A nuclear-encoded sigma factor, Arabidopsis SIG6, recognizes sigma-70 type chloroplast promoters and regulates early chloroplast development in cotyledons
A nuclear-encoded sigma factor, Arabidopsis SIG6, recognizes sigma-70 type chloroplast promoters and regulates early chloroplast development in cotyledons
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DOI：
10.1111/j.1365-313x.2005.02362.x
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发表时间：
2005-04-01
期刊：
影响因子：
7.2
通讯作者：
Shiina, T
中科院分区：
文献类型：
--
作者：
Ishizaki, Y;Tsunoyama, Y;Shiina, T
真细菌类型的多亚单位质体RNA聚合酶(PEP)负责叶绿体的主要转录活动。PEP由叶绿体编码的核心亚基和多种核编码的Sigma因子之一组成，这些Sigma因子赋予PEP启动子特异性。因此，与PEP相关的sigma因子的替换被认为是叶绿体发育过程中转录模式转换的主要机制。叶绿体西格玛因子基因AtSIG6的零突变体(sig6-1)表现为子叶特有的淡绿色表型。在sig6-1突变体中，光依赖的叶绿体发育明显延迟。AtSIG6基因对突变体表型的遗传互补表明，AtSIG6在光依赖的叶绿体发育过程中起着关键作用。Northern和基于阵列的全局分析表明，在sig6-1突变体中，大多数依赖于PEP的基因的转录水平大大降低，但依赖于核编码的RNA聚合酶(NEP)的转录本的积累普遍增加。由于PEPα亚基和依赖PEP的trnV在sig6-1突变体中以正常水平积累，AtSIG6基因敲除突变体可能保留了功能性PEP，转录缺陷可能是由AtSIG6缺乏直接引起的。大多数AtSIG6依赖基因的前面都有由保守的-35/-10元件组成的sigma(70)型启动子。因此，在植物发育的早期，AtSIG6可能是叶绿体中的一个主要的通用西格玛因子。另一方面，在较老的幼苗中恢复了突变的表型。拟南芥可能含有另一种晚期通用西格玛因子，其启动子的特异性与AtSIG6的启动子特异度广泛重叠。
Eubacterial-type multi-subunit plastid RNA polymerase (PEP) is responsible for the principal transcription activity in chloroplasts. PEP is composed of plastid-encoded core subunits and one of multiple nuclear-encoded sigma factors that confer promoter specificity on PEP. Thus, the replacement of sigma factors associated with PEP has been assumed to be a major mechanism for the switching of transcription patterns during chloroplast development. The null mutant (sig6-1) of plastid sigma factor gene AtSIG6 exhibited a cotyledon-specific pale green phenotype. Light-dependent chloroplast development was significantly delayed in the sig6-1 mutant. Genetic complementation of the mutant phenotype by the AtSIG6 cDNA demonstrated that AtSIG6 plays a key role in light-dependent chloroplast development. Northern and array-based global analyses for plastid transcripts revealed that the transcript levels of most PEP-dependent genes were greatly reduced in the sig6-1 mutant, but that the accumulation of nuclear-encoded RNA polymerase (NEP)-dependent transcripts generally increased. As the PEP alpha subunit and PEP-dependent trnV accumulated at normal levels in the sig6-1 mutant, the AtSIG6 knockout mutant probably retained functional PEP, and the transcriptional defects are likely to have been directly caused by AtSIG6 deficiency. Most of the AtSIG6-dependent genes are preceded by sigma(70)-type promoters comprised of conserved -35/-10 elements. Thus, AtSIG6 may act as a major general sigma factor in chloroplasts during early plant development. On the other hand, the mutant phenotype was restored in older seedlings. Arabidopsis probably contains another late general sigma factor, the promoter specificity of which widely overlaps with that of AtSIG6.