Wang Dong, Amornsiripanitch Nita, Dong Xinnian
Developmental, Cell and Molecular Biology Group, Department of Biology, Duke University, Durham, North Carolina, United States of America.
PLoS Pathog. 2006 Nov;2(11):e123. doi: 10.1371/journal.ppat.0020123.
Many biological processes are controlled by intricate networks of transcriptional regulators. With the development of microarray technology, transcriptional changes can be examined at the whole-genome level. However, such analysis often lacks information on the hierarchical relationship between components of a given system. Systemic acquired resistance (SAR) is an inducible plant defense response involving a cascade of transcriptional events induced by salicylic acid through the transcription cofactor NPR1. To identify additional regulatory nodes in the SAR network, we performed microarray analysis on Arabidopsis plants expressing the NPR1-GR (glucocorticoid receptor) fusion protein. Since nuclear translocation of NPR1-GR requires dexamethasone, we were able to control NPR1-dependent transcription and identify direct transcriptional targets of NPR1. We show that NPR1 directly upregulates the expression of eight WRKY transcription factor genes. This large family of 74 transcription factors has been implicated in various defense responses, but no specific WRKY factor has been placed in the SAR network. Identification of NPR1-regulated WRKY factors allowed us to perform in-depth genetic analysis on a small number of WRKY factors and test well-defined phenotypes of single and double mutants associated with NPR1. Among these WRKY factors we found both positive and negative regulators of SAR. This genomics-directed approach unambiguously positioned five WRKY factors in the complex transcriptional regulatory network of SAR. Our work not only discovered new transcription regulatory components in the signaling network of SAR but also demonstrated that functional studies of large gene families have to take into consideration sequence similarity as well as the expression patterns of the candidates.
许多生物过程受转录调节因子的复杂网络控制。随着微阵列技术的发展，可以在全基因组水平上检测转录变化。然而，这种分析往往缺乏关于给定系统各组成部分之间层次关系的信息。系统获得性抗性（SAR）是一种可诱导的植物防御反应，涉及水杨酸通过转录辅因子NPR1诱导的一系列转录事件。为了在SAR网络中识别其他调控节点，我们对表达NPR1-GR（糖皮质激素受体）融合蛋白的拟南芥植株进行了微阵列分析。由于NPR1-GR的核转位需要地塞米松，我们能够控制NPR1依赖性转录并鉴定NPR1的直接转录靶标。我们发现NPR1直接上调8个WRKY转录因子基因的表达。这个由74个转录因子组成的大家族参与了各种防御反应，但尚未有特定的WRKY因子被纳入SAR网络。鉴定出NPR1调控的WRKY因子使我们能够对少数WRKY因子进行深入的遗传分析，并测试与NPR1相关的单突变体和双突变体的明确表型。在这些WRKY因子中，我们发现了SAR的正调控因子和负调控因子。这种基于基因组学的方法明确地将5个WRKY因子定位在SAR复杂的转录调控网络中。我们的工作不仅在SAR信号网络中发现了新的转录调控成分，还表明对大基因家族的功能研究必须考虑序列相似性以及候选基因的表达模式。
