CHARACTERIZATION OF POST-TRANSCRIPTIONALLY SUPPRESSED TRANSGENE EXPRESSION THAT CONFERS RESISTANCE TO TEV INFECTION IN TOBACCO
M M TANZER1,2, M LAW4, W F THOMPSON2, E A WERNSMAN3 and S UKNES1 1Paradigm Genetics, Research Triangle Park, NC 27709, USA; 2Department of Botany, NCSU, Raleigh, NC 27695, USA; 3Department of Crop Science, NCSU, Raleigh, NC 27695, USA; 4Novartis BGC, Research Triangle Park, NC 27709, USA
Background and objectives
The second system is comprised of Arabidopsis thaliana lines containing transgenes encoding phosphoribosylanthranilate transferase (PAT1, a member of the tryptophan biosynthetic pathway). These lines also contain an endogenous copy of the PAT1 gene. Silencing of PAT1 mRNA results in a co-suppression phenotype and is similar to PAT1 mutant phenotypes (i.e. blue fluorescence under UV light). However, the pattern of the silenced phenotype is variable among several independent transformants and the number of plants showing the blue fluorescent phenotype varies within homozygous populations. While segregation analysis indicates that the T-DNA insertions segregate as single loci, Southern analysis shows that all lines which silence PAT1 contain multiple T-DNAs. Based on the data from these two systems and from a number of other laboratories, we propose a hypothesis for TEV CP mRNA and PAT1 mRNA silencing in which the initiation of silencing in these two systems may differ while the maintenance mechanism is shared. The implications of this hypothesis in the analysis and development of transgenic plants which stably silence the transgenes will be discussed.