Characterization of the Ferredoxin-1 mRNA instability element(s)

Abstract

Light regulates translation and stability of pea Ferredoxin-1 (Fed-1) mRNA in transgenic tobacco plants. Previous work showed that mutation of a (CAUU)4 repeat in the Fed-1 5' UTR abolished light regulated Fed-1 mRNA accumulation in transgenic tobacco. Using the tetracycline repressible promoter system we show that the (CAUU)4 repeat is necessary for dark induced destabilization of Fed-1 mRNA. Substitution of single nucleotides within this repeat had dramatically different effects on mRNA accumulation. A minimal sequence of (CAUU)3 is required for destabilization of Fed-1 mRNA in the dark. However, sequences surrounding the (CAUU)4 element are not required for light regulated Fed-1 mRNA accumulation. Furthermore, 26 nt of the 5' UTR, including the (CAUU)4 repeat and 10 nt upstream sequence are sufficient to confer a significant ~2.5-fold light regulation of mRNA accumulation when fused to a non-light- responsive plant mRNA. Significantly, dark-induced Fed-1 mRNA instability does not require Fed-1 mRNA polyribosome dissociation, and thus is an independent dark-regulated event. Finally, we have identified two proteins, ribosomal protein S2 (RP S2) and a probable RNA binding protein (pRNAbp) that bind Fed-1 5' UTR. UV-crosslinking assays reveal differential binding affinity of these proteins to sense and antisense Fed-1 mRNA.