Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2000
Publication Date: October 1, 2000
Interpretive Summary: Two cotton plants that were genetically modified for herbicide resistance were studied. Genetic analysis revealed that these supposedly random events resulted in herbicide resistance DNA being inserted into the same region of the cotton DNA. The analysis could not determine if it was the identical DNA site or very close sites. These results are contrary to conventional expectations, and they can impact on how genetically modified cotton plants are developed.
Technical Abstract: We found genetic linkage of two independent gene insertions with a single marker locus. The bacterial gene [2,4-D monooxygenase (tfdA)] was introduced into cotton to provide resistance to 2,4-dichlorophenoxyacetic acid (2,4-D). The gene was inserted by Agrobacterium tumefaciens mediated transformation, and multiple cell lines with the gene insertion were produced. Transformed cell lines were verified first to contain the introduced DNA, and transgenic plants were evaluated for expression of resistance to 2,4-D. Transgenic plants that survived the screening were then progeny tested for inheritance and level of expression of the gene insertion. Separate germlines that exhibit monogenic dominance for resistance to 2,4-D were retained, and we selected two for linkage analysis. Multiple marker lines T582 and T586 were crossed with the two 2,4-D resistant lines. F1, P2, and backcross/testcross progeny were produced and evaluated for segregation of resistance to 2,4-D and the marker loci. Linkage was found between 2,4-D resistance of both transgenic lines and the Naked seed-1 morphological marker. Only two-point linkage tests were possible, so the orientations on the chromosome with respect to the marker could not be determined. Linkage values from the two transformants were consistently different but not statistically significant. Both transgenes were inserted into the same chromosome, but we are not able to determine the specific site(s). Preliminary data suggests close but different locations. Crosses have been made to produce segregating progeny that will be able to distinguish independence of the insertion sites and chromosome orientation.