Multi-omics analysis identifies EcCS4 is negatively regulated in response to phytotoxin isovaleric acid stress in Echinochloa crus-galli.

BACKGROUND: Knowledge of herbicidal targets is critical for weed management and food safety. The phytotoxin isovaleric acid (ISA) is effective against weeds with a broad spectrum, carries low environmental risks, and is thus an excellent herbicide lead. However, the biochemical and molecular mechanisms underlying the action of ISA remain unclear. RESULTS: Multi-omics data showed that acetyl coenzyme A (acetyl-CoA) was the key affected metabolite, and that citrate synthase (CS) 4 was substantially down-regulated under ISA treatment in Echinochloa crus-galli leaves. In particular, the transcript level of EcCS4 was the most significantly regulated among the six genes involved in the top 10 different pathways. The EcCS4 encodes a protein of 472 amino acids and is localized to the cell membrane and mitochondria, similar to the CS4s of other plants. The protein content of EcCS4 was down-regulated after ISA treatment at 0.5 h. ISA markedly inhibited the CS4 activity in vitro in a concentration-dependent manner (IC50 = 41.35 µM). In addition, the transgenic rice plants overexpressing EcCS4 (IC50 = 111.8 mM for OECS4-8 line) were more sensitive, whereas loss-of-function rice mutant lines (IC50 = 746.5 mM for oscs4-19) were more resistant to ISA, compared to wild type (WT) plants (IC50 = 355.6 mM). CONCLUSION: CS4 was first reported as a negative regulator of plant responses to ISA. These results highlight that CS4 is a candidate target gene for the development of novel herbicides and for breeding herbicide-resistant crops. © 2023 Society of Chemical Industry.

A first-in-class dimethyl 2-acetamido terephthalate inhibitor targeting Conyza canadensis SHMT1 with a novel herbicidal mode-of-action.

INTRODUCTION: Herbicide application is a highly efficiency method of weed control that boots agricultural output and assures food security. The development of novel herbicides focuses on improved bioactivity and new modes of action. The amino acid biosynthesis was validated as a promising novel mode of action for herbicidal compounds. However, the amino acid biosynthesis enzyme remains largely unexplored for herbicidal targets. OBJECTIVES: Serine hydroxymethyl transferase (SHMT) is an essentialenzyme in the photorespiratory cycle. The study aims to explore Conyza canadensis SHMT1 (CcSHMT1) as a promising target for herbicide discovery. METHODS: Structure determination of CcSHMT1 was resolved by X-ray crystallography. Virtual screening docking experiments were performed with Glide version 5.5. Novel derivatives of dimethyl 2-acetamido terephthalate were further designed, synthesized, and bioassay. The druggability of the inhibitor was evidenced by ultrastructural changes in mitochondria, in vivo and vitro enzyme activity assays, and genetics analysis. RESULTS: CcSHMT1 has a typical PLP-dependent enzyme 3D structure. The dimethyl 2-acetamido terephthalate-containing compounds had herbicidal activity. Dimethyl 2-(2-(4-(2-(4-bromo-2-chlorophenoxy) acetyl)piperazin-1-yl)acetamido) terephthalate (Compound 9ay, EC50 = 193.8 g a.i./ ha) exhibited the highest herbicidal activity on tested weed among the synthesized compounds. Compound 9ay had no obvious adverse effect on the growth of maize and honeybees. Compound 9ay was verified to target CcSHMT1 as an herbicide candidate. CONCLUSION: A first-in-class CcSHMT1 inhibitor that could be developed as a potent herbicide with a new mode of action and provide an avenue for discovering novel inhibitors of pyridoxal-5-phosphate-dependent enzymes.

Phytochemical profiling and allelopathic effect of garlic essential oil on barnyard grass (Echinochloa crusgalli L.).

In agriculture, barnyard grass (Echinochloa crusgalli L.) is one of the most harmful weeds in rice fields now. In order to identify active ingredients which had inhibiting effect on barnyard grass (Echinochloa crusgalli L.), we evaluated several possible natural plant essential oils. Essential oils from twelve plant species showed inhibitory activity against barnyard grass seedlings and root length. The garlic essential oil (GEO) had the most significant allelopathic effect (EC50 = 0.0126 g mL-1). Additionally, the enzyme activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) increased during the first 8 hours of treatment at a concentration of 0.1 g mL-1 and then declined. The activities of CAT, SOD and POD increased by 121%, 137% and 110% (0-8h, compared to control), and decreased (8-72h, compared to the maximum value) by 100%, 185% and 183%, respectively. The total chlorophyll content of barnyard grass seedlings decreased by 51% (0-72h) continuously with the same dosage treatment. Twenty constituents of GEO were identified by gas chromatography-mass spectrometry, and the herbicidal activity of two main components (diallyl sulfide and diallyl disulfide) was evaluated. Results showed that both components had herbicidal activity against barnyard grass. GEO had a strong inhibitory effect (~88.34% inhibition) on barnyard grass growth, but safety studies on rice showed it did not have much inhibitory effect on rice seed germination. Allelopathy of GEO provide ideas for the development of new plant-derived herbicides.

Synthesis Candidates Herbicide Through Optimization Quinclorac Containing 3-Methyl-1H-pyrazol-5-yl.

To enhance quinclorac potency, twenty-five derivatives were synthesized containing 3-methyl-1H-pyrazol-5-yl by intermediate derivatization methods (IDMs). These compounds were confirmed by melting point (mp), 1HNMR, 13CNMR, and HRMS. The compound 1,3-dimethyl-1H-pyrazol-5-yl 3,7-dichloroquinoline-8-carboxylate (10a) was determined by X-ray diffraction. The activity of these compounds substituent on the phenyl was: electron-drawing group > neutral group > donor-drawing group, the results was like that of substituted benzyl group on pyrazole. The herbicidal activity assays showed that compounds 1-(2-fluorophenyl)-3-methyl-1H-pyrazol-5-yl 3,7-dichloroquinoline-8-carboxylate (8l, EC50 = 10.53 g/ha) and 10a (EC50 = 10.37 g/ha) had an excellent inhibition effect on barnyard grass in greenhouse experiment. Greenhouse safety experiment of rice exhibited almost no difference in plant height and fresh weight treated 10a at stage 1∼2-leaf of rice after 14 days but 8l had a detrimental effect. Two season field assays showed 10a herbicidal activity on barnyard grass at 150 g/ha as equal as 300 g/ha quinclorac in fields in 2019 and 2020. The study demonstrated that 10a could be further researched as a potential herbicide to control barnyard grass in fields.