Two Related RNA-editing Proteins Target the Same Sites in Mitochondria of Arabidopsis thaliana

Daniil Verbitskiy,Anja Zehrmann,Axel Brennicke,Barbara Härtel,Mizuki Takenaka

doi:10.1074/jbc.m112.397992

Abstract

The facilitators for specific cytosine-to-uridine RNA-editing events in plant mitochondria and plastids are pentatricopeptide repeat (PPR)-containing proteins with specific additional C-terminal domains. Here we report the related PPR proteins mitochondrial editing factor 8 (MEF8) and MEF8S with only five such repeats each to be both involved in RNA editing at the same two sites in mitochondria of Arabidopsis thaliana. Mutants of MEF8 show diminished editing in leaves but not in pollen, whereas mutants of the related protein MEF8S show reduced RNA editing in pollen but not in leaves. Overexpressed MEF8 or MEF8S both increase editing at the two target sites in a mef8 mutant. Double mutants of MEF8 and MEF8S are not viable although both identified target sites are in mRNAs for nonessential proteins. This suggests that MEF8 and MEF8S may have other essential functions beyond these two editing sites in complex I mRNAs.

Highlights

Pentatricopeptide repeat (PPR) proteins act at specific RNA-editing sites in plant mitochondria
Identification of mitochondrial editing factor 8 (MEF8) as a Factor of RNA Editing at Site nad5-676—With the recently developed multiplexed SNaPshot approach, 369 annotated editing sites were probed in 2,000 individuals of a population of ethyl methanesulfonate (EMS) mutant plants to directly find mutants impaired in RNA editing at one or more of the investigated sites in plant mitochondria (40 – 42)
RNA-editing Proteins with a Degenerated pentatricopeptide repeat (PPR) Protein Skeleton—The two PPR proteins MEF8 and MEF8S are unusual in comparison with the previously assigned editing factors of mitochondria and plastids: both contain very short PPR domains with only five PPRs (Fig. 3)

Summary

Background

Pentatricopeptide repeat (PPR) proteins act at specific RNA-editing sites in plant mitochondria. The facilitators for specific cytosine-to-uridine RNA-editing events in plant mitochondria and plastids are pentatricopeptide repeat (PPR)-containing proteins with specific additional C-terminal domains. We report the related PPR proteins mitochondrial editing factor 8 (MEF8) and MEF8S with only five such repeats each to be both involved in RNA editing at the same two sites in mitochondria of Arabidopsis thaliana. The proteins required for specific RNA-editing events in plastids and in mitochondria, including for example CRR4, the MEFs, REME1 [18], and OGR1 in rice [19], are all pentatricopeptide repeat proteins (PPR proteins) Those identified to date are characterized by containing three types of repeats that vary between 31 amino acids in short, 35 in medium, and 37 in long repeat elements and contain an additional extension (E) domain. In RNA editing at the same two specific sites in plant mitochondria

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION