Herbicide resistance and supersensitivity in Ala(250) or Ala(251) mutants of the D1 protein in Chlamydomonas reinhardtii

Various site-directed mutants at position Ala(250) or Ala(251) within the h erbicide-binding niche of the D1 subunit of photosystem II were generated b y transforming a Chlamydomonas reinhardtii strain specifically engineered t o lack a psbA gene fragment coding for the binding region. The following mu tants were obtained: Asp(250), Phe(250), His(250), Ile(250), Asn(250), Arg( 250), Tyr(250), Cys(251), Gly(251), and the double mutant Ser(250)/Ile(255) . A variety of herbicides and inhibitors, such as s-triazines, phenolic her bicides, p-benzo- and naphthoquinones, acridones, a NH-thiazol, and phenmed ipham, were assayed for their inhibitory activity in these mutants. In addi tion, in the Ser(250)/Ile(255) mutant 32 different triazinones were tested for biological activity. In all mutants, either resistance and/or supersens itivity against the herbicides and inhibitors was observed. The resistance and/or supersensitivity against inhibitors in the Ala(250) mutants demonstr ated for the first time the involvement of this amino acid in herbicide bin ding. (C) 2000 Academic Press.