Sigma factors are dissociable subunits of bacterial RNA polymerase that ensure efficient transcription initiation from gene promoters. Owing to their prokaryotic origin, chloroplasts possess a typical bacterial RNA polymerase together with its sigma factor subunit. The higher plant Arabidopsis thaliana contain as many as six sigma factors for the hundred or so of its chloroplast genes. The role of this relatively large number of transcription initiation factors for the miniature chloroplast genome, however, is not fully understood. Using two Arabidopsis T-DNA insertion mutants, we show that sigma factor 1 (SIG1) initiates transcription of a specific subset of chloroplast genes. We further show that the photosynthetic control of PSI reaction center gene transcription requires complementary regulation of the nuclear SIG1 gene at the transcriptional level. This SIG1 gene regulation is dependent on both a plastid redox signal and a light signal transduced by the phytochrome photoreceptor.

中文翻译：

---

Sigma因子1在叶绿体基因转录和光合光适应中的作用。

Sigma因子是细菌RNA聚合酶的可分解亚基，可确保从基因启动子进行有效的转录起始。由于其原核起源，叶绿体具有典型的细菌RNA聚合酶及其sigma因子亚基。高等植物拟南芥含有大约六个σ因子，涉及其约100个叶绿体基因。但是，对于微型叶绿体基因组，这种相对大量的转录起始因子的作用尚不完全清楚。使用两个拟南芥T-DNA插入突变体，我们表明sigma因子1（SIG1）启动叶绿体基因的特定子集的转录。我们进一步表明，PSI反应中心基因转录的光合作用控制需要在转录水平上对核SIG1基因的互补调控。SIG1基因调节既依赖于质体氧化还原信号，又依赖于由植物色素感光器转导的光信号。