Coronalon: a powerful tool in plant stress physiology

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.

Modulation of NaCl-induced osmotic, cytogenetic, oxidative and anatomic damages by coronatine treatment in onion (Allium cepa L.)

Coronatine (COR), a bacterial phytotoxin produced by Pseudomonas syringae, plays important roles in many plant growth processes. Onion bulbs were divided four groups to investigate the effects of COR against sodium chloride (NaCl) stress exposure in Allium cepa L. root tips. While control group bulbs were soaked in tap water medium, treatment group bulbs were grown in 0.15 M NaCl, 0.01 µM COR and 0.01 µM COR + 0.15 M NaCl medium, respectively. NaCl stress seriously inhibited the germination, root lenght, root number and fresh weight of the bulbs. It significantly decreased the mitotic index (MI), whereas dramatically increased the micronucleus (MN) frequency and chromosomal aberrations (CAs). Moreover, in order to determine the level of lipid peroxidation occurring in the cell membrane, malondialdehyde (MDA) content was measured and it was determined that it was at the highest level in the group germinated in NaCl medium alone. Similarly, it was revealed that the superoxide dismutase (SOD), catalase (CAT) and free proline contents in the group germinated in NaCl medium alone were higher than the other groups. On the other hand, NaCl stress caused significant injuries such as epidermis/cortex cell damage, MN formation in epidermis/cortex cells, flattened cells nuclei, unclear vascular tissue, cortex cell wall thickening, accumulation of certain chemical compounds in cortex cells and necrotic areas in the anatomical structure of bulb roots. However, exogenous COR application significantly alleviated the negative effects of NaCl stress on bulb germination and growth, antioxidant defense system, cytogenetic and anatomical structure. Thus, it has been proven that COR can be used as a protective agent against the harmful effects of NaCl on onion.

The genome of homosporous maidenhair fern sheds light on the euphyllophyte evolution and defences

Euphyllophytes encompass almost all extant plants, including two sister clades, ferns and seed plants. Decoding genomes of ferns is the key to deep insight into the origin of euphyllophytes and the evolution of seed plants. Here we report a chromosome-level genome assembly of Adiantum capillus-veneris L., a model homosporous fern. This fern genome comprises 30 pseudochromosomes with a size of 4.8-gigabase and a contig N50 length of 16.22 Mb. Gene co-expression network analysis uncovered that homospore development in ferns has relatively high genetic similarities with that of the pollen in seed plants. Analysing fern defence response expands understanding of evolution and diversity in endogenous bioactive jasmonates in plants. Moreover, comparing fern genomes with those of other land plants reveals changes in gene families important for the evolutionary novelties within the euphyllophyte clade. These results lay a foundation for studies on fern genome evolution and function, as well as the origin and evolution of euphyllophytes.

Screening of Indanoyl-Type Compounds as Elicitors of Isoflavonoid Phytoalexins in Colombian Common Bean Cultivars

Eleven indanoyl derivatives were synthesized and, along with methyl jasmonate, evaluated as isoflavonoid-phytoalexin elicitors in two cultivars of common bean (Phaseolus vulgaris L. cvs. ICA-Cerinza and Uribe Rosado, tolerant and susceptible to anthracnose, respectively). Indanoyl derivatives (an ester, two amides, and eight indanoyl-amino acid conjugates) were obtained from 1-oxo-indane-4-carboxylic acid. In general, the accumulation of isoflavonoid-type phytoalexins, such as isoflavones (genistein, daidzein, and 2′-hydroxygenistein), isoflavanones (dalbergioidin and kievitone), isoflavan (phaseollinisoflavan), coumestrol, and pterocarpans (phaseollidin and phaseollin), was dependent on the common bean cultivar, the post-induction time, and the elicitor structure. Isoflavones, dalbergioidin, and coumestrol reached their highest amounts during the first 48 to 72 h, whereas kievitone, phaseollinisoflavano, and the pterocarpans reached maximum levels between 72 and 96 h. The 1-oxo-indanoyl-L-isoleucine methyl ester elicited the highest levels of phytoalexins (similar to those elicited by the methyl jasmonate) and showed no significant phytotoxic effects on common bean seedlings. The indanoyl-type synthetic elicitor, 1-oxo-indanoyl-L-isoleucine methyl ester, may represent a promising agronomic alternative for disease control in common bean by enhancing the accumulation of antimicrobial isoflavonoid phytoalexins.

Elicitation of isoflavonoids in Colombian edible legume plants with jasmonates and structurally related compounds

Common bean (Phaseolus vulgaris L.), soybean (Glycine max L.) and mung bean (Vigna radiata L. Wilczek) seedlings were treated with methyl jasmonate (MeJA); then, dose-response and time-course experiments were carried out. Isoflavonoid composition was evaluated by high performance liquid chromatography. As a result of MeJA induction, all leguminous plants increase the amount of isoflavonoids, at levels that depend on the concentration of the elicitor and the time after induction. However, the application of MeJA in concentrations higher than 2.22 mM showed deleterious effects on seedlings and strong decreases in the concentration of isoflavonoids. In addition, a series of compounds structurally related to MeJA, such as jasmonic acid, cis-jasmone, coronatine, and indanoyl derivatives, were evaluated as elicitors. The results show that coronatine and the indanoyl-amino acids conjugates displayed a significant elicitor effect of isoflavonoids in common bean (cvs. Cargamanto Mocho and Corpoica LAS 106) and soybean (cv. Soyica P-34) seedlings, even higher than that found with the recognized elicitors, benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (acibenzolar S-methyl) and benzo-(1,2,3) thiadiazole-7-carbothioic acid (acibenzolar acid). Leguminous plants can be treated with jasmonates and indanoyl derivatives to increase levels of bioactive isoflavonoids and consequently improve biological and functional properties and resistance against pests.

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The accumulation of isoflavonoids in edible legume seedlings treated with jasmonates and structurally related compounds was analyzed.

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Time-course and dose-response experiments were performed using methyl jasmonate as elicitor.

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The application of jasmonates and structurally related compounds increased the concentration of bioactive isoflavonoids.

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The amount of isoflavonoids depended on the cultivar, the concentration and structure of the elicitor, and the post-induction time.

Discovery, characterization and engineering of ligases for amide synthesis

Coronatine and related bacterial phytotoxins are mimics of the hormone jasmonyl-L-isoleucine (JA-Ile), which mediates physiologically important plant signalling pathways1-4. Coronatine-like phytotoxins disrupt these essential pathways and have potential in the development of safer, more selective herbicides. Although the biosynthesis of coronatine has been investigated previously, the nature of the enzyme that catalyses the crucial coupling of coronafacic acid to amino acids remains unknown1,2. Here we characterize a family of enzymes, coronafacic acid ligases (CfaLs), and resolve their structures. We found that CfaL can also produce JA-Ile, despite low similarity with the Jar1 enzyme that is responsible for ligation of JA and L-Ile in plants5. This suggests that Jar1 and CfaL evolved independently to catalyse similar reactions-Jar1 producing a compound essential for plant development4,5, and the bacterial ligases producing analogues toxic to plants. We further demonstrate how CfaL enzymes can be used to synthesize a diverse array of amides, obviating the need for protecting groups. Highly selective kinetic resolutions of racemic donor or acceptor substrates were achieved, affording homochiral products. We also used structure-guided mutagenesis to engineer improved CfaL variants. Together, these results show that CfaLs can deliver a wide range of amides for agrochemical, pharmaceutical and other applications.

Increased accumulation of isoflavonoids in common bean (Phaseolus vulgaris L.) tissues treated with 1-oxo-indane-4-carboxylic acid derivatives

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Eleven indanoyl derivatives as potential elicitors were synthesized and characterized.

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Accumulation of nine isoflavonoid phytoalexins in two common bean (P. vulgaris L.) cultivars grown in Colombia was analyzed.

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Dose-response and time-course experiments were performed on cotyledons and hypocotyls-roots of common bean treated with the potential elicitors.

