Changes in RNA-Polymerase Activity during Biogenesis, Maturation and Senescence of Barley Chloroplasts. Comparative Analysis of Transcripts Synthesized Either in Run-on Assays or by Transcriptionally Active Chromosomes

Abstract

Summary The relative transcription rates of plastid genes were analyzed by hybridization of both run-on transcripts and TAC (transcriptionally active chromosome) derived transcripts to filter bound barley plastid DNA fragments. The results clearly demonstrate that TACs are able to transcribe all classes of genes. Development related changes in transcription were characterized by hybridization to 16 specific barley plastid DNA fragments of the transcripts derived from proplastids and from four physiologically well characterized stages of chloroplast biogenesis and senescence. Both in vitro transcription with TAC and run-on assays revealed a differential transcription of plastid genes. During biogenesis and maturation of chloroplasts relative transcription of rDNA decreases while relative transcription of psbA , psbD and psaB increases in parallel. Senescence is accompanied by converse changes in transcription. Though the main development related changes in plastid DNA transcription observed in run-on assays are retained by TAC, transcription of some genes ( atpA , rbcL , rpl , rps , rpoB ) is less pronounced in TAC preparations than in run-on assays. Differences between the two transcription systems are particularly obvious in the case of photosynthetically competent chloroplasts and might indicate that parts of the plastid transcriptional apparatus are not represented by TAC.