HERBICIDE SAFENER-BINDING PROTEIN OF MAIZE - PURIFICATION, CLONING, AND EXPRESSION OF AN ENCODING CDNA

Dichloroacetamide safeners protect maize (Zea mays L.) against injury from chloroacetanilide and thiocarbamate herbicides. Etiolated maize s eedlings have a high-affinity cytosolic-binding site for the safener ) -3-dichloroacetyl-2,2,5-trimethyl-1,3-oxazolidine ([H-3]Saf), and this safener-binding activity (SafBA) is competitively inhibited by the he rbicides. The safener-binding protein (SafBP), purified to homogeneity , has a relative molecular weight of 39,000, as shown by sodium dodecy l sulfate-polyacrylamide gel electrophoresis, and an isoelectric point of 5.5. Antiserum raised against purified SafBP specifically recogniz es a 39-kD protein in etiolated maize and sorghum (Sorghum bicolor L.) , which have SafBA, but not in etiolated wheat (Triticum aestivum L.), oat (Avena sativa L.), barley (Hordeum vulgare L.), tobacco (Nicotian a tabacum L.), or Arabidopsis, which lack SafBA. SafBP is most abundan t in the coleoptile and scarcest in the leaves, consistent with the di stribution of SafBA. SBP1, a cDNA encoding SafBP, was cloned using pol ymerase chain reaction primers based on purified proteolytic peptides. Extracts of Escherichia coli cells expressing SBP1 have strong [H-3]S af binding, which, like binding to the native maize protein, is compet itively inhibited by the safener dichlormid and the herbicides S-ethyl dipropylthiocarbamate, alachlor, and metolachlor. SBP1 is predicted t o encode a phenolic O-methyltransferase, but SafBP does not O-methylat e catechol or caffeic acid. The acquisition of its encoding gene opens experimental approaches for the evaluation of the role of SafBP in re sponse to the relevant safeners and herbicides.