Probing strigolactone perception mechanisms with rationally designed small-molecule agonists stimulating germination of root parasitic weeds

Novel anti-pyroptosis drug loaded on metal-organic framework for intervertebral disc degeneration therapy

Intervertebral disc degeneration (IVDD) is the main cause of low back pain, pyroptosis is a major contributor to various diseases, including IVDD; however, there is currently no effective drugs targeting pyroptosis for therapy. In this study, we established pyroptosis model in nucleus pulposus cells (NPCs) in vitro and searched pyroptosis inhibitors in FDA Medicine Library. High throughput screening study revealed that Pirfenidone (PFD) was the most effective pyroptosis inhibitor among 1500+ FDA drugs, which was confirmed by further experiments. As administering PFD alone may lead to poor efficacy due to short action time and low bioavailability, we designed a smart delivery system for PFD. A pH-responsive metal-organic framework (MOF), poly-His6-zinc (PHZ) assembly, loaded with PFD (PFD@PHZ) was designed for IVDD therapy. PHZ was shown to have excellent lysosomal escape properties and bioavailability of PFD. In addition, the release of PDF from PFD@PHZ could be triggered by the acidic microenvironment of degenerated intervertebral discs. PFD@PHZ was also shown to effectively inhibit pyroptosis, senescence, and extracellular matrix (ECM) degradation in NPCs, both in vitro and in vivo, thereby mitigating the progression of IVDD in rats. Thus, the current study shows PFD as a novel inhibitor for pyroptosis, and PFD@PHZ as a potential nanomaterial for efficient IVDD therapy.

Discovery of a Class of Novel Succinate Dehydrogenase Inhibitors Containing a Coumarin Structure

Succinate dehydrogenase (SDH) has emerged as a highly promising target in modern agricultural research, playing a crucial role in developing environmentally friendly and efficient fungicides for combating agricultural pathogens. This study presents the discovery of a novel class of SDH inhibitors (I-III) incorporating coumarin segments achieved through an active fragment swapping and linking strategy. Fungicidal activity assays revealed that several compounds within this series demonstrate significant inhibitory effects against the tested fungal strains. Through comprehensive structure-activity relationship studies, compound N-(1-((3-butyl-4-methyl-2-oxo-2H-chromen-7-yl)oxy)propan-2-yl)-3-(difluoromethyl)-N-methoxy-1-methyl-1H-pyrazole-4-carboxamide (IIk) exhibited potent inhibitory activity against various fungal species. Notably, it demonstrated superior efficacy against S. sclerotiorum with an EC50 value of 1.14 μg/mL, outperforming the commercial control agent thifluzamide (EC50 = 4.90 μg/mL). Molecular docking simulations indicated that hydrophobic interactions serve as the primary binding mechanism between the ligand and SDH. Intriguingly, compound IIk displayed dual functionality, not only acting as an effective fungicide but also promoting the growth of wheat seedlings and Arabidopsis thaliana, resulting in increased plant biomass. Preliminary investigations into its growth-promoting mechanism suggest that IIk enhances the nitrate reductase activity, thereby facilitating plant growth.

Design and synthesis of strigolactone analogues and mimics containing indolin-2-one scaffold for the Phelipanche control

BACKGROUND

The broomrapes are root-parasitic weeds widely distributed in the temperate zone area. The effective management on the Phelipanche and Orobanche parasitic weeds still remains challenging to date.

RESULTS

Novel strigolactone (SL) analogues (X series) and mimics (O series) derived from indolin-2-one were designed and synthesized. Of them, compound O-3 showed nearly ten-fold higher seed germination activity (median effective concentration (EC50) = 0.0066 μm) towards Phelipanche aegyptiaca seeds compared to the control GR24. Moreover, it also showed prominent seed germination activity towards Phelipanche ramosa. At a dosage of 0.2 μm, the glasshouse experiment revealed that compound O-3 not only displayed the profitable P. aegyptiaca control, but also influenced fruit and plant stalk development in tomato cultivation. Theoretical computational studies indicated that compound O-3 could perfectly interact with catalytic triad of OmKAI2d4, and the oxime linker facilitate to release the active D ring species, thereby significantly improving bioactivity.

