Sequential oxidation of Jasmonoyl-Phenylalanine and Jasmonoyl-Isoleucine by multiple cytochrome P450 of the CYP94 family through newly identified aldehyde intermediates

SlCYP94B18 and SlCYP94B19 monooxygenases for the catabolic turnover of jasmonates in tomato leaves

(3R,7S)-Jasmonoyl-L-isoleucine (JA-Ile) is a plant hormone that regulates plant defense responses and other physiological functions. The mechanism of attenuation of JA-Ile signaling in the plant body is essential because prolonged JA-Ile signaling can be detrimental to plant survival. In Arabidopsis thaliana, the cytochrome P450 monooxygenases, CYP94B1/B3/C1, inactivate JA-Ile by converting it into 12-hydroxy-jasmonoyl-L-isoleucine (12-OH-JA-Ile), and CYP94C1 converts 12-OH-JA-Ile into 12-carboxy-jasmonoyl-L-isoleucine (12-COOH-JA-Ile). In the present study, we aimed to identify the cytochrome P450 monooxygenases involved in the catabolic pathway of JA-Ile in tomato leaves. Based on a gene expression screening of SlCYP94 subfamily monooxygenases using qPCR and the time-course of JA-Ile catabolism, we identified SlCYP94B18 and SlCYP94B19 expressed in tomato leaves as candidate monooxygenases catalyzing the two-step catabolism of JA-Ile. An in vitro enzymatic assay using a yeast expression system revealed that these enzymes efficiently converted JA-Ile to 12-OH-JA-Ile, and then to 12-COOH-JA-Ile. SlCYP94B18 and SlCYP94B19 also catalyzed the oxidative catabolism of several JA-amino acid conjugates (JA-AAs), JA-Leu and JA-Val, in tomatoes. These results suggest that SlCYP94B18 and SlCYP94B19 plays a role in the two-step oxidation of JA-AAs, suggesting their broad involvement in regulating jasmonate signaling in tomatoes. Our results contribute to a deeper understanding of jasmonate signaling in tomatoes and may help to improve tomato cultivation and quality.

Far-red light modulates grapevine growth by increasing leaf photosynthesis efficiency and triggering organ-specific transcriptome remodelling : Author

BACKGROUND

Growing evidence demonstrates that the synergistic interaction of far-red light with shorter wavelength lights could evidently improve the photosynthesis efficiency of multiple species. However, whether/how far-red light affects sink organs and consequently modulates the source‒sink relationships are largely unknown.

RESULTS

Here, equal intensities of white and far-red lights were added to natural light for grape plantlets to investigate the effects of far-red light supplementation on grapevine growth and carbon assimilate allocation, as well as to reveal the underlying mechanisms, through physiological and transcriptomic analysis. The results showed that additional far-red light increased stem length and carbohydrate contents in multiple organs and decreased leaf area, specific leaf weight and dry weight of leaves in comparison with their counterparts grown under white light. Compared to white light, the maximum net photosynthetic rate of the leaves was increased by 31.72% by far-red light supplementation, indicating that far-red light indeed elevated the photosynthesis efficiency of grapes. Transcriptome analysis revealed that leaves were most responsive to far-red light, followed by sink organs, including stems and roots. Genes related to light signaling and carbon metabolites were tightly correlated with variations in the aforementioned physiological traits. In particular, VvLHCB1 is involved in light harvesting and restoring the balance of photosystem I and photosystem II excitation, and VvCOP1 and VvPIF3, which regulate light signal transduction, were upregulated under far-red conditions. In addition, the transcript abundances of the sugar transporter-encoding genes VvSWEET1 and VvSWEET3 and the carbon metabolite-encoding genes VvG6PD, VvSUS7 and VvPGAM varied in line with the change in sugar content.

CONCLUSIONS

This study showed that far-red light synergistically functioning with white light has a beneficial effect on grape photosystem activity and is able to differentially affect the growth of sink organs, providing evidence for the possible addition of far-red light to the wavelength range of photosynthetically active radiation (PAR).

