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Proc Natl Acad Sci U S A. 2006 Aug 15;103(33):12329-34. Epub 2006 Aug 7.

A codon deletion confers resistance to herbicides inhibiting protoporphyrinogen oxidase.

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  • 1Department of Crop Sciences, University of Illinois, Urbana, IL 61801, USA.


Herbicides that act by inhibiting protoporphyrinogen oxidase (PPO) are widely used to control weeds in a variety of crops. The first weed to evolve resistance to PPO-inhibiting herbicides was Amaranthus tuberculatus, a problematic weed in the midwestern United States that previously had evolved multiple resistances to herbicides inhibiting two other target sites. Evaluation of a PPO-inhibitor-resistant A. tuberculatus biotype revealed that resistance was a (incompletely) dominant trait conferred by a single, nuclear gene. Three genes predicted to encode PPO were identified in A. tuberculatus. One gene from the resistant biotype, designated PPX2L, contained a codon deletion that was shown to confer resistance by complementation of a hemG mutant strain of Escherichia coli grown in the presence and absence of the PPO inhibitor lactofen. PPX2L is predicted to encode both plastid- and mitochondria-targeted PPO isoforms, allowing a mutation in a single gene to confer resistance to two herbicide target sites. Unique aspects of the resistance mechanism include an amino acid deletion, rather than a substitution, and the dual-targeting nature of the gene, which may explain why resistance to PPO inhibitors has been rare.

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