Abstract
Although transcription termination is essential to generate functional RNAs, its underlying molecular mechanisms are still poorly understood in plastids of vascular plants. Here, we show that the RNA binding protein RHON1 participates in transcriptional termination of rbcL (encoding large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase) in Arabidopsis thaliana. Inactivation of RHON1 leads to enhanced rbcL read-through transcription and to aberrant accD (encoding β-subunit of the acetyl-CoA carboxylase) transcriptional initiation, which may result from inefficient transcription termination of rbcL. RHON1 can bind to the mRNA as well as to single-stranded DNA of rbcL, displays an RNA-dependent ATPase activity, and terminates transcription of rbcL in vitro. These results suggest that RHON1 terminates rbcL transcription using an ATP-driven mechanism similar to that of Rho of Escherichia coli. This RHON1-dependent transcription termination occurs in Arabidopsis but not in rice (Oryza sativa) and appears to reflect a fundamental difference between plastomes of dicotyledonous and monocotyledonous plants. Our results point to the importance and significance of plastid transcription termination and provide insights into its machinery in an evolutionary context.
Highlights
Transcription termination, which involves arrest of RNA biosynthesis, release of the transcript, and dissociation of the RNA polymerase from the DNA template, is essential for proper gene expression
RHON1 Is Involved in Transcription Termination of rbcL in Addition to RNA Processing
Based on the data presented here, we propose that inefficient transcription termination may account for the overaccumulation of rbcL polycistronic transcripts in rhon1-2
Summary
Transcription termination, which involves arrest of RNA biosynthesis, release of the transcript, and dissociation of the RNA polymerase from the DNA template, is essential for proper gene expression. Most plastid genes contain inverted repeat sequences at their 39 ends that are able to form stem-loop structures (Sugita and Sugiura, 1984; Kirsch et al, 1986) Such structures were initially assumed to act as transcription terminators, in a similar way as Rho-independent terminators (Sugita and Sugiura, 1984; Kirsch et al, 1986). Both in vitro and in vivo assays have shown that in plastids, 39 inverted repeat sequences function as mRNA processing and stabilizing elements rather than as efficient terminators (Stern and Gruissem, 1987; Monde et al, 2000). No factors involved in plastid transcription termination have been identified and characterized in vascular plants
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