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Application of indanoyl-type elicitors increased the concentration of isoflavonoids in tissues of common bean.

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Accumulation of isoflavonoid phytoalexins was dependent on the cultivar, the tissue type, the elicitor structure and the post-induction time.

Isoflavonoid phytoalexins (isoflavones: genistein, 2′-hydroxygenistein, and daidzein; isoflavanones: dalbergioidin and kievitone; coumestrol; pterocarpans: phaseollidin and phaseollin; and the isoflavan: phaseollinisoflavan) production in response to the application of eleven 1-oxo-indane-4-carboxylic acid derivatives (indanoyl esters and indanoyl amino acids conjugates), in cotyledons and hypocotyl/root of two common bean (Phaseolus vulgaris L.) cultivars was evaluated. The content of isoflavonoids depended on the cultivar, the treated tissue, the time after induction, the structure and concentration of the elicitor. The highest isoflavonoid contents were found when 1-oxo-indanoyl-amino acids conjugates were used as elicitors. Cotyledons and hypocotyl/root of the anthracnose-resistant cultivar produced significantly higher isoflavonoid contents as compared to the susceptible one. Maximum levels of phaseollin were obtained using 0.66 mM 1-oxo-indanoyl-l-isoleucyl methyl ester and between 72 and 96 h post-induction. So, 1-oxo-indane-4-carboxylic acid derivatives, may be used to enhance the amount of isoflavonoid phytoalexins in common bean and protect crops from phytopathogenic microorganisms.

JA-Ile-macrolactone 5b Induces Tea Plant (Camellia sinensis) Resistance to Both Herbivore Ectropis obliqua and Pathogen Colletotrichum camelliae

Jasmonates (JAs), the group of lipid-derived hormones, were found to control the defense responses in a myriad of plants. Meaningfully, the macrolactones of 12-hydroxy jasmonate isoleucine (12OH-JA-Ile) were reported to induce the defensive response of wild tobacco. However, little to nothing has been known about the elicitation effect of JA-Ile-macrolactones on woody plants to harmful organisms, let alone its underlying mechanisms. Here, we first optimized the synthetic routine using mild toxic reagent isobutyl chloroformate instead of ethyl chloroformate for conjugation, and we used acetonitrile (MeCN) instead of ethyl alcohol for the better dissolution of p-toluenesulfonic acid (p-TsOH) to gain JA-Ile-macrolactones. JA-Ile-macrolactone 5b-treated tea plants significantly inhibited the larvae weight gain of Ectropis obliqua larvae and the lesions caused by Colletotrichum camelliae. Furthermore, the expression level of CsOPR3 was significantly upregulated in 5b-treated leaves. Meanwhile, 5b reduced the accumulation of eriodictyol 7-O-glucuronide (EDG) in tea plants, which was confirmed to promote the growth rate of E. obliqua larvae by artificial diet assay. In conclusion, our study proved that the exogenous application of 5b could induce the tea plant resistance both to herbivore E. obliqua and pathogen C. camelliae, and EDG was identified as one of the secondary metabolites that could influence the growth rate of E. obliqua, but it did not directly influence the infection of C. camelliae in vitro. Further research should be carried out to clarify the mechanism through which 5b induces tea plant resistance to C. camelliae.

Recent Advances in Plant Chemical Biology of Jasmonates

Lipid-derived plant hormone jasmonates are implicated in plant growth, reproductive performance, senescence, secondary metabolite productions, and defense against both necrotrophic pathogens and feeding insects. A major jasmonate is (+)-7-iso-jasmonoyl-l-isoleucine (JA-Ile), which is perceived by the unique COI1-JAZ coreceptor system. Recent advances in plant chemical biology have greatly informed the bioscience of jasmonate, including the development of chemical tools such as the antagonist COR-MO; the agonist NOPh; and newly developed jasmonates, including JA-Ile-macrolactone and 12-OH-JA-Ile. This review article summarizes the current status of plant chemical biology as it pertains to jasmonates, and offers some perspectives for the future.

Gene Expression Profiles Deciphering the Pathways of Coronatine Alleviating Water Stress in Rice (Oryza sativa L.) Cultivar Nipponbare (Japonica)

Coronatine (COR) is a structural and functional analog of methyl jasmonic acid (MeJA), which can alleviate stress on plant. We studied the effects of COR on the drought stress of rice (Oryza sativa L.). Pre-treatment with COR significantly increased the biomass, relative water and proline content, and DPPH (1,1-diphenyl-2-picrylhydrazyl)-radical scavenging activity, decreased the electrolyte leakage and MDA (Malondialdehyde) content in order to maintain the stability of cell membrane. Meanwhile, we determined how COR alleviates water stress by Nipponbare gene expression profiles and cDNA microarray analyses. Seedlings were treated with 0.1 μmol L⁻¹ COR at the three leafed stage for 12 h, followed with 17.5% polyethylene glycol (PEG). Whole genome transcript analysis was determined by employing the Rice Gene Chip (Affymetrix), a total of 870 probe sets were identified to be up or downregulated due to COR treatment under drought stress. Meanwhile, the real-time quantitative PCR (RT-qPCR) method was used to verify some genes; it indicated that there was a good agreement between the microarray data and RT-qPCR results. Our data showed that the differentially expressed genes were involved in stress response, signal transduction, metabolism and tissue structure development. Some important genes response to stress were induced by COR, which may enhance the expression of functional genes implicated in many kinds of metabolism, and play a role in defense response of rice seedling to drought stress. This study will aid in the analysis of the expressed gene induced by COR.

A novel ABA functional analogue B2 enhances drought tolerance in wheat

Drought stress negatively affects wheat growth and yield. Application of drought agent is an effective way to improve crop drought tolerance, therefore increasing crop yield. Based on the structure of abscisic acid (ABA), Pyrabactin and coronatine (COR), we designed the target compound B2. To investigate the function of B2 in alleviating drought stress on wheat, the drought-resistant variety ND212 and drought-sensitive variety LX99 were used under hydroponic conditions. The results showed that B2 had a similar function with ABA, especially 0.01 μmol·L⁻¹ B2. Under drought stress conditions, 0.01 μmol·L⁻¹ B2 increased the water content of wheat, enhanced the osmotic adjustment ability of leaves, and reduced the toxicity of reactive oxygen species on cells. What’s more, 0.01 μmol·L⁻¹ B2 improved the expression level of ABA-responsive genes TaSnRK2.4 and TaMYB3R1. It also improved the expression level of drought-responsive genes TaSRHP and TaERF3. Taken together, B2 enhanced drought tolerance in wheat by activating ABA signaling pathway.

Recent Advances in Synthetic Chemical Inducers of Plant Immunity

Different from the conventional biocidal agrochemicals, synthetic chemical inducers of plant immunity activate, bolster, or prime plant defense machineries rather than directly acting on the pathogens. Advances in combinatorial synthesis and high-throughput screening methods have led to the discovery of various synthetic plant immune activators as well as priming agents. The availability of their structures and recent progress in the mechanistic understanding of plant immune responses have opened up the possibility of identifying new or more potent chemical inducers through rational design. In this review, we first summarize the chemical inducers identified through large-scale screening and then discuss the emerging trends in the identification and development of novel plant immune inducers including natural elicitor based chemical derivation, bifunctional combination, and computer-aided design.

