A Serine-to-Threonine Substitution in the Triazine Herbicide-Binding Protein in Potato Cells Results in Atrazine Resistance without Impairing Productivity

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Abstract
A mutation of the psbA gene was identified in photoautotrophic potato (Solanum tuberosum L. cv Superior x U.S. Department of Agriculture line 66–142) cells selected for resistance to 6-chloro-N-ethyl-N[prime]-(1-methylethyl)-1,3,5-triazine-2,4-diamine (atrazine). Photoaffinity labeling with 6-azido-N-ethyl-N[prime]-(1-methylethyl)-1,3,5-triazine-2,4-diamine detected a thylakoid membrane protein with a Mr of 32,000 in susceptible, but not in resistant, cells. This protein was identified as the secondary quinone acceptor of photosystem II (QB) protein. Atrazine resistance in selected cells was attributable to a mutation from AGT (serine) to ACT (threonine) in codon 264 of the psbA gene that encodes the QB protein. Although the mutant cells exhibited extreme levels of resistance to atrazine, no concomitant reductions in photosynthetic electron transport or cell growth rates compared to the unselected cells were detected. This is in contrast with the losses in productivity observed in atrazine-resistant mutants that contain a glycine-264 alteration.