Nucleotide substitutions in the acetolactate synthase genes of sulfonylurea-resistant biotypes of Monochoria vaginalis (Pontederiaceae)

Abstract

Some point mutations in acetolactate synthase (ALS) confer resistance to ALSinhibiting herbicides in weeds. To clarify the evolution of the herbicide resistance of Monochoria vaginalis, a weed in rice fields in Japan, the nucleotide sequences of four genes encoding ALS were surveyed in five sulfonylurea-resistant (SU-R) and five sulfonylurea-susceptible (SU-S) biotypes. In the ALS1 gene, two SU-R biotypes showed nucleotide substitutions changing Pro 197 to Ser and Leu, respectively. In a different gene, ALS3, three other SU-R biotypes showed either of the two nonsynonymous nucleotide substitutions seen in ALS1. Only two biotypes geographically located distantly from each other shared the same mutation conferring SU resistance in the same gene. These patterns of nucleotide substitutions indicate that the SU-R phenotype was acquired independently by different biotypes. Nucleotide diversity values of the genes showing SU-R mutations were higher than those of ALS2 lacking any SU-R mutation and of a putative pseudogene, ALS4. This result suggests that the maintenance of nucleotide variability within target genes provides an opportunity for the evolution of SU-R phenotypes by herbicide-driven selection for mutations conferring resistance.

Resistance to AHAS inhibitor herbicides: current understanding

“…Herbicide target gene copies in polyploid species may all be expressed, but at different levels, or some may be silenced, or become pseudogenes (e.g. with frame shift and premature stop codon) . There can be epigenetic regulation (by DNA methylation) of AHAS gene expression .…”

Properties of controlled-release formulation of pyrimisulfan as a one-shot herbicide in a paddy field

“…e mutation sites of acetolactate synthase (ALS) genes of these SU-resistant weeds have been determined by PCR-RFLP. [10][11][12] Plants of SU-resistant weeds were initially screened by applying bensulfuron-methyl (75 g (121°C, 20 min), was added to a 450 mL plastic cup, followed by the addition of 200 mL water. Pre-diluted 10% WP pyrimisulfan was then added to the cup at 0, 0.2, 1.0, 2.0, 4.0, 8.0, 12, 16, 20, 40, 80, and 120 ppb.…”

Genetic diversity of sulfonylurea‐resistant and ‐susceptible Monochoria vaginalis populations in Japan

“…However, amino acid substitutions at Ala 122 and Ser 653 result in resistant to other ALS inhibiting herbicides classes but not to SU herbicides (Tranel & Wright, 2002). Ohsako and Tominaga (2007) suggested that approximately six copies of ALS gene homologues exist in the genome of M. vaginalis . Of these copies, four – ALS1 , ALS2, ALS3 and ALS4 , were characterised and amino acid substitutions that confer resistance to ALS inhibitors have been detected only in loci ALS1 and ALS3 (Ohsako & Tominaga, 2007).…”

“…Ohsako and Tominaga (2007) suggested that approximately six copies of ALS gene homologues exist in the genome of M. vaginalis . Of these copies, four – ALS1 , ALS2, ALS3 and ALS4 , were characterised and amino acid substitutions that confer resistance to ALS inhibitors have been detected only in loci ALS1 and ALS3 (Ohsako & Tominaga, 2007). At least seven different nucleotide substitutions conferring SU‐R have been found in M. vaginalis ; Pro 197 Ser and Pro 197 Leu in ALS1 , Pro 197 Ser and Pro 197 Leu in ALS3 (Ohsako & Tominaga, 2007), Pro 197 Thr in the ALS1 and Pro 197 His in the ALS3 (H. Inagaki, T. Imaizumi, G.X.…”