CONCLUSIONS

A class of SL mimics incorporating a unique oxime linker has been developed from indolin-2-one. Compound O-3 exhibited the highest seed germination activities toward the parasitic P. aegyptiaca and P. ramosa, and could serve as a promising lead compound for the Phelipanche control. © 2025 Society of Chemical Industry.

Development of Dispersive Liquid-Liquid Microextraction Method Based on Solidification of Floating Organic Droplets for Rapid Determination of Three Strigolactones in Rice (Oryza sativa L.) Using Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry

Strigolactones (SLs) are key hormones regulating branching and tillering in rice, impacting plant architecture and yield. A rapid, sensitive, and environmentally friendly method using dispersive liquid-liquid microextraction based on the solidification of floating organic droplets (DLLME-SFO), coupled with ultra-high-performance liquid chromatography and tandem mass spectrometry (UHPLC-MS/MS), has been developed for the determination of three SLs (strigol, orobanchol, and 5-deoxystrigol). The DLLME-SFO method integrates one-step low-temperature extraction and enrichment. The DLLME-SFO conditions were optimized through a single-factor experimental design. Under the best-tested conditions, the developed method exhibited excellent linearity, with the coefficient of determination (R2) values greater than 0.9993. The recoveries ranged from 83% to 96%, with precision values ranging from 4.5% to 12.4%. The limits of detection (LODs) varied from 0.6 to 1.2 pg/g fresh weight, indicating the high sensitivity of the method. Additionally, a novel assay protocol for the quantification of SLs in rice in response to nitrogen and phosphorus stress conditions was applied.

Structural requirements of KAI2 ligands for activation of signal transduction

Karrikin Insensitive 2 (KAI2), identified as the receptor protein for karrikins (KARs), which are smoke-derived seed germination stimulants, belongs to the same α/β-hydrolase family as D14, the receptor for strigolactones (SLs). KAI2 is believed to recognize an endogenous butenolide (KAI2 ligand; KL), but the identity of this compound remains unknown. Recent studies have suggested that ligand hydrolysis by KAI2 is a prerequisite for receptor activation to induce interaction with the target proteins, similar to the situation with D14. However, direct experimental evidence has been lacking. Here, we designed KAI2 ligands (carba-dMGers) whose butenolide rings were modified so that they cannot be hydrolyzed or dissociated from the original ligand molecule by KAI2, by structurally modifying dMGer, a potent and selective KAI2 agonist. Using these dMGer analogs, we found that the strongly bioactive ligand, (+)-dMGer, was hydrolyzed by KAI2 at a lower enzymatic rate compared with the weakly bioactive ligand, (+)-1'-carba-dMGer, and the hydrolyzed butenolide ring of (+)-dMGer was transiently trapped in the catalytic pocket of KAI2. Additionally, structural analysis revealed that (+)-6'-carba-dMGer bound to the catalytic pocket of KAI2 in the unhydrolyzed state. However, this binding did not induce the interaction between KAI2 and SMAX1, indicating that ligand binding to the receptor alone was not sufficient for KAI2 signaling. This study showed experimental data from a ligand structure-activity study that ligand hydrolysis and subsequent covalent adduct formation with the catalytic triad plays a key role in KAI2 activation, providing insight into the chemical structure of the Arabidopsis KL.

The strigolactone receptor DWARF14 regulates flowering time in Arabidopsis

Multiple plant hormones, including strigolactone (SL), play key roles in regulating flowering time. The Arabidopsis (Arabidopsis thaliana) DWARF14 (AtD14) receptor perceives SL and recruits F-box protein MORE AXILLARY GROWTH2 (MAX2) and the SUPPRESSOR OF MAX2-LIKE (SMXL) family proteins. These interactions lead to the degradation of the SMXL repressor proteins, thereby regulating shoot branching, leaf shape, and other developmental processes. However, the molecular mechanism by which SL regulates plant flowering remains elusive. Here, we demonstrate that intact strigolactone biosynthesis and signaling pathways are essential for normal flowering in Arabidopsis. Loss-of-function mutants in both SL biosynthesis (max3) and signaling (Atd14 and max2) pathways display earlier flowering, whereas the repressor triple mutant smxl6/7/8 (s678) exhibits the opposite phenotype. Retention of AtD14 in the cytoplasm leads to its inability to repress flowering. Moreover, we show that nuclear-localized AtD14 employs dual strategies to enhance the function of the AP2 transcription factor TARGET OF EAT1 (TOE1). AtD14 directly binds to TOE1 in an SL-dependent manner and stabilizes it. In addition, AtD14-mediated degradation of SMXL7 releases TOE1 from the repressor protein, allowing it to bind to and inhibit the FLOWERING LOCUS T (FT) promoter. This results in reduced FT transcription and delayed flowering. In summary, AtD14 perception of SL enables the transcription factor TOE1 to repress flowering, providing insights into hormonal control of plant flowering.

