The Jasmonic Acid Pathway Positively Regulates the Polyphenol Oxidase-Based Defense against Tea Geometrid Caterpillars in the Tea Plant (Camellia sinensis).

Polyphenol oxidases (PPOs) as inducible defense proteins, contribute to tea (Camellia sinensis) resistance against tea geometrid larvae (Ectropis grisescens), and this resistance has been associated with the jasmonic acid (JA) signaling by testing geometrid performance in our previous work. However, the regulation of PPO-based defense by JA and other hormone signaling underlying these defense responses is poorly understood. Here, we investigated the role of phytohormones in regulating the PPO response to tea geometrids. We profiled levels of defense hormones, PPO activity and CsPPO genes in leaves infested with tea geometrids. Then, hormone levels were manipulated by exogenous application of methyl jasmonate (MeJA), gibberellin acid (GA3), abscisic acid (ABA), JA biosynthesis inhibitors (sodium diethyldithiocarbamate trihydrate, DIECA and salicylhydroxamic acid, SHAM) and GA inhibitor (uniconazole, UNI). Upon geometrid attack, JA levels significantly increased, whereas GA levels notably decreased and ABA level was slightly decreased. And the PPO activity significantly increased in line with the transcript levels of CsPPO2 and CsPPO4 but not CsPPO1. There were an obvious antagonistic cross-talk between JA and GA signals and an association among JA signals, PPO response and herbivore resistance in tea plants. Pretreatment with MeJA increased PPO activity by activating the transcripts of CsPPO2 and CsPPO4, whereas application of JA inhibitor DIECA suppressed PPO activity. GA3 strongly enhanced PPO activity, but ABA did not alter PPO activity. These findings strongly suggest that JA is a central player in PPO-mediated tea resistance against tea geometrids in a manner that prioritizes defense over growth.

Jasmonic acid is involved in the signaling pathway for fungal endophyte-induced volatile oil accumulation of Atractylodes lancea plantlets.

BACKGROUND: Jasmonic acid (JA) is a well-characterized signaling molecule in plant defense responses. However, its relationships with other signal molecules in secondary metabolite production induced by endophytic fungus are largely unknown. Atractylodes lancea (Asteraceae) is a traditional Chinese medicinal plant that produces antimicrobial volatiles oils. We incubated plantlets of A. lancea with the fungus Gilmaniella sp. AL12. to research how JA interacted with other signal molecules in volatile oil production. RESULTS: Fungal inoculation increased JA generation and volatile oil accumulation. To investigate whether JA is required for volatile oil production, plantlets were treated with JA inhibitors ibuprofen (IBU) and nordihydroguaiaretic acid. The inhibitors suppressed both JA and volatile oil production, but fungal inoculation could still induce volatile oils. Plantlets were further treated with the nitric oxide (NO)-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO), the H2O2 inhibitors diphenylene iodonium (DPI) and catalase (CAT), and the salicylic acid (SA) biosynthesis inhibitors paclobutrazol and 2-aminoindan-2-phosphonic acid. With fungal inoculation, IBU did not inhibit NO production, and JA generation was significantly suppressed by cPTIO, showing that JA may act as a downstream signal of the NO pathway. Exogenous H2O2 could reverse the inhibitory effects of cPTIO on JA generation, indicating that NO mediates JA induction by the fungus through H2O2-dependent pathways. With fungal inoculation, the H2O2 scavenger DPI/CAT could inhibit JA generation, but IBU could not inhibit H2O2 production, implying that H2O2 directly mediated JA generation. Finally, JA generation was enhanced when SA production was suppressed, and vice versa. CONCLUSIONS: Jasmonic acid acts as a downstream signaling molecule in NO- and H2O2-mediated volatile oil accumulation induced by endophytic fungus and has a complementary interaction with the SA signaling pathway.

Chestnut species and jasmonic acid treatment influence development and community interactions of galls produced by the Asian chestnut gall wasp, Dryocosmus kuriphilus.

Jasmonic acid (JA) is a plant-signaling hormone involved in defenses against insects and pathogens as well as the regulation of nutrient partitioning. Gall wasps (Hymenoptera: Cynipidae) induce the formation of galls on their host plants, which house immature wasps and provide them with nutrition and protection. The goal of this study was to investigate the effects of JA application on gall development and defenses. Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) galls on American chestnut, Castanea dentata (Marsh.) Borkhausen (Fagales: Fagaceae), and Chinese chestnut, C. mollissima Blume, were treated with JA or a JA- inhibitor, diethyldithiocarbamic acid (DIECA), to determine the effects of these treatments on gall characteristics and defenses. Chinese chestnut galls treated with JA had greater volume and dry weight, thicker sclerenchyma layers, and fewer external fungal lesions compared with controls. Galls from both chestnut species treated with JA contained a lower proportion of empty chambers, and elevated tannin levels compared with controls. The effects of DIECA on galls were generally opposite from those of JA. American chestnut galls treated with DIECA had lower dry weight and fewer feeding punctures caused by the lesser chestnut weevil compared with controls. Galls from both chestnut species that were treated with DIECA were smaller and had more external fungal lesions compared with controls. Compared to American chestnut galls, Chinese chestnut galls had increased parasitism rates and fewer gall wasps. This study is the first to investigate the effects of JA on an insect gall, and indicates that JA treatments benefit gall wasps by increasing gall size and defenses.

