Systematic silencing of a tobacco nitrate reductase transgene in lettuce (Lactuca sativa L.).
A population of 50 independent transgenic lettuces transformed with a nitrate reductase coding sequence under the control of the 35S promoter was studied. None of them showed significantly lower nitrate levels when compared with the untransformed plants, despite the presence of nitrate reductase (NR) activity that derives from the transgene in at least four of the transformants. No repercussion on total NR activity (endogenous+transgenic) was detected in these plants. Nevertheless, 28% of the transformants showed phenotypes characteristic of a general silencing of the NR genes as already described in tobacco and potato, i.e. bleaching of the leaves leading to the death of the plant. By northern blots, it was shown that the transgene was silenced in these chlorotic plants and also in the plants that did not show symptoms of chlorosis. Thus a silencing process specifically directed against the NR mRNA derived from the transgene occurred very early in the development of all the plants studied, whatever homologous endogenous NR mRNA is present in the plant. In some cases this transgene-specific silencing was shown subsequently to extend to the homologous endogenous NR mRNA. These results suggest that, in lettuce, the level of nitrate reductase mRNA is under tight expression control and this is able specifically to target transgenic transcripts by a post-transcriptional gene silencing (PTGS) mechanism during the first stage of development of the plantlet.
Dubois
Vincent
V
INRA, Unité de Génétique et Amélioration des Fruits et Légumes, UR 1052, domaine St Maurice BP 94, F-84143 Montfavet cedex, France.
Botton
Emmanuel
E
Meyer
Christian
C
Rieu
Aline
A
Bedu
Magali
M
Maisonneuve
Brigitte
B
Mazier
Marianne
M
D018744:DNA, Plant / Q000235:genetics; D020868:Gene Silencing; D017343:Genes, Plant; D005838:Genotype; D018545:Lactuca / Q000201:enzymology*; D018515:Plant Leaves / Q000201:enzymology; D030821:Plants, Genetically Modified / Q000201:enzymology*; D015183:Restriction Mapping; D011198:Solanum tuberosum / Q000201:enzymology / Q000235:genetics; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics
D018744:DNA, Plant