Naturally Occurring Dehydrocostus Lactone Covalently Binds to KARRIKIN INSENSITIVE 2 by Dual Serine Modifications in Orobanche cumana and Arabidopsis

Parasitic weeds, such as Orobanche and Striga, threaten crops globally. Contiguous efforts on the discovery and development of structurally novel seed germination stimulants targeting HYPOSENSITIVE TO LIGHT/KARRIKIN INSENSITIVE 2 (HTL/KAI2) have been made with the goal of weed control. Here, we demonstrate that a natural compound dehydrocostus lactone (DCL) exhibits effective "suicide germination" activity against Orobanche cumana and covalently binds to OcKAI2d2 on two catalytic serine sites with the second modification dependent on the first one. The same interactions and covalent modifications of DCL are also confirmed in AtKAI2. Further in-depth evolution analysis indicates that the proposed two catalytic sites are present throughout the streptophyte algae, hornworts, lycophytes, and seed plants. This discovery is particularly noteworthy as it signifies the first confirmation of a plant endogenous molecule directly binding to KAI2, which is valuable for unraveling the elusive identity of the KAI2 ligand and for targeting KAI2 paralogues for the development of novel germination stimulants.

Discovery of Benzothiazol-2-ylthiophenylpyrazole-4-carboxamides as Novel Succinate Dehydrogenase Inhibitors

Succinate dehydrogenase (SDH) has been considered an ideal target for discovering fungicides. To develop novel SDH inhibitors, in this work, 31 novel benzothiazol-2-ylthiophenylpyrazole-4-carboxamides were designed and synthesized using active fragment exchange and a link approach as promising SDH inhibitors. The findings from the tests on antifungal activity indicated that most of the synthesized compounds displayed remarkable inhibition against the fungi tested. Compound Ig N-(2-(((5-chlorobenzo[d]thiazol-2-yl)thio)methyl)phenyl)-3-(difluoromethyl)-1-methyl-1H-yrazole-4-carboxamide, with EC50 values against four kinds of fungi tested below 10 μg/mL and against Cercospora arachidicola even below 2 μg/mL, showed superior antifungal activity than that of commercial fungicide thifluzamide, and specifically compounds Ig and Im were found to show preventative potency of 90.6% and 81.3% against Rhizoctonia solani Kühn, respectively, similar to the positive fungicide thifluzamide. The molecular simulation studies suggested that hydrophobic interactions were the main driving forces between ligands and SDH. Encouragingly, we found that compound Ig can effectively promote the wheat seedlings and the growth of Arabidopsis thaliana. Our further studies indicated that compound Ig could stimulate nitrate reductase activity in planta and increase the biomass of plants.

Chemistry of Strigolactones, Key Players in Plant Communication

Today, the use of artificial pesticides is questionable and the adaptation to global warming is a necessity. The promotion of favorable natural interactions in the rhizosphere offers interesting perspectives for changing the type of agriculture. Strigolactones (SLs), the latest class of phytohormones to be discovered, are also chemical mediators in the rhizosphere. We present in this review the diversity of natural SLs, their analogs, mimics, and probes essential for the biological studies of this class of compounds. Their biosynthesis and access by organic synthesis are highlighted especially concerning noncanonical SLs, the more recently discovered natural SLs. Organic synthesis of analogs, stable isotope-labeled standards, mimics, and probes are also reviewed here. In the last part, the knowledge about the SL perception is described as well as the different inhibitors of SL receptors that have been developed.

