Octadecanoid Pathway Research Articles

Nitric oxide negatively modulates wound signaling in tomato plants.

Synthesis of proteinase inhibitor I protein in response to wounding in leaves of excised tomato (Lycopersicon esculentum) plants was inhibited by NO donors sodium nitroprusside and S-nitroso-N-acetyl-penicillamine. The inhibition was reversed by supplying the plants with the NO scavenger 2-(4-carboxiphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. NO also blocked the hydrogen peroxide (H(2)O(2)) production and proteinase inhibitor synthesis that was induced by systemin, oligouronides, and jasmonic acid (JA). However, H(2)O(2) generated by glucose oxidase and glucose was not blocked by NO, nor was H(2)O(2)-induced proteinase inhibitor synthesis. Although the expression of proteinase inhibitor genes in response to JA was inhibited by NO, the expression of wound signaling-associated genes was not. The inhibition of wound-inducible H(2)O(2) generation and proteinase inhibitor gene expression by NO was not due to an increase in salicylic acid, which is known to inhibit the octadecanoid pathway. Instead, NO appears to be interacting directly with the signaling pathway downstream from JA synthesis, upstream of H(2)O(2) synthesis. The results suggest that NO may have a role in down-regulating the expression of wound-inducible defense genes during pathogenesis.

Molecular cloning and mRNA expression analysis of the first rice jasmonate biosynthetic pathway gene allene oxide synthase

The octadecanoid pathway metabolite jasmonic acid (JA) plays a vital role in rice ( Oryza sativa L. cv. Nipponbare) defense/stress response(s). However, genes involved in its biosynthesis remain unidentified. Here, we cloned a novel rice cDNA highly homologous to the a llene o xide s ynthase (EC 4.2.1.92) AOS gene, the first committed step in JA biosynthesis, showing significant similarity at the amino acid level with a related monocotyledoneous barley AOS. OsAOS is a novel member of the cytochrome P450 CYP74A subfamily and exists as a single copy gene in the rice genome. An examination of its steady state mRNA level in two-week-old seedling leaves revealed that OsAOS does not express constitutively in healthy leaves, and shows a weak responsiveness to cut. Signaling components of defense/stress pathways, in particular JA itself, strongly up-regulated the OsAOS transcript, whereas salicylate, ethylene, abscisic acid, and hydrogen peroxide were not so effective. Copper, a heavy metal also significantly enhanced the OsAOS expression. Protein phosphatase inhibitors proved to be the most potent in up-regulating the OsAOS mRNA level, suggesting the involvement of phosphorylation/dephosphorylation events in its regulation. Moreover, the inducible nature of OsAOS was influenced by light signal(s). Blast pathogen ( Magnaporthe grisea) specifically elicited the accumulation of OsAOS mRNA in leaves in an incompatible versus compatible interaction, a first demonstration of pathogen responsiveness for any AOS gene to date. These results strongly suggest the importance of OsAOS in rice defense/stress response pathway(s).

Octadecanoid signaling component “burst” in rice ( Oryza sativa L.) seedling leaves upon wounding by cut and treatment with fungal elicitor chitosan

Octadecanoid pathway components, 12-oxo-phytodieonic acid (OPDA) and jasmonic acid (JA), are key biologically active regulators of plant self-defense response(s). However, to date these compounds have been studied mostly in dicots, and used large (1–10 g fresh weight, FW) samples for quantification, even when examined in mature rice plants, which is a drawback considering their rapid responsiveness to stress. Focusing on rice—a monocot cereal crop research model—this work describes an efficient and simultaneous quantification of both OPDA and JA using a minimum amount of 200 mg FW seedling leaf tissue upon wounding (by cut) and treatment with fungal elicitor, chitosan (CT) by high-pressure liquid chromatography–turboionspray tandem mass spectrometry. Transient OPDA/JA “burst” was consistently and reproducibly detected within 3 min in wounded and CT treated leaves. OPDA peaked dramatically around 5 min and returned to its basal level within 15 min, whereas JA induction upon wounding and CT treatment were in parallel to OPDA production, peaking at 30 and 60 min, respectively. Present results mark a major advance in our understanding of key inducible octadecanoid pathway components in rice, and strongly suggest a role for the octadecanoid pathway downstream of perception of at least these two fundamentally different extracellular stimuli.

