Aspirin and salicylic acid do not inhibit methyl jasmonate-inducible expression of a gene for ornithine decarboxylase in tobacco BY-2 cells

Analysis of metabolic and transcription levels provides insights into the interactions of plant hormones and crosstalk with MAPKs in the early signaling response of cherry tomato fruit induced by the yeast cell wall

Yeast cell walls (YCW) are promising bio-based elicitors for controlling post-harvest fruit decay. In this study, 1% YCW induction increased the resistance of cherry tomato fruits, reducing disease incidence by 66%. This study aimed to explore the interaction of hormones and crosstalk with MAPKs (mitogen-activated protein kinases) in the early response of resistance regulation in cherry tomato fruits treated with YCW and U0126. We analyzed the temporal changes in hormone content, the expression of critical genes involved in phytohormone biosynthesis, and signal transduction in cherry tomato fruits response to the induction. Results revealed that jasmonic acid (JA) and brassinosteroids (BR) significantly regulated early resistance response in fruit induced by 1% YCW. The salicylic acid (SA) pathway is inhibited by the activation of the JA pathway. JA and SA signaling pathway crosstalk with the MAPK3 pathway. BR plays an essential role in the regulation of fruit resistance. The BR pathway may function independently when JA/SA and MAPK3 pathways are inhibited.

The rise, fall and resurrection of chemical-induced resistance agents

Since the discovery that the plant immune system could be augmented for improved deployment against biotic stressors through the exogenous application of chemicals that lead to induced resistance (IR), many such IR-eliciting agents have been identified. Initially it was hoped that these chemical IR agents would be a benign alternative to traditional chemical biocides. However, owing to low efficacy and/or a realization that their benefits sometimes come at the cost of growth and yield penalties, chemical IR agents fell out of favour and were seldom used as crop protection products. Despite the lack of interest in agricultural use, researchers have continued to explore the efficacy and mechanisms of chemical IR. Moreover, as we move away from the approach of 'zero tolerance' toward plant pests and pathogens toward integrated pest management, chemical IR agents could have a place in the plant protection product list. In this review, we chart the rise and fall of chemical IR agents, and then explore a variety of strategies used to improve their efficacy and remediate their negative adverse effects. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Promoter analyses and transcriptional profiling of eggplant polyphenol oxidase 1 gene (SmePPO1) reveal differential response to exogenous methyl jasmonate and salicylic acid

The transcriptional regulation of multigenic eggplant (Solanum melongena) polyphenol oxidase genes (SmePPO) is orchestrated by their corresponding promoters which mediate developmentally regulated expression in response to myriad biotic and abiotic factors. However, information on structural features of SmePPO promoters and modulation of their expression by plant defense signals are lacking. In the present study, SmePPOPROMOTERs were cloned by genome walking, and their transcription start sites (TSS) were determined by RLM-RACE. Extensive sequence analyses revealed the presence of evolutionarily conserved and over-represented putative cis-acting elements involved in light-regulated transcription, biosynthetic pathways (phenylpropanoid/flavonoid), hormone signaling (abscisic acid, gibberellic acid, jasmonate and salicylate), elicitor and stress responses (cold/dehydration responses), sugar metabolism and plant defense signaling (W-BOX/WRKY) that are common to SmePPOPROMOTER1 and 2. The TSS for SmePPO genes are located 9-15bp upstream of ATG with variable lengths of 5' untranslated regions. Transcriptional profiling of SmePPOs in eggplant seedlings has indicated differential response to methyl jasmonate (MeJA) or salicylic acid (SA) treatment. In planta, while MeJA elicited expression of all the six SmePPOs, SA was only able to induce the expression of SmePPO4-6. Interestingly, in dual treatment, SA considerably repressed the MeJA-induced expression of SmePPOs. Functional dissection of SmePPOPROMOTER1 by deletion analyses using Agrobacterium-mediated transient expression in tobacco leaves has shown that MeJA enhances the SmePPOPROMOTER1-β-glucuronidase (GUS) expression in vivo, while SA does not. Histochemical and quantitative GUS assays have also indicated the negative effect of SA on MeJA-induced expression of SmePPOPROMOTER1. By combining in silico analyses, transcriptional profiling and expression of SmePPOPROMOTER1-GUS fusions, the role of SA on the modulation of MeJA-induced SmePPO1 expression has been elucidated. It is concluded that similar to the coding regions of multigenic SmePPOs, the regulatory elements are also evolutionarily conserved and fall into two distinct sub-classes based on their responses to MeJA and SA.