Understanding the Effects of Ligand Configuration on Protoporphyrinogen IX Oxidase with Rationally Designed 3-(N-Phenyluracil)but-2-enoates

Protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) is a promising target for green herbicide discovery. However, the ligand configuration effects on PPO activity were still poorly understood. Herein, we designed 3-(N-phenyluracil)but-2-enoates using our previously developed active fragments exchange and link (AFEL) approach and synthesized a series of novel compounds with nanomolar ranges of Nicotiana tabacum PPO (NtPPO) inhibitory potency and promising herbicidal potency. Our systematic structure-activity relationship investigations showed that the E isomers of 3-(N-phenyluracil)but-2-enoates displayed improved bioactivity than their corresponding Z isomers. Using molecular simulation studies, we found that the E isomers showed a relatively lower entropy change and could sample more stable binding conformation to the receptor than the Z isomers. Our density functional theory (DFT) calculations showed that the E isomers showed higher chemical reactivity and lower electronic chemical potential than their corresponding Z isomers. Compound E-Ic emerged as the optimal compound with a Ki value of 3.0 nM against NtPPO, exhibiting a broader spectrum of weed control than saflufenacil at 37.5-75 g ai/ha and also safe to maize at 75 g ai/ha, which could be considered as a promising lead herbicide for further development.

Discovery of Tetrazolamide-benzimidazol-2-ones as Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) is one of the most valuable herbicide targets due to its unique biological functions. In search of HPPD inhibitors with promising biological performance, we designed and synthesized a series of novel tetrazolamide-benzimidazol-2-ones using a structure-based drug design strategy. Among the synthesized compounds, 1-(2-chlorobenzyl)-3-methyl-N-(1-methyl-1H-tetrazol-5-yl)-2-oxo-2,3-dihydro-1H-benzo[d]imidazole-4-carboxamide, 25, IC50 = 10 nM, was identified to be the most outstanding HPPD inhibitor, which showed more than 36-fold increased Arabidopsis thaliana HPPD (AtHPPD) inhibition potency than mesotrione (IC50 = 363 nM). Our AtHPPD-25 complex indicated that one nitrogen atom on the tetrazole ring and the oxygen atom on the amide group formed a classical bidentate chelation interaction with the metal ion, the benzimidazol-2-one ring created a tight π-π stacking interaction with Phe381 and Phe424, and some hydrophobic interactions were also found between the ortho-Cl-benzyl group and surrounding residues. Compound 32 showed more than 80% inhibition against all four tested weeds at 150 g ai/ha by the postemergence application. Our results indicated that the tetrazolamide-benzimidazol-2-one scaffold may be a new lead structure for herbicide discovery.

Inspired by Nature: Isostere Concepts in Plant Hormone Chemistry

Chemical concepts such as isosteres and scaffold hopping have proven to be powerful tools in agrochemical innovation processes. They offer opportunities to modify known molecular lead structures with the aim to improve a range of parameters, including biological efficacy and spectrum, physicochemical properties, stability, and toxicity. While recent biochemical insights into plant-specific receptors and signaling pathways trigger the discovery of the first lead structures, the disclosure of such a new chemical structure sparks a broad range of synthesis activities giving rise to diverse chemical innovation and often a considerable boost in biological activity. Herein, recent examples of isostere concepts in plant-hormone chemistry will be discussed, outlining how synthetic creativity can broaden the scope of natural product chemistry and giving rise to new opportunities in research fields such as abiotic stress tolerance and growth promotion.

Discovery of Benzothiazolylpyrazole-4-Carboxamides as Potent Succinate Dehydrogenase Inhibitors through Active Fragment Exchange and Link Approach