Accumulation of chloroplast-targeted lipoxygenase in passion fruit leaves in response to methyl jasmonate

Wounding caused local and systemic induction of lipoxygenase (LOX) activity in passion fruit ( Passiflora edulis f. flavicarpa) leaves, while exposing intact plants to methyl jasmonate (MJ) vapor provoked a much stronger response. Western blot analysis of these leaf protein extracts using polyclonal antibodies against cucumber LOX, revealed an accumulation of a 90 kDa protein, consistent with LOX enzymatic assays. The inducible LOX was purified to apparent homogeneity, and in vitro analysis of LOXactivity using linoleic acid as substrate showed that it possesses C-13 specificity. Immunocytochemical localization studies using leaf tissue from MJ-treated plants demonstrated that the inducible LOX was compartmented in large quantities in the chloroplasts of mesophyll cells, associated with the stroma. The results suggest that the wound response in passion fruit plants may be mediated by a chloroplast 13-LOX, a key enzyme of the octadecanoid defense-signaling pathway.

Systemic wound signaling in plants: a new perception.

Over 100 species of plants exhibit systemic wound signaling that induces the production of defensive chemicals in leaves and stems (1). The signaling is caused by herbivore attacks and also occurs in response to some pathogens (2–5). The most intensively studied systemic signaling response is that found in species of the Solanaceae family, where a systemic wound signal that is graft transmissible regulates the expression of defensive proteinase inhibitors (PIs) and polyphenol oxidase genes (6) (Fig. 1). On wounding, an 18-aa polypeptide, called systemin (7), interacts with a cell-surface receptor (8, 9) to initiate a signaling cascade that includes the release of linolenic acid (18 carbon atoms) from plant cell membranes and its subsequent conversion to 12 oxo-phytodienoic acid (OPDA; 18 carbon atoms) and jasmonic acid (JA; 12 carbon atoms) (10) through the well known octadecanoid pathway (11). JA activates the expression of several signaling pathway genes that up-regulate JA synthesis and the production of H2O2 (12) leading to the synthesis of PIs. OPDA and JA synthesis is analogous to elements of the inflammatory pathway in animals in which arachidonic acid (20 carbon atoms) is converted to prostaglandins (13). Systemin is considered a mobile long-distance signal, and OPDA isomers (14) and JA have been considered to be localized signals produced in target cells. Li et al., in a recent issue of PNAS (15), use two mutants defective in the wound-signaling pathway to provide evidence that JA or a derivative may also act as a long-distance transmissible signal for wound signaling. Jasmonic acid or a derivative may act as a long-distance transmissible signal for wound signaling.

Distinct roles for jasmonate synthesis and action in the systemic wound response of tomato.

Plant defense responses to wounding and herbivore attack are regulated by signal transduction pathways that operate both at the site of wounding and in undamaged distal leaves. Genetic analysis in tomato indicates that systemin and its precursor protein, prosystemin, are upstream components of a wound-induced, intercellular signaling pathway that involves both the biosynthesis and action of jasmonic acid (JA). To examine the role of JA in systemic signaling, reciprocal grafting experiments were used to analyze wound-induced expression of the proteinase inhibitor II gene in a JA biosynthetic mutant (spr-2) and a JA response mutant (jai-1). The results showed that spr-2 plants are defective in the production, but not recognition, of a graft-transmissible wound signal. Conversely, jai-1 plants are compromised in the recognition of this signal but not its production. It was also determined that a graft-transmissible signal produced in response to ectopic expression of prosystemin in rootstocks was recognized by spr-2 but not by jai-1 scions. Taken together, the results show that activation of the jasmonate biosynthetic pathway in response to wounding or (pro)systemin is required for the production of a long-distance signal whose recognition in distal leaves depends on jasmonate signaling. These findings suggest that JA, or a related compound derived from the octadecanoid pathway, may act as a transmissible wound signal.