Characterization of CYP82 genes involved in the biosynthesis of structurally diverse benzylisoquinoline alkaloids in Corydalis yanhusuo

Benzylisoquinoline alkaloids (BIAs) represent a significant class of secondary metabolites with crucial roles in plant physiology and substantial potential for clinical applications. CYP82 genes are involved in the formation and modification of various BIA skeletons, contributing to the structural diversity of compounds. In this study, Corydalis yanhusuo, a traditional Chinese medicine rich in BIAs, was investigated to identify the catalytic function of CYP82s during BIA formation. Specifically, 20 CyCYP82-encoding genes were cloned, and their functions were identified in vitro. Ten of these CyCYP82s were observed to catalyze hydroxylation, leading to the formation of protopine and benzophenanthridine scaffolds. Furthermore, the correlation between BIA accumulation and the expression of CyCYP82s in different tissues of C. yanhusuo was assessed their. The identification and characterization of CyCYP82s provide novel genetic elements that can advance the synthetic biology of BIA compounds such as protopine and benzophenanthridine, and offer insights into the biosynthesis of BIAs with diverse structures in C. yanhusuo.

Jasmonic Acid as a Mediator in Plant Response to Necrotrophic Fungi

Jasmonic acid (JA) and its derivatives, all named jasmonates, are the simplest phytohormones which regulate multifarious plant physiological processes including development, growth and defense responses to various abiotic and biotic stress factors. Moreover, jasmonate plays an important mediator’s role during plant interactions with necrotrophic oomycetes and fungi. Over the last 20 years of research on physiology and genetics of plant JA-dependent responses to pathogens and herbivorous insects, beginning from the discovery of the JA co-receptor CORONATINE INSENSITIVE1 (COI1), research has speeded up in gathering new knowledge on the complexity of plant innate immunity signaling. It has been observed that biosynthesis and accumulation of jasmonates are induced specifically in plants resistant to necrotrophic fungi (and also hemibiotrophs) such as mostly investigated model ones, i.e., Botrytis cinerea, Alternaria brassicicola or Sclerotinia sclerotiorum. However, it has to be emphasized that the activation of JA-dependent responses takes place also during susceptible interactions of plants with necrotrophic fungi. Nevertheless, many steps of JA function and signaling in plant resistance and susceptibility to necrotrophs still remain obscure. The purpose of this review is to highlight and summarize the main findings on selected steps of JA biosynthesis, perception and regulation in the context of plant defense responses to necrotrophic fungal pathogens.

Rapid specialization of counter defenses enables two-spotted spider mite to adapt to novel plant hosts

Genetic adaptation, occurring over a long evolutionary time, enables host-specialized herbivores to develop novel resistance traits and to efficiently counteract the defenses of a narrow range of host plants. In contrast, physiological acclimation, leading to the suppression and/or detoxification of host defenses, is hypothesized to enable broad generalists to shift between plant hosts. However, the host adaptation mechanisms used by generalists composed of host-adapted populations are not known. Two-spotted spider mite (TSSM; Tetranychus urticae) is an extreme generalist herbivore whose individual populations perform well only on a subset of potential hosts. We combined experimental evolution, Arabidopsis thaliana genetics, mite reverse genetics, and pharmacological approaches to examine mite host adaptation upon the shift of a bean (Phaseolus vulgaris)-adapted population to Arabidopsis. We showed that cytochrome P450 monooxygenases are required for mite adaptation to Arabidopsis. We identified activities of two tiers of P450s: general xenobiotic-responsive P450s that have a limited contribution to mite adaptation to Arabidopsis and adaptation-associated P450s that efficiently counteract Arabidopsis defenses. In approximately 25 generations of mite selection on Arabidopsis plants, mites evolved highly efficient detoxification-based adaptation, characteristic of specialist herbivores. This demonstrates that specialization to plant resistance traits can occur within the ecological timescale, enabling the TSSM to shift to novel plant hosts.

Genome-wide identification and expression profiling of durian CYPome related to fruit ripening

