Stimulation Of Germination Research Articles

Discovery of strigol synthase from cotton (Gossypium hirsutum): The enzyme behind the first identified germination stimulant for Striga

Societal Impact StatementParasitic witchweeds (Striga species) pose a serious threat to food security in Africa, attacking cereal grains and legumes. Chemicals released from the host roots that initiate the life cycle of Striga are known as germination stimulants, predominantly strigolactones (SLs). Strigol, the first identified SL, was isolated from the root exudates of cotton (Gossypium hirsutum), a false host of Striga, over 50 years ago. The identification of strigol synthase in cotton establishes the complete biosynthesis pathway of this emblematic SL. This discovery has the potential to advance our understanding of SL‐mediated rhizosphere interactions and enhance cotton's effectiveness as a trap crop.

Seed Priming: A Key to Sustainability in Drought Stress

Abiotic stresses spot lights the field crops at all growth phases and results in significant yield losses in important crops, endangering the safety of the world's food supply. Numerous physiological, biochemical, and molecular tactics have been examined by crop researchers to battle drought stress/water limiting stress, but in the current environment, these measures are meager. It is so claimed that plants can be primed by various organic and inorganic stimulants for exceptional toughness under stressful circumstances. In order to confer tolerance, novel seed priming techniques are promising field of research in stress biology and crop stress management. Seed priming is the process of carefully hydrating seeds with germination stimulants so that pre- germinative metabolic activity can continue while the radicle's emergence is halted. The terms "hydro-priming," "osmo-priming," "halo-priming," "solid matrix priming," "bio-priming," and "hormonal priming" refer to various priming techniques. It will speed up and synchronize germination, improve plant growth and stand establishment, raise stress tolerance, improve fertilizer and water use efficiency, and have superior weed suppression effects. This review paper covers the physiological and biochemical changes through several seed priming techniques, Nano-priming and its significance in sustainable agriculture.

Cytokinins as an alternative suicidal Striga germination compound

AbstractThe witchweed Striga hermonthica, an obligate and noxious root–parasitic plant, remains a persistent threat to cereal production and poses a great challenge to smallholder farmers in Sub‐Saharan Africa. Inducing suicidal germination of Striga seeds by applying strigolactone analogs is a promising strategy to deplete the Striga seed bank of infested soils. Nevertheless, there is a need to increase the efficiency and improve the applicability of this strategy, which may be achieved by testing further Striga germination stimulants. Herein, we explored the potential of cytokinins in inducing Striga seed germination. We investigated their activity as a suicidal germination agent along with fluridone that inhibits carotenoid biosynthesis and hence reduces abscisic acid formation and facilitates breaking of seed dormancy. Under lab conditions, application of fluridone (at 100 μM) or cytokinins (at 100 μM) showed 19% and 63% Striga germination, respectively, while combining different cytokinins with fluridone led to above 93% germination of treated seeds, with thidiazuron as the most active cytokinin. Using rice (cv IAC‐165), we also show that co‐application of fluoridone and thidiazuron to Striga infested pots before planting the host led to up to 86%–100% reduction in Striga emergence. In summary, cytokinins, particularly thidiazuron, could be useful suicidal agents to induce Striga seed germination and ultimately deplete the seedbank in Striga‐infested regions.

Changes in Medicago truncatula seed proteome along the rehydration-dehydration cycle highlight new players in the genotoxic stress response.

