Inhibition of acyl‐ACP thioesterase as site of action of the commercial herbicides cumyluron, oxaziclomefone, bromobutide, methyldymron and tebutam

Abstract

BACKGROUND: Understanding the mode and site of action of a herbicide is key for its efficient development, the evaluation of its toxicological risk, efficient weed control and resistance management. Recently, the mode of action (MoA) of the herbicide cinmethylin was identified in lipid biosynthesis with acyl-ACP thioesterase (FAT) as the site of action (SoA). Cinmethylin was registered for selective use in cereal crops for the control of grass weeds in 2020.RESULTS: Here, we present a high-resolution co-crystal structure of FAT in complex with cumyluron identified by a high throughput crystallization screen. We show binding to and inhibition of FAT by cumyluron. Furthermore, in an array of experiments consisting of FAT binding assays, FAT inhibition assays, physiological and metabolic profiling, we tested compounds that are structurally related to cumyluron and identified the commercial herbicides oxaziclomefone, methyldymron, tebutam and bromobutide, with so far unknown sites of action, as FAT inhibitors. Additionally, we show that the previously described FAT inhibitors cinmethylin and methiozolin bind to FAT in a nanomolar range, inhibit FAT enzymatic activity and lead to similar metabolic changes.CONCLUSION: Based on presented data, we corroborate cinmethylin and methiozolin as potent FAT inhibitors and identify FAT as the SoA of the herbicides cumyluron, oxaziclomefone, bromobutide, methyldymron and tebutam.

Herbicide effects on dormant and postdormant hybrid bermudagrass putting green turf

“…Cumyluron is also a FAT-inhibiting herbicide (Johnen et al 2022) that controls annual bluegrass before it emerges (Askew and McNulty 2014; Reicher et al 2015). Limited peer-reviewed information exists regarding cumyluron usage; however, the patent indicates that it inhibits annual bluegrass germination at rates of 500 to 30,000 g ai ha –1 (Tomita and Tonaka 2003).…”

A Study in Scaffold Hopping: Discovery and Optimization of Thiazolopyridines as Potent Herbicides That Inhibit Acyl-ACP Thioesterase

“…With a library of 28 compounds in hand (Table ), we evaluated them in a series of in vitro assays to determine whether they inhibited any known herbicidal targets. We observed that the thiazolopyridines 8a-8ab inhibited acyl-ACP thioesterase (FAT) in a fluorescence polarization (FP) assay, thus this new compound class exhibits in vitro inhibitory activity against the same site of action (SoA) as the commercial herbicides cinmethylin, methiozolin and oxaziclomefone . From the pI 50 values obtained, we were able to understand more about the SAR of the thiazolopyridine class with regard to its inhibitory activity against the FAT A protein.…”

“…We observed that the thiazolopyridines 8a-8ab inhibited acyl-ACP thioesterase (FAT) in a fluorescence polarization (FP) assay, thus this new compound class exhibits in vitro inhibitory activity against the same site of action (SoA) as the commercial herbicides cinmethylin, 21 methiozolin 36 and oxaziclomefone. 37 From the pI 50 values obtained, we were able to understand more about the SAR of the thiazolopyridine class with regard to its inhibitory activity against the FAT A protein. When comparing the thiazolopyridines 8a−8k, we observed that the highest inhibitory pI 50 values against FAT A were obtained when the phenyl ring in the R 1 position was bearing a small substituent in the ortho position, such as the compounds 8b, 8e and 8g (Table 2).…”

Molecular Targets of Herbicides and Fungicides─Are There Useful Overlaps for Fungicide Discovery?

“…Six commercial herbicides (HRAC group 30), including cinmethylin, target this enzyme. 163,164 FATs are also required for fatty acid production in fungi. 165,166 We have found no literature on the effects of these herbicides on fungi.…”

“…Because FATs have not been annotated in the B. cinerea genome yet, this target is not included in Table . Six commercial herbicides (HRAC group 30), including cinmethylin, target this enzyme. , FATs are also required for fatty acid production in fungi. , We have found no literature on the effects of these herbicides on fungi. However, the natural microbial metabolite cerulenin inhibits this enzyme in both fungi ( S. cerevisiae ) and plants. , Cerulenin was first mentioned as an antifungal antibiotic and later reported to be phytotoxic .…”