A subset of chemosensory genes differs between two populations of a specialized leaf beetle after host plant shift

Due to its fundamental role in shaping host selection behavior, we have analyzed the chemosensory repertoire of Chrysomela lapponica. This specialized leaf beetle evolved distinct populations which shifted from the ancestral host plant, willow (Salix sp., Salicaceae), to birch (Betula rotundifolia, Betulaceae). We identified 114 chemosensory candidate genes in adult C. lapponica: 41 olfactory receptors (ORs), eight gustatory receptors, 17 ionotropic receptors, four sensory neuron membrane proteins, 32 odorant binding proteins (OBPs), and 12 chemosensory proteins (CSP) by RNA-seq. Differential expression analyses in the antennae revealed significant upregulation of one minus-C OBP (Clap OBP27) and one CSP (Clap CSP12) in the willow feeders. In contrast, one OR (Clap OR17), four minus-C OBPs (Clap OBP02, 07, 13, 20), and one plus-C OBP (Clap OBP32) were significantly upregulated in birch feeders. The differential expression pattern in the legs was more complex. To narrow down putative ligands acting as cues for host discrimination, the relative abundance and diversity of volatiles of the two host plant species were analyzed. In addition to salicylaldehyde (willow-specific), both plant species differed mainly in their emission rate of terpenoids such as (E,E)-α-farnesene (high in willow) or 4,8-dimethylnona-1,3,7-triene (high in birch). Qualitatively, the volatiles were similar between willow and birch leaves constituting an "olfactory bridge" for the beetles. Subsequent structural modeling of the three most differentially expressed OBPs and docking studies using 22 host volatiles indicated that ligands bind with varying affinity. We suggest that the evolution of particularly minus-C OBPs and ORs in C. lapponica facilitated its host plant shift via chemosensation of the phytochemicals from birch as novel host plant.

Jasmonate-Elicited Stress Induces Metabolic Change in the Leaves of Leucaena leucocephala

The plant Leucaena leucocephala was exposed to four jasmonate elicitors, i.e., jasmonic acid (JA), methyl jasmonic acid (MeJA), jasmonoyl-l-isoleucine (JA-Ile) and 6-ethyl indanoyl glycine conjugate (2-[(6-ethyl-1-oxo-indane-4-carbonyl)-amino]-acetic acid methyl ester) (CGM). The treatment was to mimic the herbivores and wounding stresses. By using NMR spectroscopy along with chemometric analysis, including principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA), the changes of metabolites in the leaves of L. leucocephala were determined under the stress as induced by the four elicitors. The challenge of JA-Ile caused an accumulation of lactic acid (6), β-glucose (10), alanine (12), threonine (13), steroids (18), 3,4-dihydroxypyridine (19) and an unidentified compound 20. The chemometric analysis of the PCA and PLS-DA models indicated that the alternation of metabolites triggered by JA, MeJA, and CGM treatments were very minimum. In contrast, the treatment by JA-Ile could induce the most significant metabolic changes in the leaves. Moreover, there was very minimal new metabolite being detected in responding to the jasmonate-induced stresses. The results showed some metabolite concentrations changed after application of the elicitors, which may be related to a high level of tolerance to stress conditions as well as the strong ecological suitability of L. leucocephala.

Jasmonate signaling in plant stress responses and development - active and inactive compounds

Jasmonates (JAs) are lipid-derived signals mediating plant responses to biotic and abiotic stresses and in plant development. Following the elucidation of each step in their biosynthesis and the important components of perception and signaling, several activators, repressors and co-repressors have been identified which contribute to fine-tuning the regulation of JA-induced gene expression. Many of the metabolic reactions in which JA participates, such as conjugation with amino acids, glucosylation, hydroxylation, carboxylation, sulfation and methylation, lead to numerous compounds with different biological activities. These metabolites may be highly active, partially active in specific processes or inactive. Hydroxylation, carboxylation and sulfation inactivate JA signaling. The precursor of JA biosynthesis, 12-oxo-phytodienoic acid (OPDA), has been identified as a JA-independent signaling compound. An increasing number of OPDA-specific processes is being identified. To conclude, the numerous JA compounds and their different modes of action allow plants to respond specifically and flexibly to alterations in the environment.

Additional evidence against jasmonate-induced jasmonate induction hypothesis

Jasmonates are phytohormones involved in development and stress reactions. The most prominent jasmonate is jasmonic acid, however, the bioactive jasmonate is (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile). Biosynthesis of jasmonates is long time known; compartmentalization, enzymes and corresponding genes are well studied. Because all genes encoding these biosynthetic enzymes are jasmonate inducible, a hypothesis of jasmonate-induced-jasmonate-biosynthesis is widely accepted. Here, this hypothesis was revisited by employing the synthetic JA-Ile mimic coronalon to intact and wounded leaves, which excludes structural cross-contamination with endogenous jasmonates. At an effective concentration that induced various jasmonate-responsive genes in Arabidopsis, neither accumulation of endogenous jasmonic acid, JA-Ile, nor of their hydroxylated metabolites was detected. Results indicate that in spite of jasmonate-induced biosynthetic gene expression, no jasmonate biosynthesis/accumulation takes place supporting a post-translational regulation.

Phytotoxin coronatine enhances heat tolerance via maintaining photosynthetic performance in wheat based on Electrophoresis and TOF-MS analysis

Coronatine (COR) is a phytotoxin produced by Pseudomonas syringae. Its structure is similar to Jasmonates, which play a number of diverse roles in plant defense. Both have the COI1 plant receptor, so coronatine can manipulate plant hormone signaling to access nutrients and counteract defense responses. In addition to the hormone system, coronatine affects plant nitrogenous metabolism and chloroplast ultrastructure. In this study, we first examined a typical nitrogen-losing phenotype, and used the polyacrylamide gel approach to demonstrate soluble total protein patterns in a time-course experiment under different temperature conditions. We then employed dimensional gel electrophoresis technology (2-DE) and MALDI-TOF-MS to sequester and identify the sensitive proteins. We found a total of 27 coronatine sensitive proteins, 22 of which were located in the chloroplast and 6 of which were directly involved in photosynthesis. Finally, we measured levels of chlorophyll and photosynthetic performance to reveal the phenotypic effect of these proteins. Taken together, these results demonstrated that coronatine enhanced heat tolerance by regulating nitrogenous metabolism and chloroplast ultrastructure to maintain photosynthetic performance and reduce yield loss under heat stress.

Synthetic plant defense elicitors

To defend themselves against invading pathogens plants utilize a complex regulatory network that coordinates extensive transcriptional and metabolic reprogramming. Although many of the key players of this immunity-associated network are known, the details of its topology and dynamics are still poorly understood. As an alternative to forward and reverse genetic studies, chemical genetics-related approaches based on bioactive small molecules have gained substantial popularity in the analysis of biological pathways and networks. Use of such molecular probes can allow researchers to access biological space that was previously inaccessible to genetic analyses due to gene redundancy or lethality of mutations. Synthetic elicitors are small drug-like molecules that induce plant defense responses, but are distinct from known natural elicitors of plant immunity. While the discovery of some synthetic elicitors had already been reported in the 1970s, recent breakthroughs in combinatorial chemical synthesis now allow for inexpensive high-throughput screens for bioactive plant defense-inducing compounds. Along with powerful reverse genetics tools and resources available for model plants and crop systems, comprehensive collections of new synthetic elicitors will likely allow plant scientists to study the intricacies of plant defense signaling pathways and networks in an unparalleled fashion. As synthetic elicitors can protect crops from diseases, without the need to be directly toxic for pathogenic organisms, they may also serve as promising alternatives to conventional biocidal pesticides, which often are harmful for the environment, farmers and consumers. Here we are discussing various types of synthetic elicitors that have been used for studies on the plant immune system, their modes-of-action as well as their application in crop protection.

Insect Herbivory-Elicited GABA Accumulation in Plants is a Wound-Induced, Direct, Systemic, and Jasmonate-Independent Defense Response

The non-proteinogenic amino acid γ-aminobutyric acid (GABA) is present in all organisms analyzed so far. In invertebrates GABA acts as a neurotransmitter; in plants different functions are under discussion. Among others, its involvement in abiotic stress reactions and as a defensive compound against feeding insects is suggested. GABA is synthesized from glutamate by glutamate decarboxylases and degraded by GABA-transaminases. Here, in Arabidopsis thaliana, gad1/2 double mutants showing reduced GABA concentrations as well as GABA-enriched triple mutants (gad1/2 x pop2-5) were generated and employed for a systematic study of GABA induction, accumulation and related effects in Arabidopsis leaves upon herbivory. The results demonstrate that GABA accumulation is stimulated by insect feeding-like wounding by a robotic caterpillar, MecWorm, as well as by real insect (Spodoptera littoralis) herbivory. Higher GABA levels in both plant tissue and artificial dietary supplements in turn affect the performance of feeding larvae. GABA enrichment occurs not only in the challenged but also in adjacent leaf. This induced response is neither dependent on herbivore defense-related phytohormones, jasmonates, nor is jasmonate induction dependent on the presence of GABA. Thus, in Arabidopsis the rapid accumulation of GABA very likely represents a general, direct and systemic defense reaction against insect herbivores.