Durian (Durio zibethinus L.) is a major economic crop native to Southeast Asian countries, including Thailand. Accordingly, understanding durian fruit ripening is an important factor in its market worldwide, owing to the fact that it is a climacteric fruit with a strikingly limited shelf life. However, knowledge regarding the molecular regulation of durian fruit ripening is still limited. Herein, we focused on cytochrome P450, a large enzyme family that regulates many biosynthetic pathways of plant metabolites and phytohormones. Deep mining of the durian genome and transcriptome libraries led to the identification of all P450s that are potentially involved in durian fruit ripening. Gene expression validation by RT-qPCR showed a high correlation with the transcriptome libraries at five fruit ripening stages. In addition to aril-specific and ripening-associated expression patterns, putative P450s that are potentially involved in phytohormone metabolism were selected for further study. Accordingly, the expression of CYP72, CYP83, CYP88, CYP94, CYP707, and CYP714 was significantly modulated by external treatment with ripening regulators, suggesting possible crosstalk between phytohormones during the regulation of fruit ripening. Interestingly, the expression levels of CYP88, CYP94, and CYP707, which are possibly involved in gibberellin, jasmonic acid, and abscisic acid biosynthesis, respectively, were significantly different between fast- and slow-post-harvest ripening cultivars, strongly implying important roles of these hormones in fruit ripening. Taken together, these phytohormone-associated P450s are potentially considered additional molecular regulators controlling ripening processes, besides ethylene and auxin, and are economically important biological traits.

Plant cytochrome P450 plasticity and evolution

The superfamily of cytochrome P450 (CYP) enzymes plays key roles in plant evolution and metabolic diversification. This review provides a status on the CYP landscape within green algae and land plants. The 11 conserved CYP clans known from vascular plants are all present in green algae and several green algae-specific clans are recognized. Clan 71, 72, and 85 remain the largest CYP clans and include many taxa-specific CYP (sub)families reflecting emergence of linage-specific pathways. Molecular features and dynamics of CYP plasticity and evolution are discussed and exemplified by selected biosynthetic pathways. High substrate promiscuity is commonly observed for CYPs from large families, favoring retention of gene duplicates and neofunctionalization, thus seeding acquisition of new functions. Elucidation of biosynthetic pathways producing metabolites with sporadic distribution across plant phylogeny reveals multiple examples of convergent evolution where CYPs have been independently recruited from the same or different CYP families, to adapt to similar environmental challenges or ecological niches. Sometimes only a single or a few mutations are required for functional interconversion. A compilation of functionally characterized plant CYPs is provided online through the Plant P450 Database (erda.dk/public/vgrid/PlantP450/).

Metabolic Interactions between Brachypodium and Pseudomonas fluorescens under Controlled Iron-Limited Conditions

Rhizosphere bacteria influence the growth of their host plant by consuming and producing metabolites, nutrients, and antibiotic compounds within the root system that affect plant metabolism. Under Fe-limited growth conditions, different plant and microbial species have distinct Fe acquisition strategies, often involving the secretion of strong Fe-binding chelators that scavenge Fe and facilitate uptake.

Iron (Fe) availability has well-known effects on plant and microbial metabolism, but its effects on interspecies interactions are poorly understood. The purpose of this study was to investigate metabolite exchange between the grass Brachypodium distachyon strain Bd21 and the soil bacterium Pseudomonas fluorescens SBW25::gfp/lux (SBW25) during Fe limitation under axenic conditions. We compared the transcriptional profiles and root exudate metabolites of B. distachyon plants grown semihydroponically with and without SBW25 inoculation and Fe amendment. Liquid chromatography-mass spectrometry analysis of the hydroponic solution revealed an increase in the abundance of the phytosiderophores mugineic acid and deoxymugineic acid under Fe-limited conditions compared to Fe-replete conditions, indicating greater secretion by roots presumably to facilitate Fe uptake. In SBW25-inoculated roots, expression of genes encoding phytosiderophore biosynthesis and uptake proteins increased compared to that in sterile roots, but external phytosiderophore abundances decreased. P. fluorescens siderophores were not detected in treatments without Fe. Rather, expression of SBW25 genes encoding a porin, a transporter, and a monooxygenase was significantly upregulated in response to Fe deprivation. Collectively, these results suggest that SBW25 consumed root-exuded phytosiderophores in response to Fe deficiency, and we propose target genes that may be involved. SBW25 also altered the expression of root genes encoding defense-related enzymes and regulators, including thionin and cyanogenic glycoside production, chitinase, and peroxidase activity, and transcription factors. Our findings provide insights into the molecular bases for the stress response and metabolite exchange of interacting plants and bacteria under Fe-deficient conditions.