Several molecular aspects underlying the seed response to priming and the resulting vigor profile are still poorly understood. Mechanisms involved in genome maintenance deserve attention since the balance between stimulation of germination and DNA damage accumulation versus active repair is a key determinant for designing successful seed priming protocols. Changes in the Medicago truncatula seed proteome were investigated in this study, using discovery mass spectrometry and label-free quantification, along the rehydration-dehydration cycle of a standard vigorization treatment (hydropriming plus dry-back), and during post-priming imbibition. From 2056 to 2190 proteins were detected in each pairwise comparison, among which six were differentially accumulated and 36 were detected only in one condition. The following proteins were selected for further investigation: MtDRP2B (DYNAMIN-RELATED PROTEIN), MtTRXm4 (THIOREDOXIN m4), and MtASPG1 (ASPARTIC PROTEASE IN GUARD CELL 1) showing changes in seeds under dehydration stress; MtITPA (INOSINE TRIPHOSPHATE PYROPHOSPHORYLASE), MtABA2 (ABSCISIC ACID DEFICIENT 2), MtRS2Z32 (SERINE/ARGININE-RICH SPLICING FACTOR RS2Z32), and MtAQR (RNA HELICASE AQUARIUS) that were differentially regulated during post-priming imbibition. Changes in the corresponding transcript levels were assessed by qRT-PCR. In animal cells, ITPA hydrolyses 2'-deoxyinosine triphosphate and other inosine nucleotides, preventing genotoxic damage. A proof of concept was performed by imbibing primed and control M. truncatula seeds in presence/absence of 20 mM 2'-deoxyinosine (dI). Results from comet assay highlighted the ability of primed seeds to cope with dI-induced genotoxic damage. The seed repair response was assessed by monitoring the expression profiles of MtAAG (ALKYL-ADENINE DNA GLYCOSILASE) and MtEndoV (ENDONUCLEASE V) genes that participate in the repair of the mismatched I:T pair in BER (base excision repair) and AER (alternative excision repair) pathways, respectively.

A Stereoselective Strigolactone Biosynthesis Catalyzed by a 2-Oxoglutarate-Dependent Dioxygenase in Sorghum.

Seeds of root parasitic plants, Striga, Orobanche and Phelipanche spp., are induced to germinate by strigolactones exudated from host roots. In Striga-resistance cultivars of Sorghum bicolor, the loss-of-function of the Low Germination Stimulant 1 (LGS1) gene changes the major strigolactone from 5-deoxystrigol to orobanchol having the opposite C-ring stereochemistry. However, the biosynthetic pathway of 5-deoxystrigol catalyzed by LGS1 has not been fully elucidated. Since the other unknown regulator in addition to LGS1 encoding a sulfotransferase appeared to be necessary for the stereoselective biosynthesis of 5-deoxystrigol, we examined Sobic.005G213500 (Sb3500) encoding a 2-oxoglutarate-dependent dioxygenase as a candidate, which is co-expressed with LGS1 and located on the 5'-upstream of LGS1 in the sorghum genome. When LGS1 was expressed with known strigolactone biosynthetic enzyme genes including the cytochrome P450 SbMAX1a but not Sb3500 in Nicotiana benthamiana leaves, 5-deoxystrigol and its diastereomer 4-deoxyorobanchol were produced in approximately equal amounts, while the production of 5-deoxystrigol was significantly larger than that of 4-deoxyorobanchol when Sb3500 was co-expressed in addition to them. We also confirmed the stereoselective 5-deoxystrigol production by an in vitro feeding experiment using synthetic chemicals with recombinant proteins expressed in E. coli and yeast. This finding demonstrated that Sb3500 is a stereoselective regulator in the conversion of the strigolactone precursor carlactone to 5-deoxystrigol catalyzed by LGS1 and SbMAX1a, providing a detailed understanding of how different strigolactones are produced to combat parasitic weed infestations.

Culture-Dependent and Metabarcoding Characterization of the Sugar Beet (Beta vulgaris L.) Microbiome for High-Yield Isolation of Bacteria with Plant Growth-Promoting Traits.

