RHON1 is a novel ribonucleic acid-binding protein that supports RNase E function in the Arabidopsis chloroplast

Abstract

The Arabidopsis endonuclease RNase E (RNE) is localized in the chloroplast and is involved in processing of plastid ribonucleic acids (RNAs). By expression of a tandem affinity purification-tagged version of the plastid RNE in the Arabidopsis rne mutant background in combination with mass spectrometry, we identified the novel vascular plant-specific and co-regulated interaction partner of RNE, designated RHON1. RHON1 is essential for photoautotrophic growth and together with RNE forms a distinct ∼800 kDa complex. Additionally, RHON1 is part of various smaller RNA-containing complexes. RIP-chip and other association studies revealed that a helix-extended-helix-structured Rho-N motif at the C-terminus of RHON1 binds to and supports processing of specific plastid RNAs. In all respects, such as plastid RNA precursor accumulation, protein pattern, increased number and decreased size of chloroplasts and defective chloroplast development, the phenotype of rhon1 knockout mutants resembles that of rne lines. This strongly suggests that RHON1 supports RNE functions presumably by conferring sequence specificity to the endonuclease.

RHON1 Mediates a Rho-Like Activity for Transcription Termination in Plastids of Arabidopsis thaliana

“…The accumulation of the rbcL polycistronic precursor might result from processing defects in the rbcL-accD intercistronic region, as suggested by Stoppel et al (2012). Based on the data presented here, we propose that inefficient transcription termination may account for the overaccumulation of rbcL polycistronic transcripts in rhon1-2.…”

“…This study and that of Stoppel et al (2012) show that a large rbcL polycistronic transcript normally undetectable in wild-type plants is present in two rhon1 mutants from different genetic backgrounds (Figure 2A). The accumulation of the rbcL polycistronic precursor might result from processing defects in the rbcL-accD intercistronic region, as suggested by Stoppel et al (2012).…”

“…RHON1 was originally identified in a screen for interaction partners of the endonuclease RNase E (RNE) and was proposed to be involved in RNE-mediated plastid RNA processing (Stoppel et al, 2012). We show that RHON1 is also involved in the transcription termination of rbcL, encoding the large subunit of ribulose bisphosphate carboxylase oxygenase.…”

“…Sequencing of the 33 genes in the interval revealed a T-DNA insertion within the second exon of At1g06190 ( Figure 1C). In a previous study, the AT1G06190 protein was given the name RHON1 because its C-terminal domain is similar to the N-terminal part of the bacterial transcription terminator Rho (Stoppel et al, 2012). Accordingly, we designated our high chlorophyll fluorescence mutant as rhon1-2.…”

“…Two NEP promoters (PaccD-172, 252) have been found to drive transcription of the Arabidopsis accD gene (promoters are specified by the gene name and the position of the initiation nucleotide with respect to the start of the coding sequence) (SwiateckaHagenbruch et al, 2007). However, a large polycistronic precursor transcript spanning the rbcL, accD, psaI, ycf4, cemA, and petA genes was also reported (Walter et al, 2010;Stoppel et al, 2012). This large polycistronic precursor is barely detectable in wild-type plants.…”