Hydrogen Peroxide Generated Via the Octadecanoid Pathway is Neither Necessary nor Sufficient for Methyl Jasmonate-Induced Hypersensitive Cell Death in Woody Plants

Exogenously applied methyl jasmonate (MeJA) might induce the formation of necrotic lesions that closely resemble hypersensitive response lesions. Cellular damage, restricted to the infiltrated zone, was accompanied with the production of H2O2 from the oxidative burst. H2O2 generated in response to MeJA can be histochemically detected in cells surrounding the necrotic lesions as well as in the vascular tissues. The response is systemic and maximizes with time. Among 12 plant species from different families that were assayed for both hypersensitive reaction (HR)-like response and H2O2 generation, only woody species exhibited both MeJA-inducible HR cell death and the generation of H2O2. To assess the role of H2O2 in MeJA-induced HR-like cell death, a gain and loss of function strategy was employed. The cumulative results indicate that H2O2 is neither necessary nor sufficient for MeJA-inducible cell death and that O2- rather than H2O2 might be responsible.

Molecular cloning and characterization of the gene encoding osmotin protein in Petunia hybrida

A cDNA clone encoding osmotin, PhOSM, was isolated from a cDNA library constructed from petal protoplast cultures of Petunia hybrida. PhOSM cDNA was composed of an open reading frame corresponding to protein of 246 amino acids and had a calculated molecular weight of 26.7 kDa. Database comparisons of the PhOSM protein sequences revealed high identity (89%) with the tobacco osmotin and tobacco OLP (Osmotin-Like-Protein). The increased accumulation of PhOSM mRNA in petal protoplast cultures was completely inhibited by treatment with Dhp (3,4-dehydro- l-proline), which is a inhibitor of peptydyl proline hydroxylation in cell wall regeneration. RNA blot analyses revealed that PhOSM was expressed primarily in roots and slightly in the pistil, 3 days after flowering. PhOSM expression was strongly induced in leaves that were exposed to Penicillium funiculosum, Erwinia stewartii and Pseudomonas syringae but not to Aspergillus nidulans. Upon wounding, PhOSM transcripts were induced in the directly damaged leaf but not systemically. Moreover, PhOSM transcript levels increased in response to octadecanoid pathway intermediates and treatments with aspirin and salicylic acid. Our results indicate that PhOSM is developmentally regulated as well as involved in wound-stress signal transduction.

Brief Note : Stimulation of jasmonic acid production in Zea Mays L. infected by the maize rough dwarf virus - R韔 Cuarto. Reversion of symptoms by salicylic acid

In the present paper we study the possible biological relevance of endogenous jasmonic acid (JA) and exogenous salicylic acid (SA) in a plant-microbial system maize-virus. The virus disease "Mal de Río Cuarto" is caused by the maize rough dwarf virus-Río Cuarto. The characteristic symptoms are the appearance of galls or "enations" in leaves, shortening of the stem internodes, poor radical system and general stunting. Changes in JA and protein pattern in maize control and infected plants of a virus-tolerant cultivar were investigated. Healthy and infected-leaf discs were collected for JA measurement at different post-infection times (20, 40, 60 and 68 days). JA was also measured in roots on day 60 after infection. For SDS-PAGE protein analysis, leaf discs were also harvested on day 60 after infection. Infected leaves showed higher levels of JA than healthy leaves, and the rise in endogenous JA coincided with the enation formation. The soluble protein amount did not show differences between infected and healthy leaves; moreover, no difference in the expression of soluble protein was revealed by SDS-PAGE. Our results show that the octadecanoid pathway was stimulated in leaves and roots of the tolerant maize cultivar when infected by this virus. This finding, together with fewer plants with the disease symptoms, suggest that higher foliar and roots JA content may be related to disease tolerance. SA exogenous treatment caused the reversion of the dwarfism symptom.

