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 259 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.

Intraplastidial trafficking of a phage-type RNA polymerase is mediated by a thylakoid RING-H2 protein

“…However, only two genes (RPOTp and RPOTm) have been detected in monocotyledons (4,7,8), thus raising the question of the function of RPOTmp in plastids of dicotyledon plants. Recent results have shown that RPOTp can be regarded as the principal NEP enzyme in chloroplasts playing an important role in chloroplast transcription, biogenesis, and mesophyll cell proliferation (9,10). Results obtained with RPOTmp indicate partial replacement of RPOTp in RPOTp mutants (10,11), an early function in lightinduced accumulation of several plastid mRNAs (12,13), and specific transcription of the rrn operon of Arabidopsis from the PC promoter during seed imbibition and germination (10).…”

“…Recently, we have shown that the plastid phage-type RNA polymerase RPOTmp transcribes specifically the rrn operon at the PC promoter, and in this way is distinct from the second plastid phage-type RNA polymerase RPOTp (10). To further characterize the way of functioning of this phage-type RNA polymerase, we have used the yeast two-hybrid system to clone cDNAs encoding RPOTmp interacting proteins.…”

The Primary Transcriptome of Barley Chloroplasts: Numerous Noncoding RNAs and the Dominating Role of the Plastid-Encoded RNA Polymerase

“…Moreover, the Arabidopsis RPOTmp gene coding for a mitochondrial and chloroplast (NEP) RNA polymerase is particularly active in nongreen tissues and in very young leaves (Emanuel et al, 2006). Similarly, the expression of the previously described NEP-dependent genes was distinctly higher in developing compared with mature chloroplasts (Courtois et al, 2007;Zoschke et al, 2007). Therefore, it should be worth investigating developing chloroplasts for the usage of the NEP promoters exclusively detected in white albostrians plastids.…”

“…It recognizes distinct types of promoters with sequence similarity to plant mitochondrial promoters (Allison et al, 1996;Vera et al, 1996;Liere and Bö rner, 2007). NEP promoters were found to be more active in early leaf development, while transcription activity of PEP is reported to increase during chloroplast maturation (Courtois et al, 2007;Swiatecka-Hagenbruch et al, 2008). According to the current view, based on studies of only a small subset of plastid genes, most genes coding for housekeeping proteins are transcribed by both PEP and NEP; genes of photosystems I and II are completely dependent on PEP transcription; and a few housekeeping genes, including the rpoB operon, are transcribed exclusively from NEP promoters (Hajdukiewicz et al, 1997;SwiateckaHagenbruch et al, 2007).…”

Expression of the chloroplast genome: modern concepts and experimental approaches

“…Показана функциональная значимость RpoTp как на ранней, так и на поздней стадиях вегетативного развития растений (арабидопсис). RpoTmp особенно важна на ранней стадии (арабидопсис), на которой она выполняет специфическую функцию транскрипции rrn оперона (Courtois et al, 2007).…”