The diversity of plant-associated bacteria is vast and can be determined by 16S rRNA gene metabarcoding. Fewer of them have plant-beneficial properties. To harness their benefits for plants, we must isolate them. This study aimed to check whether 16S rRNA gene metabarcoding has predictive power in identifying the majority of known bacteria with plant-beneficial traits that can be isolated from the sugar beet (Beta vulgaris L.) microbiome. Rhizosphere and phyllosphere samples collected during one season at different stages of plant development were analyzed. Bacteria were isolated on rich unselective media and plant-based media enriched with sugar beet leaves or rhizosphere extracts. The isolates were identified by sequencing the 16S rRNA gene and tested in vitro for their plant-beneficial properties (stimulation of germination; exopolysaccharide, siderophore, and HCN production; phosphate solubilization; and activity against sugar beet pathogens). The highest number of co-occurring beneficial traits was eight, found in isolates of five species: Acinetobacter calcoaceticus, Bacillus australimaris, B. pumilus, Enterobacter ludwiigi, and Pantoea ananatis. These species were not detected by metabarcoding and have not previously been described as plant-beneficial inhabitants of sugar beets. Thus, our findings point out the necessity of a culture-dependent microbiome analysis and advocate for low-nutrient plant-based media for high-yield isolation of plant-beneficial taxa with multiple beneficial traits. A culture-dependent and -independent approach is required for community diversity assessment. Still, isolation on plant-based media is the best approach to select isolates for potential use as biofertilizers and biopesticides in sugar beet cultivation.

Transcriptome atlas of Striga germination: Implications for managing an intractable parasitic plant

Societal Impact StatementWitchweeds, parasitic plants of the genus Striga, are nicknamed “cereal killers” because of their devastating destruction of Africa's most staple cereals, including maize, sorghum, millets, and upland rice. The parasite relies on biomolecules emitted from the host roots to germinate and therefore initiate its infectious lifecycle. Some sorghum varieties have evolved to not produce effective germination stimulants, making them resistant to the parasite. Here, the genetic factors that underpin Striga germination were assessed, followed by a discussion of how such knowledge can be used to develop new Striga management strategies through the disruption of host–parasite communication exchange.Summary Seeds of the parasitic plant Striga are dormant. They only germinate in response to biomolecules emitted from the host's root exudate, strigolactones (SL). But it is now emerging that Striga germination is a much more complex process regulated by crosstalk of hormone signaling pathways. To further understand the genetic basis of the communication exchange between Striga and its host sorghum, we performed a comparative transcriptomic analysis. We sought to identify major transcriptomic changes that define the germination process in Striga and a set of genes that may contribute to the differences in germination rates. Results showed that germination proceeds immediately after SL perception and is marked by a wave of transcriptional reprogramming to allow for metabolic processes of energy mobilization. Cluster analysis using self‐organizing maps revealed a time‐phased and genotype‐differentiated response to germination stimulation. The variation in germination was also a function of hormonal crosstalk. The early germination stage was associated with significant repression of genes in the abscisic acid (ABA) biosynthesis pathway. Other hormones influenced germination as follows: (i) ABA and auxin repressed germination; (ii) brassinosteroid, ethylene, and jasmonic acid promoted germination; and (iii) cytokinin had a more prominent role post‐germination rather than during germination. Perception of SL sets the germination program leading to different rates of germination in sorghum, followed by a complex hormonal regulation network that acts to either repress or enhance germination. We discuss the implications of these findings and present new plausible Striga management strategies.

Strigolactones in rhizosphere communication: multiple molecules with diverse functions.

Strigolactones (SLs) are root-secreted small molecules that influence organisms living in the rhizosphere. While SLs are known as germination stimulants for root parasitic plants, and as hyphae branching factors for arbuscular mycorrhizal fungi, recent studies have also identified them as chemoattractants for parasitic plants, sensors of neighboring plants, and key players in shaping the microbiome community. Furthermore, the discovery of structurally diverged SLs, including so-called canonical and non-canonical SLs in various plant species, raises the question whether the same SLs are responsible for their diverse functions in planta and the rhizosphere or whether different molecules play different roles. Emerging evidence supports the latter, with each SL exhibiting different activities as rhizosphere signals and plant hormones. The evolution of D14/KAI2 receptors has enabled the perception of various SLs or SL-like compounds to control downstream signaling, highlighting the complex interplay between plants and their rhizosphere environment. This review summarizes the recent advances in our understanding of the diverse functions of SLs in the rhizosphere.