Lipoxygenase H1 Gene Silencing Reveals a Specific Role in Supplying Fatty Acid Hydroperoxides for Aliphatic Aldehyde Production

Lipoxygenases catalyze the formation of fatty acid hydroperoxide precursors of an array of compounds involved in the regulation of plant development and responses to stress. To elucidate the function of the potato 13-lipoxygenase H1 (LOX H1), we have generated transgenic potato plants with reduced expression of the LOX H1 gene as a consequence of co-suppression-mediated gene silencing. Three independent LOX H1-silenced transgenic lines were obtained, having less than 1% of the LOX H1 protein present in wild-type plants. This depletion of LOX H1 has no effect on the basal or wound-induced levels of jasmonates derived from 13-hydroperoxylinolenic acid. However, LOX H1 depletion results in a marked reduction in the production of volatile aliphatic C6 aldehydes. These compounds are involved in plant defense responses, acting as either signaling molecules for wound-induced gene expression or as antimicrobial substances. LOX H1 protein was localized to the chloroplast and the protein, expressed in Escherichia coli, showed activity toward unesterified linoleic and linolenic acids and plastidic phosphatidylglycerol. The results demonstrate that LOX H1 is a specific isoform involved in the generation of volatile defense and signaling compounds through the HPL branch of the octadecanoid pathway.

Wound-response regulation of the sweet potato sporamin gene promoter region.

Sporamin, a tuberous storage protein of sweet potato, was systemically expressed in leaves and stems by wound stimulation. In an effort to demonstrate the regulatory mechanism of wound response on the sporamin gene, a 1.25 kb sporamin promoter was isolated for studying the wound-induced signal transduction. Two wound response-like elements, a G box-like element and a GCC core-like sequence were found in this promoter. A construct containing the sporamin promoter fused to a beta-glucuronidase (GUS) gene was transferred into tobacco plants by Agrobacterium-mediated transformation. The wound-induced high level of GUS activity was observed in stems and leaves of transgenic tobacco, but not in roots. This expression pattern was similar to that of the sporamin gene in sweet potatoes. Exogenous application of methyl jasmonate (MeJA) activated the sporamin promoter in leaves and stems of sweet potato and transgenic tobacco plants. A competitive inhibitor of ethylene (2,5-norbornadiene; NBD) down-regulated the effect of MeJA on sporamin gene expression. In contrast, salicylic acid (SA), an inhibitor of the octadecanoid pathway, strongly suppressed the sporamin promoter function that was stimulated by wound and MeJA treatments. In conclusion, wound-response expression of the sporamin gene in aerial parts of plants is regulated by the octadecanoid signal pathway.

Adaptations to biotic and abiotic stress: Macaranga-ant plants optimize investment in biotic defence.

Obligate ant plants (myrmecophytes) in the genus Macaranga produce energy- and nutrient-rich food bodies (FBs) to nourish mutualistic ants which live inside the plants. These defend their host against biotic stress caused by herbivores and pathogens. Facultative, 'myrmecophilic' interactions are based on the provision of FBs and/or extrafloral nectar (EFN) to defending insects that are attracted from the vicinity. FB production by the myrmecophyte, M. triloba, was limited by soil nutrient content under field conditions and was regulated according to the presence or absence of an ant colony. However, increased FB production promoted growth of the ant colonies living in the plants. Ant colony size is an important defensive trait and is negatively correlated to a plant's leaf damage. Similar regulatory patterns occurred in the EFN production of the myrmecophilic M. tanarius. Nectar accumulation resulting from the absence of consumers strongly decreased nectar flow, which increased again when consumers had access to the plant. EFN flow could be induced via the octadecanoid pathway. Leaf damage increased levels of endogenous jasmonic acid (JA), and both leaf damage and exogenous JA application increased EFN flow. Higher numbers of nectary visiting insects and lower numbers of herbivores were present on JA-treated plants. In the long run, this decreased leaf damage significantly. Ant food production is controlled by different regulatory mechanisms which ensure that costs are only incurred when counterbalanced by defensive effects of mutualistic insects.