IMPORTANCE Rhizosphere bacteria influence the growth of their host plant by consuming and producing metabolites, nutrients, and antibiotic compounds within the root system that affect plant metabolism. Under Fe-limited growth conditions, different plant and microbial species have distinct Fe acquisition strategies, often involving the secretion of strong Fe-binding chelators that scavenge Fe and facilitate uptake. Here, we studied interactions between P. fluorescens SBW25, a plant-colonizing bacterium that produces siderophores with antifungal properties, and B. distachyon, a genetic model for cereal grain and biofuel grasses. Under controlled growth conditions, bacterial siderophore production was inhibited in the root system of Fe-deficient plants, bacterial inoculation altered transcription of genes involved in defense and stress response in the roots of B. distachyon, and SBW25 degraded phytosiderophores secreted by the host plant. These findings provide mechanistic insight into interactions that may play a role in rhizosphere dynamics and plant health in soils with low Fe solubility.

Biotransformation of α-terpineol by Alternaria alternata

α-Terpineol (1), the main volatile constituent in some traditional Chinese medicines, has been reported to be metabolized to 4R-oleuropeic acid by the larvae of common cutworms. The present study verified that α-terpineol could be converted to 4R-oleuropeic acid (2) and (1S,2R,4R)-p-menthane-1,2,8-triol (3) by Alternaria alternata fermentation. Using shortened fermentation times, 7-hydroxy-α-terpineol (2a) was identified as an oxidative intermediate, which was consistent with the hypothesis put forward by previous studies. Cytochrome P450 enzymes were also confirmed to catalyze this biotransformation. This is the first study on the biotransformation of α-terpineol by microbial fermentation.

α-Terpineol was converted to 4R-oleuropeic acid by the enzyme P450 of Alternaria alternata.

Mass Spectrometric Approaches to Study the Metabolism of Jasmonates: Biotransformation of Exogenously Supplemented Methyl Jasmonate by Cell Suspension Cultures of Moringa oleifera

Jasmonic acid (JA) and derivatives play a crucial role in plant adaptation to environmental stress. The exogenous application of methyl jasmonate (MeJA) results in activation of stress-related genes and subsequent production of secondary metabolites. This implies the biotransformation of the hormone into a more active form. In this study, Moringa oleifera cell suspension cultures were treated with 100 μM MeJA. Methanolic cell extracts were analyzed with reverse phase ultrahigh performance liquid chromatography (UHPLC) coupled to a quadrupole time-of-flight high definition mass spectrometer (QTOF-HDMS, with MS^E data acquisition). Using a targeted approach for jasmonate profiling, extracted ion chromatograms were generated. MS fragmentation patterns were subsequently derived and molecular formulae calculated from the MS data of each ion. Furthermore, triple quadrupole (QqQ) MS, operated in selected reaction monitoring (SRM) mode, was employed to target masses of interest. In addition to MeJA and JA, three jasmonoyl-amino acids were annotated: jasmonoyl-valine (JA-Val), jasmonoyl-isoleucine/leucine (JA-Ile/Leu), and jasmonoyl-phenylalanine (JA-Phe), based on characteristic precursor and product ions. Furthermore, JA conjugated to a hexose was observed, as well as hydroxylated and carboxylated derivatives of JA-amino acid conjugates. The data point to active metabolism of the externally added MeJA by the M. oleifera cells through biotransformation and bioconversion reactions that can be investigated in depth using advanced mass spectrometric analyses.

Characterization of Jasmonoyl-Isoleucine (JA-Ile) Hormonal Catabolic Pathways in Rice upon Wounding and Salt Stress

BACKGROUND

Jasmonate (JA) signaling and functions have been established in rice development and response to a range of biotic or abiotic stress conditions. However, information on the molecular actors and mechanisms underlying turnover of the bioactive jasmonoyl-isoleucine (JA-Ile) is very limited in this plant species.

RESULTS

Here we explored two gene families in rice in which some members were described previously in Arabidopsis to encode enzymes metabolizing JA-Ile hormone, namely cytochrome P450 of the CYP94 subfamily (CYP94, 20 members) and amidohydrolases (AH, 9 members). The CYP94D subclade, of unknown function, was most represented in the rice genome with about 10 genes. We used phylogeny and gene expression analysis to narrow the study to candidate members that could mediate JA-Ile catabolism upon leaf wounding used as mimic of insect chewing or seedling exposure to salt, two stresses triggering jasmonate metabolism and signaling. Both treatments induced specific transcriptional changes, along with accumulation of JA-Ile and a complex array of oxidized jasmonate catabolites, with some of these responses being abolished in the JASMONATE RESISTANT 1 (jar1) mutant. However, upon response to salt, a lower dependence on JAR1 was evidenced. Dynamics of CYP94B5, CYP94C2, CYP94C4 and AH7 transcripts matched best the accumulation of JA-Ile catabolites. To gain direct insight into JA-Ile metabolizing activities, recombinant expression of some selected genes was undertaken in yeast and bacteria. CYP94B5 was demonstrated to catalyze C12-hydroxylation of JA-Ile, whereas similarly to its Arabidopsis bi-functional homolog IAR3, AH8 performed cleavage of JA-Ile and auxin-alanine conjugates.

