Molecular basis of diverse responses to acetolactate synthase‐inhibiting herbicides in sulfonylurea‐resistant biotypes ofSchoenoplectus juncoides

Abstract

Sulfonylurea-resistant biotypes of Schoenoplectus juncoides were collected from Nakafurano, Shiwa, Matsuyama, and Yurihonjyo in Japan. All of the four biotypes showed resistance to bensulfuron-methyl and thifensulfuron-methyl in whole-plant experiments. The growth of the Nakafurano, Shiwa, and Matsuyama biotypes was inhibited by imazaquin-ammonium and bispyribac-sodium, whereas the Yurihonjyo biotype grew normally after treatment with these herbicides. The herbicide concentration required to inhibit the acetolactate synthase (ALS) enzyme by 50% (I 50 ), obtained using in vivo ALS assays, indicated that the four biotypes were > 10-fold more resistant to thifensulfuron-methyl than a susceptible biotype. The Nakafurano, Shiwa, and Matsuyama biotypes exhibited no or little resistance to imazaquin-ammonium, whereas the Yurihonjyo biotype exhibited 6700-fold resistance to the herbicide. The Nakafurano and Shiwa biotypes exhibited no resistance to bispyribac-sodium, but the Matsuyama biotype exhibited 21-fold resistance and the Yurihonjyo biotype exhibited 260-fold resistance to the herbicide. Two S. juncoides ALS genes (ALS1 and ALS2) were isolated and each was found to contain one intron and to encode an ALS protein of 645 amino acids. Sequencing of the ALS genes revealed an amino acid substitution at Pro 197 in either encoded protein (ALS1 or ALS2) in the biotypes from Nakafurano (Pro 197 →Ser 197 ), Shiwa (Pro 197 →His 197 ), and Matsuyama (Pro 197 →Leu 197 ). The ALS2 of the biotype from Yurihonjyo was found to contain a Trp 574 →Leu 574 substitution. The relationships between the responses to ALS-inhibiting herbicides and the amino acid substitutions, which are consistent with previous reports in other plants, indicate that the substitutions at Pro 197 and Trp 574 are the basis of the resistance to sulfonylureas in these S. juncoides biotypes.

Molecular Basis of Blackgrass (Alopecurus Myosuroides HUDS.) Resistance to Sulfonylurea Herbicides

“…Substitutions in position 197 were previously described for A. myosuroides biotypes originated from France (Délye and Boucansaud 2008), as well as in biotypes of other species: Bromus tectorum L. (Park and Mallory-Smith 2004), Hordeum leporinum (Yu et al 2007), Schoenoplectus juncoides var. Ohwianus (Uchino et al 2007) and Lolium rigidum Gaudin (Yu et al 2008). In each mentioned case, mutation of Pro197 conferred a high level of resistance to sulfonylureas -which corresponds perfectly with the results of the experiment described in this paper.…”

Herbicide sensitivities of mutated enzymes expressed from artificially generated genes of acetolactate synthase

“…11) Among these weeds, Lindenia spp., Schoenoplectus juncoides and Monochoria vaginalis have been strictly evaluated for mutations of ALS genes, and it has been elucidated that biotypes of these weeds resistant to SU herbicides had mutations at the P171 position or the W548 position. [12][13][14][15] As for the W548 position, only leucine (L) substitution for tryptophan (W) has been shown in weeds, and this substitution confers resistance to all types of ALS-inhibiting herbicides, while substitutions of various amino acids for proline (P) have been reported in the P171 position of various weeds, and resistance levels of mutated ALSs to ALS-inhibiting herbicides are known to vary among amino acid substitutions and the tested herbicides.…”

“…It has been shown that Arabidopsis ALS is composed of 4 catalytic subunits and 4 regulatory subunits, 16,17) and a point-mutation occurred in one of multi-ALS genes of weed species. 11,13,14) This indicated that the ALS of an ALS-inhibiting herbicide-resistant weed becomes chimeric, which is composed of both the wild-type form and the mutant form of the catalytic subunit, with the re- When the I 50 value could not be obtained, each inhibitory activity was represented as the mean of inhibition percentages at 100 mM concentration of the herbicide and expressed in parentheses. When the I 50 value could not be obtained, each inhibitory activity was represented as the mean of inhibition percentages at 100 mM concentration of the herbicide and expressed in parentheses.…”

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

“…Metal halide lamps for plants (360 W×2) were used to provide light at speci c times. A sandy soil was added to 200 cm 2 Wagner pots a er the underdrain was constructed, and gravel was placed inside. As a basal dressing, fertilizer was applied at 72, 96, and 84 mg of N, P 2 O 5 , and K 2 O per pot, respectively.…”

“…2,3) Currently, SU-resistant weeds are controlled by mixing SU herbicides with other herbicides having modes of action di erent from that of SU herbicides. 4) Moreover, since SU herbicides used in paddy elds in Japan are not su ciently effective against grass weeds, other grass herbicides are o en added.…”