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This work started while J. Walton was on sabbatical in the laboratory of John Casida, UC Berkeley, in 1993 and 1994. The work has been supported by Ciba-Geigy (now Syngenta).Abstract from Scott-Craig et al. (1998):
Dichloroacetamide safeners protect maize against injury from chloroacetanilide and thiocarbamate herbicides. Etiolated maize seedlings have a high-affinity cytosolic binding site for the safener [3H](R,S)-3-dichloroacetyl-2,2,5-trimethyl-1,3-oxazolidine ([3H]Saf) and this safener binding activity (SafBA) is competitively inhibited by the herbicides themselves. The safener binding protein (SafBP), purified to homogeneity, has an Mr of 39,000 by SDS-PAGE and an isoelectric point of 5.5. Antiserum raised against purified SafBP specifically recognizes a 39-kD protein in etiolated maize and sorghum, which have SafBA, but not in etiolated wheat, oat, barley, tobacco, or Arabidopsis, which lack SafBA. SafBP is most abundant in the coleoptile and scarcest in leaves, consistent with the distribution of SafBA. A cDNA, SBP1, encoding SafBP was cloned using PCR primers based on purified proteolytic peptides. Extracts of Escherichia coli cells expressing SBP1 have strong [3H]Saf binding that, like binding to the native maize protein, is competitively inhibited by the safener dichlormid and the herbicides EPTC, alachlor, and metolachlor. SBP1 is predicted to encode a phenolic O-methyltransferase, but SafBP does not O-methylate catechol or caffeic acid. The availability of its encoding gene opens experimental approaches for the evaluation of the role of SafBP in response to the relevant safeners and herbicides.
Figure: [coming soon] Structures of representative safeners (R-29148, dichlormid) and herbicides against which the safeners protect (EPTC, alachlor). Safeners also protect against metolachlor and acetochlor. Of the cereals, only sorghum and maize respond to safeners. Our work shows that only these two plants have safener activity, safener binding protein, and the gene safener binding protein.
Papers on Safeners:
Scott-Craig, J.S., L. Poduje, J.E. Casida, and J.D. Walton (1998) Herbicide safener binding protein of maize: purification, and cloning and expression of an encoding cDNA. Plant Physiol. 116:1083-1089.
Walton, J.D. and J.E. Casida (1995) Specific binding of a dichloroacetamide herbicide safener in maize at a site that also binds thiocarbamate and chloroacetanilide herbicides. Plant Physiol. 109:213-219.
Patents
U. S. 5,973,229 "Gene encoding herbicide safener binding protein". Inventors: J.D. Walton and J.S. Scott-Craig. Issued October 26, 1999