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 elon-gation. 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.

Ferredoxin-1 mRNA is destabilized by changes in photosynthetic electron transport

“…Previously, we showed that changes in Fed-1 mRNA abundance are correlated with the ability of the mRNA to be translated (2). The data presented here support the suggestion that Fed-1 is preferentially degraded when it is not associated with polyribosomes.…”

“…Mutation of the Fed-1 initiation codon to either a missense or nonsense codon abolishes light regulation of the mRNA (2). Similarly, mutation of the surrounding translational initiation context also compromises light regulation of the Fed-1 mRNA (7).…”