The biosynthesis of acetovanillone in tobacco cell-suspension cultures

A soluble enzyme, extracted from tobacco cell-suspension cultures 24h after treatment with 100 microM methyl jasmonate, has been shown to synthesize acetovanillone (apocynin) from feruloyl-CoA in the presence of NAD. The enzyme displayed Michaelis-Menten kinetics with apparent K(m) values of 5.6 microM for feruloyl-CoA and 260 microM for NAD and exhibited very high specificity for its substrates. The increase in acetovanillone synthase activity was followed by an increase in the concentration of both acetovanillone and acetosyringone in the culture medium. No intermediate could be detected when analysing the reaction medium by HPLC during the formation of acetovanillone in cell-free extracts. The apparent molecular mass estimated by gel permeation on an FPLC column was ca. 79 kDa. To our knowledge, this is the first report of an enzymic system catalysing the synthesis of an acetophenone. This work demonstrates that the biosynthesis of acetophenones in tobacco proceeds from hydroxycinnamic acids through a CoA-dependent beta-oxidation pathway. Interestingly in methyl jasmonate-treated cells, which synthesize very large amounts of hydroxycinnamoylputrescines, inhibition of the synthesis of these conjugates increased the concentration of acetovanillone and acetosyringone in the culture medium, suggesting that the two metabolic pathways can compete for their common precursors, i.e. hydroxycinnamoyl-CoA thioesters.

Jasmonate- and salicylate-mediated plant defense responses to insect herbivores, pathogens and parasitic plants

While extensive research has examined plant defense responses to attack by herbivores and pathogens, plant responses to parasitism by other plants are not well characterized. The expression of induced plant defenses is mediated by complex signaling networks in which the plant hormones jasmonic acid (JA) and salicylic acid (SA) play key roles. In general, JA-mediated signaling pathways are implicated in the regulation of antiherbivore defenses, while the SA pathway is associated with defense responses against pathogens. However, there are many exceptions to this basic framework, and recent work suggests that interactions between the JA and SA pathways may play important roles in fine-tuning defense responses. The few studies that have addressed plant responses to parasitism by other plants suggest that both salicylates and jasmonates can mediate effective defenses. Here, a review is given of recent work on these defense signaling molecules with relevance for understanding their role in plant responses to parasitism.

The phytotoxin coronatine contributes to pathogen fitness and is required for suppression of salicylic acid accumulation in tomato inoculated with Pseudomonas syringae pv. tomato DC3000

The roles of the phytotoxin coronatine (COR) and salicylic acid (SA)-mediated defenses in the interaction of Pseudomonas syringae pv. tomato DC3000 and tomato (Solanum lycopersicum) were investigated. Unlike findings reported for Arabidopsis thaliana, DC3000 mutants impaired for production of COR or one of its components, coronafacic acid (CFA) or coronamic acid (CMA), induced distinctly different disease lesion phenotypes in tomato. Tomato plants inoculated with the CFA- CMA- mutant DB29 showed elevated transcript levels of SlICS, which encodes isochorismate synthase, an enzyme involved in SA biosynthesis in S. lycopersicum. Furthermore, expression of genes encoding SA-mediated defense proteins were elevated in DB29-inoculated plants compared with plants inoculated with DC3000, suggesting that COR suppresses SlICS-mediated SA responses. Sequence analysis of SlICS revealed that it encodes a protein that is 55 and 59.6% identical to the A. thaliana ICS-encoded proteins AtICS1 and AtICS2, respectively. Tomato plants silenced for SlICS were hypersusceptible to DC3000 and accumulated lower levels of SA after infection with DC3000 compared with inoculated wild-type tomato plants. Unlike what has been shown for A. thaliana, the COR- mutant DB29 was impaired for persistence in SlICS-silenced tomato plants; thus, COR has additional roles in virulence that are SA independent and important in the latter stages of disease development. In summary, the infection assays, metabolic profiling, and gene expression results described in this study indicate that the intact COR molecule is required for both suppression of SA-mediated defense responses and full disease symptom development in tomato.

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.