Inducible expression of the heterologous PAL2 promoter from bean in white pine (Pinus strobus) transgenic cells.

To elucidate heterologous promoter function in gymnosperms, we introduced the bean phenylalanine ammonia-lyase-beta-glucuronidase (PAL2-GUS) gene fusion into white pine (Pinus strobus L.). Over 15 lines were produced and integration of Agrobacterium T-DNA was confirmed by Southern analysis. Induction of the reporter gene was detected in all of the lines tested following UV illumination. In contrast, a weak but constant induction was seen in only a few lines following treatment with salicylic acid (SA) or jasmonic acid (JA). However, pretreatment of suspension cultures with SA or JA enhanced the induction of PAL2-GUS expression by UV irradiation. This specific enhancement or potentiation was reduced by 50% by treating the cells with indomethacin, an inhibitor of phospholipase activity, suggesting that the observed potentiation of UV induction involves the octadecanoid pathway. The UV induction was completely abolished by treating the cells with okadaic acid, an inhibitor of phosphatase activity. Thus, the induction of the heterologous PAL2 promoter from bean is consistent with the induction of phenylalanine ammonia-lyase (PAL) in angiosperms. Furthermore, our findings suggest that conifers, although phylogenetically distant to angiosperms, share some conserved promoter elements and some signal transduction mechanisms for UV-light perception.

Isolation and characterization of signal transduction mutants of Arabidopsis thaliana that constitutively activate the octadecanoid pathway and form necrotic microlesions.

Thionins are a group of antimicrobial polypeptides that form part of the plant's defense mechanism against pathogens. The Thi 2.1 thionin gene of Arabidopsis thaliana has been shown to be inducible by jasmonic acid (JA), an oxylipin-like hormone derived from oxygenated linolenic acid and synthesized via the octadecanoid pathway. The JA-dependent regulation of the Thi 2.1 gene has been exploited for setting up a genetic screen for the isolation of signal transduction mutants that constitutively express the Thi 2.1 gene. Ten cet-mutants have been isolated which showed a constitutive expression of the thionin gene. Allelism tests revealed that they represent at least five different loci. Some mutants are dominant, others recessive, but all cet mutations behaved as monogenic traits when backcrossed with Thi 2.1-GUS plants. Some of the mutants overproduce JA and its bioactive precursor 12-oxophytodienoic acid (OPDA) up to 40-fold while others have the same low levels as the control wildtype plants. Two of the mutants showed a strong induction of both the salicylic acid (SA)- and the JA-dependent signaling pathways, while the majority seems to be affected only in the octadecanoid pathway. The Thi 2.1 thionin gene and the Pdf 1.2 defensin gene are activated independently, though both are regulated by JA. The cet-mutants, except for one, also show a spontaneous leaf cell necrosis, a reaction often associated with the systemic acquired resistance (SAR) pathway.

Induction of systemic acquired resistance in cotton by BTH has a negligible effect on phytophagous insects

AbstractWhether or not chemical changes in plants in response to pests (insects and pathogens) are general or specific remains unclear. Some evidence indicates that an induced response (IR) to arthropods via the octadecanoid pathway represents a distinct mechanism from the salicylic acid‐based pathway of systemic acquired resistance (SAR) to pathogens. To further test this hypothesis, young cotton seedlings were activated with benzo (1,2,3) thiadiazole‐7‐carbothioic acid (S) methyl ester (BTH), an elicitor of SAR. The enzymatic activities of a number of pathogenesis‐related (PR) proteins in young and old leaves of control and BTH treated plants were measured. BTH applications elicited marked increases in the activity levels of chitinase, peroxidase, and β‐1,3‐glucanase both locally and systemically. The highest levels of induction were detected systemically in young leaves. Except for some local effects on whitefly oviposition, the induction of SAR by BTH had no effect on either host preference of whiteflies Bemisia tabaci (Gennadius) or on feeding efficiency of cotton bollworms Helicoverpa armigera (Hübner). We conclude that SAR induction via the salicylic acid pathway in ‘Acala’ cotton has negligible effect on the tested insect herbivores.

