Light modulation of ferredoxin mRNA abundance requires an open reading frame.

Abstract

Ferredoxin I (Fed-l) mRNA abundance is modulated by an Interna1 light regulatory element that includes sequences both L'and 3'of the translational initiation site. To test the hypothesis that the light response mediated by this element might be coupled to translation, we transformed tobacco plants with gene constructs blocked in translational initiation or elongation. Here, we report that such mutations abollsh the light response ln vivo. A nonsense mutation could be rescued by restorlng the open reading frame with a different sequence, even when the new codon caused an amino acld substitution. Our data establlsh that the light response requires a translatable reading frame and thus pmvide strong circumstantial evidence for post-transcriptional modulation of Fed-1 mRNA levels. The Fed-1 system 1s presently the only higher plant example of a developmentally regulated change in mRNA abundance that requires translation of the affected mRNA. INTRODUCTIONFerredoxin I (Fed-7) is a nuclear gene encoding chloroplast ferredoxin in Pisum (Dobres et al., 1987; Dickey et al., 1992a). Like most genes encoding plastid proteins, Fed-7 is expressed more strongly in the light than in the dark. However, its light response differs in severa1 respects from those of other wellcharacterized light-responsive genes (Kaufman et al., 1986) and involves different molecular events (Thompson, 1988;Thompson and White, 1991;Neuhaus et al., 1993). Among the important differences is the fact that a major light response element in the pea Fed-7 gene is located within the transcription unit (Elliott et al., 1989), while other light-responsive genes are regulated mainly by upstream elements (Thompson and White, 1991;Kuhlemeier, 1992). We have recently shown that the Fed-7 interna1 light regulatory element (iLRE) is located within the 5' portion of the transcribed sequence and that it includes portions of both the leader and coding region (Dickey et ai., 1992b).The location of the Fed-7 iLRE within the transcribed portion of an intronless gene rules out transcriptional regulatory mechanisms that depend on upstream control elements and is consistent with models in which light modulates mRNA abundance by directly or indirectly affecting its rate of degradation. Direct observation of a light effect on mRNA stability has thus far been prevented by the fact that Ad-7 mRNA is stabilized when cellular RNA synthesis is inhibited by actinomycin-D (G.C. Allen, unpublished data). However, other data provide indirect support for a post-transcriptional model. In both tobacco andTo whom correspondence should be addressed.Arabidopsis, changes in mRNA abundance in light-grown versus dark-adapted plants occur in the absence of corresponding changes in the transcriptional activity of isolated nuclei (Dickey et ai., 1992b;Vorst et al., 1993), and the 5' portion of a pea Fed-7::GUS (P-glucuronidase) chimeric mRNA is stabilized in the light, whereas reporter sequences in the 3' portion of the transcript are degraded (Dickey et al., 1992b).Recent reports indicate that ...

Posttranscriptional Regulation of the Sesbania rostrata Early Nodulin Gene SrEnod2 by Cytokinin

“…Silver and F.J. de Bruijn, unpublished data), making this type of analysis impossible. The effect of mRNA stabilization due to transcription inhibitors has also been observed in the case of the PhyA (Seeley et al, 1992), rbcS (Fritz et al, 1991), PvPrPl (Zhang et al, 1993), and Fd mRNAs (Dickey et al, 1994).…”

“…It is a common observation that the level of mRNA, which is unstable, is increased by the translational inhibitor cycloheximide (Zhang et al, 1993;Dickey et al, 1994;Gil et al, 1994). There are three possible reasons for this.…”

Both 5[prime] and 3[prime] Sequences of Maize adh1 mRNA Are Required for Enhanced Translation under Low-Oxygen Conditions

“…In only a few cases have sequences downstream of the initiation codon been shown to be important in the posttranscriptional regulation of gene expression in plants. Sequences within the first one-third of the coding region of the pea Fd gene are required for light-mediated regulation of mRNA abundance in transgenic tobacco (Dickey et al, 1994). This posttranscriptional regulation is abrogated if a nonsense codon is present in the first portion of the coding region (Dickey et al, 1994).…”

“…Sequences within the first one-third of the coding region of the pea Fd gene are required for light-mediated regulation of mRNA abundance in transgenic tobacco (Dickey et al, 1994). This posttranscriptional regulation is abrogated if a nonsense codon is present in the first portion of the coding region (Dickey et al, 1994). Modification of the insect-control protein gene c y I A of Bacillus thuringiensis to the synonymous codon usage of the host plant increased steady-state mRNA levels and, even more significantly, increased translation of the mRNA (Perlack et al, 1991).…”

Heat Shock Protein HSP101 Binds to the Fed-1 Internal Light Regulatory Element and Mediates Its High Translational Activity

“…Light regulation is observed even with the coding region component of the Fed-1 iLRE shortened to the first 13 codons . Active translation of Fed-1 mRNA is required for light regulation of its stability (Dickey et al, 1994), and most mutations that abolish light regulation also reduce the association of Fed-1 mRNA with polyribosomes . However, at least one mutation that affects Fed-1 light regulation does not disrupt translation or its light-regulated polyribosome association , suggesting that despite a requirement for active translation in the control of Fed-1 mRNA stability, additional components may be required for the light-mediated regulation of transcript abundance.…”