Methyl jasmonate induced expression of the tobacco putrescine N -methyltransferase genes requires both G-box and GCC-motif elements

Putrescine N-methyltransferase (PMT) catalyzes the first committed step of nicotine biosynthesis, converting putrescine into N-methylputrescine. A variety of chemical, environmental, and developmental cues have been implicated in its regulation. Here we have examined the differential expression of beta-glucuronidase (GUS) transgenes under the control of the transcriptional regulatory sequences of four distinct members of the NtPMT gene family from tobacco (Nicotiana tabacum L.). BY-2 cell cultures expressing various NtPMT promoter-GUS constructs were examined for their response to treatment with various combinations of methyl jasmonate (MeJA), auxin (AUX), and ethylene (ETH). All four NtPMT gene promoters examined were inducible by MeJA, although the extent of the induction varied dramatically, with the NtPMT1a promoter being the most responsive. High AUX levels in the cell growth media repressed NtPMT::GUS transgene expression and inhibited their MeJA-induced transcription. Treatment of BY-2 cells with ETH alone did not result in a significant alteration in NtPMT::GUS expression. However, similar to AUX, ETH treatment led to the suppression of MeJA-induced transcription. Detailed deletion analysis of the NtPMT1a gene promoter showed that as little as 111 bp upstream of the transcriptional start site were sufficient to confer MeJA-responsiveness. Deletion of a conserved G-box element (GCACGTTG) at -103 to -96 bp completely abolished MeJA-responsiveness. Further mutagenesis studies revealed that in addition to a functional G-box, MeJA-responsiveness of the NtPMT1a promoter also required a TA-rich region and a GCC-motif (TGCGCCC) located at -80 to -69 bp and -62 to -56 bp relative to the start site, respectively. A synthetic G-box tetramer (4 X syn G-box) fused to a -83 bp fragment from the NtPMT1a promoter (containing the TA-rich region, GCC-box, and TATA-box) displayed a 30-fold induction by MeJA treatment, whereas when the 4 X syn G-box was fused to a minimal (-46 bp) promoter fragment derived from the CaMV 35S gene, no induction by MeJA treatment was detected. Our results indicate that multiple intersecting signal transduction pathways and different transcriptional regulatory factors are involved in mediating JA-responsiveness of NtPMT expression in tobacco.

Role of conserved residues of the WRKY domain in the DNA-binding of tobacco WRKY family proteins

Four cDNA clones of tobacco that could code for polypeptides with two WRKY domains were isolated. Among four NtWRKYs and other WRKY family proteins, sequence similarity was basically limited to the two WRKY domains. Glutathione S-transferase fusion proteins with the C-terminal WRKY domain of four NtWRKYs bound specifically to the W-box (TTGACC), and the N-terminal WRKY domain showed weaker binding activity with the W-box compared to the C-terminal domain. The DNA-binding activity of the WRKY domain was abolished by o-phenanthroline and this inhibition was recovered specifically by Zn2+. Substitution of the conserved cysteine and histidine residues of the plant-specific C2H2-type zinc finger-like motif in the WRKY domain abolished the DNA binding. In addition, mutations in the invariable WRKYGQK sequence at the N-terminal side of the zinc finger-like motif also significantly reduced the DNA-binding activity, suggesting that these residues are required for proper folding of the DNA-binding zinc finger.

Molecular interactions between the specialist herbivore Manduca sexta (Lepidoptera, Sphingidae) and its natural host Nicotiana attenuata. IV. Insect-Induced ethylene reduces jasmonate-induced nicotine accumulation by regulating putrescine N-methyltransferase transcripts

Attack by the specialist herbivore, Manduca sexta, on its native host Nicotiana attenuata Torr. ex Wats. produces a dramatic ethylene release, a jasmonate burst, and a suppression of the nicotine accumulation that results from careful simulations of the herbivore's damage. Methyl-jasmonate (MeJA) treatment induces nicotine biosynthesis. However, this induction can be suppressed by ethylene as pretreatment of plants with 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene receptors, restores the full MeJA-induced nicotine response in herbivore attacked plants (J. Kahl, D.H. Siemens, R.J. Aerts, R. Gäbler, F. Kühnemann, C.A. Preston, I.T. Baldwin [2000] Planta 210: 336-342). To understand whether this herbivore-induced signal cross-talk occurs at the level of transcript accumulation, we cloned the putrescine methyltransferase genes (NaPMT1 and NaPMT2) of N. attenuata, which are thought to represent the rate limiting step in nicotine biosynthesis, and measured transcript accumulations by northern analysis after various jasmonate, 1-MCP, ethephon, and herbivory treatments. Transcripts of both root putrescine N-methyltransferase (PMT) genes and nicotine accumulation increased dramatically within 10 h of shoot MeJA treatment and immediately after root treatments. Root ethephon treatments suppressed this response, which could be reversed by 1-MCP pretreatment. Moreover, 1-MCP pretreatment dramatically amplified the transcript accumulation resulting from both wounding and M. sexta herbivory. We conclude that attack from this nicotine-tolerant specialist insect causes N. attenuata to produce ethylene, which directly suppresses the nitrogen-intensive biosynthesis of nicotine.

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.