Endogenous Jasmonic Acid Levels Research Articles

Potential of jasmonic acid (JA) in accelerating postharvest yellowing of broccoli by promoting its chlorophyll degradation

Chlorophyll degradation is the main reason for postharvest yellowing of broccoli. To uncover the role of jasmonic acid (JA) on the degradation of chlorophyll, broccoli flowers were treated with exogenous methyl jasmonate (MeJA) and diethyldithiocarbamic acid (DIECA). We found a surge of endogenous JA content with the yellowing process, and a significant correlation between JA and chlorophyll content. MeJA treatments led to increased endogenous JA, increased allene oxide cyclase (AOC) activity, and enhanced expression of JA synthesis genes. MeJA caused a stronger reduction in the maximum quantum yield (Fv/Fm), fluorescence decline ratio (Rfd), and total chlorophyll content, advanced the peak of pheide a oxygenase (PAO) activity, and up-regulated the expression of chlorophyll degradation genes. The DIECA treatment resulted in lower endogenous levels of JA, and AOC and 12-oxo-phytodienoic acid reductase (OPR) activity. This study revealed that the potential role of JA on broccoli yellowing is to promote the chlorophyll degradation.

Microbial Volatile Organic Compounds Produced by Bacillus amyloliquefaciens GB03 Ameliorate the Effects of Salt Stress in Mentha piperita Principally Through Acetoin Emission

We investigated the effects of microbial volatile organic compounds (mVOC) emitted by Bacillus amyloliquefaciens GB03 on Mentha piperita growing under different levels of NaCl stress, by evaluating their growth-promoting potential and ability to increase salt tolerance effects. Plants were exposed to bacterial VOCs without having any physical contact with the rhizobacteria. The VOCs emitted by the rhizobacteria (mVOCs) were analyzed using SPME fibers. An increase in the level of salt concentration led to a decrease in plant growth. However, these negative effects of salinity were inhibited in the plants exposed to mVOCs. Plants grown in a saline media and exposed to GB03 VOCs had significantly better morphological characteristics and higher total chlorophyll content compared to controls. The level of endogenous jasmonic acid (JA), salicylic acid, and abscisic acid increased in salt-stressed plants compared to controls. The level of JA did not show any change in plants grown in a saline media either exposed to mVOCs or not. In contrast, the amount of salicylic acid increased remarkably in salt-stressed plants exposed to mVOCs compared to controls (salt-stressed plants not exposed to mVOCs), but the levels of abscisic acid decreased in salt-stressed plants exposed to mVOCs. The chromatographic analyses of the mVOCs produced by salt-stressed GB03 bacteria were similar, regardless of the concentration of salt in the media where the bacteria were grown, although it was observed that the relative percentage of acetoin increased with salt concentration. After determining that acetoin was the main VOCs compound, we exposed plants to acetoin, which demonstrated that acetoin caused similar effects on plants grown under salt stress conditions as those exposed to GB03 mVOCs. Based on these results, the use of mVOCs from PGPR is suggested as a useful technological innovation to facilitate the growth of M. piperita in salt-stressed environments.

OsPEX5 regulates rice spikelet development through modulating jasmonic acid biosynthesis.

Spikelet is the primary reproductive structure and a critical determinant of grain yield in rice. The molecular mechanisms regulating rice spikelet development still remain largely unclear. Here, we report that mutations in OsPEX5, which encodes a peroxisomal targeting sequence 1 (PTS1) receptor protein, cause abnormal spikelet morphology. We show that OsPEX5 can physically interact with OsOPR7, an enzyme involved in jasmonic acid (JA) biosynthesis and is required for its import into peroxisome. Similar to Ospex5 mutant, the knockout mutant of OsOPR7 generated via CRISPR-Cas9 technology has reduced levels of endogenous JA and also displays an abnormal spikelet phenotype. Application of exogenous JA can partially rescue the abnormal spikelet phenotype of Ospex5 and Osopr7. Furthermore, we show that OsMYC2 directly binds to the promoters of OsMADS1, OsMADS7 and OsMADS14 to activate their expression, and subsequently regulate spikelet development. Our results suggest that OsPEX5 plays a critical role in regulating spikelet development through mediating peroxisomal import of OsOPR7, therefore providing new insights into regulation of JA biosynthesis in plants and expanding our understanding of the biological role of JA in regulating rice reproduction.

