Intron position as an evolutionary marker of thioredoxins and thioredoxin domains |
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Authors: | Mariam Sahrawy Valérie Hecht Javier Lopez-Jaramillo Ana Chueca Yvette Chartier Yves Meyer |
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Institution: | (1) Department of Plant Biochemistry, Estacion Experimental del Zaidin, Consejo Superior de Investigaciones, Cientificas, Professor Alberada 1, 18008 Granada, Spain;(2) Laboratoire de Physiologie et Biologie Moléculaire des Plantes, Université/Centre National de la Recherche Scientifique URA, 565 Avenue de Villeneuve, 66860 Perpignan, Cedex, France |
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Abstract: | In contrast to prokaryotes, which typically possess one thioredoxin gene per genome, three different thioredoxin types have
been described in higher plants. All are encoded by nuclear genes, but thioredoxins m and f are chloroplastic while thioredoxins
h have no transit peptide and are probably cytoplasmic. We have cloned and sequencedArabidopsis thaliana genomic fragments encoding the five previously described thioredoxins h, as well as a sixth gene encoding a new thioredoxin
h. In spite of the high divergence of the sequences, five of them possess two introns at positions identical to the previously
sequenced tobacco thioredoxin h gene, while a single one has only the first intron. The recently published sequence ofChlamydomonas thioredoxin h shows three introns, two at the same positions as in higher plants. This strongly suggests a common origin
for all cytoplasmic thioredoxins of plants and green algae. In addition, we have cloned and sequenced pea DNA genomic fragments
encoding thioredoxins m and f. The thioredoxin m sequence shows only one intron between the regions encoding the transit peptide
and the mature protein, supporting the prokaryotic origin of this sequence and suggesting that its association with the transit
peptide has been facilitated by exon shuffling. In contrast, the thioredoxin f sequence shows two introns, one at the same
position as an intron in various plant and animal thioredoxins and the second at the same position as an intron in thioredoxin
domains of disulfide isomerases. This strongly supports the hypothesis of a eukaryotic origin for chloroplastic thioredoxin
f. |
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Keywords: | Thioredoxins Introns Phylogeny |
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