Biochemical mechanism and molecular basis for ALS-inhibiting herbicide resistance in sugarbeet (Beta vulgaris) somatic cell selections

Abstract

Three sugarbeet selections differing in cross-resistance to three classes of acetolactate synthase (ALS)-inhibiting herbicides have been developed using somatic cell selection. Sugarbeet selections resistant to imidazolinone herbicides,Sir-13and93R30B, do not metabolize [14C]-imazethapyr any faster or differently than sensitive, wild-type sugarbeets or a sulfonylurea-resistant/imidazolinone-sensitive selection, Sur. ALS specific activity from the three herbicide-resistant selections ranged from 73 to 93% of the wild-type enzyme extracts in the absence of herbicide, indicating enzyme overexpression was not a factor in resistance. Acetolactate synthase from Sir-13 plants showed a 40-fold resistance to imazethapyr but no resistance to chlorsulfuron or flumetsulam. Polymerase chain reaction amplification and sequencing of two regions of the ALS gene spanning all known sites for ALS-based herbicide resistance in plants indicated a single nucleotide change in theSir-13gene (G337to A337) resulting in a deduced substitution of threonine for alanine at position 113 in the sugarbeet amino acid sequence. Sur ALS was not significantly resistant to imazethapyr, but was 1,000- and 50-fold resistant to chlorsulfuron and flumetsulam, respectively.Surgene sequencing indicated a single nucleotide change(C562to T562) resulting in a serine for proline substitution at position 188 of the ALS primary structure. The93R30Bnucleotide sequence indicated two mutations resulting in two deduced amino acid substitutions: threonine for alanine at position 113 plus serine for proline at position 188. The93R30Bdouble mutant incorporated the changes observed in each of the single mutants above and correlated with higher resistance levels to imazethapyr (> 1,000-fold), chlorsulfuron (4,300-fold), and flumetsulam (200-fold) at the ALS level than observed in either of the single mutants.93R30Brepresents the first double mutant derived by a two-step selection process that incorporates two class-specific ALS-inhibitor resistance mutations to form a single broad cross-resistance trait. The interaction of the two altered amino acids is synergistic with respect to enzyme resistance vs. the resistance afforded by each of the individual mutations.

Mutations inALSconfer herbicide resistance in redroot pigweed (Amaranthus retroflexus) and Powell amaranth (Amaranthus powellii)

“…A guanine to adenine mutation at position 349 of the gene encoded the Ala 122 Thr substitution that was found in individuals from redroot pigweed population Caledonia 43 and Powell amaranth populations McKillop 9, Brigden 33, Brigden 36, and Brigden 39. This amino acid substitution has previously been reported in field-selected common cocklebur and eastern black nightshade (Solanum ptycanthum L.) and in laboratory-selected mutants of sugar beet (Beta vulgaris L.), tobacco, and corn (Bernasconi et al 1996;Chong and Choi 2000;Milliman et al 2003;Siehl et al 1996;Wright et al 1998). It is generally agreed that this mutation confers resistance to IMI herbicides but not to SUs (Tranel and Wright 2002).…”

Cross‐resistance pattern and alternative herbicides for Cyperus difformis resistant to sulfonylurea herbicides in Korea

“…These are single point mutations, which can occur at multiple sites in the ALS gene, resulting in a variable pattern of cross‐resistance between different classes of ALS inhibitors 32. Point mutations in at least four domains of the ALS protein have been associated with in vivo resistance in field‐ or laboratory‐grown plants 33. In resistant biotypes selected by sulfonylureas and triazolopyrimidines, the point mutation occurs in domain A, which codes for 13 amino acids, wherein any substitution for Pro confers resistance 31, 34.…”

Glutamine synthetase mutation conferring target‐site‐based resistance to glufosinate in soybean cell selections

“…Use of plant tissue culture for this purpose has facilitated the development of herbicide‐resistant plants and paved the way to better understanding of the biochemical and molecular bases of resistance to herbicides. Resistant cell lines have been reported in many crops: rice resistant to cyhalofop‐butyl,1 soybean resistant to protoporphyrinogen oxidase (Protox) inhibiting herbicides,2, 3 sugarbeet resistant to imidazolinone herbicides4 and sugarcane resistant to glyphosate 5. In addition, cell cultures resistant to glutamine synthetase (GS) inhibitors have been selected and characterized 6–8.…”