Circadian Network Interactions with Jasmonate Signaling and Defense.

Plants experience specific stresses at particular, but predictable, times of the day. The circadian clock is a molecular oscillator that increases plant survival by timing internal processes to optimally match these environmental challenges. Clock regulation of jasmonic acid (JA) action is important for effective defenses against fungal pathogens and generalist herbivores in multiple plant species. Endogenous JA levels are rhythmic and under clock control with peak JA abundance during the day, a time when plants are more likely to experience certain types of biotic stresses. The expression of many JA biosynthesis, signaling, and response genes is transcriptionally controlled by the clock and timed through direct connections with core clock proteins. For example, the promoter of Arabidopsis transcription factor MYC2, a master regulator for JA signaling, is directly bound by the clock evening complex (EC) to negatively affect JA processes, including leaf senescence, at the end of the day. Also, tobacco ZEITLUPE, a circadian photoreceptor, binds directly to JAZ proteins and stimulates their degradation with resulting effects on JA root-based defenses. Collectively, a model where JA processes are embedded within the circadian network at multiple levels is emerging, and these connections to the circadian network suggest multiple avenues for future research.

Transcriptome Analysis of Rlm2-Mediated Host Immunity in the Brassica napus-Leptosphaeria maculans Pathosystem.

Our study investigated disease resistance in the Brassica napus-Leptosphaeria maculans pathosystem using a combination of laser microdissection, dual RNA sequencing, and physiological validations of large-scale gene sets. The use of laser microdissection improved pathogen detection and identified putative L. maculans effectors and lytic enzymes operative during host colonization. Within 24 h of inoculation, we detected large shifts in gene activity in resistant cotyledons associated with jasmonic acid and calcium signaling pathways that accelerated the plant defense response. Sequencing data were validated through the direct quantification of endogenous jasmonic acid levels. Additionally, resistance against L. maculans was abolished when the calcium chelator EGTA was applied to the inoculation site, providing physiological evidence of the role of calcium in B. napus immunity against L. maculans. We integrated gene expression data with all available information on cis-regulatory elements and transcription factor binding affinities to better understand the gene regulatory networks underpinning plant resistance to hemibiotrophic pathogens. These in silico analyses point to early cellular reprogramming during host immunity that are coordinated by CAMTA, BZIP, and bHLH transcription factors. Together, we provide compelling genetic and physiological evidence into the programming of plant resistance against fungal pathogens.

SAPK10-Mediated Phosphorylation on WRKY72 Releases Its Suppression on Jasmonic Acid Biosynthesis and Bacterial Blight Resistance

SummaryBacterial blight caused by the infection of Xanthomonas oryzae pv. oryzae (Xoo) is a devastating disease that severely challenges the yield of rice. Here, we report the identification of a “SAPK10-WRKY72-AOS1” module, through which Xoo infection stimulates the suppression of jasmonic acid (JA) biosynthesis to cause Xoo susceptibility. WRKY72 directly binds to the W-box in the promoter of JA biosynthesis gene AOS1 and represses its transcription by inducing DNA hypermethylation on the target site, which finally led to lower endogenous JA level and higher Xoo susceptibility. Abscisic acid (ABA)-inducible SnRK2-type kinase SAPK10 phosphorylates WRKY72 at Thr 129. The SAPK10-mediated phosphorylation impairs the DNA-binding ability of WRKY72 and releases its suppression on AOS1 and JA biosynthesis. Our work highlights a module of how pathogen stimuli lead to plant susceptibility, as well as a potential pathway for ABA-JA interplay with post-translational modification and epigenetic regulation mechanism involved.