Use of biosurfactants produced by Bacillus subtilis H1 and Pseudomonas aeruginosa PAO1 as a disinfectant and plant growth stimulation

Sustainable agriculture involves the maximum use of the resource potential of the earth, with the constant renewal of the fertility of the ecosystem. One method of transition to sustainable agriculture is the use of biological control agents, which include biosurfactants. We assessed the possibility of using crude biosurfactants obtained from Bacillus subtilis H1 and Pseudomonas aeruginosa PAO1 as dressing agents for untreated wheat seeds and the presence of seed germination stimulating properties. It was shown that crude rhamnolipids obtained from Pseudomonas aeruginosa PAO1 inhibited the area occupied by fungal mycelia at a concentration of 500 mg/l. Surfactin, derived from Bacillus subtilis H1, inhibited fungal growth at a concentration of 100 mg/L. Stimulation of germination of wheat seeds by 1.9 and 2 times was determined by rhamnolipid at a concentration of 500 mg/l and surfactin at a concentration of 100 mg/l for 168 hours of germination. The use of biocontrol agents is a promising method that can improve product quality while reducing the negative impact on the environment.

Actions and reactions of plants derived zinc-oxide nano-particles

Nanotechnology has emerged as a pivotal industry in the twenty-first century, with nanoparticles (NPs) occupying a crucial role due to their small size ranging from 1 to 100 nm, rendering them versatile for both organic and inorganic applications. The extensive use of NPs in various domains with an estimated yearly worldwide production range between 550 and 33,400 metric tonnes, has led to an escalation in the possibility of their release into the environment. These nanoparticles are recognized as a biosafe substance, have gained immense significance, given their facile application and broad spectrum of usage in different industry including agriculture, pharmaceuticals, cosmetics etc. Capacity of ZnO-NPs in prior studies have been demonstrated as seed germination stimulants, crop production enhancers, curb disease, and shield plants from bacterial action. Therefore, it is imperative to develop a non-toxic, eco-friendly, simple, cost effective, scalable NPs production methodology. Several biological systems, including yeast, fungus, bacteria, and plant extracts, are widely utilized in green synthesis methodologies for NPs production. ZnO-NPs have been observed to modulate plant metabolism and growth in diverse ways, both favourable and unfavourable, during distinct developmental stages depending upon the ZnO-NPs' unique properties and the physiology of the recipient plant have an impact on how well they are absorbed, behave, and ultimately end up in plants. This review aims to extend the current understanding of current trends in green synthesis and plant-derived NPs, with a specific emphasis on ZnO-NP uptake, distribution, transformation and reaction in plants.

Recent advances in the regulation of root parasitic weed damage by strigolactone-related chemicals.

Root parasitic weeds such as Striga spp. and Orobanche spp. dramatically reduce the yields of important agricultural crops and cause economic losses of over billions of US dollars worldwide. One reason for the damage by root parasitic weeds is that they germinate after specifically recognizing the host cues, strigolactones (SLs). SLs were identified ˃50 years ago as germination stimulants for root parasitic weeds, and various studies have been conducted to control parasitic weeds using SLs and related chemicals. Recently, biochemical and molecular biological approaches have revealed the SL biosynthesis and SL receptors; using these findings, various SL-related chemicals have been developed. This review summarizes recent research on SLs and their related chemicals for controlling root parasitic weeds.

Karrikin perception and signalling.