Characterization and localization of a wound-inducible type I serine-carboxypeptidase from leaves of tomato plants (Lycopersicon esculentum Mill.).

During the course of characterization of the wound-response related proteins from tomato (Lycopersicon esculentum Mill.) leaves, a serine carboxypeptidase (EC 3.4.16.1) was identified. An increase in peptidase activity in response to wounding, and the isolation of a protein with carboxypeptidase (CP) activity from tomato leaves had been reported previously, but the mRNA coding for the enzyme was not identified. We now report the isolation of a tomato leaf type I serine-CP cDNA whose corresponding mRNA is induced by wounding, systemin and methyl jasmonate. The protein sequence deduced from the cDNA exhibits homology to tomato CP, and barley and rice type I CPs. Southern blot results indicated that the CP gene is probably a member of a small gene family. Tomato CP mRNA was detected within 3 h after wounding, or treatment with systemin or methyl jasmonate. Employing Western blot analysis, CP protein was shown to increase 12 h after the treatments. Using the tomato def1 mutant, we have demonstrated that a functional octadecanoid pathway is necessary for CP transcription in response to wounding. Carboxypeptidase protein was immunolocalized as protein aggregates within the central vacuoles of palisade mesophyll cells as well as in vascular parenchyma where it had previously been found. Double labeling using antibodies specific for CP and inhibitor II indicated that the two proteins are colocalized in the vacuolar aggregates. Tomato CP is a member of the "late wound-inducible genes" whose mRNAs increase 4-12 h following wounding, in contrast to several "early wound-inducible genes", whose mRNAs appear within 30 min. The data support a role for the enzyme in protein turnover that occurs systemically in leaf cells in response to wounding.

Ontogeny constrains systemic protease inhibitor response in Nicotiana attenuata.

Protease inhibitors (PIs) are plant compounds that can inhibit proteases of mammal, insect, or pathogen origin and are frequently induced by mechanical wounding, insect feeding, or pathogen infection. Nicotiana attenuata is a species that induces nicotine, volatiles, and phenolics in response to damage. Here we examine the distribution of PIs in N. attenuata to determine if they are part of the induced response in this species and if this response is ontogenetically constrained. We found that N. attenuata shoot extracts inhibited trypsin (Tryp) and chymotrypsin (Chym) activities, while root extracts inhibited Tryp, Chym, and the bacterial protease subtilisin (Sub). The highest TrypPI levels were found at midday in the source-sink transition leaf, while older or younger leaves contained lower TrypPI levels and did not show significant diurnal fluctuations. Rosette plants, bolting plants, and flowering plants all contained TrypPIs in leaves, stems, and flowers, while seed capsules, seeds, and young seedlings did not contain any PIs. PIs in N. attenuata rosette plants were induced by Manduca sexta larval feeding, methyl jasmonate (MeJA) treatment, wounding, and application of M. sexta oral secretion and regurgitant. The response to MeJA application was stronger and longer lasting than to mechanical wounding. The direction and magnitude of the systemic response to mechanical wounding or larval damage depended on the age of the leaf that was damaged and the frequency of wounding. The systemic signal for TrypPI induction appears to follow source-sink relations in the plant and to be regulated by the octadecanoid pathway. Interestingly, by the time plants reach the flowering stage, they had lost the ability to increase PI levels after MeJA treatment. We concluded that plant ontogeny constrains both constitutive and inducible PI production in N. attenuata.