Local and systemic hormonal responses in pepper (Capsicum annuum L.) leaves under green peach aphid (Myzus persicae Sulzer) infestation

This study examined the temporal changes in the leaf content of defence-involved phytohormones in pepper (Capsicum annuum L.) plants responding to the green peach aphid (Myzus persicae Sulzer) infestation, at both local and systemic level. Aphid infestation did not alter the content of cis-12-oxo-phytodienoic acid, the jasmonic acid (JA) precursor, even though endogenous levels of JA and its bioactive isoleucine-conjugated form (JA-Ile) significantly increased from 8 to 96 h in local infested leaves. Systemic effects in jasmonates were only showed at 48 h for JA, and 8 and 48 h in the case of JA-Ile. SA accumulated only in local infested leaves after 96 h of infestation, when the level of JA-Ile decreased in these leaves. This suggests a possible antagonistic interaction between JA and SA pathways, although other pathways may be also involved. Endogenous level of indole-3-acetic acid was higher in systemic relative to local infested leaves at 3 and 24 h, although no significant changes in its content were found compared to control leaves. Abscisic acid content was lower in local infested relative to control leaves at 24 h, but was higher at 48 h when it also increased systemically. The possible roles of the studied phytohormones in plant defence responses against aphids are discussed.

SUMO Suppresses the Activity of the Jasmonic Acid Receptor CORONATINE INSENSITIVE1.

Plants respond rapidly to sudden environmental cues, often responding prior to changes in the hormone levels that coordinate these responses. How this is achieved is not fully understood. The integrative role of the phytohormone jasmonic acid (JA) relies upon the plant's ability to control the levels of JASMONATE ZIM (JAZ) domain-containing repressor proteins. Here, we demonstrate that regardless of intrinsic JA levels, Small Ubiquitin-like Modifier (SUMO)-conjugated JAZ proteins inhibit the JA receptor CORONATINE INSENSITIVE1 (COI1) from mediating non-SUMOylated JAZ degradation. The SUMO-deconjugating proteases OVERLY TOLERANT TO SALT1 (OTS1) and OTS2 regulate JAZ protein SUMOylation and stability. The ots1 ots2 double mutants accumulate SUMOylated and non-SUMOylated JAZ repressor proteins but show no change in endogenous JA levels compared with wild-type plants. SUMO1-conjugated JAZ proteins bind to COI1 independently of the JA mimic coronatine. SUMO inhibits JAZ binding to COI1. We identify the SUMO interacting motif in COI1 and demonstrate that this is vital to SUMO-dependent inhibition of COI1. Necrotroph infection of Arabidopsis thaliana promotes SUMO protease degradation, and this increases JAZ SUMOylation and abundance, which in turn inhibits JA signaling. This study reveals a mechanism for rapidly regulating JA responses, allowing plants to adapt to environmental changes.

The Octadecanoid Pathway, but Not COI1, Is Required for Nectar Secretion in Arabidopsis thaliana.

Over 75% of crop species produce nectar and are dependent on pollinators to achieve maximum seed set, yet little is known about the mechanisms regulating nectar secretion. The phytohormone jasmonic acid (JA) is recognized to be involved in several plant processes including development and defense. JA was also recently shown to positively influence nectar secretion in both floral and extrafloral nectaries. For example, endogenous JA levels peak in flowers just prior to nectar secretion, but the details of how JA regulates nectar secretion have yet to be elucidated. We have found that the octadecanoid pathway does indeed play a role in the production and regulation of floral nectar in Arabidopsis. Null alleles for several JA biosynthesis and response genes had significantly reduced amounts of nectar, as well as altered expression of genes known to be involved in nectar production. We additionally identified crosstalk between the JA and auxin response pathways in nectaries. For example, the nectar-less JA synthesis mutant aos-2 showed no auxin response in nectaries, but both nectar production and the auxin response were restored upon exogenous JA and auxin treatment. Conversely, coi1-1, a JA-Ile-insensitive receptor mutant, displayed no auxin response in nectaries under any circumstance, even in older flowers that produced nectar. Surprisingly, opr3-1, a mutant for 12-oxophytodienoate reductase 3 [an enzyme further down the JA biosynthetic pathway that reduces 12-oxo phytodienoic acid (OPDA)], produced no nectar in newly opened flowers, but did secrete nectar in older flowers. Furthermore, a similar phenotype was observed in coi1-1. Cumulatively, these observations strongly suggest an indispensable role for an octadecanoic acid- and auxin-dependent, but JA- and COI1-dispensible, pathway in regulating nectar production in Arabidopsis.

