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Caractérisation d’éléments transposables de type mariner chez les microalgues marines

Abstract : Transposable elements (TE) are sequences able to move between two loci in the host genomes. Mariner-like element (MLE) are well characterized in animal and land plant genomes but not in marine microalgae. In this work, we have looked for MLE in marine diatoms (Bacillariophyceae) that are microalgae having a siliceous wall. They have colonized all aquatic environments and are a major component of the phytoplankton, so they play a major role in the ecology of marine environments.To characterize the diatom MLE, molecular and bio-informatics approaches were used. The presence of MLE was detected in ten diatom species which exhibited sequence fragments of about 380 pb. These fragments were identified as a section of the conserved sequence which encodes the enzyme responsible for MLE transposition, the transposase. Phylogeny and classification analysis of these fragments revealed that diatom MLE belong to the Tc1-mariner superfamily, and more precisely to the vegetal MLE group. Nevertheless, diatom MLE sequences diverged from the flowering plant MLE. In order to determine if MLE transposase is produced in diatoms, MLE expression was looked for in diatoms under thermal stresses. Our results showed that diatom MLE were expressed in the three species tested, including the model diatom Phaeodactylum tricornutum which was completely sequenced recently. Diatom MLE expression was dependent on the thermal conditions and on the species.Our results suggest that MLE are widespread in diatom genomes and that they have an ancestral presence in the green lineage. Diatom MLE cluster in three subfamilies in the huge ET Tc1-mariner superfamilly. Finally, the diatom MLE expression detected could reflect the existence of active MLE in diatom genomes. If this hypothesis were verified, it could lead to the development of mutagenesis tools.
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Dorothée Hermann. Caractérisation d’éléments transposables de type mariner chez les microalgues marines. Sciences agricoles. Université du Maine, 2011. Français. ⟨NNT : 2011LEMA1021⟩. ⟨tel-00732952⟩

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