Disruption of plastid-encoded RNA polymerase genes in tobacco: expression of only a distinct set of genes is not based on selective transcription of the plastid chromosome

Citation
K. Krause et al., Disruption of plastid-encoded RNA polymerase genes in tobacco: expression of only a distinct set of genes is not based on selective transcription of the plastid chromosome, MOL G GENET, 263(6), 2000, pp. 1022-1030
Citations number
40
Categorie Soggetti
Molecular Biology & Genetics
Journal title
MOLECULAR AND GENERAL GENETICS
ISSN journal
00268925 → ACNP
Volume
263
Issue
6
Year of publication
2000
Pages
1022 - 1030
Database
ISI
SICI code
0026-8925(200007)263:6<1022:DOPRPG>2.0.ZU;2-U
Abstract
Plastids of higher plants operate with at least two distinct DNA-dependent RNA polymerases, which are encoded in the organelle (PEP) and in the nucleu s (NEP), respectively. Plastid run-on assays and Northern analyses were emp loyed to analyse gene expression in tobacco mutant plastids lacking the PEP genes rpoA, rpoB or rpoC1. Hybridisation of run-on transcripts to restrict ion fragments representing the entire tobacco plastid chromosome, as well a s to selected plastid gene-specific probes, shows that all parts of the pla stid DNA are transcribed in rpo-deficient plastids. In comparison to wild-t ype chloroplasts, which are characterized by preferential transcription of photosynthesis-related genes in the light, mutant plastids exhibit a differ ent transcription pattern with less pronounced differences in the hybridisa tion intensities between the individual genes. The analysis of steady-state transcript patterns and transcription rates of selected genes in both type s of plastids demonstrates that differences in transcription rates are not necessarily paralleled by corresponding changes in transcript levels. The a ccumulation of large transcripts in the mutant plastids indicates that proc essing of primary transcripts may be impaired in the absence of PEP. These data suggest that, contrary to the prevailing view, much of the regulation of NEP-driven plastid gene expression in the rpo-deficient mutants is not b ased on differential promoter usage but is exerted at post-transcriptional levels.