Comparative transcriptome analysis identifies genes involved in the regulation of the pollen cytoskeleton in a genic male sterile wheat line

Male sterility is a widespread phenomenon in plants. The regulation of the pollen cytoskeleton is closely related to fertility in wheat. In this study, the distribution of the pollen cytoskeleton was observed by fluorescence staining in the conventional controlled wheat line CP806 and the genic male sterile wheat line BS366 throughout meiosis. The distribution of microfilaments and microtubules was disordered and asymmetrical in pollen cells of BS366, and the structure of the spindle body was unclear and nearly undetectable. Based on Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses, five cytoskeleton-related KEGG pathways, four GO terms, and 35 differentially expressed genes (DEGs) were identified, including eight genes assigned to GO functions and 27 genes assigned to KEGG pathways. Additionally, 86 differentially expressed transcription factors (TFs), belonging to seven TF families, were obtained. We performed qRT-PCR assays for four genes among the eight genes identified in GO enrichment analyses, eight genes among the 27 genes identified in KEGG pathway analyses, and seven TFs from seven TF families. All of these 19 candidate genes showed disparate expression patterns in CP806 and BS366, suggesting that these genes are involved in the regulation of the pollen cytoskeleton in BS366. In addition, we found lower levels of endogenous jasmonic acid (JA) and brassinolide (BR) in BS366 than that in CP806, suggesting that the biosynthetic pathways of JA and BR are abnormal in BS366. These findings provide gene resources for clarifying cytoskeleton-mediated male sterility in genic male sterile wheat lines.

Halo-tolerant rhizospheric Arthrobacter woluwensis AK1 mitigates salt stress and induces physio-hormonal changes and expression of GmST1 and GmLAX3 in soybean

In the present study rhizospheric bacteria were isolated from sand dune-dwelling Artemisia princeps, Chenopodium ficifolium, Oenothera biennis, and Echinochloa crus-galli and evaluated the ability of the bacterial isolates to produce jasmonic acid (JA) and abscisic acid (ABA) under NaCl-induced salt stress. We observed that 7 of 126 bacterial isolates were capable of producing siderophores, gibberellic acid (GA), indole-3-acetic acid (IAA), phosphate solubilisation, organic acids e.g., quinic acid, succinic acid, acetic acid and butyric acid. A bioassay of the seven selected isolates on rice showed that the isolate AK1 significantly promoted rice growth. Moreover, AK1 produced IAA and ABA in broth spiked with elevated levels of NaCl (100 mM, 200 mM, 300 mM, and 400 mM). The isolate AK1 was further investigated for plant growth promotion and mitigation of NaCl-induced salt stress in soybean grown under 100 mM, 200 mM, and 300 mM stress. Application of AK1 upregulated the expression of GmLAXs, and GmST genes in plants exposed to salt stress as compared to uninoculated plants. Interestingly, the bacteria-treated soybean showed significant increase in growth attributes with or without salinity stress. The endogenous ABA and JA level of inoculated soybean plants declined under elevated salt stress, thus showing an enhanced stress mitigation. A similar ameliorative trend was observed for total proteins, polyphenol oxidase, and peroxidase activity under saline conditions. The isolate AK1 was identified as Arthrobacter woluwensis AK1 based on its 16S rDNA gene sequencing and subsequent phylogenetic analysis.

Development of an efficient high-performance thin layer chromatography method for determination of jasmonic acid in leaf tissue of Stevia rebaudiana (Bertoni) Bertoni

Determination of endogenous levels of jasmonic acid (JA) is essential, as it plays a pivotal role in the physiological processes during a plant’s life cycle. A high performance thin layer chromatography (HPTLC) method was developed for the detection and quantification of JA in leaf extracts of medicinal plant, Stevia rebaudiana (Bertoni) Bertoni. The separation was achieved using the solvents ethyl acetate–benzene (1:1, v/v) as the mobile phase, followed by scanning and quantification at 295 nm. Densitometric analysis of leaf extract resulted in compact spots for JA at Rf = 0.45 ± 0.02. The linear regression analysis showed good relationship with r value. The recovery rate of JA indicated good reproducibility and repeatability of the assay. The statistical analysis proved the reproducibility of the method; therefore, it can be employed for routine quantification of JA in different tissue samples of S. rebaudiana and may also be extrapolated to other biological samples.