Karrikins (KARs) are a class of butenolide compounds found in smoke that were first identified as seed germination stimulants for fire-following species. Early studies of KARs classified the germination and postgermination responses of many plant species and investigated crosstalk with plant hormones that regulate germination. The discovery that Arabidopsis thaliana responds to KARs laid the foundation for identifying mutants with altered KAR responses. Genetic analysis of KAR signalling revealed an unexpected link to strigolactones (SLs), a class of carotenoid-derived plant hormones. Substantial progress has since been made towards understanding how KARs are perceived and regulate plant growth, in no small part due to advances in understanding SL perception. KAR and SL signalling systems are evolutionarily related and retain a high degree of similarity. There is strong evidence that KARs are natural analogues of an endogenous signal(s), KAI2 ligand (KL), which remains unknown. KAR/KL signalling regulates many developmental processes in plants including germination, seedling photomorphogenesis, and root and root hair growth. KAR/KL signalling also affects abiotic stress responses and arbuscular mycorrhizal symbiosis. Here, we summarise the current knowledge of KAR/KL signalling and discuss current controversies and unanswered questions in this field.

Strigolactone, a neglected plant hormone, with a great potential for crop improvement: Crosstalk with other plant hormones

Strigolactones (SLs), initially reported as germination stimulants for Striga lutea were later described for their role in Phelipanche and Orobanche species. SLs were reported in major cereals such as sorghum and maize, which established their importance in host-parasite interaction. Over the past decade, several roles of SLs have been elucidated in root and shoot architecture, pathogen interaction, plant defense mechanism, and nutrition uptake. Additionally, SL plays a key role in abiotic and biotic stress tolerance associated with other phytohormones. The review provides a comprehensive overview of various aspects of SLs and their complex interaction networks with other phytohormones that exist in the plant system. The review also highlights pivotal points for establishing SLs in commercial agriculture to fully explore their potential in crop improvement and shaping modern agriculture.

Development of an Environmentally Friendly Technology for the Treatment of Aqueous Solutions with High-Purity Plasma for the Cultivation of Cotton, Wheat and Strawberries

The microwave setup for obtaining plasma-activated water (PAW) has been created. PAW contains significant concentrations of H2O2 and NO3−, has a reduced content of O2, high conductivity, a high redox potential and low pH. Likewise, the specific electrical conductivity and concentration of H2O2 and NO3− linearly depend on the treatment time. These parameters are simple and convenient markers for controlling the preparation of PAW. It has been established that PAW solutions with a concentration of 0.5–1.0% increase the germination energy, protect against fusarium and hyperthermia in cotton, wheat and strawberry seeds. In addition, PAWs have a positive effect on the growth rate of plants in the early stages of development. The use of PAW provides significant benefits over the chemical preparations Dalbron and Bakhor, so-called seed germination stimulators (SDS).

Stimulation role of pollen grains in the initial development of Botrytis cinerea: The importance of host compatibility, cultivation status and pollen size

AbstractPlant pollens and fungal spores are massively produced in natural habitats and large‐scaled agricultural areas, and the airborne transported biomass can be accumulated on relatively large crop surfaces. A pollen grain contains a specific chemical composition in quantity and quality, highly varied among plant species. So, the accumulated pollens could provide a species‐specific nutrient supply for the initial fungal development in a pollen trap. Thus, this could increase the variation of the pathogen infection risk in certain plants due to selection mechanisms such as host–pathogen coevolution, crop breeding or pollination type. However, the role of the pollen‐stimulated spore germination and the species‐specific differences in the pollen‐spore interferences is still less understood. Therefore, we performed a multispecies experimental comparison (including 20 plant species) to test the role of the taxon‐specific attributes (i.e. host–pathogen compatibility, cultivation, pollination type and pollen size) in the dose and temporal response of the spore germination in Botrytis cinerea. We found a strong pollen‐stimulating effect on spore germination; however, the triggering effect highly varied among plant species and differed between specific functional categories across temporal and concentration gradients. Specifically, the B. cinerea hosts, the non‐cultivated plants and species with larger pollen size, increased the spore germination's stimulation effects, but not the pollination type. The systematic taxonomic and functional differences might reflect indirectly the diversity of the pollens' chemical profile (i.e. composition matrix or specific trigger molecules) which different selection mechanisms might shape. In the crop–pathogen interactions, the pollen‐stimulation effect could play an essential role in early fungal development.

