The molecular basis of sulfonylurea herbicide resistance in tobacco

Abstract

The enzyme acetolactate synthase (ALS) is the target enzyme for the sulfonylurea and imidazolinone herbicides. We describe the isolation and characterization of the ALS genes from two herbicide‐resistant mutants, C3 and S4‐Hra, of Nicotiana tabacum. There are two distinct ALS genes in tobacco which are 0.7% divergent at the amino acid sequence level. The C3 mutant has a single Pro–Gln replacement at amino acid 196 in one ALS gene. This gene is termed the class I gene and is equivalent to the SuRA locus. The S4‐Hra mutant has two amino acid changes in the other ALS gene. This gene is termed the class II gene or the SuRB locus. The S4‐Hra mutant includes a Pro–Ala substitution at amino acid 196 and a Trp–Leu substitution at amino acid 573. Gene reintroduction experiments have confirmed that these amino acid substitutions are responsible for the herbicide resistance phenotypes. Transgenic plants carrying these genes are highly resistant to sulfonylurea herbicide applications.

A Mutation Causing Imidazolinone Resistance Maps to the Csr1 Locus of Arabidopsis thaliana

“…Single dominant mutations resulting in resistance to sulfonylurea compounds in microorganisms (6,23) and plants (2,3,7) have been shown to be due to single base pair substitutions in genes encoding the AHAS catalytic subunit (10,14,23).…”

Transgenic Tall Fescue and Maize with Resistance to ALS-Inhibiting Herbicides

“…The most commonly encountered mutations involve the residues of alanine at position 96 (A96), proline at position 171 (P171), tryptophane at position 548 (W548) and serine at position 627 (S627); Mutations were described using the rice numbering system. The mutation of the residue of tryptophane 548 substituted with leucine (W548L) was first isolated together with the mutation of the residue of proline at position 171 substituted with alanine (P171A) in tobacco (Nicotiana tabacum L.) by selection using SU (Lee et al, 1988). Subsequently, the mutation has been found in maize (Bernasconi et al, 1995) and canola ( Hattori et al, 1995).…”

“…The mutation at this position leading to S627A, S627N, S627T and S627F has been analyzed in Arabidopsis by site-directed mutagenesis (Lee et al 1999). Double mutations such as P171A/W548L in tobacco (Lee et al, 1988), P171S/S627N in Arabidopsis (Hattori et al, 1992) and A96T/P171S in sugar beets (Beta vulgaris L.) (Wright et al, 1998) have been reported. Some amino acid substitutions conferring herbicide resistance are well conserved in plant ALS (Tan et al, 2005).…”

A system for insertional mutagenesis and chromosomal rearrangement using the Ds transposon and Cre—lox

“…The transposon was inserted into a 35S-surA,B fusion (Lee et aL, 1988;Mazur et aL, 1987), which confers resistance to the herbicide chlorsulfuron (Cs, or sulfonylurea). The insertion of Dslox into T-DNAIox inactivates 35S-surA,B, and Dslox excision confers a Cs R phenotype.…”