Synthesis of 6-substituted 1-oxoindanoyl isoleucine conjugates and modeling studies with the COI1-JAZ co-receptor complex of lima bean

The conjugates of 6-substituted 1-oxoindanoyl carboxylic acids with L-isoleucine are mimics of the plant hormone (+)-7-iso-JA-L-Ile (3) that controls and regulates secondary metabolism and stress responses. In order to generate ligands that can be used as hormone-like compounds possessing different biological activities, an efficient and short synthesis of 6-bromo-1-oxoindane-4-carboxylic acid opens a general route to 6-Br-1-oxoindanoyl L-isoleucine conjugate (Br-In-L-Ile) (9a) as a key intermediate for several bioactive 6-halogen-In-L-Ile analogs (7a, 8a, 10a). The 6-ethynyl-In-L-Ile analog (11a) might be a valuable tool to localize macromolecular receptor molecules by click-chemistry. The activities of In-Ile derivatives were evaluated by assays inducing the release of volatile organic compounds (VOCs) in lima bean (Phaseolus lunatus). Each compound showed slightly different VOC induction patterns. To correlate such differences with structural features, modeling studies of In-Ile derivatives with COI-JAZa/b/c co-receptors of P. lunatus were performed. The modeling profits from the rigid backbone of the 1-oxoindanonoyl conjugates, which allows only well defined interactions with the receptor complex.

The phytotoxin coronatine induces abscission-related gene expression and boll ripening during defoliation of cotton

Defoliants can increase machine harvest efficiency of cotton (Gossypium hirusutum L.), prevent lodging and reduce the time from defoliation to harvest. Coronatine (COR) is a chlorosis-inducing non-host-specific phytotoxin that induces leaf and/or fruit abscission in some crops. The present study investigates how COR might induce cotton leaf abscission by modulating genes involved in cell wall hydrolases and ACC (ethylene precursor) in various cotton tissues. The effects of COR on cotton boll ripening, seedcotton yield, and seed development were also studied. After 14 d of treatment with COR, cells within the leaf abscission zone (AZ) showed marked differentiation. Elevated transcripts of GhCEL1, GhPG and GhACS were observed in the AZs treated with COR and Thidiazuron (TDZ). The relative expression of GhCEL1 and GhACS in TDZ treated plants was approximately twice that in plants treated with COR for 12 h. However, only GhACS expression increased in leaf blade and petiole. There was a continuous increase in the activity of hydrolytic enzymes such as cellulase (CEL) and polygalacturonase (PG), and ACC accumulation in AZs following COR and TDZ treatments, but there was greater increase in ACC activity of COR treated boll crust, indicating that COR had greater ripening effect than TDZ. Coronatine significantly enhanced boll opening without affecting boll weight, lint percentage and seed quality. Therefore, COR can be a potential cotton defoliant with different physiological mechanism of action from the currently used TDZ.

Coronatine enhances drought tolerance via improving antioxidative capacity to maintaining higher photosynthetic performance in soybean

Coronatine (COR), a structural and functional mimic of jasmonates, is involved in a wide array of effects on plant development and defence responses. This study was conducted to explore the role of exogenously applied COR in alleviating the adversities of drought stress in soybean. COR treatment markedly increased the activities of antioxidant enzymes and proline content, and reduced the accumulation of malondialdehyde and hydrogen peroxide under drought stress. Thus, COR-treated plants had higher leaf relative water content and lower electrolye leakage, which led to higher chlorophyll content, activities of RuBPCase and PEPCase, and net photosynthetic rate compared to control plants exposed to drought. COR also increased maximal efficiency of PS II photochemical reaction and photochemical quenching coefficient, but decreased non-photochemical quenching coefficient. These beneficial effects led to enhanced photosynthetic performance and the translocation of assimilated (14)C which promoted growth and accumulation of dry biomass in COR-treated soybean plants subjected to drought. Interestingly, COR application did not affect the growth and biomass accumulation under well-watered condition. These results suggested the involvement of COR on improving drought tolerance in soybean by modulating antioxidant systems and membrane stability to maintain higher photosynthetic performance.

Biosynthesis of tetraoxygenated phenylphenalenones in Wachendorfia thyrsiflora

The biosynthetic origin of 1,2,5,6-tetraoxygenated phenylphenalenones and the sequence according to which their oxygen functionalities are introduced during the biosynthesis in Wachendorfia thyrsiflora were studied using two approaches. (1) Oxygenated phenylpropanoids were probed as substrates of recombinant W. thyrsiflora polyketide synthase 1 (WtPKS1), which is involved in the diarylheptanoid and phenylphenalenone biosynthetic pathways, (2) Root cultures of W. thyrsiflora were incubated with (13)C-labelled precursors in an (18)O2 atmosphere to observe incorporation of the two isotopes at defined biosynthetic steps. NMR- and HRESIMS-based analyses were used to unravel the isotopologue composition of the biosynthetic products, lachnanthoside aglycone and its allophanyl glucoside. Current results suggest that the oxygen atoms decorating the phenalenone tricycle are introduced at different biosynthetic stages in the sequence O-1→O-2→O-5. In addition, the incubation of W. thyrsiflora root cultures with (13)C-labelled lachnanthocarpone established a direct biosynthetic precursor-product relationship with 1,2,5,6-tetraoxygenated phenylphenalenones.

Volatile emission in bracken fern is induced by jasmonates but not by Spodoptera littoralis or Strongylogaster multifasciata herbivory

Jasmonate-mediated regulation of VOC emission has been extensively investigated in higher plants, however, only little is known about VOC production and its regulation in ferns. Here, we investigate whether the emission of VOCs from bracken fern Pteridium aquilinum is triggered by herbivory and if so - whether it is regulated by the octadecanoid signaling pathway. Interestingly, feeding of both generalist (Spodoptera littoralis) and specialist (Strongylogaster multifasciata) herbivores as well as application of singular and continuous mechanical wounding of fronds induced only very low levels of VOC emission. In contrast, treatment with jasmonic acid (JA) led to the emission of a blend of VOCs that was mainly comprised of terpenoids. Likewise, treatment with the JA precursor 12-oxo-phytodienoic acid (OPDA) and α-linolenic acid also induced VOC emission, albeit to a lower intesity than the JA treatment. Accumulation of endogenous JA was low in mechanically wounded fronds and these levels were unaffected by the application of oral secretions from both generalist or specialist herbivores. The emission of terpenoids upon JA treatment could be blocked with fosmidomycin and mevinolin, which are inhibitors of the MEP- and MVA pathways, respectively. These results indicate that similar to higher plants, terpenoid VOCs are produced via these pathways in bracken fern and that these pathways are JA-responsive. However, the very low amounts of terpenoids released after herbivory or mechanical damage are in stark contrast to what is known from higher plants. We speculate that S. multifasciata and S. littoralis feeding apparently did not induce the threshold levels of JA required for activating the MEP and MVA pathways and the subsequent volatile emission in bracken fern.