CONCLUSIONS

Our data shed light on two rice gene families encoding enzymes related to hormone homeostasis. Expression data along with JA profiling and functional analysis identifies likely actors of JA-Ile catabolism in rice seedlings. This knowledge will now enable to better understand the metabolic fate of JA-Ile and engineer optimized JA signaling under stress conditions.

Tasselseed5 overexpresses a wound-inducible enzyme, ZmCYP94B1, that affects jasmonate catabolism, sex determination, and plant architecture in maize

Maize is monecious, with separate male and female inflorescences. Maize flowers are initially bisexual but achieve separate sexual identities through organ arrest. Loss-of-function mutants in the jasmonic acid (JA) pathway have only female flowers due to failure to abort silks in the tassel. Tasselseed5 (Ts5) shares this phenotype but is dominant. Positional cloning and transcriptomics of tassels identified an ectopically expressed gene in the CYP94B subfamily, Ts5 (ZmCYP94B1). CYP94B enzymes are wound inducible and inactivate bioactive jasmonoyl-L-isoleucine (JA-Ile). Consistent with this result, tassels and wounded leaves of Ts5 mutants displayed lower JA and JA-lle precursors and higher 12OH-JA-lle product than the wild type. Furthermore, many wounding and jasmonate pathway genes were differentially expressed in Ts5 tassels. We propose that the Ts5 phenotype results from the interruption of JA signaling during sexual differentiation via the upregulation of ZmCYP94B1 and that its proper expression maintains maize monoecy.

VcRR2 regulates chilling-mediated flowering through expression of hormone genes in a transgenic blueberry mutant

The molecular mechanism underlying dormancy release and the induction of flowering remains poorly understood in woody plants. Mu-legacy is a valuable blueberry mutant, in which a transgene insertion caused increased expression of a RESPONSE REGULATOR 2-like gene (VcRR2). Mu-legacy plants, compared with nontransgenic 'Legacy' plants, show dwarfing, promotion of flower bud formation, and can flower under nonchilling conditions. We conducted transcriptomic comparisons in leaves, chilled and nonchilled flowering buds, and late-pink buds, and analyzed a total of 41 metabolites of six groups of hormones in leaf tissues of both Mu-legacy and 'Legacy' plants. These analyses uncovered that increased VcRR2 expression promotes the expression of a homolog of Arabidopsis thaliana ENT-COPALYL DIPHOSPHATE SYNTHETASE 1 (VcGA1), which induces new homeostasis of hormones, including increased gibberellin 4 (GA4) levels in Mu-legacy leaves. Consequently, increased expression of VcRR2 and VcGA1, which function in cytokinin responses and gibberellin synthesis, respectively, initiated the reduction in plant height and the enhancement of flower bud formation of the Mu-legacy plants through interactions of multiple approaches. In nonchilled flower buds, 29 differentially expressed transcripts of 17 genes of five groups of hormones were identified in transcriptome comparisons between Mu-legacy and 'Legacy' plants, of which 22 were chilling responsive. Thus, these analyses suggest that increased expression of VcRR2 was collectively responsible for promoting flower bud formation in highbush blueberry under nonchilling conditions. We report here for the first time the importance of VcRR2 to induce a suite of downstream hormones that promote flowering in woody plants.

A succinct access to ω-hydroxylated jasmonates via olefin metathesis

In higher plants, jasmonates are lipid-derived signaling molecules that control many physiological processes, including responses to abiotic stress, defenses against insects and pathogens, and development. Among jasmonates, ω-oxidized compounds form an important subfamily. The biological roles of these ω-modified derivatives are not fully understood, largely due to their limited availability. Herein, a brief (two-step), simple and efficient (>80% yield), versatile, gram-scalable, and environmentally friendly synthetic route to ω-oxidized jasmonates is described. The approach utilizes olefin cross-metathesis as the key step employing inexpensive, commercially available substrates and catalysts.

