Address of Corresponding Author

Cytogenet Genome Res 2005;110:229-241 (DOI: 10.1159/000084957)

  Abstract.

Tnt1 elements are a superfamily of LTR-retrotransposons distributed in the Solanaceae plant family and represent good model systems for studying regulatory and evolutionary controls established between hosts and transposable elements. Tnt1 retrotransposons tightly control their activation, by restricting expression to specific conditions. The Tnt1A element, originally discovered in tobacco, is expressed in response to stress, and its activation by microbial factors is followed by amplification, demonstrating that factors of pathogen origin can generate genetic diversity in plants. The Tnt1A promoter has the potential to be activated by various biotic and abiotic stimuli but a number of these are specifically repressed in tobacco and are revealed only when the LTR promoter is placed in a heterologous context. We propose that a tobacco- and stimulus-specific repression has been established in order to minimize activation in conditions that might generate germinal transposition. In addition to tight transcriptional controls, Tnt1A retrotransposons self-regulate their activity through gradual generation of defective copies that have reduced transcriptional activity. Tnt1 retrotransposons found in various Solanaceae species are characterized by a high level of variability in the LTR sequences involved in transcription, and have evolved by gaining new expression patterns, mostly associated with responses to diverse stress conditions. Tnt1A insertions associated with genic regions are initially favored but seem subsequently counter-selected, while insertions in repetitive DNA are maintained. On the other hand, amplification and loss of insertions may result from more brutal occurrences, as suggested by the large restructuring of Tnt1 populations observed in tobacco compared to each of its parental species. The distribution of Tnt1 elements thus appears as a dynamic flux, with amplification counterbalanced by loss of insertions. Tnt1 insertion polymorphisms are too high to reveal species relationships in the Nicotiana genus, but can be used to evaluate species relationships in the Lycopersicon and Capsicum genera. This also demonstrates that the behavior of Tnt1 retrotransposons differs between host species, most probably in correlation to differences in expression conditions and in the evolutionary and environmental history of each host.   

Copyright © 2005 S. Karger AG, Basel

  Author Contacts

Request reprints from Marie-Angele Grandbastien
Laboratoire de Biologie Cellulaire, INRA, Centre de Versailles
FR-78026 Versailles cedex (France)
telephone: +33 1 30 83 30 24; fax: +33 1 30 83 30 99
e-mail: gbastien@versailles.inra.fr
Present address of E.B.: Systématique, Adaptation, Evolution
Equipe: Génétique et Evolution, UMR 7138/CNRS/Paris VI/MNHN/IRD
Université Pierre et Marie Curie, Bât A porte 427
7 quai St Bernard, FR-75252 Paris cedex 05 (France)
Present address of B.C.:
Unité de Recherches en Génomique Végétale (URGV-INRA)
2 rue Gaston Crémieux, CP 5708, FR-91057 Evry cedex (France)
Present address of D.M.: Ecologie Microbienne, UMR CNRS/UCBL1 5557
Université Claude Bernard LYON 1, 43 Boulevard du 11 Novembre 1918
FR-69622 Villeurbanne cedex (France)
Present address of C.P.: INRA UMR Diversité et Génomes des Plantes Cultivées
2 place Viala, bat 33, FR-34060 Montpellier cedex 1 (France)

  Article Information

Manuscript received 24 October 2003;
accepted in revised form for publication by J.-N. Volff 6 April 2004.
Number of Print Pages : 13
Number of Figures : 6, Number of Tables : 0, Number of References : 78