Chemical and genetic exploration of jasmonate biosynthesis and signaling paths

Jasmonates are lipid-derived compounds that act as signals in plant stress responses and developmental processes. Enzymes participating in biosynthesis of jasmonic acid (JA) and components of JA signaling have been extensively characterized by biochemical and molecular-genetic tools. Mutants have helped to define the pathway for synthesis of jasmonoyl-L-isoleucine (JA-Ile), the bioactive form of JA, and to identify the F-box protein COI1 as central regulatory unit. Details on the molecular mechanism of JA signaling were recently unraveled by the discovery of JAZ proteins that together with the adaptor protein NINJA and the general co-repressor TOPLESS form a transcriptional repressor complex. The current model of JA perception and signaling implies the SCF(COI1) complex operating as E3 ubiquitin ligase that upon binding of JA-Ile targets JAZ proteins for degradation by the 26S proteasome pathway, thereby allowing MYC2 and other transcription factors to activate gene expression. Chemical strategies, as integral part of jasmonate research, have helped the establishment of structure-activity relationships and the discovery of (+)-7-iso-JA-L-Ile as the major bioactive form of the hormone. The transient nature of its accumulation highlights the need to understand catabolism and inactivation of JA-Ile and recent studies indicate that oxidation of JA-Ile by cytochrome P450 monooxygenase is the major mechanism for turning JA signaling off. Plants contain numerous JA metabolites, which may have pronounced and differential bioactivity. A major challenge in the field of plant lipid signaling is to identify the cognate receptors and modes of action of these bioactive jasmonates/oxylipins.

The broad-leaf herbicide 2,4-dichlorophenoxyacetic acid turns rice into a living trap for a major insect pest and a parasitic wasp

Synthetic chemical elicitors of plant defense have been touted as a powerful means for sustainable crop protection. Yet, they have never been successfully applied to control insect pests in the field. We developed a high-throughput chemical genetics screening system based on a herbivore-induced linalool synthase promoter fused to a β-glucuronidase (GUS) reporter construct to test synthetic compounds for their potential to induce rice defenses. We identified 2,4-dichlorophenoxyacetic acid (2,4-D), an auxin homolog and widely used herbicide in monocotyledonous crops, as a potent elicitor of rice defenses. Low doses of 2,4-D induced a strong defensive reaction upstream of the jasmonic acid and ethylene pathways, resulting in a marked increase in trypsin proteinase inhibitor activity and volatile production. Induced plants were more resistant to the striped stem borer Chilo suppressalis, but became highly attractive to the brown planthopper Nilaparvata lugens and its main egg parasitoid Anagrus nilaparvatae. In a field experiment, 2,4-D application turned rice plants into living traps for N. lugens by attracting parasitoids. Our findings demonstrate the potential of auxin homologs as defensive signals and show the potential of the herbicide to turn rice into a selective catch crop for an economically important pest.

Investigation of Phenolic Acids in Suspension Cultures of Vitis vinifera Stimulated with Indanoyl-Isoleucine, N-Linolenoyl-L-Glutamine, Malonyl Coenzyme A and Insect Saliva

Vitis vinifera c.v. Muscat de Frontignan (grape) contains various high valuable bioactive phenolic compounds with pharmaceutical properties and industrial interest which are not fully exploited. The focus of this investigation consists in testing the effects of various biological elicitors on a non-morphogenic callus suspension culture of V. vinifera. The investigated elicitors: Indanoyl-isoleucine (IN), N-linolenoyl-L-glutamine (LG), insect saliva (IS) and malonyl coenzyme A (MCoA) were aimed at mimicking the influence of environmental pathogens on plants in their natural habitats and at provoking exogenous induction of the phenylpropanoid pathway. The elicitors’ indanoyl-isoleucine (IN), N-linolenoyl-L-glutamine (LG) and insect saliva (IS), as well as malonyl coenzyme A (MCoA), were independently inoculated to stimulate the synthesis of phenylpropanoids. All of the enhancers positively increased the concentration of phenolic compounds in grape cells. The highest concentration of phenolic acids was detected after 2 h for MCoA, after 48 h for IN and after 24 h for LG and IS respectively. At the maximum production time, treated grape cells had a 3.5-fold (MCoA), 1.6-fold (IN) and 1.5-fold (IS) higher phenolic acid content compared to the corresponding control samples. The HPLC results of grape cells showed two major resveratrol derivatives: 3-O-Glucosyl-resveratrol and 4-(3,5-dihydroxyphenyl)-phenol. Their influences of the different elicitors, time of harvest and biomass concentration (p < 0.0001) were statistically significant on the synthesis of phenolic compounds. The induction with MCoA was found to demonstrate the highest statistical effect corresponding to the strongest stress response within the phenylpropanoid pathway in grape cells.

12-hydroxyjasmonic acid glucoside is a COI1-JAZ-independent activator of leaf-closing movement in Samanea saman

Jasmonates are ubiquitously occurring plant growth regulators with high structural diversity that mediate numerous developmental processes and stress responses. We have recently identified 12-O-β-D-glucopyranosyljasmonic acid as the bioactive metabolite, leaf-closing factor (LCF), which induced nyctinastic leaf closure of Samanea saman. We demonstrate that leaf closure of isolated Samanea pinnae is induced upon stereospecific recognition of (-)-LCF, but not by its enantiomer, (+)-ent-LCF, and that the nonglucosylated derivative, (-)-12-hydroxyjasmonic acid also displays weak activity. Similarly, rapid and cell type-specific shrinkage of extensor motor cell protoplasts was selectively initiated upon treatment with (-)-LCF, whereas flexor motor cell protoplasts did not respond. In these bioassays related to leaf movement, all other jasmonates tested were inactive, including jasmonic acid (JA) and the potent derivates JA-isoleucine and coronatine. By contrast, (-)-LCF and (-)-12-hydroxyjasmonic acid were completely inactive with respect to activation of typical JA responses, such as induction of JA-responsive genes LOX2 and OPCL1 in Arabidopsis (Arabidopsis thaliana) or accumulation of plant volatile organic compounds in S. saman and lima bean (Phaseolus lunatus), generally considered to be mediated by JA-isoleucine in a COI1-dependent fashion. Furthermore, application of selective inhibitors indicated that leaf movement in S. saman is mediated by rapid potassium fluxes initiated by opening of potassium-permeable channels. Collectively, our data point to the existence of at least two separate JA signaling pathways in S. saman and that 12-O-β-D-glucopyranosyljasmonic acid exerts its leaf-closing activity through a mechanism independent of the COI1-JAZ module.

Regulation of extrafloral nectar secretion by jasmonates in lima bean is light dependent

To maximize fitness, plants need to perceive changes in their light environment and adjust their physiological responses accordingly. Whether and how such changes also affect the regulation of their defense responses against herbivores remains largely unclear. We addressed this issue by studying the secretion of extrafloral nectar (EFN) in lima bean (Phaseolus lunatus), which is known to be activated by the phytohormone jasmonic acid (JA) and functions as an indirect defense mechanism against herbivores. We found that the plant's EFN secretion in response to JA was light dependent: In the dark, JA reduced EFN secretion, whereas under light conditions, JA induced EFN secretion relative to controls. This modulation was affected by the light's spectral composition [i.e., ratio of red to far-red (R:FR) radiation], but not light intensity. These findings demonstrate a unique differential effect of JA on EFN secretion depending on the ambient light conditions. Interestingly, treatment with the isoleucine-JA conjugate (JA-Ile) enhanced EFN secretion under light conditions yet did not reduce EFN secretion in the dark. Moreover, inhibition of Ile biosynthesis in light-exposed plants significantly decreased the EFN secretion rate. This reduction could be recovered by additional application of JA-Ile, suggesting that JA-Ile is the active compound required to up-regulate EFN secretion. Finally, experiments with mechanically damaged plants revealed that light was required for the formation of JA-Ile, but not of JA. These results demonstrate that in lima bean, the light environment modulates the plant's response to jasmonates as well as JA-Ile biosynthesis, which controls the subsequent EFN secretion.

