title: RNR1, a 3'-5' exoribonuclease belonging to the RNR superfamily, catalyzes 3' maturation of chloroplast ribosomal RNAs in Arabidopsis thaliana.
abstract: Arabidopsis thaliana chloroplasts contain at least two 3' to 5' exoribonucleases, polynucleotide phosphorylase (PNPase) and an RNase R homolog (RNR1). PNPase has been implicated in both mRNA and 23S rRNA 3' processing. However, the observed maturation defects do not affect chloroplast translation, suggesting that the overall role of PNPase in maturation of chloroplast rRNA is not essential. Here, we show that this role can be largely ascribed to RNR1, for which homozygous mutants germinate only on sucrose-containing media, and have white cotyledons and pale green rosette leaves. Accumulation of chloroplast-encoded mRNAs and tRNAs is unaffected in such mutants, suggesting that RNR1 activity is either unnecessary or redundant for their processing and turnover. However, accumulation of several chloroplast rRNA species is severely affected. High-resolution RNA gel blot analysis, and mapping of 5' and 3' ends, revealed that RNR1 is involved in the maturation of 23S, 16S and 5S rRNAs. The 3' extensions of the accumulating 5S rRNA precursors can be efficiently removed in vitro by purified RNR1, consistent with this view. Our data suggest that decreased accumulation of mature chloroplast ribosomal RNAs leads to a reduction in the number of translating ribosomes, ultimately compromising chloroplast protein abundance and thus plant growth and development.
authors.affiliation: Boyce Thompson Institute for Plant Research, Cornell University Tower Rd., Ithaca, NY 14853, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Bollenbach
authors.forename: Heike
authors.initials: H
authors.lastname: Lange
authors.forename: Ryan
authors.initials: R
authors.lastname: Gutierrez
authors.forename: Mathieu
authors.initials: M
authors.lastname: Erhardt
authors.forename: David B
authors.initials: DB
authors.lastname: Stern
authors.forename: Dominique
authors.initials: D
authors.lastname: Gagliardi
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002384:Catalysis; D005095:Exoribonucleases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D016254:Mutagenesis, Insertional; D010788:Photosynthesis; D011132:Polyribosomes / Q000378:metabolism; D026721:RNA 3' End Processing; D012322:RNA Precursors / Q000378:metabolism; D018747:RNA, Chloroplast / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018749:RNA, Plant / Q000096:biosynthesis; D012335:RNA, Ribosomal / Q000378:metabolism*; D012341:RNA, Ribosomal, 5S / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D012322:RNA Precursors; D018747:RNA, Chloroplast; D012333:RNA, Messenger; D018749:RNA, Plant; D012335:RNA, Ribosomal; D012341:RNA, Ribosomal, 5S; D005095:Exoribonucleases; C492330:mitochondrial RNase II, Arabidopsis