First published online September 14, 2004; 10.1105/tpc.104.024547
The Plant Cell 16:2561-2572 (2004)
© 2004 American Society of Plant Biologists
Silencing in Arabidopsis T-DNA Transformants: The Predominant Role of a Gene-Specific RNA Sensing Mechanism versus Position Effects
Daniel Schubert1,2,
Berthold Lechtenberg1,3,
Alexandra Forsbach4,
Mario Gils5,
Sultan Bahadur6 and
Renate Schmidt7
Max-Planck-Institut für Molekulare Pflanzenphysiologie, 14476 Golm, Germany
7 To whom correspondence should be addressed. E-mail rschmidt{at}mpimp-golm.mpg.de; fax 49-331-567-8408.
Pronounced variability of transgene expression and transgene silencing are commonly observed among independent plant lines transformed with the same construct. Single-copy T-DNA lines harboring reporter genes of various kind and number under the control of a strong promoter were established in Arabidopsis thaliana for a comprehensive analysis of transgene expression. Characterization of 132 independent transgenic lines revealed no case of silencing as a result of site of T-DNA integration. Below a certain number of identical transgenes in the genome, gene copy number and expression were positively correlated. Expression was high, stable over all generations analyzed, and of a comparable level among independent lines harboring the same copy number of a particular transgene. Conversely, RNA silencing was triggered if the transcript level of a transgene surpassed a gene-specific threshold. Transcript levelmediated silencing effectively accounts for the pronounced transgene expression variability seen among transformants. It is proposed that the RNA sensing mechanism described is a genome surveillance system that eliminates RNA corresponding to excessively transcribed genes, including transgenes, and so plays an important role in genome defense.
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