Jasmonic Acid Oxidase 2 Hydroxylates Jasmonic Acid and Represses Basal Defense and Resistance Responses against Botrytis cinerea Infection

Jasmonates (JAs) orchestrate immune responses upon wound/herbivore injury or infection by necrotrophic pathogens. Elucidation of catabolic routes has revealed new complexity in jasmonate metabolism. Two integrated pathways attenuate signaling by turning over the active hormone jasmonoyl-isoleucine (JA-Ile) through ω-oxidation or deconjugation, and define an indirect route forming the derivative 12OH-JA. Here, we provide evidence for a second 12OH-JA formation pathway by direct jasmonic acid (JA) oxidation. Three jasmonic acid oxidases (JAOs) of the 2-oxoglutarate dioxygenase family catalyze specific oxidation of JA to 12OH-JA, and their genes are induced by wounding or infection by the fungus Botrytis cinerea. JAO2 exhibits the highest basal expression, and its deficiency in jao2 mutants strongly enhanced antifungal resistance. The resistance phenotype resulted from constitutive expression of antimicrobial markers rather than from their higher induction in infected jao2 plants and could be reversed by ectopic expression of any of the three JAOs in jao2. Elevated defense in jao2 was dependent on the activity of JASMONATE RESPONSE 1 (JAR1) and CORONATINE-INSENSITIVE 1 (COI1) but was not correlated with enhanced JA-Ile accumulation. Instead, jao2 mutant lines displayed altered accumulation of several JA species in healthy and challenged plants, suggesting elevated metabolic flux through JA-Ile. Collectively, these data identify the missing enzymes hydroxylating JA and uncover an important metabolic diversion mechanism for repressing basal JA defense responses.

Optimized Jasmonic Acid Production by Lasiodiplodia theobromae Reveals Formation of Valuable Plant Secondary Metabolites

Jasmonic acid is a plant hormone that can be produced by the fungus Lasiodiplodia theobromae via submerged fermentation. From a biotechnological perspective jasmonic acid is a valuable feedstock as its derivatives serve as important ingredients in different cosmetic products and in the future it may be used for pharmaceutical applications. The objective of this work was to improve the production of jasmonic acid by L. theobromae strain 2334. We observed that jasmonic acid formation is dependent on the culture volume. Moreover, cultures grown in medium containing potassium nitrate as nitrogen source produced higher amounts of jasmonic acid than analogous cultures supplemented with ammonium nitrate. When cultivated under optimal conditions for jasmonic acid production, L. theobromae secreted several secondary metabolites known from plants into the medium. Among those we found 3-oxo-2-(pent-2-enyl)-cyclopentane-1-butanoic acid (OPC-4) and hydroxy-jasmonic acid derivatives, respectively, suggesting that fungal jasmonate metabolism may involve similar reaction steps as that of plants. To characterize fungal growth and jasmonic acid-formation, we established a mathematical model describing both processes. This model may form the basis of industrial upscaling attempts. Importantly, it showed that jasmonic acid-formation is not associated to fungal growth. Therefore, this finding suggests that jasmonic acid, despite its enormous amount being produced upon fungal development, serves merely as secondary metabolite.

Fatty acid ω-hydroxylases from Solanum tuberosum

Potato StCYP86A33 complements the Arabidopsis AtCYP86A1 mutant, horst - 1. Suberin is a cell-wall polymer that comprises both phenolic and aliphatic components found in specialized plant cells. Aliphatic suberin is characterized by bi-functional fatty acids, typically ω-hydroxy fatty acids and α,ω-dioic acids, which are linked via glycerol to form a three-dimensional polymer network. In potato (Solanum tuberosum L.), over 65 % of aliphatics are either ω-hydroxy fatty acids or α,ω-dioic acids. Since the biosynthesis of α,ω-dioic acids proceeds sequentially through ω-hydroxy fatty acids, the formation of ω-hydroxy fatty acids represents a significant metabolic commitment during suberin deposition. Four different plant cytochrome P450 subfamilies catalyze ω-hydroxylation, namely, 86A, 86B, 94A, and 704B; though to date, only a few members have been functionally characterized. In potato, CYP86A33 has been identified and implicated in suberin biosynthesis through reverse genetics (RNAi); however, attempts to express the CYP86A33 protein and characterize its catalytic function have been unsuccessful. Herein, we describe eight fatty acid ω-hydroxylase genes (three CYP86As, one CYP86B, three CYP94As, and a CYP704B) from potato and demonstrate their tissue expression. We also complement the Arabidopsis cyp86A1 mutant horst-1 using StCYP86A33 under the control of the Arabidopsis AtCYP86A1 promoter. Furthermore, we provide preliminary analysis of the StCYP86A33 promoter using a hairy root transformation system to monitor pStCYP86A33::GUS expression constructs. These data confirm the functional role of StCYP86A33 as a fatty acid ω-hydroxylase, and demonstrate the utility of hairy roots in the study of root-specific genes.

