Abscisic acid induces rapid subnuclear reorganization in guard cells
Abscisic acid induces rapid subnuclear reorganization in guard cells
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DOI：
10.1104/pp.103.034728
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发表时间：
2004-04-01
期刊：
影响因子：
7.4
通讯作者：
Assmann, SM
中科院分区：
文献类型：
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作者：
Ng, CKY;Kinoshita, T;Assmann, SM
虽然植物激素脱落酸(ABA)被认为是基因转录和离子通道活性的调节因子(Rock，2000；Assmann和Wang 2001；Schroeder等人，2001；Finkelstein等人，2002)，但最近发现的RNA结合蛋白ABH1(ABA超敏)、SAD1(对ABA和干旱超敏感)和HYL1(低钠叶片)，它们的突变赋予了ABA超敏的表型(Lu和Fedoroff，2000；Hugouvieux等人，2001,2002；熊等人，2001)，这表明ABA可能也在转录后RNA加工中发挥重要作用。在这里，我们表明ABA动态调节保卫细胞的亚核结构，促进异质性核核糖核蛋白(HnRNP)型蛋白AKIP1的分裂，通过一个既有Ca21依赖步骤又有Ca21非依赖步骤的过程，需要一个活跃的转录机制。HnRNP是与RNA结合并影响其新陈代谢的mRNA-蛋白质复合体(mRNP蛋白质)(Kregc和Swanson，1999；Dreyfuss等人，2002)。HnRNP家族的成员参与RNA代谢的各个方面，包括mRNA前剪接、mRNA定位、mRNA稳定性、mRNA的核输出和翻译控制(Dreyfuss等人，1996,2002；Kregc和Swanson，1999；Mili等人，2001；Reed和Magni，2001)。HnRNPs与新生RNA转录本结合形成核糖核蛋白复合体(RNPs)。RNPs是高度动态的，在哺乳动物细胞中已经被证明，在mRNA成熟的不同阶段，hnRNPs与目标RNA结合或解离，直到形成一个不同的mRNP，并从细胞核转移到细胞质进行翻译启动(Dreyfuss等人，2002年)。在植物中，对hnRNP的功能知之甚少(Albaand Pages，1998；Lorkovic等人，2000；Lambermon等人，2002；Lorkovic和Barta，2002)。我们以前(Li等，2002)报道了AKIP1是一个来自蚕豆(Vicia Faba)的hnRNP样RNA结合蛋白。AKIP1与哺乳动物hnRNP A/B和D蛋白具有最高的序列同源性，并具有两个RNA识别基序。AKIP1被保卫细胞AAPK磷酸化，AAPK是一种ABA激活的、不依赖于Ca21的蛋白激酶，参与ABA调节气孔关闭和质膜阴离子通道活性(Li和Assmann，1996；Li等人，2000)。一旦磷酸化，AKIP1就有能力结合脱水蛋白mRNA，后者编码一类应激保护蛋白(Close，1996,1997)。ABA处理表达AKIP1-绿色荧光蛋白(GFP)的保卫细胞也导致AKIP1-GFP快速亚核聚集。在这份报告中，我们研究了与这一现象有关的信号转导机制。
While the phytohormone abscisic acid (ABA) is well established as a regulator of gene transcription and ion channel activity (Rock, 2000; Assmann and Wang 2001; Schroeder et al., 2001; Finkelstein et al., 2002), recent identification of RNA-binding proteins ABH1 (ABA hypersensitive), SAD1 (supersensitive to ABA and drought), and HYL1 (hyponastic leaves), whose mutation confers an ABA-hypersensitive phenotype (Lu and Fedoroff, 2000; Hugouvieux et al., 2001, 2002; Xiong et al., 2001), suggests that ABA may also play important roles in posttranscriptional RNA processing. Here we show that ABA dynamically regulates subnuclear architecture in guard cells, promoting the partitioning of a heterogeneous nuclear ribonucleoprotein (hnRNP)-type protein, AKIP1, into discrete subnuclear bodies or speckles via a process that has both Ca21-dependent and Ca21-independent steps and requires an active transcriptional machinery. hnRNPs are mRNA-protein complex proteins (mRNP proteins) that bind RNA and affect its metabolism (Krecic and Swanson, 1999; Dreyfuss et al., 2002). Members of the hnRNP family are involved in all aspects of RNA metabolism, including pre-mRNA splicing, mRNA localization, mRNA stability, nuclear export of mRNA, and translational control (Dreyfuss et al., 1996, 2002; Krecic and Swanson, 1999; Mili et al., 2001; Reed and Magni, 2001). Binding of hnRNPs with nascent RNA transcripts results in the formation of ribonucleoprotein complexes (RNPs). RNPs are highly dynamic, and it has been demonstrated in mammalian cells that hnRNPs bind or dissociate from the target RNA at various stages of mRNA maturation until a distinct mRNP is formed and translocated from the nucleus to the cytoplasm for translation initiation (Dreyfuss et al., 2002). In plants, little is known about the function of hnRNPs (Albaand Pages, 1998; Lorkovic et al., 2000; Lambermon et al., 2002; Lorkovic and Barta, 2002). We reported previously (Li et al., 2002) that AKIP1 is an hnRNP-like RNA binding protein from broad bean (Vicia faba). AKIP1 exhibits greatest sequence homology to mammalian hnRNP A/B and D proteins and has two RNA-recognition motifs. AKIP1 is phosphorylated by guard cell AAPK, an ABA-activated, Ca21-independent protein kinase involved in ABA-regulation of stomatal closure and plasma membrane anion channel activity (Li and Assmann, 1996; Li et al., 2000). Upon phosphorylation, AKIP1 becomes competent to bind dehydrin mRNA, which encodes a class of stress-protectant proteins (Close, 1996, 1997). ABA treatment of guard cells expressing AKIP1-green fluorescent protein (GFP) also results in rapid subnuclear clustering of AKIP1-GFP. In this report, we examine the signal transduction machinery involved in this phenomenon.