Synthesis of ribosomal RNA in ribosome-deficient plastids of the mutant ?albostrians? of Hordeum vulgare L.

Abstract

The nuclear gene-induced plastome mutant "albostrians" of Hordeum vulgare L. is characterized by a plastid ribosome-deficiency. This ribosome deficiency could be caused by the lack of or a defect in chloroplast RNA polymerase. However in our investigations we found an activity of chloroplast RNA polymerase in wild-type and mutant leaves of "albostrians" barley by (1) electron microscopic autoradio-graphy after in vivo labelling of RNA, (2) determination of RNA polymerase activity in isolated plastids, and (3) characterization of the newly synthesized RNA by electrophoresis in polyacrylamide gels. The genes of 23S and 16S rRNA are transcribed in mutant plastids and the RNAs are processed. From these results we conclude that the enzymes involved in transcription and processing of chloroplast rRNA are synthesized on cytoplasmic ribosomes and that the plastid ribosome deficiency in albostrians barley is probably not caused by a defective chloroplast DNA dependent RNA polymerase or by a mutation in the genes of 23S and 16S chloroplast rRNA.

The Primary Transcriptome of Barley Chloroplasts: Numerous Noncoding RNAs and the Dominating Role of the Plastid-Encoded RNA Polymerase

“…Therefore, it is still unclear why NEP cannot rescue the albino phenotype in DrpoB tobacco plastids (i.e., PEP-deficient mutants with functional translation). The amount of transcripts generated by NEP instead of PEP might be simply insufficient to meet the demands for the extensive translation required for greening (Siemenroth et al, 1981;Allison et al, 1996). Alternatively or additionally, NEP may not transcribe a small number of genes for which we found TSSs in green but not in white plastids.…”

“…In stark contrast with the eubacterial RNA polymerase, PEP is not sufficient to transcribe all genes in plastids of higher plants. A second polymerase, denoted nuclear-encoded plastid RNA polymerase (NEP), was found to participate in plastid transcription (Siemenroth et al, 1981;Hess et al, 1993;Allison et al, 1996). NEP is represented by one or more phage-type RNA polymerase (Hedtke et al, 1997(Hedtke et al, , 2000.…”

Natural Variation in Sensitivity to a Loss of Chloroplast Translation in Arabidopsis

“…The ability of some angiosperms to survive a localized loss of chloroplast translation was first revealed through studies with the maize iojap and barley (Hordeum vulgare) albostrians mutants deficient in chloroplast ribosomes (Walbot and Coe, 1979;Siemenroth et al, 1981). Subsequent work on chloroplast splicing mutants provided further evidence that grasses tolerate disruptions in chloroplast translation that cause embryo lethality in Arabidopsis (Asakura and Barkan, 2006).…”

Plastid Genes Encoding the Transcription/Translation Apparatus Are Differentially Transcribed Early in Barley (Hordeum vulgare) Chloroplast Development (Evidence for Selective Stabilization of psbA mRNA)

“…The strongest evidence for a nuclear-encoded RNA polymerase comes from studies of albostrians, a barley mutant that lacks plastid ribosomes (Siemenroth et al, 1981) and Epifagus, which lacks rpoB, rpoC1, and rpoCz (Morden et al, 1991). In both of these cases, 16s rRNA synthesis occurs in plastids that lack the ability to synthesize the plastid-encoded RNA polymerase.…”