Biology subjects

Betz, M.

Publications and source records attributed to Betz, M..

4 recordsLinked to original sources

bioRxiv2026

Biochemical Characterization of Fatty Acid Thioesterase Target Site Mutants and their Implication on Herbicide Resistance

Herbicide resistance threatens effective weed control in modern agriculture, particularly in grass weeds such as Alopecurus myosuroides and Lolium multiflorum. Cinmethylin is a pre-emergence herbicide with a novel mode of action that inhibits plastidial fatty acid thioesterases (FATs), enzymes essential for fatty acid biosynthesis. Although no cases of field resistance to cinmethylin have been reported, its resistance risk has not been fully assessed. In this study, we biochemically characterized defined amino acid substitutions in FAT A and FAT B to evaluate their effects on cinmethylin inhibition profile. Some substitutions in FAT A reduced inhibition in vitro, with mutations at residue R171 causing the largest shifts in sensitivity. However, these highly resistant variants required multiple specific nucleotide polymorphisms and are therefore predicted to be unlikely to arise in weed populations. In FAT B, sensitivity shifts were generally moderate. Importantly, most substitutions that reduced cinmethylin sensitivity also impaired enzymatic activity, suggesting limited viability in planta. Overall, these results indicate that while theoretical target-site resistance mechanisms exist, the practical risk of rapid resistance evolution to cinmethylin is low, supporting its value for integrated grass weed management

biochemistry↗

bioRxiv2026

Novel Protoporphyrinogen oxidase 1 mutations endow resistance to PPO-inhibiting herbicides in Bassia scoparia

PPO-inhibiting herbicides are widely used to manage weeds in different cropping systems, yet resistance evolution threatens their long-term efficacy. Here, we investigated the molecular basis of resistance to PPO-inhibiting herbicides in Bassia scoparia biotypes collected from four locations in North Dakota, USA. Greenhouse dose-response assays revealed high levels of resistance to saflufenacil and carfentrazone-ethyl, while fomesafen retained full efficacy across all biotypes. Resistant plants did not show increased copy number or elevated expression of PPO1 or PPO2. Sequencing of survivor plants revealed conserved PPO2 sequences, but consistent target-site substitutions at position F454 in PPO1, including F454I, F454L, and F454V. In vitro enzyme assays demonstrated that these substitutions impair PPO1 sensitivity to saflufenacil and carfentrazone-ethyl, but not to fomesafen. Ectopic expression of B. scoparia PPO1 F454 mutant variants in Arabidopsis thaliana conferred tolerance to saflufenacil and carfentrazone-ethyl, but not to fomesafen, supporting greenhouse and in vitro results. Molecular modeling indicated that the conformational flexibility and interaction profile of fomesafen enables it to maintain binding to mutated PPO1 variants, in contrast to the more rigid structures of saflufenacil and carfentrazone-ethyl. A yeast-based complementation system further confirmed that F454 substitutions decrease herbicide sensitivity. In addition, developmental profiling showed distinct expression patterns of PPO1 and PPO2 during early growth stages in B. scoparia and Amaranthus spp., highlighting isoform-specific roles. Together, these findings represent the first reported PPO1 target-site mutations in a broadleaf weed species as a key mechanism of resistance and highlight that fomesafen is effective to control resistant B. scoparia populations.

biochemistry↗

bioRxiv2026

Fendioxypyracil, a new and systemic PPO-inhibiting herbicide for X-spectrum weed control

BackgroundFendioxypyracil is a novel protoporphyrinogen oxidase (PPO)-inhibiting herbicide (HRAC Group 14) developed to address the increasing prevalence of herbicide-resistant weeds and to expand available weed control options. PPO inhibitors disrupt chlorophyll biosynthesis by blocking the conversion of protoporphyrinogen IX to protoporphyrin IX, resulting in light-promoted formation of reactive oxygen species and rapid plant necrosis. Building on established PPO chemistry, fendioxypyracil incorporates a pyridine-based core and an aryloxy sidechain designed to enhance binding affinity and post-emergence activity. ResultsGreenhouse evaluations demonstrated high efficacy of fendioxypyracil against key grass weeds, including wild oat (Avena fatua), crabrass (Digitaria Sanginalis), goosegrass (Eleusina indica) and barnyard grass (Echinochloa crus-galli), as well as strong control of major broadleaf species. Physiological characterization and enzyme inhibition assays confirmed PPO as the primary site and mode of action, with IC values lower than those of the commercial standard saflufenacil for both PPO isoforms. ConclusionFendioxypyracil represents a next-generation PPO inhibitor with broad-spectrum and systemic activity, offering a valuable new tool for integrated weed management. Its high biological activity and efficacy across multiple weed taxa supports its potential to enhance on-farm weed control strategies and contributes to resistance management programs.

plant biology↗

bioRxiv2025

Analysis of glutamine synthetase target-site mutations and their role in endowing glufosinate-ammonium resistance

Glufosinate-ammonium (GFA) is a key non-selective herbicide for controlling Amaranthus palmeri and other weeds by targeting glutamine synthetase (GS). GS copy number, expression, sequence polymorphisms, and enzymatic properties in a GFA-resistant population (CCR) were studied. Digital PCR revealed no major GS amplification or target upregulation: most CCR plants had copy numbers and expression comparable to the susceptible reference, with only minor increases in GS2.1 and GS2.2 in a few individuals. Sequencing identified a non-synonymous substitution, G255D, in GS2.2 within a conserved region adjacent to the GFA-binding site. G255D retained [~]58% of wild-type activity in vitro assays, but was completely insensitive to GFA, with no measurable inhibition at tested concentrations. However, ectopic expression of G255D in Arabidopsis thaliana did not confer GFA tolerance, indicating the mutation alone is insufficient for resistance. In vitro analysis of the Eleusine indica GS1.1 S59G substitution revealed increased catalytic activity without affecting GFA sensitivity. A mutational panel of GS1.1 variants showed that substitutions at E131, E192, G245, H249, R291, R311, and R332 abolished enzyme activity or inhibitor sensitivity, with most variants retaining <2% of wild-type function. Among a broader set of predicted GS1.1 variants, high resistance indices were consistently linked to strong reductions in catalytic efficiency, underscoring the fitness costs of target-site alterations. Collectively, GS2.2 G255D appears to be a rare substitution combining substantial residual activity with complete GFA insensitivity and suggest that resistance via target-site modifications studied is constrained by trade-offs between catalytic function and herbicide binding.

biochemistry↗