Ueda Akihiro, Li Pinghua, Feng Yue, Vikram Meenu, Kim Sewon, Kang Chang Ho, Kang Jae Sook, Bahk Jeong Dong, Lee Sang Yeol, Fukuhara Toshiyuki, Staswick Paul E, Pepper Alan E, Koiwa Hisashi
Department of Horticultural Science and Vegetable and Fruit Improvement Center, Texas A&M University, College Station, TX 77843-2133, USA.
Plant Mol Biol. 2008 Aug;67(6):683-97. doi: 10.1007/s11103-008-9348-y. Epub 2008 May 28.
More than 20 genes in the Arabidopsis genome encode proteins similar to phosphatases that act on the carboxyl-terminal domain (CTD) of RNA polymerase II. One of these CTD-phosphatase-like (CPL) proteins, CPL2, dephosphorylates CTD-Ser5-PO4 in an intact RNA polymerase II complex and contains a double-stranded (ds)-RNA-binding motif (DRM). Although the dsRNA-binding activity of CPL2 DRM has not been shown to date, T-DNA insertion mutants that express CPL2 variants lacking either a part of DRM (cpl2-1) or the entire DRM (cpl2-2) exhibited leaf expansion defects, early flowering, low fertility, and increased salt sensitivity. cpl2 mutant plants produced shorter hypocotyls than wild-type plants in the light, but were indistinguishable from wild type in the dark. CPL2 was expressed in shoot and root meristems and vasculatures, expanding rosette leaves, and floral organs suggesting a focal role for growth. Microarray and RT-PCR analyses revealed that basal levels of several auxin-responsive transcripts were reduced in cpl2. On the other hand, the levels of endogenous auxin and its conjugates were similar in wild type and cpl2. Overexpression of ARF5 but not all activator ARF transcription factors restored the auxin-responsive DR5-GUS reporter gene expression and the leaf expansion of cpl2 mutant plants but not early flowering phenotype. These results establish CPL2 as a multifunctional regulator that modulates plant growth, stress, and auxin responses.
拟南芥基因组中有20多个基因编码的蛋白质与作用于RNA聚合酶II羧基末端结构域（CTD）的磷酸酶相似。其中一种CTD磷酸酶样（CPL）蛋白CPL2，能在完整的RNA聚合酶II复合物中使CTD-Ser5-PO4去磷酸化，并含有一个双链（ds）RNA结合基序（DRM）。尽管CPL2 DRM的dsRNA结合活性迄今尚未得到证实，但表达缺失部分DRM（cpl2-1）或整个DRM（cpl2-）的CPL2变体的T-DNA插入突变体表现出叶片扩展缺陷、早花、低育性和盐敏感性增加。cpl2突变体植株在光照下产生的下胚轴比野生型植株短，但在黑暗中与野生型无差异。CPL2在茎尖和根尖分生组织、维管组织、莲座叶扩展部位以及花器官中表达，表明其在生长过程中发挥关键作用。微阵列和RT-PCR分析显示，cpl2中几种生长素响应转录本的基础水平降低。另一方面，野生型和cpl2中内源生长素及其共轭物的水平相似。ARF5的过表达而非所有激活剂ARF转录因子恢复了cpl2突变体植株中生长素响应的DR5-GUS报告基因表达和叶片扩展，但未恢复早花表型。这些结果确立了CPL2作为一种多功能调节因子，可调节植物生长、胁迫和生长素反应。