Variation of herbivore-induced volatile terpenes among Arabidopsis ecotypes depends on allelic differences and subcellular targeting of two terpene synthases, TPS02 and TPS03

When attacked by insects, plants release mixtures of volatile compounds that are beneficial for direct or indirect defense. Natural variation of volatile emissions frequently occurs between and within plant species, but knowledge of the underlying molecular mechanisms is limited. We investigated intraspecific differences of volatile emissions induced from rosette leaves of 27 accessions of Arabidopsis (Arabidopsis thaliana) upon treatment with coronalon, a jasmonate mimic eliciting responses similar to those caused by insect feeding. Quantitative variation was found for the emission of the monoterpene (E)-beta-ocimene, the sesquiterpene (E,E)-alpha-farnesene, the irregular homoterpene 4,8,12-trimethyltridecatetra-1,3,7,11-ene, and the benzenoid compound methyl salicylate. Differences in the relative emissions of (E)-beta-ocimene and (E,E)-alpha-farnesene from accession Wassilewskija (Ws), a high-(E)-beta-ocimene emitter, and accession Columbia (Col-0), a trace-(E)-beta-ocimene emitter, were attributed to allelic variation of two closely related, tandem-duplicated terpene synthase genes, TPS02 and TPS03. The Ws genome contains a functional allele of TPS02 but not of TPS03, while the opposite is the case for Col-0. Recombinant proteins of the functional Ws TPS02 and Col-0 TPS03 genes both showed (E)-beta-ocimene and (E,E)-alpha-farnesene synthase activities. However, differential subcellular compartmentalization of the two enzymes in plastids and the cytosol was found to be responsible for the ecotype-specific differences in (E)-beta-ocimene/(E,E)-alpha-farnesene emission. Expression of the functional TPS02 and TPS03 alleles is induced in leaves by elicitor and insect treatment and occurs constitutively in floral tissues. Our studies show that both pseudogenization in the TPS family and subcellular segregation of functional TPS enzymes control the variation and plasticity of induced volatile emissions in wild plant species.

Flavone synthase II (CYP93B16) from soybean (Glycine max L.)

Flavonoids are a very diverse group of plant secondary metabolites with a wide array of activities in plants, as well as in nutrition and health. All flavonoids are derived from a limited number of flavanone intermediates, which serve as substrates for a variety of enzyme activities, enabling the generation of diversity in flavonoid structures. Flavonoids can be characteristic metabolites, like isoflavonoids for legumes. Others, like flavones, occur in nearly all plants. Interestingly, there exist two fundamentally different enzymatic systems able to directly generate flavones from flavanones, flavone synthase (FNS) I and II. We describe an inducible flavone synthase activity from soybean (Glycine max) cell cultures, generating 7,4'-dihydroxyflavone (DHF), which we classified as FNS II. The corresponding full-length cDNA (CYP93B16) was isolated using known FNS II sequences from other plants. Functional expression in yeast allowed the detailed biochemical characterization of the catalytic activity of FNS II. A direct conversion of flavanones such as liquiritigenin, naringenin, and eriodictyol into the corresponding flavones DHF, apigenin and luteolin, respectively, was demonstrated. The enzymatic reaction of FNSII was stereoselective, favouring the (S)- over the (R)-enantiomer. Phylogenetic analyses of the subfamily of plant CYP93B enzymes indicate the evolution of a gene encoding a flavone synthase which originally catalyzed the direct conversion of flavanones into flavones, via early gene duplication into a less efficient enzyme with an altered catalytic mechanism. Ultimately, this allowed the evolution of the legume-specific isoflavonoid synthase activity.

The role of jasmonates in floral nectar secretion

Plants produce nectar in their flowers as a reward for their pollinators and most of our crops depend on insect pollination, but little is known on the physiological control of nectar secretion. Jasmonates are well-known for their effects on senescence, the development and opening of flowers and on plant defences such as extrafloral nectar. Their role in floral nectar secretion has, however, not been explored so far. We investigated whether jasmonates have an influence on floral nectar secretion in oil-seed rape, Brassica napus. The floral tissues of this plant produced jasmonic acid (JA) endogenously, and JA concentrations peaked shortly before nectar secretion was highest. Exogenous application of JA to flowers induced nectar secretion, which was suppressed by treatment with phenidone, an inhibitor of JA synthesis. This effect could be reversed by additional application of JA. Jasmonoyl-isoleucine and its structural mimic coronalon also increased nectar secretion. Herbivory or addition of JA to the leaves did not have an effect on floral nectar secretion, demonstrating a functional separation of systemic defence signalling from reproductive nectar secretion. Jasmonates, which have been intensively studied in the context of herbivore defences and flower development, have a profound effect on floral nectar secretion and, thus, pollination efficiency in B. napus. Our results link floral nectar secretion to jasmonate signalling and thereby integrate the floral nectar secretion into the complex network of oxylipid-mediated developmental processes of plants.

O-Methylation of phenylphenalenone phytoalexins in Musaacuminata and Wachendorfia thyrsiflora

Biosynthetic O-methylation at various sites along the backbone of inducible phenylphenalenones in Musaacuminata var. "Williams" (Musaceae) and Wachendorfiathyrsiflora (Haemodoraceae) was investigated using 13C-labelled precursors. The inducibility of O-methylated metabolites was demonstrated in both species and the origin of methoxyl group from [methyl-13C]L-methionine was confirmed. In addition to known phenylphenalenones, a methoxylated metabolite, 4-(4-hydroxy-3-methoxy-phenyl)-benzo[de]isochromene-1,3-dione, was detected and its structure elucidated mainly by NMR spectroscopic techniques. The experiments were used to discriminate methionine-derived and artificial methoxy groups formed during methanolic extraction. Finally, demethylation of 4'-methoxycinnamic acid and subsequent conversion to 3',4'-methylenedioxycinnamic acid was demonstrated in M.acuminata.

Jasmonates: structural requirements for lipid-derived signals active in plant stress responses and development

Jasmonates are lipid-derived signals that mediate plant stress responses and development processes. Enzymes participating in biosynthesis of jasmonic acid (JA) (1, 2) and components of JA signaling have been extensively characterized by biochemical and molecular-genetic tools. Mutants of Arabidopsis and tomato have helped to define the pathway for synthesis of jasmonoyl-isoleucine (JA-Ile), the active form of JA, and to identify the F-box protein COI1 as central regulatory unit. However, details of the molecular mechanism of JA signaling have only recently been unraveled by the discovery of JAZ proteins that function in transcriptional repression. The emerging picture of JA perception and signaling cascade implies the SCF(COI1) complex operating as E3 ubiquitin ligase that upon binding of JA-Ile targets JAZ repressors for degradation by the 26S-proteasome pathway, thereby allowing the transcription factor MYC2 to activate gene expression. The fact that only one particular stereoisomer, (+)-7-iso-JA-l-Ile (4), shows high biological activity suggests that epimerization between active and inactive diastereomers could be a mechanism for turning JA signaling on or off. The recent demonstration that COI1 directly binds (+)-7-iso-JA-l-Ile (4) and thus functions as JA receptor revealed that formation of the ternary complex COI1-JA-Ile-JAZ is an ordered process. The pronounced differences in biological activity of JA stereoisomers also imply strict stereospecific control of product formation along the JA biosynthetic pathway. The pathway of JA biosynthesis has been unraveled, and most of the participating enzymes are well-characterized. For key enzymes of JA biosynthesis the crystal structures have been established, allowing insight into the mechanisms of catalysis and modes of substrate binding that lead to formation of stereospecific products.

