Relocating a gene for herbicide tolerance: A chloroplast gene is converted into a nuclear gene.
The chloroplast gene psbA codes for the photosynthetic quinone-binding membrane protein Q(B), which is the target of the herbicide atrazine. This gene has been converted into a nuclear gene. The psbA gene from an atrazine-resistant biotype of Amaranthus hybridus has been modified by fusing its coding region to transcription-regulation and transit-peptide-encoding sequences of a bona fide nuclear gene. The constructs were introduced into the nuclear genome of tobacco by using the Agrobacterium tumor-inducing (Ti) plasmid system, and the protein product of nuclear psbA has been identified in the photosynthetic membranes of chloroplasts. Recovery of atrazine-tolerant transgenic plants shows that the product of the transplanted gene functions in photosynthesis. These experiments show that it is possible to modify chloroplast-gene-specified functions via nuclear-genome transformation and also raise evolutionary questions.
Department of Cellular and Developmental Biology, 16 Divinity Avenue, The Biological Laboratories, Harvard University, Cambridge, MA 02138.
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Cheung
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Bogorad
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Van Montagu
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Schell