Screening of Sorghum Mutant Lines in Vitro and Greenhouse Against Striga Hermonthica Infestation

The parasitic weed, Striga hermonthica (Del.) Benth is a major constraint to cereal productions such as sorghum. In Burkina Faso, sorghum is the first of the cereals, in terms of cultivated areas and human consumption per capita. This study aimed to identify resistant lines by screening 31 sorghum mutant lines. Experimental assays were carried out in vitro and under greenhouse. The results shown that mutant lines SbEMS0937-1, SbEMS3105-2 were low producers of Striga seeds germination stimulant in vitro. There was a positive and significant correlation (r = 0.72; p < 0.0001) between the germination maximum distance (GMD) and the germination rates (GR) of the different sorghum varieties and mutant lines. In the greenhouse conditions, the mutant SbEMS2311-1 was leading with two resistant controls to having significantly low numbers (5 plants/pot) of Striga 60 DAS (Days After Sowing) and featured the lowest number of Striga 90 DAS (10 plants/pot). The sorghum production variables that are the weights of the stems, panicles, and grains and the plant height at 21 days after sowing (DAS) and at the harvest were all positively related. However, the emergence date and the number of Striga plants which emerged at 90 DAS were negatively correlated (r = -0.21; p = 0.02). Otherwise, the GMD in vitro was positively correlated with the number of the Striga plants emerged at 60 DAS and 90 DAS in greenhouse. These results revealed that the mutagenesis of the sorghum lead to resistance or tolerance to S. hermonthica. Therefore, the growing of each of the three resistant mutants should contribute to reducing highly the density of this pest plant in the sorghum field. Furthermore, the transfer of gene (s) inducing this Striga-resistance/tolerance from mutant lines could improve Sorghum varieties preferred by local farmers.

ИСПОЛЬЗОВАНИЕ ЛАЗЕРНОГО ИМПУЛЬСНОГО ИЗЛУЧЕНИЯ И РАСТВОРОВ ЭКОПЕРОКСИДА ДЛЯ АКТИВАЦИИ СЕМЯН САХАРНОЙ СВЕКЛЫ

Sugar beet, a biennial industrial agricultural crop, is used for the production of ethanol, biofuels, sugar and contains up to 70% sucrose. It is difficult to obtain seeds, the collection of which takes place in the second year of cultivation of root crops. The possibility of accelerating seed activation, increasing germination by methods of pre-sowing treatment of dry seeds: laser pulsed radiation and ecoperoxide solutions was studied. The first test indicating the beginning of seed awakening (one hour after treatment) was a test for determining the release of metabolites into the aqueous culture medium. The metabolites determined by spectrophotometry. They have a characteristic absorption spectrum in the UV region with a clear maximum at λmax – 207 nm and absorption up to the boundary with the visible region of 
 λmax – 330 nm. A copper vapor laser was used. Parameters: simultaneous generation of two wavelengths – green 510.5 nm and yellow 578.2 nm. The duration of the radiation pulse is 15 ns, the repetition rate is 10 kHz. The irradiation time is 10, 20, 90 s. The greatest effect of seed germination stimulation at 10 s of irradiation exceeded the control by 30%. Increasing the interval to 24 hours or more between irradiation and placing seeds for germination reduced the number of germinated seeds. Ecoperoxide was obtained by high-energy non-contact exposure to distilled water with high-voltage electric discharge streamers. An increase in seed germination by 30-40% was noted when they came into contact with a peroxide solution for 30 minutes.

Stimulation of Germination of Freshly Collected and Cold-Stored Seeds of Ambrosia artemisiifolia L.

