Post-Transcriptional Control of Chloroplast Gene Expression

Abstract

Chloroplasts contain their own genome, organized as operons, which are generally transcribed as polycistronic transcriptional units. These primary transcripts are processed into smaller RNAs, which are further modifi ed to produce functional RNAs. The RNA processing mechanisms remain largely unknown and represent an important step in the control of chloroplast gene expression. Such mechanisms include RNA cleavage of pre-existing RNAs, RNA stabilization, intron splicing, and RNA editing. Recently, several nuclear-encoded proteins that participate in diverse plastid RNA processing events have been characterised. Many of them seem to belong to the pentatricopeptide repeat (PPR) protein family that is implicated in many crucial functions including organelle biogenesis and plant development. This review will provide an overview of current knowledge of the post-transcriptional processing in chloroplasts.

Translational regulation in chloroplasts for development and homeostasis

“…Second, both TCA1p and the repressor motif control translation via the petA 5′ UTR, a feature of CES (covered earlier in this section). Finally, the repressor motif requires factors encoded by TCA1 and MCA1 to control petA translation [125][126][127].…”

Function of chloroplast RNA-binding proteins

“…In chloroplasts, most RNA editing events involve cytidine (C) to uridine (U) exchanges, while the conversion of U to C, at least in angiosperms, occurs rarely [123,124]. Generally, RNA editing sites are found in ORFs, but in some cases, sites can also be found in noncoding regions located mostly upstream of the start codon [15,17]. There are notable differences in editing frequencies between different species, e.g.…”

“…Crosstalk between the two genetic systems is enabled by a variety of anterograde and retrograde signalling pathways [13]. Important mechanisms of anterograde signalling are the transcriptional, post-transcriptional, and translational regulation of chloroplast gene expression by means of nuclear-encoded trans-acting factors [13][14][15]. These nuclear-encoded proteins play key roles since they act as RNA-binding factors in crucial post-transcriptional processing steps such as RNA stabilization, splicing and editing ( Fig.…”

A chloroplast-localized DEAD-box RNA helicaseAtRH3 is essential for intron splicing and plays an important role in the growth and stress response in Arabidopsis thaliana

“…The splicing of group I and group II introns is one particular example in which, instead of selfsplicing, intron splicing in chloroplasts requires many nuclearencoded proteins (Jenkins et al, 1997;Barkan, 2006, 2007;Barkan et al, 2007). A variety of nuclear-encoded RNAbinding proteins (RBPs) are targeted to chloroplasts and play indispensible roles in posttranscriptional regulation of RNA metabolism and gene expression in chloroplasts (del Campo, 2009;Schmitz-Linneweber and Small, 2008;Stern et al, 2010).…”

“…Chloroplast gene expression is commonly regulated during the process of posttranscriptional RNA metabolism, including mRNA processing, splicing, editing, decay, and translation (del Campo, 2009;Stern et al, 2010). Chloroplast RNA metabolism involves several complicated processes that have both prokaryotic and eukaryotic characteristics (SchmitzLinneweber and .…”