Multiple Pro₁₉₇Substitutions in the Acetolactate Synthase of Corn Poppy (Papaver rhoeas) Confer Resistance to Tribenuron

Abstract

Variations in the acetolactate synthase (ALS) gene sequence were determined from 28 populations of corn poppy resistant (R) to tribenuron and from 6 populations susceptible (S) to this herbicide. TheALSgene fragment (634 bp) sequence revealed in R populations five point mutations at the codon Pro197, and among them the substitution of Pro197by Ala was the most common. The sequencing chromatograms revealed that nine R individuals had only the mutantALSgene and were homozygous (RR), 18 R individuals had both the wild type and the mutantALSgene and were heterozygous (RS), whereas one R individual was heterozygous but with two different mutantALSalleles (R1R2). The use of restriction digestion profile analysis to verify the DNA sequence results by detecting the existence of point mutations at the codon 197 managed to distinguish the R and S alleles and confirmed the results obtained from the sequencing chromatograms analysis. The secondary protein structure prediction suggested the formation of novelβ-strands for each of the five mentioned amino acid substitutions that was not present in wild type ALS around the mutant site. These findings support the hypothesis that the substitution of Pro197by Ser, Thr, Ala, Arg, or Leu resulted in altered secondary structure, which stabilizes an ALS tertiary conformation that prevents tribenuron binding and thus confers resistance to this herbicide.

Tribenuron-methyl resistance and mutation diversity of Pro197 in flixweed (Descurainia Sophia L.) accessions from China

“…Several DNA based techniques have been developed for resistance diagnosis. These included PCR-RFLP [33], dCAPS [3,8] and CAPS [34]. All these DNA-based methods are rapid, low-cost and readily available, and thus suitable for screening of hundreds of samples.…”

Occurrence, genetic control and evolution of non-target-site based resistance to herbicides inhibiting acetolactate synthase (ALS) in the dicot weed Papaver rhoeas

“…Resistance endowed by mutant ALS alleles (i.e., TSR) is the resistance mechanism to ALS inhibitors most frequently reported in P. rhoeas [29][30][31][32][33]. However, observation of differences in sensitivity to ALS inhibitors among plants with the same TSR genotype had recently led to question whether TSR to ALS inhibitors could occur together with NTSR mechanisms in the same P. rhoeas plant [33].…”

“…Previous studies that addressed resistance to ALS inhibitors in P. rhoeas identified TSR and left it at that or assumed TSR was the only resistance mechanism present in P. rhoeas. Thus, possible occurrence of NTSR was not investigated [29][30][31][32]. It is thus highly likely that NTSR occurrence in P. rhoeas populations is largely underestimated because of the widespread and frequent occurrence of TSR that deters investigators to check whether NTSR may also be present in the resistant plants.…”

“…In all cases studied, TSR has been identified. The mutation(s) responsible for the resistance were essentially found at codon Pro197 in the ALS gene [29][30][31][32][33] and, in extremely low frequency, at codon Trp574 [33]. However, recent results have shown that P. rhoeas plants with identical genotypes at ALS could exhibit differences in sensitivity to ALS inhibitors [33].…”

Management of herbicide-resistant Papaver rhoeas in dry land cereal fields

“…Spain (Duran-Prado et al 2004;Cirujeda et al 2001), Italy (Scarabel et al 2004), Greece (Kaloumenos et al 2009), Denmark and UK (Heap 2009), threatening the profitability of cereal production systems. Moreover, P. rhoeas populations resistant to photosystem II inhibiting herbicides have recently been found in Poland (Kucharski and Rola 2007).…”