Exogenous polyamines elicit herbivore-induced volatiles in lima bean leaves: involvement of calcium, H2O2 and Jasmonic acid

We investigated the role of polyamines (PAs) in lima bean (Phaseolus lunatus) leaves on the production of herbivorous mite (Tetranychus urticae)-induced plant volatiles that attract carnivorous natural enemies of the herbivores. To do this, we focused on the effects of the exogenous PAs [cadaverine, putrescine, spermidine and spermine (Spm)] on the production of volatiles, H(2)O(2) and jasmonic acid (JA) and the levels of defensive genes, cytosolic calcium and reactive oxygen species (ROS). Among the tested PAs, Spm was the most active in inducing the production of volatile terpenoids known to be induced by T. urticae. An increase in JA levels was also found after Spm treatment, indicating that Spm induces the biosynthesis of JA, which has been shown elsewhere to regulate the production of some volatile terpenoids. Further, treatment with JA and Spm together resulted in greater volatile emission than that with JA alone. In a Y-tube olfactometer, leaves treated with Spm + JA attracted more predatory mites (Phytoseiulus persimilis) than those treated with JA alone. After treatment with Spm + JA, no effects were found on the enzyme activity of polyamine oxidase and copper amine oxidase. However, induction of calcium influx and ROS production, and increased enzyme activities and gene expression for NADPH oxidase complex, superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and glutathione peroxidase were found after treatment with Spm + JA. These results indicate that Spm plays an important role in the production of T. urticae-induced lima bean leaf volatiles.

No evidence for the induction of brown algal chemical defense by the phytohormones jasmonic acid and methyl jasmonate

Induced chemical defense reactions are widespread in marine brown algae. Despite the evidence that the biosynthesis of defense metabolites can be up-regulated upon herbivory, we do not know how this regulation of biosynthetic pathways to secondary metabolites is achieved in brown algae. In higher plants, the phytohormone jasmonic acid (JA) is crucial for the mediation of induced chemical defenses, and several findings of this metabolite from marine sources have been reported. We tested the hypothesis that JA or related metabolites play a role in induced brown algal defense. Quantification of oxylipins with a detection limit around 20 ng g(-1) algal tissue did not reveal the presence of JA in the seven examined brown algal species Dictyota dichotoma, Colpomenia peregrina, Ectocarpus fasciculatus, Fucus vesiculosus, Himanthalia elongata, Saccharina latissima (formerly Laminaria saccharina), and Sargassum muticum. Moreover, treatment with ecologically relevant concentrations of JA and methyl jasmonate did not lead to a significant change in the profile of medium- and non-polar metabolites of the tested algae. Only when high concentrations of > or =500 microg ml(-1) medium of the phytohormones were applied that a metabolic response which could be attributed to unspecific stress was observed. Bioassays with D. dichotoma that focused on medium- and non-polar compounds confirmed the lack of a biological role of JA and methyl jasmonate in the induction of algal induced chemical defenses. The phytohormone-treated samples did not exhibit any increased defense potential towards the amphipod Ampithoe longimana and the isopod Paracerceis caudata. JA and related phytohormones, known to be active in higher plants, thus appear to play no role in brown algae for induction of the defense chemicals studied here.

Significance of terpenoids in induced indirect plant defence against herbivorous arthropods

Many plants respond to herbivory by arthropods with an induced emission of volatiles such as green leaf volatiles and terpenoids. These herbivore-induced plant volatiles (HIPVs) can attract carnivores, for example, predators and parasitoids. We investigated the significance of terpenoids in attracting herbivores and carnivores in two tritrophic systems where we manipulated the terpenoid emission by treating the plants with fosmidomycin, which inhibits one of the terpenoid biosynthetic pathways and consequently terpenoid emission. In the 'lima bean' system, volatiles from spider-mite-infested fosmidomycin-treated plants were less attractive to the predatory mite Phytoseiulus persimilis than from infested control plants. In the 'cabbage' system, fosmidomycin treatment did not alter the attractiveness of Brussels sprouts to two Pieris butterflies for oviposition. The parasitoid Cotesia glomerata did not discriminate between the volatiles of fosmidomycin-treated and water-treated caterpillar-infested cabbage. Both P. persimilis and C. glomerata preferred volatiles from infested plants to uninfested ones when both were treated with fosmidomycin. Chemical analysis showed that terpenoid emission was inhibited more strongly in infested lima bean plants than in Brussels sprouts plants after fosmidomycin treatment. This study shows an important role of terpenoids in the indirect defence of lima bean, which is discussed relative to the role of other HIPVs.

Coronatine alleviates salinity stress in cotton by improving the antioxidative defense system and radical-scavenging activity

Coronatine (COR) is a chlorosis-inducing phytotoxin that mimics some biological activities of methyl jasmonate. This study investigated whether COR confers salinity tolerance to cotton and whether such tolerance is correlated with changes in the activity of antioxidant enzymes. COR at 0.01microM was applied hydroponically to cotton seedlings at the two-leaf stage for 24h. A salinity stress of 150mM NaCl was imposed after completion of COR treatment for 15d. Salinity stress reduced biomass of seedlings and increased leaf superoxide radicals, hydrogen peroxide, lipid peroxidation, and electrolyte leakage. Activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione reductase (GR), and of the stable free radical, 1,1-diphenyl-2-picrylhydrazyl (DPPH), scavenging activity were altered by salinity to varying degrees. Pretreatment with COR increased the activities of CAT, POD, GR, and DPPH scavenging activity in leaf tissues of salinity-stressed seedlings. Thus, COR might reduce the production of reactive oxygen species by activating antioxidant enzymes and DPPH-radical scavenging, thereby preventing membrane peroxidation and denaturation of biomolecules.

Enhancement of alkaloid production in opium and California poppy by transactivation using heterologous regulatory factors

Genes encoding regulatory factors isolated from Arabidopsis, soybean and corn have been screened to identify those that modulate the expression of genes encoding for enzymes involved in the biosynthesis of morphinan alkaloids in opium poppy (Papaver somniferum) and benzophenanthridine alkaloids in California poppy (Eschscholzia californica). In opium poppy, the over-expression of selected regulatory factors increased the levels of PsCOR (codeinone reductase), Ps4'OMT (S-adenosyl-l-methionine:3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase) and Ps6OMT [(R,S)-norcoclaurine 6-O-methyltransferase] transcripts by 10- to more than 100-fold. These transcriptional activations translated into an enhancement of alkaloid production in opium poppy of up to at least 10-fold. In California poppy, the transactivation effect of regulatory factor WRKY1 resulted in an increase of up to 60-fold in the level of EcCYP80B1 [(S)-N-methylcoclaurine 3'-hydroxylase] and EcBBE (berberine bridge enzyme) transcripts. As a result, the accumulations of selected alkaloid intermediates were enhanced up to 30-fold. The transactivation effects of other regulatory factors led to the accumulation of the same intermediates. These regulatory factors also led to the production of new alkaloids in California poppy callus culture.

Jasmonates and its mimics differentially elicit systemic defence responses in Nicotiana attenuata

Coronalon (6-ethyl indanoyl isoleucine), a synthetic jasmonate mimic, is known to regulate levels of transcripts and secondary metabolites that are commonly elicited by methyl jasmonate (MeJA) in a variety of plants. The ability of coronalon and its derivative (In-L-Ile-Me) to elicit MeJA-activated transcriptional and defence responses [nicotine and trypsin proteinase inhibitors (TPIs)] was compared in treated and systemic untreated tissues of wild-type (WT) and NaLOX3-silenced Nicotiana attenuata plants which are unable to activate either local or systemic defence responses. Coronalon and its derivative significantly regulated 71% and 86% of genes up-regulated by MeJA and 53% and 66% of the genes down-regulated by MeJA in the treated leaves, but only 3% and 7% of all regulated genes in untreated, but phylotactically connected, leaves of WT plants. Consistent with their ability to elicit transcriptional responses in treated tissues, coronalon and In-L-Ile-Me increased nicotine and TPIs when applied to the tissues in which these metabolites are produced, namely roots and leaves. However, treating roots elicited TPI activity in leaves in both WT and NaLOX3-silenced plants, suggesting that mimics can be transported apoplastically from roots to leaves in the xylem. This response was lower in NaLOX3-silenced plants, suggesting that the ability of coronalon and In-L-Ile-Me to elicit TPI responses in leaves after root treatments requires intact jasmonic acid (JA) signalling. Treating leaves did not elicit detectable changes in endogenous JA levels but did decrease free salicylic acid contents. It is concluded that coronalon and In-L-Ile-Me elicit jasmonate responses in treated tissues and could be valuable tools for dissecting local and systemic jasmonate signalling networks in plants.

