like proteins, ICME-LIKE1 and ICME-LIKE2, which were encoded by two related genes At1g26120 and At3g02410, respectively.
Bioinformatics investigations showed that the ICME and other two ICME-like homologs comprise a small subfamily of carboxylesterase (EC 3.1.1.1) in Arabidopsis. Sub-cellular localization of GFP tagged ICME and its homologs showed that the ICME and ICME-like proteins are intramembrane proteins predominantly localizing in the endoplasmic reticulum (ER) and Golgi apparatus. Semi-quantitative and real-time quantitative PCR revealed that the ICME and ICME-like genes are expressed in all examined tissues, including roots, rosette leaves, cauline leaves, stems, flowers, and siliques, with differential expression levels. Within the gene family, the base transcript abundance of ICME-LIKE2 gene is very low with higher expression in reproductive organs (flowers and siliques). Time-course analysis uncovered that both ICME and ICME-like genes are up-regulated by mannitol, NaCl and ABA treatment, with ICME showing the highest level of up-regulation by these treatments. Heat stress resulted in up-regulation of the ICME gene significantly but down-regulation of the ICME-LIKE1 and ICME-LIKE2 genes. Cold and dehydration stimuli led to no significant change of both ICME and ICME-like gene expression. Mutant icme-like2-1 showed increased sensitivity to ABA but slightly decreased sensitivity to salt and osmotic stresses during seed germination.
It is concluded that the ICME family is involved in stress and ABA signaling in Arabidopsis, probably through mediating the process of demethylating prenylated proteins. Identification of these prenylated proteins will help to better understand the significance of protein prenylation in Planta.
异戊烯基半胱氨酸甲硫醚酶（ICME）在真核细胞中使异戊烯基化蛋白去甲基化。直到现在，在植物物种中，关于它们的分子信息、定位和表达模式的知识还很缺乏。拟南芥中一个由 At5g15860 编码的 ICME 最近被鉴定出来。过表达 At5g15860 导致转基因拟南芥植物 ABA 超敏表型，表明它作为 ABA 信号的正调节剂发挥作用。此外，ABA 在拟南芥幼苗中诱导该基因的表达。本研究通过研究 ICME 和另外两个 ICME 样蛋白（ICME-LIKE1 和 ICME-LIKE2）的亚细胞定位、表达谱和生理功能，扩展了这些发现，这两个 ICME 样蛋白分别由两个相关基因 At1g26120 和 At3g02410 编码。
生物信息学研究表明，ICME 和其他两个 ICME 样同系物在拟南芥中构成了羧酸酯酶（EC 3.1.1.1）的一个小亚家族。GFP 标记的 ICME 及其同源物的亚细胞定位表明，ICME 和 ICME 样蛋白是主要定位于内质网（ER）和高尔基体的跨膜蛋白。半定量和实时定量 PCR 显示，ICME 和 ICME 样基因在所有检测的组织中表达，包括根、莲座叶、茎生叶、茎、花和蒴果，表达水平不同。在基因家族中，ICME-LIKE2 基因的基础转录丰度非常低，在生殖器官（花和蒴果）中表达水平较高。时程分析显示，甘露醇、NaCl 和 ABA 处理均能上调 ICME 和 ICME 样基因的表达，其中 ICME 基因的上调水平最高。热应激显著上调 ICME 基因的表达，但下调 ICME-LIKE1 和 ICME-LIKE2 基因的表达。冷和脱水刺激对 ICME 和 ICME 样基因的表达没有显著影响。icme-like2-1 突变体在种子萌发过程中对 ABA 的敏感性增加，但对盐和渗透胁迫的敏感性略有降低。
综上所述，ICME 家族参与拟南芥的应激和 ABA 信号转导，可能通过介导去甲基化异戊烯基化蛋白的过程。这些异戊烯基化蛋白的鉴定将有助于更好地理解蛋白质异戊烯化在植物中的意义。
