Expression during Salt Stress and Nucleotide Sequence of cDNA for Ferredoxin-NADP+ Reductase from Mesembryanthemum crystallinum1

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In the facultative halophyte Mesembryanthemum crystallinum (common ice plant) the enzyme ferredoxin-NADP+-reductase (FNR) is coded for by a small family of 2 to 3 genes. We have determined the expression characteristics as the plants adapt to high salt and the nucleotide sequence of a full-length cDNA coding for the precursor of this chloroplast-located enzyme. On a developmental scale amounts of FNR transcripts and protein are highest in young emerging leaves. The FNR cDNA is a member of a class of genes whose expression is only slightly affected by salt stress. Even less pronounced than mRNA fluctuations, the amount of FNR protein is unaffected by salt stress. The longest FNR cDNA found was 1,419 nucleotides in size. It consisted of 74 nucleotides 5′-leader sequence, 1,095 nucleotides of protein coding sequence encoding 365 amino acids, and 247 nucleotides 3-region excluding a short poly(A+) tail. As expected for a nucleus-coded chloroplast protein an amino terminal transit peptide (52 amino acids in length) was found. The mature FNR protein is predicted to contain 313 amino acids corresponding to a protein of Mr 35,713. The deduced amino acid sequence of the mature FNR protein is 93.2 and 85.9% identical to those of spinach and pea. The transit peptide of pea and spinach have 55.8 and 69.2% identity with that from ice plant.

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