Changes in Chloroplast mRNA Stability during Leaf Development.

Abstract

During spinach leaf development, chloroplast-encoded mRNAs accumulate to different steady-state levels. Their relative transcription rates alone, however, cannot account for the changes in mRNA amount. In this study, we examined the importance of mRNA stability for the regulation of plastid mRNA accumulation using an in vivo system to measure mRNA decay in intact leaves by inhibiting transcription with actinomycin D. Decay of psbA and rbcL mRNAs was assayed in young and mature leaves. The psbA mRNA half-life was increased more than twofold in mature leaves compared with young leaves, whereas rbcL mRNA decayed with a similar relative half-life at both leaf developmental stages. The direct in vivo measurements demonstrated that differential mRNA stability in higher plant plastids can account for differences in mRNA accumulation during leaf development. The role of polysome association in mRNA decay was also investigated. Using organelle-specific translation inhibitors that force mRNAs into a polysome-bound state or deplete mRNAs of ribosomes, we measured mRNA decay in vivo in either state. The results showed that rbcL and psbA mRNAs are less stable when bound to polysomes relative to the polysome-depleted mRNAs and that their stabilities are differentially affected by binding to polysomes. The results suggested that ribosome binding and/or translation of the psbA and rbcL mRNAs may function to modulate the rate of their decay in chloroplasts.

Nuclear Mutants of Maize with Defects in Chloroplast Polysome Assembly Have Altered Chloroplast RNA Metabolism

“…The conclusion that a decrease in polysome recruitment destabilizes the rbcL mRNA may appear to be at odds with the results of Klaff and Gruissem (1991) who found that lincomycin, an antibiotic that decreases the association of chloroplast mRNAs with polysomes, stabilized the rbcL mRNA in spinach leaves. The mutations described here also decrease polysome association of mRNAs, but result in the destabilization of the maize rbcL mRNA.…”

“…A reduction in the elongation rate would, by itself, result in an increase in the number of ribosomes associated with mRNAs, as is observed after treatment of chloroplasts with chloramphenicol (A. Barkan, unpublished results;Klaff and Gruissem, 1991), or eukaryotic cells with cycloheximide (Peltz et al, 1992).…”

“…The stabilities of certain chloroplast mRNAs appear to change during the maturation of spinach leaves (Klaff and Gruissem, 1991) and after illumination of dark-grown barley seedlings (Klein and Mullet, 1990). It is not clear what mediates these changes, although a role for specific mRNA binding proteins has been proposed (Stern and Gruissem, 1987).…”

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

“…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). Light activates nuclear genes for plastid ' Portions of this study were supported by funds from the proteins, stimulates the formation of thylakoids, regulates the stoichiometry and turnover of photosynthetic reaction center components, and controls enzyme activity (Melis, 1991;Thompson and White, 1991;Christopher and Mullet, 1994).…”

hcf5, a Nuclear Photosynthetic Electron Transport Mutant of Arabidopsis thaliana with a Pleiotropic Effect on Chloroplast Gene Expression

“…The lowered levels of the vbcL transcript could be an indirect effect of a decrease in translation, because it has been shown that in spinach this mRNA is highly sensitive to changes in chloroplast translation and processing (Klaff and Gruissem, 1991;Schuster and Gruissem, 1991 (Barkan, 1993). It h a s been suggested that this message, b u t not other chloroplast messages, was destabilized when not associated with ribosomes (Barkan, 1993).…”