Phage-type RNA polymerase RPOTmp transcribes the rrn operon from the PC promoter at early developmental stages in Arabidopsis.
ABSTRACT The plastid genome of higher plants is transcribed by two different types of RNA polymerases named nucleus encoded RNA polymerase (NEP) and plastid encoded RNA polymerase. Plastid encoded RNA polymerase is a multimeric enzyme comparable to eubacterial RNA polymerases. NEP enzymes represent a small family of monomeric phage-type RNA polymerases. Dicotyledonous plants harbor three different phage-type enzymes, named RPOTm, RPOTp, and RPOTmp. RPOTm is exclusively targeted to mitochondria, RPOTp is exclusively targeted to plastids, and RPOTmp is targeted to plastids as well as to mitochondria. In this article, we have made use of RPOTp and RPOTmp T-DNA insertion mutants to answer the question of whether both plastid-located phage-type RNA polymerases have overlapping or specific functions in plastid transcription. To this aim, we have analyzed accD and rpoB messenger RNAs (mRNA; transcribed from type I NEP promoters), clpP mRNA (transcribed from the -59 type II NEP promoter), and the 16S rRNA (transcribed from the exceptional PC NEP promoter) by primer extension. Results suggest that RPOTp represents the principal RNA polymerase for transcribing NEP-controlled mRNA genes during early plant development, while RPOTmp transcribes specifically the rrn operon from the PC promoter during seed imbibition.
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ABSTRACT: Plant sigma factors determine the promoter specificity of the major RNA polymerase of plastids and thus regulate the first level of plastome gene expression. In plants, sigma factors are encoded by a small family of nuclear genes, and it is not yet clear if the family members are functionally redundant or each paralog plays a particular role. The review presents the analysis of the information on plant sigma factors obtained since their discovery a decade ago and focuses on similarities and differences in structure and functions of various paralogs. Special attention is paid to their interaction with promoters, the regulation of their expression, and their role in the development of a whole plant. The analysis suggests that though plant sigma factors are basically similar, at least some of them perform distinct functions. Finally, the work presents the scheme of this gene family evolution in higher plants.Plant Cell Reports 08/2007; 26(7):845-59. · 2.27 Impact Factor
Article: The A and B forms of plastid DNA-dependent RNA polymerase from mustard (Sinapis alba L.) transcribe the same genes in a different developmental context.[show abstract] [hide abstract]
ABSTRACT: Two RNA polymerases, termed A (cp-pol A) and B (cp-pol B), are known to be present in mustard plastids. In vitro, the two enzymes have different requirements for DNA binding, but both bind to, and transcribe from, the same set of chloroplast promoters. The B enzyme is sensitive to rifampicin (Rif), whereas the A enzyme is not. When seedlings were grown in the presence of Rif, RNA pool sizes of the photosynthesis-related plastid genes rbcL and psbA were smaller than in untreated controls, whereas transcripts of the non-photosynthetic genes rps16, trnG, rrn and rpoB remained virtually unaffected by the drug. The Rif inhibition patterns of rbcL and psbA transcripts reflect the relative abundance of the A and B enzymes at different stages and light/dark conditions. These genes can thus be transcribed by either of the two enzymes in vivo, whereas the non-photosynthetic genes are transcribed mostly or exclusively by the A enzyme, or by another Rif-resistant plastid polymerase. Among several nuclear gene transcripts that were tested for Rif inhibition, only those of the RbcS gene family for the plastid-bound small subunit of Rubisco revealed a decrease in pool size, which may imply that mechanisms exist that serve to coordinate patterns of gene expression in the different cellular compartments.MGG - Molecular and General Genetics 01/1998; 257(1):35-44.
Nature Reviews Genetics 03/2004; 5(2):123-35. · 38.08 Impact Factor