Chloroplast development affects expression of phage-type RNA polymerases in barley leaves.
We have identified the barley gene and cDNA encoding the plastid phage-type RNA polymerase (RNAP), nuclear-encoded plastid RNAP (RpoTp), and the nearly full-length cDNA of the mitochondrial RNAP, nuclear-encoded mitochondrial RNAP (RpoTm). RpoTp spans more than 9000 nt, consists of 19 exons and 18 introns, gives rise to a 3632-nt mRNA and is localized to the long arm of chromosome 1 (7H). The length of the deduced polypeptide is 948 residues. The mRNA levels of RpoTp and RpoTm were determined in roots and primary leaf sections of 7-day-old barley seedlings of the albostrians mutant, which were either phenotypically normal and exhibited a gradient of chloroplast development, or contained ribosome-deficient undifferentiated plastids. Transcript levels of RpoTp and RpoTm in almost all sections reached higher concentrations in plastid ribosome-deficient leaves than in the wild-type material, except in the most basal part of the leaf. These data indicate a role of plastid-to-nucleus signalling in the expression of the two RpoT genes. The mRNA levels of the plastid genes, beta-subunit of plastid-encoded RNAP (rpoB), proteolytic subunit of the Clp protease (clpP) and ribosomal protein Rpl2 (rpl2), all known to be transcribed by the nuclear-encoded RNAP (NEP), followed closely the pattern of RpoTp mRNA accumulation, strongly suggesting that RpoTp and NEP are identical. Transcripts of RpoTm and RpoTm-transcribed mitochondrial genes cytochrome oxidase subunit 2 (coxII) and ATPase subunit 9 (atp9) accumulated to the highest levels in the most basal parts of the leaf and declined considerably towards the leaf tip with a pronounced reduction in green versus white leaves. Our data revealed a marked influence of the developmental stage of the plastid on the expression and activity of organellar phage-type RNAPs and their target genes. Thus, interorganellar cross-talk in the regulated expression of nuclear-encoded plastid and mitochondrial RNAP genes might be a key element governing the concerted expression of genes located within plastids, mitochondria and the nucleus of the plant cell.
Emanuel
Carola
C
Humboldt-University, Department of Biology/Genetics, Chausseestr. 117, D-10115 Berlin, Germany.
Weihe
Andreas
A
Graner
Andreas
A
Hess
Wolfgang R
WR
Börner
Thomas
T
D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000235:genetics* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D008928:Mitochondria / Q000201:enzymology / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D018515:Plant Leaves / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D018076:DNA, Complementary; D018744:DNA, Plant; D010940:Plant Proteins; D014157:Transcription Factors; D012321:DNA-Directed RNA Polymerases; C486920:RpoTm protein, Hordeum vulgare; C486921:RpoTp protein, Hordeum vulgare