Herbicides are the most commonly used means of controlling the growth of Ambrosia artemisiifolia L. Their constant use has led to the development of resistant populations. They can be evaluated by studying seed germination and the corresponding grown plants, but A. artemisiifolia exhibits seed dormancy, preventing germination and delaying research. Here, we developed a simple and rapid method to stimulate germination of freshly collected or stored A. artemisiifolia seeds. The germination of A. artemisiifolia freshly collected/stored seeds was evaluated after storage, stratification, and chemical treatments (ethephon, gibberellic acid (GA3), thiourea, KNO3). Ethephon or ethephon + GA3 improved freshly collected seed germination by 88 and 95%, respectively, and germination of stored seeds by 78 and 80%, respectively. In addition, placing the seeds of A. artemisiifolia in ethephon, GA3, ethephon + GA3, or thiourea solutions caused the freshly collected seeds to germinate faster than stored seeds or nontreated seeds. In contrast, the conditioning of seeds in these solutions favored germination of stored seeds, especially when ethephon + GA3 or GA3 was used. Imbibition of the freshly collected A. artemisiifolia seeds in a mixture of ethephon and GA3 can effectively overcome primary dormancy when rapid experimental results are needed. For seeds requiring prolonged storage, conditioning in ethephon, GA3, or thiourea solutions may be applied to promote germination.

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

The development of potent strigolactone (SL) agonists as suicidal germination inducers could be a useful strategy for controlling root parasitic weeds, but uncertainty about the SL perception mechanism impedes real progress. Here we describe small-molecule agonists that efficiently stimulate Phelipanchce aegyptiaca, and Striga hermonthica, germination in concentrations as low as 10−8 to 10−17 M. We show that full efficiency of synthetic SL agonists in triggering signaling through the Striga SL receptor, ShHTL7, depends on the receptor-catalyzed hydrolytic reaction of the agonists. Additionally, we reveal that the stereochemistry of synthetic SL analogs affects the hydrolytic ability of ShHTL7 by influencing the probability of the privileged conformations of ShHTL7. Importantly, an alternative ShHTL7-mediated hydrolysis mechanism, proceeding via nucleophilic attack of the NE2 atom of H246 to the 2′C of the D-ring, is reported. Together, our findings provide insight into SL hydrolysis and structure-perception mechanisms, and potent suicide germination stimulants, which would contribute to the elimination of the noxious parasitic weeds.

Noncanonical Strigolactone Analogues Highlight Selectivity for Stimulating Germination in Two Phelipanche ramosa Populations.

Strigolactones (SLs) are plant hormones exuded in the rhizosphere with a signaling role for the development of arbuscular mycorrhizal (AM) fungi and as stimulants of seed germination of the parasitic weeds Orobanche, Phelipanche, and Striga, the most threatening weeds of major crops worldwide. Phelipanche ramosa is present mainly on rape, hemp, and tobacco in France. P. ramosa 2a preferentially attacks hemp, while P. ramosa 1 attacks rapeseed. The recently isolated cannalactone (14) from hemp root exudates has been characterized as a noncanonical SL that selectively stimulates the germination of P. ramosa 2a seeds in comparison with P. ramosa 1. In the present work, (-)-solanacol (5), a canonical orobanchol-type SL exuded by tobacco and tomato, was established to possess a remarkable selective germination stimulant activity for P. ramosa 2a seeds. Two cannalactone analogues, named (±)-SdL19 and (±)-SdL118, have been synthesized. They have an unsaturated acyclic carbon chain with a tertiary hydroxy group and a methyl or a cyclopropyl group instead of a cyclohexane A-ring, respectively. (±)-SdL analogues are able to selectively stimulate P. ramosa 2a, revealing that these minimal structural elements are key for this selective bioactivity. In addition, (±)-SdL19 is able to inhibit shoot branching in Pisum sativum and Arabidopsis thaliana and induces hyphal branching in the AM fungus Rhizophagus irregularis, like SLs.