NF-kappaB: a stress-regulated switch for cell survival.

Nuclear factor-kappaB (NF-kappaB), a stress-regulated transcription factor belonging to the Rel family, has a pivotal role in the control of the inflammatory and the innate immune responses. Its activation rapidly induces the transcription of a variety of genes encoding cell adhesion molecules, inflammatory and chemotactic cytokines, cytokine receptors, and enzymes that produce inflammatory mediators. More recently, NF-kappaB activation has been connected with multiple aspects of oncogenesis, including the control of cell proliferation, migration, cell cycle progression, and apoptosis. Interestingly, NF-kappaB is constitutively activated in several types of cancer cells, including hematological and epithelial malignancies. In addition, activation of NF-kappaB in cancer cells by chemotherapy or radiation therapy has been associated with the acquisition of resistance to apoptosis, which has emerged as a significant impediment to effective cancer treatment. Selective cyclopentenone inhibitors of the IkappaB kinase, the key enzyme controlling NF-kappaB activation, were recently shown to be potent inducers of apoptosis in chemoresistant lymphoid malignancies. Increasing evidence, summarized in this review, indicates that the development of selective NF-kappaB inhibitors may represent a promising therapeutic tool to sensitize tumor cells to apoptosis and increase the efficacy of conventional anticancer drugs in a wide spectrum of malignancies.

The outcomes of concentration-specific interactions between salicylate and jasmonate signaling include synergy, antagonism, and oxidative stress leading to cell death.

Salicylic acid (SA) has been proposed to antagonize jasmonic acid (JA) biosynthesis and signaling. We report, however, that in salicylate hydroxylase-expressing tobacco (Nicotiana tabacum) plants, where SA levels were reduced, JA levels were not elevated during a hypersensitive response elicited by Pseudomonas syringae pv phaseolicola. The effects of cotreatment with various concentrations of SA and JA were assessed in tobacco and Arabidopsis (Arabidopsis thaliana). These suggested that there was a transient synergistic enhancement in the expression of genes associated with either JA (PDF1.2 [defensin] and Thi1.2 [thionin]) or SA (PR1 [PR1a-beta-glucuronidase in tobacco]) signaling when both signals were applied at low (typically 10-100 microm) concentrations. Antagonism was observed at more prolonged treatment times or at higher concentrations. Similar results were also observed when adding the JA precursor, alpha-linolenic acid with SA. Synergic effects on gene expression and plant stress were NPR1- and COI1-dependent, SA- and JA-signaling components, respectively. Electrolyte leakage and Evans blue staining indicated that application of higher concentrations of SA + JA induced plant stress or death and elicited the generation of apoplastic reactive oxygen species. This was indicated by enhancement of hydrogen peroxide-responsive AoPR10-beta-glucuronidase expression, suppression of plant stress/death using catalase, and direct hydrogen peroxide measurements. Our data suggests that the outcomes of JA-SA interactions could be tailored to pathogen/pest attack by the relative concentration of each hormone.

Mutual antagonism of ethylene and jasmonic acid regulates ozone-induced spreading cell death in Arabidopsis.

Ethylene (ET) and jasmonic acid (JA) have opposite effects on ozone (O(3))-induced spreading cell death; ET stimulates, and is required for the spreading cell death, whereas JA protects tissues. We studied the underlying molecular mechanisms with the O(3)-sensitive, JA-insensitive jasmonate resistant 1 (jar1), and the O(3)-tolerant, ET-insensitive ethylene insensitive 2 (ein2) mutants. Blocking ET perception pharmacologically with norbornadiene (NBD) in jar1, or ET signaling genetically in the jar1 ein2 double mutant prevented the spread of cell death. This suggests that EIN2 function is epistatic to JAR1, and that the JAR1-dependent JA pathway halts oxidative cell death by directly inhibiting ET signaling. JAR1-dependent suppression of the ET pathway was apparent also as increased EIN2-dependent gene expression and ET hypersensitivity of jar1. Physiological experiments suggested that the target of JA is upstream of Constitutive Triple Response 1 (CTR1), but downstream of ET biosynthesis. Gene expression analysis of 1-aminocyclopropane-1-carboxylic acid (ACC)-treated and O(3)-exposed ein2 and jar1 revealed reciprocal antagonism: the EIN2-mediated suppression of the JA pathway. The results imply that the O(3)-induced spreading cell death is stimulated by early, rapid accumulation of ET, which can suppress the protecting function of JA thereby allowing cell death to proceed. Extended spreading cell death induces late accumulation of JA, which inhibits the propagation of cell death through inhibition of the ET pathway.

Differential actions of PKA and PKC in the regulation of glutamate release by group III mGluRs in the entorhinal cortex.

