title: PPR motifs of the nucleus-encoded factor, PGR3, function in the selective and distinct steps of chloroplast gene expression in Arabidopsis.
abstract: Plastid 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 fluorescence because of defects in chloroplast gene expression. High chlorophyll fluorescence (HCF) because of a reduced level of the cytochrome b6/f complex was observed in two alleles, pgr3-1 and pgr3-2 but not in pgr3-3. In contrast, a transient increase in fluorescence after turning off the actinic light, which was ascribed to chloroplast NADPH 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 final 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.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0101, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yamazaki
authors.forename: Masao
authors.initials: M
authors.lastname: Tasaka
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Shikanai
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics; D017124:Conserved Sequence; D045346:Cytochrome b6f Complex / Q000378:metabolism; D018744:DNA, Plant / Q000235:genetics; D005453:Fluorescence; D015870:Gene Expression; D017343:Genes, Plant; D008969:Molecular Sequence Data; D009154:Mutation; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009876:Operon; D010641:Phenotype; D045322:Photosynthetic Reaction Center Complex Proteins; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; C465062:PGR5 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D018749:RNA, Plant; D002734:Chlorophyll; D045346:Cytochrome b6f Complex; D009252:NADPH Dehydrogenase