The germin-like protein OsGLP2-1 enhances resistance to fungal blast and bacterial blight in rice.

This is the first report that GLP gene (OsGLP2-1) is involved in panicle blast and bacterial blight resistance in rice. In addition to its resistance to blast and bacterial blight, OsGLP2-1 has also been reported to co-localize with a QTLs for sheath blight resistance in rice. These suggest that the disease resistance provided by OsGLP2-1 is quantitative and broad spectrum. Its good resistance to these major diseases in rice makes it to be a promising target in rice breeding. Rice (Oryza sativa) blast caused by Magnaporthe oryzae and bacterial blight caused by Xanthomonas oryzae pv. oryzae are the two most destructive rice diseases worldwide. Germin-like protein (GLP) gene family is one of the important defense gene families which have been reported to be involved in disease resistance in plants. Although GLP proteins have been demonstrated to positively regulate leaf blast resistance in rice, their involvement in resistance to panicle blast and bacterial blight, has not been reported. In this study, we reported that one of the rice GLP genes, OsGLP2-1, was significantly induced by blast fungus. Overexpression of OsGLP2-1 quantitatively enhanced resistance to leaf blast, panicle blast and bacterial blight. The temporal and spatial expression analysis revealed that OsGLP2-1is highly expressed in leaves and panicles and sub-localized in the cell wall. Compared with empty vector transformed (control) plants, the OsGLP2-1 overexpressing plants exhibited higher levels of H2O2 both before and after pathogen inoculation. Moreover, OsGLP2-1 was significantly induced by jasmonic acid (JA). Overexpression of OsGLP2-1 induced three well-characterized defense-related genes which are associated in JA-dependent pathway after pathogen infection. Higher endogenous level of JA was also identified in OsGLP2-1 overexpressing plants than in control plants both before and after pathogen inoculation. Together, these results suggest that OsGLP2-1 functions as a positive regulator to modulate disease resistance. Its good quantitative resistance to the two major diseases in rice makes it to be a promising target in rice breeding.

Jasmonic acid protects etiolated seedlings of Arabidopsis thaliana against herbivorous arthropods

ABSTRACTSeed predators can cause mass ingestion of larger seed populations. As well, herbivorous arthropods attempt to attack etiolated seedlings and chose the apical hook for ingestion, aimed at dropping the cotyledons for later consumption. Etiolated seedlings, as we show here, have established an efficient mechanism of protecting their Achilles' heel against these predators, however. Evidence is provided for a role of jasmonic acid (JA) in this largely uncharacterized plant-herbivore interaction during skotomorphogenesis and that this comprises the temporally and spatially tightly controlled synthesis of a cysteine protease inhibitors of the Kunitz family. Interestingly, the same Kunitz protease inhibitor was found to be expressed in flowers of Arabidopsis where endogenous JA levels are high for fertility. Because both the apical hook and inflorescences were preferred isopod targets in JA-deficient plants that could be rescued by exogenously administered JA, our data identify a JA-dependent mechanism of plant arthropod deterrence that is recalled in different organs and at quite different times of plant development.

Proteomic Analysis of Phloem Proteins Leads to the Identification of Potential Candidates for JA-Mediated RKN-Resistant Elements in Solanum lycopersicum

Tomato production has been severely affected by root-knot nematode (RKN) diseases, leading to huge economic losses in tomato cultivation, production, and processing. To gain insight into the signal mechanism of resistance to RKN (Meloidogyne incongnita), tomato lines with different endogenous jasmonic acid levels were inoculated with RKN, and the differential proteome of their phloem was analyzed with two-dimensional gel electrophoresis. Analysis of 1400 protein spots from each gel revealed 74 differentially expressed proteins, 30 of which were identifed via matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF–MS). Among these 30, the abundance of 25 proteins was elevated in 35S::PS, and five proteins were not expressed in spr2. The total differentially expressed proteins were grouped into multiple functional categories, the largest of which was energy conversion (38 %). Furthermore, we proposed several candidates that might function as potential signal molecules under RKN stress and dissected the multiple roles of proteins related to photosynthesis and energy conversion. The mRNA levels of nine proteins associated with defense responses and energy metabolism were analyzed by qRT-PCR, and the expression levels of five were in line with the proteome data.

