Direct evidence for selective modulation of psbA, rpoA, rbcL and 16S RNA stability during barley chloroplast development

Abstract

The turnover of RNAs encoded by seven different barley chloroplast genes was analyzed after treatment of barley shoots with tagetitoxin, a selective inhibitor of chloroplast transcription. Changes in RNA stability were examined during chloroplast development using basal and apical leaf sections of 4.5-day-old dark-grown seedlings and apical leaf sections of 4.0-day-old dark-grown seedlings which had been illuminated for 12 h. Of the RNAs examined, a 2.6 kb unspliced precursor of tRNA(lys) exhibited the shortest half-life, which was estimated to be 3 h. The 16S rRNA and psbA mRNA had the longest estimated half-lives, which were greater than 40 h. Among mRNAs, half-lives were estimated to range from 6 h for psaA mRNA, to over 40 h for psbA mRNA. Therefore, barley chloroplast mRNAs have long half-lives relative to bacterial mRNAs. The stability of atpB mRNA and the unspliced precursor of tRNA-lys was not altered during chloroplast development, while the stability of psaA mRNA decreased 2-fold. In contrast, the stability of the 16S rRNA and mRNAs for rpoA, psbA and rbcL increased during chloroplast development. The stability of 16S rRNA increased markedly during chloroplast development in the dark and this increase was maintained in illuminated seedlings. The stability of rbcL mRNA increased 2.5-fold during chloroplast development in the dark, and then decreased 2-fold in chloroplasts of light-grown plants. The initial increase in rpoA and psbA mRNA stability was also light-independent, with total increases in stability of at least 5-fold. In the case of rpoA, the stability of 2 of the 13 polycistronic rpoA transcripts that were detected in dark-grown plants was selectively increased during chloroplast development. In conclusion, the stability of some transcripts is selectively increased and further modulated during chloroplast development in barley. We propose that the selective stabilization of chloroplast mRNA, which occurred independent of light, is an indication that non-light regulated developmental signals are involved in barley chloroplast mRNA stability.

Involvement of Protein Kinase and Extraplastidic Serine/Threonine Protein Phosphatases in Signaling Pathways Regulating Plastid Transcription and the psbD Blue Light- Responsive Promoter in Barley

“…2). The leve1 of psbA mRNA, which is one of the most stable plastid mRNAs (Kim et al, 1993), was unusually low in blue light plus OA. These differences in plastid RNA levels cannot be explained solely by differences in transcription.…”

“…Cytokinins stimulate chlorophyll synthesis and the proper development of chloroplasts (Parthier, 1979). Developmental signals cause changes in plastid transcription, RNA stability, and splicing that occur independently of light (Barkan, 1989; Baumgartner et al, 1993;Kim et al, 1993). In addition, light influences chloroplast gene expression at transcriptional, posttranscriptional, and translational levels (Klein et al, 1988; Berry et al, 1990;Klein and Mullet, 1990;Schrubar et al, 1990;Sexton et al, 1990a;Klaff and Gruissem, 1991; for review, see Gruissem and Tonkyn, 1993;Mullet, 1993;Mayfield et al, 1995).…”

Green Light Adjusts the Plastid Transcriptome during Early Photomorphogenic Development

“…In the microarray trials, psaA decreased by approximately 5-fold (P 5 0.1712), psbD decreased approximately 5-fold (P 5 0.0013), and rbcL decreased approximately 4-fold (P 5 0.1494). Furthermore, all three have been studied previously with respect to light regulation (Klein et al, 1988;Kim et al, 1993;Christopher and Mullet, 1994;Thum et al, 2001;Dhingra et al, 2004a;Mochizuki et al, 2004). Defining the photophysiological parameters of the GL response is important, as this information will define the relationship, if any, between GL-induced rapid stem growth promotion and the decrease in plastid transcript abundance.…”

Blocking polyadenylation of mRNA in the chloroplast inhibits its degradation

“…It is thus apparent that mRNA degradation can play an important role in gene expression. In chloroplasts of higher plants, mRNA stability is known to vary at different developmental stages (Deng and Gruissem, 1987;Gruissem and Schuster, 1993;Kim et aL, 1993;Klaff and Gruissem, 1991;Rapp et aL, 1992). The control of chloroplast mRNA degradation is therefore likely to play a significant role in regulation of gene expression.…”