Hess W R, Prombona A, Fieder B, Subramanian A R, Börner T
Humboldt University Berlin, Department of Genetics, Germany.
EMBO J. 1993 Feb;12(2):563-71. doi: 10.1002/j.1460-2075.1993.tb05688.x.
Transcription of plastid genes and transcript accumulation were investigated in white leaves of the albostrians mutant of barley (Hordeum vulgare) and in heat-bleached leaves of rye (Secale cereale) as well as in normal green leaves of both species. Cells of white leaves of the mutant and cells of heat-bleached leaves bear undifferentiated plastids lacking ribosomes and, consequently, plastid translation products, among them the subunits of a putative chloroplast RNA polymerase encoded by the plastid genes rpoA, B, C1 and C2. The following results were obtained. (i) Plastid genes are transcribed despite the lack of chloroplast gene-encoded RNA polymerase subunits. The plastid origin of these transcripts was proven. This finding provides evidence for the existence of a plastid RNA polymerase encoded entirely by nuclear genes. (ii) Transcripts of the rpo genes and of rps15, but not of genes involved in photosynthesis and related processes (psbA, rbcL, atpI-H), were abundantly accumulated in ribosome-deficient plastids. In contrast, chloroplasts accumulated transcripts of photosynthetic, but not of the rpo genes. (iii) Differences in transcript accumulation between chloroplasts and ribosome-deficient plastids are due to different relative transcription rates and different transcript stability. (iv) The observed differences in transcription are not caused by an altered pattern of methylation of plastid DNA. Thus, the prokaryotic plastid genome of higher plants is transcribed by two RNA polymerases. The observed differences in transcription between chloroplasts and undifferentiated plastids might reflect different functions of the two enzymes.
对大麦（Hordeum vulgare）白化突变体的白色叶片、黑麦（Secale cereale）热漂白叶片以及这两个物种的正常绿色叶片中的质体基因转录和转录本积累进行了研究。突变体白色叶片的细胞和热漂白叶片的细胞含有未分化的质体，这些质体缺乏核糖体，因此也缺乏质体翻译产物，包括由质体基因rpoA、B、C1和C2编码的一种假定叶绿体RNA聚合酶的亚基。获得了以下结果。（i）尽管缺乏叶绿体基因编码的RNA聚合酶亚基，质体基因仍可转录。这些转录本的质体来源得到了证实。这一发现为完全由核基因编码的质体RNA聚合酶的存在提供了证据。（ii）rpo基因和rps15的转录本，但参与光合作用及相关过程的基因（psbA、rbcL、atpI-H）的转录本，在缺乏核糖体的质体中大量积累。相反，叶绿体积累光合作用相关基因的转录本，而不是rpo基因的转录本。（iii）叶绿体和缺乏核糖体的质体之间转录本积累的差异是由于相对转录速率不同和转录本稳定性不同。（iv）观察到的转录差异不是由质体DNA甲基化模式的改变引起的。因此，高等植物的原核质体基因组由两种RNA聚合酶转录。叶绿体和未分化质体之间观察到的转录差异可能反映了这两种酶的不同功能。