Succinate dehydrogenase (SDH) is an attractive target for developing green fungicides to manage agricultural pathogens in modern agriculture research. Herein, in this work, we report the discovery of benzothiazolylpyrazole-4-carboxamides I-III as potent SDH inhibitors using active fragment exchange and link approach. The results of the fungicidal activity assays showed that some of the synthesized compounds exhibited excellent inhibition against the tested fungi. Systematic structure-activity relationship studies led to the discovery of compound Ip, N-(1-((4,6-difluorobenzo[d]thiazol-2-yl)thio)propan-2-yl)-3-(difluoromethyl)-N-methoxy-1-methyl-1H-pyrazole-4-carboxamide, which showed higher fungicidal activity against Fusarium graminearum Schw (EC50 = 0.93 μg/mL) than the commercial fungicides thifluzamide (EC50 > 50 μg/mL) and boscalid (EC50 > 50 μg/mL). The molecular simulation studies suggested that hydrophobic interactions were the primary driving forces between ligands and SDH. Promisingly, we found that Ip could stimulate the growth of wheat seedlings and Arabidopsis thaliana and increase the biomass of the treated plants. Preliminary studies on the plant growth promoter mechanism of Ip indicated that it could increase nitrate reductase activity in planta, that, in turn, stimulates the growth of plants.

Structural analysis of a hormone-bound Striga strigolactone receptor

Strigolactones (SLs) regulate many aspects of plant development, but ambiguities remain about how this hormone is perceived because SL-complexed receptor structures do not exist. We find that when SL binds the Striga receptor, ShHTL5, a series of conformational changes relative to the unbound state occur, but these events are not sufficient for signalling. Ligand-complexed receptors, however, form internal tunnels that posit an explanation for how SL exits its receptor after hydrolysis.

Design, Synthesis, and Metabolism Studies of N-1,4-Diketophenyltriazinones as Protoporphyrinogen IX Oxidase Inhibitors

Protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) is an established site for green herbicide discovery. In this work, based on structural analysis, we develop an active fragment exchange and link (AFEL) approach to designing a new class of N-1,4-diketophenyltriazinones I-III as potent Nicotiana tabacum PPO (PPO) inhibitors. After systematic structure-activity relationship optimizations, a series of new compounds with Ki values in the single-digit nanomolar range toward NtPPO and promising herbicidal activity were discovered. Among them, Ii (Ki = 0.11 nM) displays 284- and 90-fold improvement in NtPPO inhibitory activity over trifludimoxazin (Ki = 31 nM) and saflufenacil (Ki = 10 nM), respectively. In addition, Ip (Ki = 2.14 nM) not only exhibited good herbicidal activity at 9.375-37.5 g ai/ha but also showed high crop safety to rice at 75 g ai/ha by the postemergence application, indicating that Ip could be developed as a potential herbicide for weed control in rice fields. Additionally, our molecular dynamic simulation clarified the molecular basis for the interactions of these molecules with NtPPO. The metabolism studies in planta showed that IIIc could be converted to Ic, which displayed higher herbicidal activity than IIIc. The density functional theory analysis showed that due to the effect of two sulfur atoms at the triazinone moiety, IIIc is more reactive than Ic, making it more easily degraded in planta. Our work indicates that the AFEL strategy could be used to design new molecules with improved bioactivity.

Strigolactone regulates adventitious root formation via the MdSMXL7-MdWRKY6-MdBRC1 signaling cascade in apple

Propagation through stem cuttings is a popular method worldwide for species such as fruit tree rootstocks and forest trees. Adventitious root (AR) formation from stem cuttings is crucial for effective and successful clonal propagation of apple rootstocks. Strigolactones (SLs) are newly identified hormones involved in AR formation. However, the regulatory mechanisms underpinning this process remain elusive. In the present study, weighted gene co-expression network analysis, as well as rooting assays using stable transgenic apple materials, revealed that MdBRC1 served as a key gene in the inhibition of AR formation by SLs. We have demonstrated that MdSMXL7 and MdWRKY6 synergistically regulated MdBRC1 expression, depending on the interactions of MdSMXL7 and MdWRKY6 at the protein level downstream of SLs as well as the direct promoter binding on MdBRC1 by MdWRKY6. Furthermore, biochemical studies and genetic analysis revealed that MdBRC1 inhibited AR formation by triggering the expression of MdGH3.1 in a transcriptional activation pathway. Finally, the present study not only proposes a component, MdWRKY6, that enables MdSMXL7 to regulate MdBRC1 during the process of SL-controlled AR formation in apple, but also provides prospective target genes to enhance AR formation capacity using CRISPR (i.e. clustered regularly interspaced short palindromic repeats) technology, particularly in woody plants.