rifampin and tagetitoxin

The Chlamydomonas reinhardtii plastid and mitochondrial transcriptomes were surveyed for changes in RNA profiles resulting from growth in 12 culture conditions representing 8 abiotic stimuli. Organellar RNA abundance exhibited marked changes during nutrient stress and exposure to UV light, as revealed by both RNA gel blot and DNA microarray analyses. Of particular note were large increases in tufA and clpP transcript abundance during nutrient limitation. Phosphate and sulfur limitation resulted in the most global, yet opposite, effects on organellar RNA abundance, changes that were dissected further using run-on transcription assays. Removal of sulfate from the culture medium, which is known to reduce photosynthesis, resulted in 2-fold to 10-fold decreases in transcription rates, which were reflected in lower RNA abundance. The decrease in transcriptional activity was completely reversible and recovered to twice the control level after sulfate replenishment. Conversely, phosphate limitation resulted in a twofold to threefold increase in RNA abundance that was found to be a post-transcriptional effect, because it could be accounted for by increased RNA stability. This finding is consistent with the known metabolic slowdown under phosphate stress. Additionally, inhibitor studies suggested that unlike those in higher plants, Chlamydomonas chloroplasts lack a nucleus-encoded plastid RNA polymerase. The apparently single type of polymerase could contribute to the rapid and genome-wide transcriptional responses observed within the chloroplast.

Topics: Animals; Anti-Bacterial Agents; Chlamydomonas reinhardtii; Chloroplast Proton-Translocating ATPases; Conserved Sequence; Cytochrome b Group; Cytochrome b6f Complex; Cytochromes; Cytochromes f; Dactinomycin; Dicarboxylic Acids; DNA-Directed RNA Polymerases; DNA, Chloroplast; Gene Expression Profiling; Novobiocin; Oligonucleotide Array Sequence Analysis; Organelles; Organophosphorus Compounds; Phosphates; Phylogeny; Protozoan Proteins; Rifampin; RNA, Chloroplast; Sulfates; Transcription, Genetic

The transcriptional activity of nucleoids changes during plastid development, presumably due to the morphological and molecular differences of the nucleoids. Pea chloroplast nucleoids have an abundant 70-kDa protein identified as sulfite reductase (SiR) that can compact DNA. Using an in vitro transcription assay, we show here that heparin increased the transcriptional activity of chloroplast nucleoids with concomitant release of SiR. Using a fluorometric method we developed for analyzing DNA compaction, we found that the fluorescence intensity of chloroplast DNA stained with 4',6-diamidino-2-phenylindole was decreased by the addition of SiR and increased by the subsequent addition of heparin. Addition of exogenous SiR increased the compaction of isolated nucleoids, and the addition of heparin relaxed it. SiR effectively repressed the in vitro transcription activity of nucleoids and counteracted the activation by heparin. These results suggest that SiR regulates the transcriptional activity of chloroplast nucleoids through changes in DNA compaction.

Topics: Amanitins; Chloroplasts; Dactinomycin; Dicarboxylic Acids; DNA, Plant; Heparin; Kinetics; Organophosphorus Compounds; Oxidoreductases Acting on Sulfur Group Donors; Pisum sativum; Rifampin; Transcription, Genetic