Hydrogen Peroxide Acts as a Signaling Molecule for the Methyl Jasmonate-Induced Antioxidant Defense in Wheat Callus to Promote Enhanced Drought Tolerance

Drought stress is a major challenge in agriculture, causing severe loss of crops throughout the world. Methyl jasmonate (MeJA) regulates a variety of plant developmental process and responds to many biotic and abiotic stresses. To explore the physiological mechanisms of drought stress mitigated by exogenous MeJA, we subjected callus of wheat (Triticum aestivum L.) to drought induced medium after pretreatment with 10 ml sterile solution that contained the following singly or in combinations: MeJA (0, 0.25, and 2.5µM) and the lipoxygenase (LOX) inhibitor salicylhydroxamic acid (SHAM; 0 and 0.5 mM) for 24 hours. The endogenous jasmonic acid (JA) content, activity of LOX, hydrogen peroxide (H2O2) content, antioxidant enzymes activities, levels of reactive oxygen species (ROS), content of malondialdehyde (MDA), and cell viability were measured. The results showed that exogenous MeJA induced the activity of LOX and resulted in rapid increase in endogenous JA levels in a concentration-dependent manner; JA declined gradually after reaching its maximum. The level of H2O2 increased with increases in LOX activity and endogenous JA level, which are involved in the octadecanoid signaling pathway. However, SHAM inhibited the LOX activity, the endogenous JA level, and the accumulation of H2O2 in wheat callus. In addition, the activities of several antioxidant enzymes increased after MeJA-pretreatment, but this effect was also inhibited by SHAM. The cumulative results suggest that H2O2 was generated through the octadecanoid signaling pathway, and some antioxidant defense genes were provoked by the accumulation of H2O2. Therefore, we inferred that H2O2 might act as a signaling molecule for the MeJA-induced antioxidant defense. Drought stress can be improved by MeJA-pretreatment, leading to decrease in endogenous MDA and ROS contents, which are normally induced by drought conditions. Both drought stress and exogenous MeJA-pretreatment increased in LOX activity, endogenous JA level, and antioxidant enzymes. Combinatorial treatments showed an apparent synergistic effect on the activities of these antioxidant enzymes and resulted in improved cell viability. These results confirmed the hypothesis that H2O2 acts as a signaling molecule for the MeJA-induced antioxidant defense and could alleviate the negative effects of drought stress on wheat callus.

Identification of jasmonic acid-associated microRNAs and characterization of the regulatory roles of the miR319/TCP4 module under root-knot nematode stress in tomato.

MicroRNAs (miRNAs) are important transcriptional and post-transcriptional modulators of gene expression that play crucial roles in the responses to diverse stresses. To explore jasmonic acid (JA)-dependent miRNA-mediated regulatory networks that are responsive to root-knot nematode (RKN), two small RNA libraries were constructed from wild-type (WT) and JA mutant (spr2) plants. A total of 263 known miRNAs and 441 novel miRNAs were significantly regulated under RKN stress in the two libraries. The spatio-temporal expression of candidate miRNAs and their corresponding targets were analysed by qRT-PCR under RKN stress. A clear negative correlation was observed between miR319 and its target TEOSINTE BRANCHED1/CYCLOIDEA/PRO-LIFERATING CELL FACTOR 4 (TCP4) in leaf, stem, and root under RKN stress, implying that the miR319/TCP4 module is involved in the systemic defensive response. Reverse genetics demonstrated that the miR319/TCP4 module affected JA synthetic genes and the endogenous JA level in leaves, thereby mediating RKN resistance. These results suggested that the action of miR319 in serving as a systemic signal responder and regulator that modulated the RKN systemic defensive response was mediated via JA. The potential cross-talk between miR319/TCP4 and miR396/GRF (GROWTH RESPONDING FACTOR) in roots under RKN invasion is discussed, and a predictive model regarding miR319/TCP4-mediated RKN resistance is proposed.

