Insertion of transgenes in oats resulted in modification of both the
transgenic construct and host DNA.
Oat (Avena sativa).
Transgenic oat line 3830 contained a gene construct with
two marker genes: gusA fused to the AdhI promoter, and
nptII fused to the cauliflower mosaic virus (CaMV-35S) promoter.
Transgenic oat line 11929 contained two different gene constructs: the
nptII marker gene fused to the CaMV-35S promoter and the gusA
marker gene fused to the sugarcane bacilliform virus promoter. Both
transgenic lines expressed the transgenes.
Goal of This Study:
Investigate how gene constructs are integrated into the plant's
genome. The two lines chosen had been selected from other transgenic
lines because their introduced gene constructs appeared to be integrated
in the host genome at only one site (locus). These lines were developed
by microprojectile bombardment.
Results of This Study:
In both lines the gene constructs were not
integrated into single sites in an unchanged fashion, which would have
been the desired result. Rather, "full-length and partially truncated
copies of the delivered DNA were integrated in different orientations,
interspersed with regions of extensively scrambled transgene and genomic
[oat] DNA sequences, and, in two cases, flanked by rearranged genomic
[oat] DNA" (p. 429).
These specific transgenic lines of oats had been selected for this study
because each gene construct appeared to be integrated at a single site
in the oat genome. In the majority of transgenic lines derived through
microprojectile bombardment, this is not the case. Line 3830 was one of
only three lines that showed simple and single integration sites, from
a total of 16 lines. Line 11929 was one of only four lines that showed
simple insertions, from a total of 20 lines. Closer investigation of line
3830 showed that there were two smaller integration sites, which had gone
undetected in previous studies, in addition to the major integration site
with the functional gene. This study indicates, therefore, that simple
transgene integration occurs in a minority of cases and even when it
occurs there is extensive alteration in the gene construct as well as
in host-plant DNA in and around the integration site.
Since this study focused only on transgene integration, the researchers
did not investigate whether there were any physiological or morphological
nontarget effects associated with the integration.
Makarevitch, I., S. K. Svitashev, and D. A. Somers (2003).
"Complete Sequence Analysis of Transgene Loci From Plants Transformed
Via Microprojectile Bombardment," Plant Molecular Biology vol. 52,
Department of Agronomy and Plant Genetics, University
USDA National Research Initiative Plant Genome Program grant.
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