Hydrogen Peroxide Acts as a Second Messenger for the Induction of Defense Genes in Tomato Plants in Response to Wounding, Systemin, and Methyl Jasmonate

The systemic accumulation of both hydrogen peroxide (H(2)O(2)) and proteinase inhibitor proteins in tomato leaves in response to wounding was inhibited by the NADPH oxidase inhibitors diphenylene iodonium (DPI), imidazole, and pyridine. The expression of several defense genes in response to wounding, systemin, oligosaccharides, and methyl jasmonate also was inhibited by DPI. These genes, including those of four proteinase inhibitors and polyphenol oxidase, are expressed within 4 to 12 hr after wounding. However, DPI did not inhibit the wound-inducible expression of genes encoding prosystemin, lipoxygenase, and allene oxide synthase, which are associated with the octadecanoid signaling pathway and are expressed 0.5 to 2 hr after wounding. Accordingly, treatment of plants with the H(2)O(2)-generating enzyme glucose oxidase plus glucose resulted in the induction of only the later-expressed defensive genes and not the early-expressed signaling-related genes. H(2)O(2) was cytochemically detected in the cell walls of vascular parenchyma cells and spongy mesophyll cells within 4 hr after wounding of wild-type tomato leaves, but not earlier. The cumulative results suggest that active oxygen species are generated near cell walls of vascular bundle cells by oligogalacturonide fragments produced by wound-inducible polygalacturonase and that the resulting H(2)O(2) acts as a second messenger for the activation of defense genes in mesophyll cells. These data provide a rationale for the sequential, coordinated, and functional roles of systemin, jasmonic acid, oligogalacturonides, and H(2)O(2) signals for systemic signaling in tomato plants in response to wounding.

Regulatory roles of benzyl adenine and sucrose during wound response of the ribosomal protein gene, rpL34

We previously reported that a large subunit ribosomal protein gene, rpL34, was wound-inducible in tobacco leaves, and that benzyl adenine (BA) enhanced the wound-inducible expression of the gene. Here we report that the wound-inducible expression of the rpL34 gene is enhanced by sucrose. The regulatory roles of BA and sucrose in wound-signalling pathways were investigated using transgenic plants expressing a fusion molecule between the rpL34 promoter and the chloramphenicol acetyltransferase (cat) gene. Wounding caused a progressive increase in CAT activity; BA and sucrose enhanced the response. This indicates that regulation occurs at the transcriptional level. Diethyldithiocarbamic acid (DIECA) and other potent inhibitors of the octadecanoid pathway inhibited the rpL34 promoter, and also reduced BA inducibility of that wound response. However, inhibitors of the octadecanoid pathway did not affect the sucrose response. Protein kinase inhibitors increased BA enhancement while decreasing the sucrose effect, suggesting that protein kinases differentially regulate BA- and sucrose-signalling in the promoter's wound response. Taken together, BA and sucrose enhanced the wound response of the rpL34 promoter via different signalling pathways, although they exerted overlapping effects on wound-induction of the promoter.

The octadecanoid pathway is required for pathogen-induced multi-functional acetyl-CoA carboxylase accumulation in common bean ( Phaseolus vulgaris L.)

A partial cDNA clone corresponding to the multi-functional acetyl-CoA carboxylase (ACCase, EC 6.4.1.2) was isolated using RNA extracted from methyl jasmonate (MeJA)-induced common bean cell cultures. Most of this clone corresponds to the 3′ untranslated region and it showed high identity to alfalfa and soybean ACCase sequences. Southern hybridization revealed one copy of this gene in the common bean genome. In addition to being induced by MeJA in cell cultures and leaves, ACCase mRNA accumulated after yeast elicitor or Pseudomonas syringae pv tabaci treatment. Inhibitors of the octadecanoid pathway severely reduced ACCase mRNA and protein accumulation induced by yeast elicitor or P. syringae pv tabaci, indicating that jasmonates or a precursor mediate ACCase induction after pathogen infection. These results provide a role for the eukaryotic ACCase during the defense response to pathogens in common bean.