Novel, unnatural benzo-1,2,3-thiadiazole-7-carboxylate elicitors of taxoid biosynthesis

In order to establish the chemical biological technology for production of valuable secondary metabolites, a novel family of unnatural elicitors derived from the plant activator benzo-1,2,3-thiadiazole-7-carboxylic acid were designed and synthesized. New synthetic elicitors that showed powerful eliciting activities upon taxoid biosynthesis by Taxus chinensis suspension cells were obtained. For example, benzo-1,2,3-thiadiazole-7-carboxylic acid 2-(2-hydroxybenzoxyl)ethyl ester was more effective and resulted in nearly 40% increase in taxuyunnanine C content and production in comparison with methyl jasmonate, which was previously reported as the most powerful chemical elicitor for taxoid biosynthesis. The novel class of elicitors was found to induce plant defense responses, including promotion of H(2)O(2) levels originating from oxidative burst and activation of phenylalanine ammonia lyase. Interestingly the plant defense responses induced corresponded well to the superior stimulating activity in T. chinensis cell cultures. The work indicates that the newly synthesized benzothiadiazoles can act as a new family of elicitors for taxoid biosynthesis in plant cells.

Using nutritional indices to study LOX3-dependent insect resistance

Induced resistance to biotic attackers is thought to be mediated by responses elicited by jasmonic acid (JA), a subset of which are lipoxygenase 3 (LOX3) dependent. To understand the importance of LOX3-mediated insect resistance, we analysed the performance of Manduca sexta larvae on wild-type (WT) and on isogenic Nicotiana attenuata plants silenced in NaLOX3 expression and JA signalling, and we used Waldbauer nutritional indices to measure the pre- and post-ingestive effects. LOX3-mediated defenses reduced larval growth, consumption and frass production. These defenses reduced how efficiently late-instar larvae converted digested food to body mass (ECD). In contrast, LOX3-mediated defenses decreased approximate digestibility (AD) in early instar larvae without affecting the ECD and total food consumption. Larvae of all instars feeding on defended WT plants behaviourally compensate for their reduced body mass by consuming more food per unit of body mass gain. We suggest that larvae feeding on plants silenced in NaLOX3 expression (as-lox) initially increase their AD, which in turn enables them to consume more food in the later stages and consequently, to increase their ECD and efficiency of conversion of ingested food (ECI). We conclude that N. attenuata's oxylipin-mediated defenses are important for resisting attack from M. sexta larvae, and that Waldbauer nutritional assays reveal behavioural and physiological counter responses of insects to these plant defenses.

Exploiting scents of distress: the prospect of manipulating herbivore-induced plant odours to enhance the control of agricultural pests

In response to feeding by arthropods, plants actively and systemically emit various volatile substances. It has been proposed that these herbivore-induced volatiles (HIPVs) can be exploited in agricultural pest control because they might repel herbivores and because they serve as attractants for the enemies of the herbivores. Indeed, recent studies with transgenic plants confirm that odour emissions can be manipulated in order to enhance the plants' attractiveness to beneficial arthropods. An additional advantage of manipulating HIPV emissions could be their effects on neighbouring plants, as a rapidly increasing number of studies show that exposure to HIPVs primes plants for augmented defence expression. Targeting the right volatiles for enhanced emission should lead to ecologically and economically sound ways of combating important pests.

A type III polyketide synthase from Wachendorfia thyrsiflora and its role in diarylheptanoid and phenylphenalenone biosynthesis

Chalcone synthase (CHS) related type III plant polyketide synthases (PKSs) are likely to be involved in the biosynthesis of diarylheptanoids (e.g. curcumin and polycyclic phenylphenalenones), but no such activity has been reported. Root cultures from Wachendorfia thyrsiflora (Haemodoraceae) are a suitable source to search for such enzymes because they synthesize large amounts of phenylphenalenones, but no other products that are known to require CHSs or related enzymes (e.g. flavonoids or stilbenes). A homology-based RT-PCR strategy led to the identification of cDNAs for a type III PKS sharing only approximately 60% identity with typical CHSs. It was named WtPKS1 (W. thyrsiflora polyketide synthase 1). The purified recombinant protein accepted a large variety of aromatic and aliphatic starter CoA esters, including phenylpropionyl- and side-chain unsaturated phenylpropanoid-CoAs. The simplest model for the initial reaction in diarylheptanoid biosynthesis predicts a phenylpropanoid-CoA as starter and a single condensation reaction to a diketide. Benzalacetones, the expected release products, were observed only with unsaturated phenylpropanoid-CoAs, and the best results were obtained with 4-coumaroyl-CoA (80% of the products). With all other substrates, WtPKS1 performed two condensation reactions and released pyrones. We propose that WtPKS1 catalyses the first step in diarylheptanoid biosynthesis and that the observed pyrones are derailment products in the absence of downstream processing proteins.

The Arabidopsis thaliana JASMONATE INSENSITIVE 1 gene is required for suppression of salicylic acid-dependent defenses during infection by Pseudomonas syringae

Many plant pathogens suppress antimicrobial defenses using virulence factors that modulate endogenous host defenses. The Pseudomonas syringae phytotoxin coronatine (COR) is believed to promote virulence by acting as a jasmonate analog, because COR-insensitive 1 (coil) Arabidopsis thaliana and tomato mutants are impaired in jasmonate signaling and exhibit reduced susceptibility to P. syringae. To further investigate the role of jasmonate signaling in disease development, we analyzed several jasmonate-insensitive A. thaliana mutants for susceptibility to P. syringae pv. tomato strain DC3000 and sensitivity to COR. Jasmonate-insensitive 1 (jin1) mutants exhibit both reduced susceptibility to P. syringae pv. tomato DC3000 and reduced sensitivity to COR, whereas jasmonate-resistant 1 (jar1) plants exhibit wild-type responses to both COR and P. syringae pv. tomato DC3000. A jin1 jar1 double mutant does not exhibit enhanced jasmonate insensitivity, suggesting that JIN1 functions downstream of jasmonic acid-amino acid conjugates synthesized by JAR1. Reduced disease susceptibility in jin1 mutants is correlated with elevated expression of pathogenesis-related 1 (PR-1) and is dependent on accumulation of salicylic acid (SA). We also show that JIN1 is required for normal P. syringae pv. tomato DC3000 symptom development through an SA-independent mechanism. Thus, P. syringae pv. tomato DC3000 appears to utilize COR to manipulate JIN1-dependent jasmonate signaling both to suppress SA-mediated defenses and to promote symptom development.

Enhancement of lignan biosynthesis in suspension cultures of Linum nodiflorum by coronalon, indanoyl-isoleucine and methyl jasmonate

The effect of the two synthetic elicitors coronalon and indanoyl-isoleucine and of methyl jasmonate (MeJA) on the accumulation and biosynthesis of lignans by cell suspension cultures of Linum nodiflorum (Linaceae) was investigated. The production of 6-methoxypodophyllotoxin (MPTOX) could be increased more than tenfold, the maximal content reaching up to over 2.5% of the cell dry weight. The highest yield was achieved by administering 50 microM of the synthetic elicitors on the fourth day and extracting the products on the tenth day of the culture period. An additional lignan accumulated in elicitor-treated cultures. Its structure was elucidated by extensive 1D and 2D NMR measurements, revealing its identity as 5'-demethoxy-MPTOX (5'-dMPTOX). Its average content amounted up to over 5% of the cell dry weight. Growth was only slightly affected by the addition of the elicitors. Methyl jasmonate exerted a moderate stimulating effect on the L. nodiflorum cells with MPTOX and 5'-dMPTOX contents going up to 1.4 and 2.1% of the cell dry weight, respectively. The activities of deoxypodophyllotoxin 6-hydroxylase and beta-peltatin 6-O-methyltransferase, two enzymes involved in MPTOX biosynthesis, were increased up to 21.9-fold and 14.6-fold, respectively, in the treated cultures.