In a previous study we showed that activation of a presynaptically located metabotropic glutamate receptor (mGluR) with pharmacological properties of mGluR4a causes a facilitation of glutamate release in layer V of the rat entorhinal cortex (EC) in vitro. In the present study we have begun to investigate the intracellular coupling linking the receptor to transmitter release. We recorded spontaneous alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated excitatory postsynaptic currents (EPSCs) in the whole cell configuration of the patch-clamp technique, from visually identified neurons in layer V. Bath application of the protein kinase A (PKA) activator, forskolin, resulted in a marked facilitation of EPSC frequency, similar to that seen with the mGluR4a specific agonist, ACPT-1. Preincubation of slices with the PKA inhibitor H-89 abolished the effect of ACPT-1, as did preincubation with the adenylate cyclase inhibitor, SQ22536. Activation of protein kinase C (PKC) using phorbol 12 myristate 13-acetate (PMA) did not affect sEPSC frequency; however, it did abolish the facilitatory effect of ACPT-1 on glutamate release. A robust enhancement of EPSC frequency was seen in response to bath application of the specific PKC inhibitor, GF 109203X. Both H-89 and the group III mGluR antagonist (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG) abolished the effects of GF 109203X. These data suggest that in layer V of the EC, presynaptic group III mGluRs facilitate release via a positive coupling to adenylate cyclase and subsequent activation of PKA. We have also demonstrated that the PKC system tonically depresses transmitter release onto layer V cells of the EC and that an interaction between mGluR4a, PKA, and PKC may exist at these synapses.

Ethylene suppresses jasmonate-induced gene expression in nicotine biosynthesis.

In Nicotiana sylvestris, a set of nicotine biosynthesis genes were activated by exogenous application of methyl jasmonate, but the activation was effectively suppressed by simultaneous treatment with ethylene. When N. sylvestris transgenic hairy roots were treated with a natural ethylene precursor, the jasmonate-responsive expression of the promoter from a nicotine pathway enzyme gene was completely suppressed, and this suppressive effect was abolished when ethylene perception was blocked with silver cation. These and additional immunoblot results suggest that ethylene signal antagonizes jasmonate signal in nicotine biosynthesis.

Action of brefeldin A blocked by activation of a pertussis-toxin-sensitive G protein.

In many mammalian cells brefeldin A interferes with mechanisms that keep the Golgi appartus separate from the endoplasmic reticulum. The earliest effect of brefeldin A is release of the coat protein beta-COP from the Golgi. This release is blocked by pretreatment with GTP-gamma S or AlF4- (ref. 12). The AlF4- ion activates heterotrimeric G proteins but not proteins of the ras superfamily, suggesting that a heterotrimeric G protein might control membrane transfer from the endoplasmic reticulum to the Golgi. We report here that mastoparan, a peptide that activates heterotrimeric G proteins, promotes binding of beta-COP to Golgi membranes in vitro and antagonizes the effect of brefeldin A on beta-COP in perforated cells and on isolated Golgi membranes. This inhibition is greatly diminished if cells are pretreated with pertussis toxin before perforation. Thus, a heterotrimeric G protein of the Gi/Go subfamily regulates association of coat components with Golgi membranes.

Forskolin inhibits and reverses the effects of brefeldin A on Golgi morphology by a cAMP-independent mechanism.

Brefeldin A (BFA) causes rapid redistribution of Golgi proteins into the ER, leaving no definable Golgi apparatus, and blocks transport of proteins into post-Golgi compartments in the cell. In this study we follow the disassembly of the Golgi apparatus in BFA-treated, living cells labeled with NBD-ceramide and demonstrate that forskolin can both inhibit and reverse this process. Long, tubular processes labeled with NBD-ceramide were observed emerging from Golgi elements and extending out to the cell periphery in cells treated with BFA for 5 min. With longer incubations in BFA, the NBD label was dispersed in a fine reticular pattern characteristic of the ER. Treatment with forskolin inhibited these effects of BFA as well as BFA's earliest morphologic effect on the Golgi apparatus: the redistribution to the cytosol of a 110-kD Golgi peripheral membrane protein. In addition, forskolin could reverse BFA's block in protein secretion. Forskolin inhibition of BFA's effects was dose dependent and reversible. High concentrations of BFA could overcome forskolin's inhibitory effect, suggesting forskolin and BFA interact in a competitive fashion. Remarkably, in cells already exposed to BFA, forskolin could reverse BFA's effects causing the 110-kD Golgi peripheral membrane protein to reassociate with Golgi membrane and juxtanuclear Golgi complexes to reassemble. Neither membrane permeant cAMP analogues nor cAMP phosphodiesterase inhibitors could replicate or enhance forskolin's inhibition of BFA. 1,9-Dideoxyforskolin, which does not activate adenylyl cyclase, was equally as effective as forskolin in antagonizing BFA. A derivative of forskolin, 7-HPP-forskolin, that is less potent than forskolin at binding to adenylyl cyclase, was also equally effective as forskolin in antagonizing BFA. In contrast a similar derivative, 6-HPP-forskolin, that is equipotent with forskolin at binding to adenylyl cyclase, did not inhibit BFA's effects. These results suggest that forskolin acts as a competitive antagonist to BFA, using a cAMP-independent mechanism to prevent and reverse the morphologic effects induced by BFA.