Cloning and characterization of a cabbage BoAOS gene with enhanced drought tolerance

Allene oxide synthase (AOS), which is a cytochrome P450 (CYP74A), catalyses the first step in the biosynthesis of jasmonic acid from lipoxygenase-derived hydroperoxides of free fatty acids. The full-length cDNA of an AOS-like gene was cloned from Brassica oleracea using rapid amplification of cDNA ends and was designated as BoAOS. The BoAOS expression level was higher in alabastrums and flowers than in other tissues of cabbage, as determined by real-time reverse transcription polymerase chain reaction (RT-PCR). To characterize the BoAOS gene, Arabidopsis was transformed via Agrobacterium tumefaciens with a vector to express the gene under the control of a strong constitutive promoter, CaMV35S (Cauliflower Mosaic Virus). Based on analyses of tolerance to drought stress, compared with control plants, the overexpression of BoAOS in transgenic plants increased the endogenous jasmonic acid level and conferred higher tolerance to drought stress. Therefore, we suggest that BoAOS may be a suitable candidate gene to produce transgenic plants with tolerance to drought stress.

Arbuscular mycorrhiza increase artemisinin accumulation in Artemisia annua by higher expression of key biosynthesis genes via enhanced jasmonic acid levels.

It is becoming increasingly evident that the formation of arbuscular mycorrhiza (AM) enhances secondary metabolite production in shoots. Despite mounting evidence, relatively little is known about the underlying mechanisms. This study suggests that increase in artemisinin concentration in Artemisia annua colonized by Rhizophagus intraradices is due to altered trichome density as well as transcriptional patterns that are mediated via enhanced jasmonic acid (JA) levels. Mycorrhizal (M) plants had higher JA levels in leaf tissue that may be due to induction of an allene oxidase synthase gene (AOS), encoding one of the key enzymes for JA production. Non-mycorrhizal (NM) plants were exogenously supplied with a range of methyl jasmonic acid concentrations. When leaves of NM and M plants with similar levels of endogenous JA were compared, these matched closely in terms of shoot trichome density, artemisinin concentration, and transcript profile of artemisinin biosynthesis genes. Mycorrhization increased artemisinin levels by increasing glandular trichome density and transcriptional activation of artemisinin biosynthesis genes. Transcriptional analysis of some rate-limiting enzymes of mevalonate and methyl erythritol phosphate (MEP) pathways revealed that AM increases isoprenoids by induction of the MEP pathway. A decline in artemisinin concentration in shoots of NM and M plants treated with ibuprofen (an inhibitor of JA biosynthesis) further confirmed the implication of JA in the mechanism of artemisinin production.

Symptomless endophytic fungi suppress endogenous levels of salicylic acid and interact with the jasmonate-dependent indirect defense traits of their host, lima bean (Phaseolus lunatus).

Symptomless ‘type II’ fungal endophytes colonize their plant host horizontally and exert diverse effects on its resistance phenotype. Here, we used wild Lima bean (Phaseolus lunatus) plants that were experimentally colonized with one of three strains of natural endophytes (Bartalinia pondoensis, Fusarium sp., or Cochliobolus lunatus) to investigate the effects of fungal colonization on the endogenous levels of salicylic acid (SA) and jasmonic acid (JA) and on two JA-dependent indirect defense traits. Colonization with Fusarium sp. enhanced JA levels in intact leaves, whereas B. pondoensis suppressed the induction of endogenous JA in mechanically damaged leaves. Endogenous SA levels in intact leaves were significantly decreased by all strains and B. pondoensis and Fusarium sp. decreased SA levels after mechanical damage. Colonization with Fusarium sp. or C. lunatus enhanced the number of detectable volatile organic compounds (VOCs) emitted from intact leaves, and all three strains enhanced the relative amount of several VOCs emitted from intact leaves as well as the number of detectable VOCs emitted from slightly damaged leaves. All three strains completely suppressed the induced secretion of extrafloral nectar (EFN) after the exogenous application of JA. Symptomless endophytes interact in complex and strain-specific ways with the endogenous levels of SA and JA and with the defense traits that are controlled by these hormones. These interactions can occur both upstream and downstream of the defense hormones.