[Show abstract][Hide abstract] ABSTRACT: Altered pigmentation is an easily scored and sensitive monitor of plastid function. We analyzed in detail a yellow colored transposon-tagged mutant (dal1-2) that is allelic to the dal mutant previously identified (Babiychuk et al., 1997). Mesophyll cells of mutant plants possess abnormal nucleoids and more but smaller plastids than wild type cells. Plastid development in dal1-2 is not altered in the dark but is arrested at the early steps of thylakoid assembly. The amino acid sequence of the protein deduced from our cDNA clone is 21 amino acids longer than the previously published DAL sequence (Babiychuk et al., 1997) and allowed us to show that DAL codes for a chloroplast protein. The dal1-2 mutation has a global negative effect on plastid RNA accumulation and on expression of nuclear encoded photosynthetic genes. We show that the plastid RNA polymerases, the nuclear-encoded NEP and the plastid-encoded PEP, are functional in the mutant. Precursor 16S and 23S rRNA species specifically accumulate at a high level in the mutant but the 5'-end and the long 3'-end trailer are not modified. We suggest that the dal mutation is involved in plastid rRNA processing and consequently in translation and early chloroplast differentiation.
[Show abstract][Hide abstract] ABSTRACT: The plastid genome is known to be transcribed by a plastid-encoded prokaryotic-type RNA polymerase (PEP) and by a nucleus-encoded phage-type RNA polymerase (NEP). The spinach plastid rrn operon promoter region harbours three different, overlapping promoters. Two of them are of the prokaryotic type. The third promoter is a non-consensus-type NEP promoter. We separated three different transcriptional activities from spinach chloroplasts: PEP, the phage-type RNA polymerase NEP-1, and a third, hitherto undescribed transcriptional activity (NEP-2). NEP-2 specifically transcribes the rrn operon in the presence of the transcription factor CDF2. CDF2 was previously shown to recruit PEP to the rrn promoter to repress transcription. Together, our results suggest the existence of a third RNA polymerase in plastids and a mechanism of rDNA transcriptional regulation that is based on the interaction of the transcription factor CDF2 with two different transcriptional systems.
[Show abstract][Hide abstract] ABSTRACT: We have characterized two maize cDNAs, rpoTm and rpoTp, that encode putative T7-like RNA polymerases. In vivo cellular localization experiments using transient expression of the green fluorescent protein suggest that their encoded proteins are targeted exclusively to mitochondria and plastids, respectively. An antibody raised against the C terminus of the rpoTp gene product identified mitochondrial polypeptides of approximately 100 kD. Their presence was correlated with RNA polymerase activity, and the antibody inhibited mitochondrial in vitro transcription activity. Together, these results strongly suggest that the product of rpoTm is involved in maize mitochondrial transcription. By contrast, immunoblot analysis and an antibody-linked polymerase assay indicated that rpoTp specifies a plastid RNA polymerase component. A quantitative reverse transcription-polymerase chain reaction assay was used to study the transcription of rpoTp and rpoTm in different tissues and under different environmental conditions. Although both genes were constitutively expressed, rpoTm transcripts were generally more prevalent in nonphotosynthetic tissues, whereas an increase in rpoTp transcripts paralleled chloroplast development. We suggest that these two genes encode constitutive components of the organelle transcription machinery but that their expression is nonetheless subject to modulation during plant development.
[Show abstract][Hide abstract] ABSTRACT: The spinach rrn operon is used as a model system to study transcriptional regulation in higher plant photosynthetic and non-photosynthetic
plastids. We performed capping experiments to determine whether P1, PC, or P2 promoters are employed for rrn transcription start sites in cotyledon and root tissues. By using a new method of analysis of capped RNA we demonstrate for
the first time that 1) in both organs the rrn operon is expressed in a constitutive manner by cotranscription with the preceding tRNA(GAC)Val gene, and 2) the PC transcription start site is used only in cotyledons and leaves, i.e. we demonstrate the organ-specific usage of a plastid promoter. Both start sites, PC and that of the tRNA(GAC)Val cotranscript, lackEscherichia coli-like consensus sequences. The cotranscript is initiated 457 base pairs upstream of the tRNA(GAC)Valgene. The PC-specific DNA-binding factor, CDF2, is not detectable in root tissues confirming its regulatory role in PC-initiatedrrn expression and the organ specificity of PC expression. Furthermore, our results show that rrn operon expression patterns differ in spinach and tobacco indicating species-specific transcriptional regulation of plant
plastid gene expression.
No preview · Article · Jun 1997 · Journal of Biological Chemistry