Mangelsen Elke, Kilian Joachim, Berendzen Kenneth W, Kolukisaoglu Uner H, Harter Klaus, Jansson Christer, Wanke Dierk
Department of Plant Biology and Forest Genetics, The Swedish University of Agricultural Sciences (SLU), PO Box 7080, SE-750 07Uppsala, Sweden.
BMC Genomics. 2008 Apr 28;9:194. doi: 10.1186/1471-2164-9-194.
WRKY proteins belong to the WRKY-GCM1 superfamily of zinc finger transcription factors that have been subject to a large plant-specific diversification. For the cereal crop barley (Hordeum vulgare), three different WRKY proteins have been characterized so far as regulators in sucrose signaling, pathogen defense, and in response to cold and drought. However, their phylogenetic relationship remained unresolved.
In this study, we used available sequence information to identify a minimum number of 45 barley WRKY transcription factor (HvWRKY) genes. According to their structural features, the HvWRKY factors were classified into the previously defined polyphyletic WRKY subgroups 1 to 3. Furthermore, we could assign putative orthologs of the HvWRKY proteins in Arabidopsis and rice. While in most cases clades of orthologous proteins were formed within each group or subgroup, other clades were composed of paralogous proteins for the grasses and Arabidopsis only, which is indicative of specific gene radiation events. To gain insight into their putative functions, we examined expression profiles of WRKY genes from publicly available microarray data resources and found group specific expression patterns. While putative orthologs of the HvWRKY transcription factors have been inferred from phylogenetic sequence analysis, we performed a comparative expression analysis of WRKY genes in Arabidopsis and barley. Indeed, highly correlative expression profiles were found between some of the putative orthologs.
HvWRKY genes have not only undergone radiation in monocot or dicot species, but exhibit evolutionary traits specific to grasses. HvWRKY proteins exhibited not only sequence similarities between orthologs with Arabidopsis, but also relatedness in their expression patterns. This correlative expression is indicative for a putative conserved function of related WRKY proteins in monocot and dicot species.
WRKY蛋白属于锌指转录因子的WRKY - GCM1超家族，该家族经历了大规模的植物特异性多样化。对于谷类作物大麦（Hordeum vulgare），迄今为止，已有三种不同的WRKY蛋白被鉴定为蔗糖信号传导、病原体防御以及对寒冷和干旱响应的调节因子。然而，它们的系统发育关系仍未解决。
在本研究中，我们利用现有序列信息鉴定出至少45个大麦WRKY转录因子（HvWRKY）基因。根据其结构特征，HvWRKY因子被分类到先前定义的多系WRKY亚组1至3中。此外，我们还确定了拟南芥和水稻中HvWRKY蛋白的推定直系同源物。虽然在大多数情况下，直系同源蛋白的分支在每个组或亚组内形成，但其他分支仅由禾本科植物和拟南芥的旁系同源蛋白组成，这表明存在特定的基因辐射事件。为了深入了解它们的推定功能，我们从公开的微阵列数据资源中检查了WRKY基因的表达谱，并发现了组特异性表达模式。虽然通过系统发育序列分析推断出了HvWRKY转录因子的推定直系同源物，但我们对拟南芥和大麦中的WRKY基因进行了比较表达分析。实际上，在一些推定的直系同源物之间发现了高度相关的表达谱。
HvWRKY基因不仅在单子叶或双子叶物种中经历了辐射，而且表现出禾本科植物特有的进化特征。HvWRKY蛋白不仅在与拟南芥的直系同源物之间表现出序列相似性，而且在其表达模式上也具有相关性。这种相关表达表明相关WRKY蛋白在单子叶和双子叶物种中可能具有保守功能。
