Target-site and non-target-site resistance mechanisms confer mesosulfuron-methyl resistance in Alopecurus aequalis.

BACKGROUND: Shortawn foxtail (Alopecurus aequalis Sobol.) is a noxious weed in China. The resistance of A. aequalis developed rapidly due to the long-term application of acetolactate synthase (ALS)-inhibiting herbicides. Here, a suspected mesosulfuron-methyl-resistant A. aequalis population, Aa-R, was collected from a wheat field in China. RESULTS: A dose‒response test showed that the Aa-R population has evolved a high level of resistance to mesosulfuron-methyl, and its growth was suppressed by imazamox, pyroxsulam and bispyribac-sodium. ALS gene sequence analysis revealed that a known resistance-related mutation (Pro-197-Thr) was present in the Aa-R population. Moreover, ALS gene overexpression was detected in the Aa-R population. The mesosulfuron-methyl resistance could be reversed by cytochrome P450 monooxygenase (CYP450) and glutathione S-transferase (GST) inhibitors. In addition, enhanced metabolism of mesosulfuron-methyl was detected in the Aa-R population compared with the susceptible population. NADPH-cytochrome P450 reductase and GST activities were strongly inducible in the Aa-R population. One CYP450 gene, CYP74A2, and one GST gene, GST4, were constitutively upregulated in the Aa-R population. Molecular docking results showed the binding affinity of CYP74A2 and GST4 for the tested ALS-inhibiting herbicides, respectively. CONCLUSION: This study confirmed that target-site resistance and non-target-site resistance involving CYP450 and GST were the main mechanisms involved in resistance in the mesosulfuron-methyl-resistant A. aequalis population.

A glutathione S-transferase and a cytochrome P450 may confer cyhalofop-butyl resistance in Leptochloa chinensis (L.) Nees.

BACKGROUND: Leptochloa chinensis (L.) Nees is a troublesome weed across China in rice fields, and a suspected L. chinensis resistant population (R) that has survived the recommended field dose of cyhalofop-butyl was collected in a rice field of Hunan Province, China. In this study, we aimed to determine the acetyl-CoA carboxylase-inhibiting herbicide resistance profile of this R population and to investigate its mechanisms of resistance to cyhalofop-butyl. RESULTS: Compared with the susceptible population (S), the R population was confirmed to be 18.9-, 3.2-, 4.1-, 3.6- and 5.8- fold resistant to the APP herbicides cyhalofop-butyl, haloxyfop-P-methyl, clodinafop-propargyl, metamifop and fenoxaprop-P-ethyl, respectively. ACCase gene sequencing analysis revealed no known resistance mutations for TSR in the R population. Pretreatment with the glutathione S-transferase (GST) inhibitor 4-chloro-7-nitrobenzoxadiazole (NBD-Cl) and cytochrome P450 (CYP450) inhibitor malathion reversed resistance to cyhalofop-butyl. The GST gene GSTU1 and CYP450 gene CYP707A5 were constitutively upregulated in the R population according to RNA-seq analysis and RT-qPCR verification. The molecular docking results indicated a good affinity of the active site for five APP herbicides with GSTU1 and CYP707A5. CONCLUSION: This study shows that the GSTU1 and CYP707A5 genes expressed highly in the R population may be responsible for cyhalofop-butyl resistance in L. chinensis.

Comparative analysis of fungal communities between herbicide-resistant and -susceptible Alopecurus aequalis.