Functional Characterization of CYP94-Genes and Identification of a Novel Jasmonate Catabolite in Flowers

Over the past decades much research focused on the biosynthesis of the plant hormone jasmonyl-isoleucine (JA-Ile). While many details about its biosynthetic pathway as well about its physiological function are established nowadays, knowledge about its catabolic fate is still scarce. Only recently, the hormonal inactivation mechanisms became a stronger research focus. Two major pathways have been proposed to inactivate JA-Ile: i) The cleavage of the jasmonyl-residue from the isoleucine moiety, a reaction that is catalyzed by specific amido-hydrolases, or ii), the sequential oxidation of the ω-end of the pentenyl side-chain. This reaction is catalyzed by specific members of the cytochrome P450 (CYP) subfamily CYP94: CYP94B1, CYP94B3 and CYP94C1. In the present study, we further investigated the oxidative fate of JA-Ile by expanding the analysis on Arabidopsis thaliana mutants, lacking only one (cyp94b1, cyp94b2, cyp94b3, cyp94c1), two (cyp94b1xcyp94b2, cyp94b1xcyp94b3, cyp94b2xcyp94b3), three (cyp94b1xcyp94b2xcyp94b3) or even four (cyp94b1xcyp94b2xcyp94b3xcyp94c1) CYP94 functionalities. The results obtained in the present study show that CYP94B1, CYP94B2, CYP94B3 and CYP94C1 are responsible for catalyzing the sequential ω-oxidation of JA-Ile in a semi-redundant manner. While CYP94B-enzymes preferentially hydroxylate JA-Ile to 12-hydroxy-JA-Ile, CYP94C1 catalyzes primarily the subsequent oxidation, yielding 12-carboxy-JA-Ile. In addition, data obtained from investigating the triple and quadruple mutants let us hypothesize that a direct oxidation of unconjugated JA to 12-hydroxy-JA is possible in planta. Using a non-targeted metabolite fingerprinting analysis, we identified unconjugated 12-carboxy-JA as novel jasmonate derivative in floral tissues. Using the same approach, we could show that deletion of CYP94-genes might not only affect JA-homeostasis but also other signaling pathways. Deletion of CYP94B1, for example, led to accumulation of metabolites that may be characteristic for plant stress responses like systemic acquired resistance. Evaluation of the in vivo function of the different CYP94-enzymes on the JA-sensitivity demonstrated that particularly CYP94B-enzymes might play an essential role for JA-response, whereas CYP94C1 might only be of minor importance.

Hormone crosstalk in wound stress response: wound-inducible amidohydrolases can simultaneously regulate jasmonate and auxin homeostasis in Arabidopsis thaliana

Jasmonate (JA) and auxin are essential hormones in plant development and stress responses. While the two govern distinct physiological processes, their signaling pathways interact at various levels. Recently, members of the Arabidopsis indole-3-acetic acid (IAA) amidohydrolase (IAH) family were reported to metabolize jasmonoyl-isoleucine (JA-Ile), a bioactive form of JA. Here, we characterized three IAH members, ILR1, ILL6, and IAR3, for their function in JA and IAA metabolism and signaling. Expression of all three genes in leaves was up-regulated by wounding or JA, but not by IAA. Purified recombinant proteins showed overlapping but distinct substrate specificities for diverse amino acid conjugates of JA and IAA. Perturbed patterns of the endogenous JA profile in plants overexpressing or knocked-out for the three genes were consistent with ILL6 and IAR3, but not ILR1, being the JA amidohydrolases. Increased turnover of JA-Ile in the ILL6- and IAR3-overexpressing plants created symptoms of JA deficiency whereas increased free IAA by overexpression of ILR1 and IAR3 made plants hypersensitive to exogenous IAA conjugates. Surprisingly, ILL6 overexpression rendered plants highly resistant to exogenous IAA conjugates, indicating its interference with IAA conjugate hydrolysis. Fluorescent protein-tagged IAR3 and ILL6 co-localized with the endoplasmic reticulum-localized JA-Ile 12-hydroxylase, CYP94B3. Together, these results demonstrate that in wounded leaves JA-inducible amidohydrolases contribute to regulate active IAA and JA-Ile levels, promoting auxin signaling while attenuating JA signaling. This mechanism represents an example of a metabolic-level crosstalk between the auxin and JA signaling pathways.

