title: Distinct non-target site mechanisms endow resistance to glyphosate, ACCase and ALS-inhibiting herbicides in multiple herbicide-resistant Lolium rigidum.
abstract: This study investigates mechanisms of multiple resistance to glyphosate, acetyl-coenzyme A carboxylase (ACCase) and acetolactate synthase (ALS)-inhibiting herbicides in two Lolium rigidum populations from Australia. When treated with glyphosate, susceptible (S) plants accumulated 4- to 6-fold more shikimic acid than resistant (R) plants. The resistant plants did not have the known glyphosate resistance endowing mutation of 5-enolpyruvylshikimate-3 phosphate synthase (EPSPS) at Pro-106, nor was there over-expression of EPSPS in either of the R populations. However, [(14)C]-glyphosate translocation experiments showed that the R plants in both populations have altered glyphosate translocation patterns compared to the S plants. The R plants showed much less glyphosate translocation to untreated young leaves, but more to the treated leaf tip, than did the S plants. Sequencing of the carboxyl transferase domain of the plastidic ACCase gene revealed no resistance endowing amino acid substitutions in the two R populations, and the ALS in vitro inhibition assay demonstrated herbicide-sensitive ALS in the ALS R population (WALR70). By using the cytochrome P450 inhibitor malathion and amitrole with ALS and ACCase herbicides, respectively, we showed that malathion reverses chlorsulfuron resistance and amitrole reverses diclofop resistance in the R population examined. Therefore, we conclude that multiple glyphosate, ACCase and ALS herbicide resistance in the two R populations is due to the presence of distinct non-target site based resistance mechanisms for each herbicide. Glyphosate resistance is due to reduced rates of glyphosate translocation, and resistance to ACCase and ALS herbicides is likely due to enhanced herbicide metabolism involving different cytochrome P450 enzymes.
authors: Western Australian Herbicide Resistance Initiative, School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, WA 6009, Australia.
authors: Qin
authors: Q
authors: Yu
authors: Ibrahim
authors: I
authors: Abdallah
authors: Heping
authors: H
authors: Han
authors: Mechelle
authors: M
authors: Owen
authors: Stephen
authors: S
authors: Powles
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase / Q000235:genetics; D000095:Acetolactate Synthase / Q000037:antagonists & inhibitors*; D000103:Acetyl-CoA Carboxylase / Q000037:antagonists & inhibitors; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D065607:Cytochrome P-450 Enzyme Inhibitors; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005998:Glycine / Q000031:analogs & derivatives* / Q000633:toxicity; D055768:Halogenated Diphenyl Ethers / Q000633:toxicity; D053209:Herbicide Resistance; D006540:Herbicides / Q000633:toxicity*; D008129:Lolium / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012765:Shikimic Acid / Q000378:metabolism; D000097797:Glyphosate
chemical_list: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D000095:Acetolactate Synthase; D000103:Acetyl-CoA Carboxylase; D002250:Carbon Radioisotopes; D065607:Cytochrome P-450 Enzyme Inhibitors; D005998:Glycine; D055768:Halogenated Diphenyl Ethers; D006540:Herbicides; D012765:Shikimic Acid; D000097797:Glyphosate; C012891:dichlorfop-methyl