Introduction: Alopecurus aequalis is a grass species invading Chinese canola and wheat fields. An A. aequalis KMN-R population surviving mesosulfuron-methyl treatment with recommended rates was acquired from wheatland. Here, we aimed to confirm the resistance profiles of KMN-R to acetolactate synthetase (ALS) inhibiting herbicides and explore the possible resistance mechanisms to mesosulfuron-methyl in this weed population. Methods: The dose-response tests performed in our study were used to test the toxicity of A. aequalis to ALS-inhibiting herbicides. Sanger sequencing was used to analyze the ALS gene of mesosulfuron-methyl -resistant and -susceptible A. aequalis. RNA sequencing analysis was used to find candidate genes that may confer metabolic resistance to the mesosulfuron-methyl in resistant A. aequalis population. Mesosulfuron-methyl -resistant and -susceptible A. aequalis populations fungal composition was measured via Illumina MiSeq Sequencing. Results: Dose-response results indicated that KMN-R population evolved resistance to mesosulfuron-methyl and other tested ALS-inhibiting herbicides. Known resistance-conferring Trp-574-Leu gene mutation in A. aequalis ALS was detected in the KMN-R population. Pretreatment with 4-chloro-7-nitrobenzoxadiazole reversed mesosulfuron-methyl resistance in KMN-R. Glutathione S-transferases (GST) gene GSTZ2 and GSTT3 were highly expressed in KMN-R population. In addition, we evaluated the alpha diversity in A. aequalis, centering on OTU abundance, equality, and multiplicity, and found that the fungal community composition had more unexplained variance between KMN-R and KMN-S A. aequalis. We also observed higher abundances of specific fungi in KMN-R A. aequalis. Discussion: The results proved that resistance to mesosulfuron-methyl in A. aequalis KMN-R population is probably caused by target site- and non-target site-based relating GST and provided the basis for further research between fungal interaction and herbicide resistance.

Electrical Conductivity of Copper Hexamers Tuned by their Ground-State Valences.

A new design concept has been realized for the construction of molecular conductors, whereby the building unit contains a core reservoir of carriers made up of metal ions with controllable valence states and shelled by flat organic ligands having an extended π-system to promote supramolecular electronic communication. Therefore, reacting the conjugated multidentate ligand 5,5'-pyridyl-3,3'-bi-1 H-pyrazole with different copper salts solvothermally led to three interesting hexameric salts having different ground-state valences, [CuII6(L)4(NO3)(CH3OH)2](NO3)3·4CH3OH, [(CH3)2NH2][CuICuII5(L)4](SO4)2·4H2O, and [CuI2CuII4(L)4](NO3)2·2CH3OH. The monovalent CuII6 salt is an insulator, but the mixed-valent CuII5-CuI and CuII4-CuI2 salts are semiconductors. Magnetic exchange interactions up to JNN = -158 cm-1 dominate the susceptibilities and lead to ground-state spin ST = 1 (CuII6), 1/2 (CuII5-CuI), and 0 (CuII4-CuI2) at 40 K. Cyclic voltammetry shows the stepwise one-electron oxidation-reduction through all the possible valence states. The theoretical calculations of the electronic and band structures of the three compounds substantiate the experimentally observed physical properties.

Magnetostructural relationship for µ2-phenoxido bridged ferric dimers.

Three Fe(iii) dimers, [Fe2(L-H)2]·2CH3CN (1), [Fe2(L-OCH3)2] (2) and [Fe2(L-OC2H5)2]·2CH3CN (3), containing the pentadentate O,N,N,O,O-donor Schiff-base ligands with variable size pendants, were synthesized and structurally characterized. The three ligands were generated in situ from 2-(iminomethyl)phenol, 2-methoxy-6-(iminomethyl)phenol and 2-ethoxy-6-(iminomethyl)phenol, respectively. All three crystal structures contain centrosymmetric dimers of edge-sharing octahedra of Fe(iii) ions through a pair of µ2-phenoxido bridges. The exchange coupling is ferromagnetic for 1 (J = +0.47(1) cm-1, ∠Fe-O-Fe = 98.02°) and 2 (J = +0.86(1) cm-1, ∠Fe-O-Fe = 97.17°), but antiferromagnetic for 3 (J = -0.72(1) cm-1, ∠Fe-O-Fe = 98.53°), which are correlated by high-field electron paramagnetic resonance revealing moderate magneto-anisotropy of D = -0.24(3) cm-1, E = 0.08(1) cm-1 for 1, D = -0.38(1) cm-1, E = 0.11(1) cm-1 for 2, and D = 0.30(3) cm-1, E = 0.02(1) cm-1 for 3. The exchange couplings were further estimated by DFT calculations, which gave the finest Fe-O-Fe angle of 97.83° for the ferromagnetic-antiferromagnetic crossover.