Dynamics of Jasmonate Metabolism upon Flowering and across Leaf Stress Responses in Arabidopsis thaliana

The jasmonic acid (JA) signaling pathway plays important roles in adaptation of plants to environmental cues and in specific steps of their development, particularly in reproduction. Recent advances in metabolic studies have highlighted intricate mechanisms that govern enzymatic conversions within the jasmonate family. Here we analyzed jasmonate profile changes upon Arabidopsis thaliana flower development and investigated the contribution of catabolic pathways that were known to turnover the active hormonal compound jasmonoyl-isoleucine (JA-Ile) upon leaf stress. We report a rapid decline of JA-Ile upon flower opening, concomitant with the massive accumulation of its most oxidized catabolite, 12COOH-JA-Ile. Detailed genetic analysis identified CYP94C1 as the major player in this process. CYP94C1 is one out of three characterized cytochrome P450 enzymes that define an oxidative JA-Ile turnover pathway, besides a second, hydrolytic pathway represented by the amido-hydrolases IAR3 and ILL6. Expression studies combined with reporter gene analysis revealed the dominant expression of CYP94C1 in mature anthers, consistent with the established role of JA signaling in male fertility. Significant CYP94B1 expression was also evidenced in stamen filaments, but surprisingly, CYP94B1 deficiency was not associated with significant changes in JA profiles. Finally, we compared global flower JA profiles with those previously reported in leaves reacting to mechanical wounding or submitted to infection by the necrotrophic fungus Botrytis cinerea. These comparisons revealed distinct dynamics of JA accumulation and conversions in these three biological systems. Leaf injury boosts a strong and transient JA and JA-Ile accumulation that evolves rapidly into a profile dominated by ω-oxidized and/or Ile-conjugated derivatives. In contrast, B. cinerea-infected leaves contain mostly unconjugated jasmonates, about half of this content being ω-oxidized. Finally, developing flowers present an intermediate situation where young flower buds show detectable jasmonate oxidation (probably originating from stamen metabolism) which becomes exacerbated upon flower opening. Our data illustrate that in spite conserved enzymatic routes, the jasmonate metabolic grid shows considerable flexibility and dynamically equilibrates into specific blends in different physiological situations.

The Rise and Fall of Jasmonate Biological Activities

Jasmonates (JAs) constitute a major class of plant regulators that coordinate responses to biotic and abiotic threats and important aspects of plant development. The core biosynthetic pathway converts linolenic acid released from plastid membrane lipids to the cyclopentenone cis-oxo-phytodienoic acid (OPDA) that is further reduced and shortened to jasmonic acid (JA) in peroxisomes. Abundant pools of OPDA esterified to plastid lipids also occur upon stress, mainly in the Arabidopsis genus. Long thought to be the bioactive hormone, JA only gains its pleiotropic hormonal properties upon conjugation into jasmonoyl-isoleucine (JA-Ile). The signaling pathway triggered when JA-Ile promotes the assembly of COI1-JAZ (Coronatine Insensitive 1-JAsmonate Zim domain) co-receptor complexes has been the focus of most recent research in the jasmonate field. In parallel, OPDA and several other JA derivatives are recognized for their separate activities and contribute to the diversity of jasmonate action in plant physiology. We summarize in this chapter the properties of different bioactive JAs and review elements known for their perception and signal transduction. Much progress has also been gained on the enzymatic processes governing JA-Ile removal. Two JA-Ile catabolic pathways, operating through ω-oxidation (cytochromes P450) or conjugate cleavage (amido hydrolases) shape signal dynamics to allow optimal control on defense. JA-Ile turnover not only participates in signal attenuation, but also impact the homeostasis of the entire JA metabolic pathway.

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.