PPR motifs of the nucleus‐encoded factor, PGR3, function in the selective and distinct steps of chloroplast gene expression in Arabidopsis

Abstract

SummaryPlastid gene expression is regulated by a variety of nuclear genes. We have isolated Arabidopsis thaliana proton gradient regulation 3 (pgr3) mutants, which display aberrant chlorophyll¯uorescence because of defects in chloroplast gene expression. High chlorophyll¯uorescence (HCF) because of a reduced level of the cytochrome b 6 /f complex was observed in two alleles, pgr3-1 and pgr3-2 but not in pgr3-3. In contrast, a transient increase in¯uorescence after turning off the actinic light, which was ascribed to chloroplast NAD(P)H dehydrogenase (NDH) activity, was impaired in pgr3-1 and pgr3-3 but not in pgr3-2. Both phenotypes were complemented by the introduction of a single gene, PGR3, encoding a protein containing 27 pentatrico-peptide repeat (PPR) motifs. PPR motifs are present in proteins functioning in the post-transcriptional regulation of organellar gene expression. The conserved threonine in the motif was substituted by isoleucine in the 15th and 12th PPR motifs in pgr3-1 and pgr3-2, respectively, and the conserved leucine by phenylalanine in the ®nal incomplete motif of pgr3-3. We consider that the different domains of the PPR repeats in PGR3 might have different functions in conferring RNA stability and probably allowing translation as well as recognizing at least two distinct target RNAs.

Effects of Reduced Chloroplast Gene Copy Number on Chloroplast Gene Expression in Maize

“…The authors proposed that proteins that stabilize chloroplast mRNAs are in limiting concentrations such that only a fraction of newly synthesized transcripts escape rapid degradation. Several nucleus-encoded proteins that stabilize specific chloroplast RNAs have been discovered in maize and Arabidopsis (Barkan et al, 1994;Felder et al, 2001;Meierhoff et al, 2003;Lezhneva and Meurer, 2004;Yamazaki et al, 2004;Beick et al, 2008;Pfalz et al, 2009;Johnson et al, 2010;Stoppel et al, 2011;Hammani et al, 2012), and there is evidence that the majority of chloroplast mRNAs in angiosperms are stabilized by proteins that block exoribonucleases (Ruwe and Schmitz-Linneweber, 2012;Zhelyazkova et al, 2012a). Our results imply that such proteins may typically be in limiting concentrations in mature chloroplasts in angiosperms, as in C. reinhardtii chloroplasts.…”

Disruption of a Rice Pentatricopeptide Repeat Protein Causes a Seedling-Specific Albino Phenotype and Its Utilization to Enhance Seed Purity in Hybrid Rice Production

“…Fisk et al (1999) first reported a maize PPR gene, (for CHLOROPLAST RNA PROCESSING1), which was implicated by genetic analysis in processing and translation of plastid pet transcripts. Similar effects on plastid transcripts were subsequently observed in other mutants from Arabidopsis (Hashimoto et al, 2003;Meierhoff et al, 2003;Yamazaki et al, 2004;ChateignerBoutin et al, 2008ChateignerBoutin et al, , 2011Chi et al, 2008;Okuda et al, 2009Okuda et al, , 2010Yu et al, 2009;Johnson et al, 2010), rice (Kazama and Toriyama, 2003;Komori et al, 2004;Gothandam et al, 2005), and maize (Williams and Barkan, 2003;Schmitz-Linneweber et al, 2006;Pfalz et al, 2009;Prikryl et al, 2011). Additional evidence for a role of PPR proteins in regulating organelle gene expression has also come from positional cloning of several cytoplasmic male sterility (CMS) restorer genes from petunia (Petunia hybrida; Bentolila et al, 2002) and radish (Raphanus sativus; Brown et al, 2003;Desloire et al, 2003;Koizuka et al, 2003).…”

pTAC2, -6, and -12 Are Components of the Transcriptionally Active Plastid Chromosome That Are Required for Plastid Gene Expression

“…The pyg8 mutant (lane 10; J. Stö ckel and R. Oelmü ller, unpublished data) and the corresponding wild type [wt(pyg8); lane 9] were used as independent controls for transcriptional activity. PTAC2, -6, and -12 exhibit no obvious sequence similarities to other known proteins from prokaryotic organisms, except that pTAC2 contains PPR and TPR motifs, which are characteristic for proteins involved in mRNA processing, stability, and/or translation (Fisk et al, 1999;Boudreau et al, 2000;Yamazaki et al, 2004). Thus, these genes must have newly developed after the establishment of eukaryotism.…”