title: A codon deletion confers resistance to herbicides inhibiting protoporphyrinogen oxidase.
abstract: 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.
authors.affiliation: Department of Crop Sciences, University of Illinois, Urbana, IL 61801, USA.
authors.forename: William L
authors.initials: WL
authors.lastname: Patzoldt
authors.forename: Aaron G
authors.initials: AG
authors.lastname: Hager
authors.forename: Joel S
authors.initials: JS
authors.lastname: McCormick
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Tranel
mesh_terms: D027721:Amaranthus / Q000201:enzymology* / Q000235:genetics; D001665:Binding Sites; D003062:Codon; D005816:Genetic Complementation Test; D055768:Halogenated Diphenyl Ethers; D006540:Herbicides / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010647:Phenyl Ethers / Q000378:metabolism; D050768:Protoporphyrinogen Oxidase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
chemical_list: D003062:Codon; D055768:Halogenated Diphenyl Ethers; D006540:Herbicides; D010647:Phenyl Ethers; D050768:Protoporphyrinogen Oxidase; C055370:lactofen