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Unintended Effects of Genetic Manipulation
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Insertion of transgenes in oats resulted in modification of both the transgenic construct and host DNA.

Manipulated Organism: Oat (Avena sativa).

Inserted Transgenes: 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).

Additional Comments: 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.

Source: 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, pp. 421-32.

Author Affiliations: Department of Agronomy and Plant Genetics, University of Minnesota.

Funding: USDA National Research Initiative Plant Genome Program grant.

Product Status: Not on the market as of 2008.

Copyright 2008 The Nature Institute.

This document: http://natureinstitute.org/nontarget/reports/oat_001.php

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