RESUMEN
Plant defense metabolites are well known to be regulated developmentally. The optimal defense (OD) theory posits that a tssue's fitness values and probability of attack should determine defense metabolite allocations. Young leaves are expected to provide a larger fitness value to the plant, and therefore their defense allocations should be higher when compared with older leaves. The mechanisms that coordinate development with defense remain unknown and frequently confound tests of the OD theory predictions. Here we demonstrate that cytokinins (CKs) modulate ontogeny-dependent defenses in Nicotiana attenuata. We found that leaf CK levels highly correlate with inducible defense expressions with high levels in young and low levels in older leaves. We genetically manipulated the developmental patterns of two different CK classes by using senescence- and chemically inducible expression of CK biosynthesis genes. Genetically modifying the levels of different CKs in leaves was sufficient to alter ontogenic patterns of defense metabolites. We conclude that the developmental regulation of growth hormones that include CKs plays central roles in connecting development with defense and therefore in establishing optimal patterns of defense allocation in plants.
Asunto(s)
Citocininas/metabolismo , Nicotiana/metabolismo , Hojas de la Planta/metabolismo , Proteínas de Plantas/metabolismo , Acetatos/metabolismo , Acetatos/farmacología , Animales , Ciclopentanos/metabolismo , Ciclopentanos/farmacología , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Herbivoria/fisiología , Interacciones Huésped-Parásitos/efectos de los fármacos , Manduca/fisiología , Oxilipinas/metabolismo , Oxilipinas/farmacología , Enfermedades de las Plantas/genética , Enfermedades de las Plantas/parasitología , Reguladores del Crecimiento de las Plantas/metabolismo , Reguladores del Crecimiento de las Plantas/farmacología , Hojas de la Planta/genética , Hojas de la Planta/parasitología , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Factores de Tiempo , Nicotiana/genética , Nicotiana/parasitologíaRESUMEN
Herbivory-induced changes in photosynthesis have been documented in many plant species; however, the complexity of photosynthetic regulation and analysis has thwarted progress in understanding the mechanism involved, particularly those elicited by herbivore-specific elicitors. Here, we analysed the early photosynthetic gas exchange responses in Nicotiana attenuata plants after wounding and elicitation with Manduca sexta oral secretions and the pathways regulating these responses. Elicitation with M. sexta oral secretions rapidly decreased photosynthetic carbon assimilation (AC ) in treated and systemic (untreated, vascularly connected) leaves, which were associated with changes in stomatal conductance, rather than with changes in Rubisco activity and 1-5 ribulose-1,5-bisphosphate turnover. Phytohormone profiling and gas exchange analysis of oral secretion-elicited transgenic plants altered in phytohormone regulation, biosynthesis and perception, combined with micrografting techniques, revealed that the local photosynthetic responses were mediated by 12-oxo-phytodienoic acid, while the systemic responses involved interactions among jasmonates, cytokinins and abscisic acid signalling mediated by mitogen-activated protein kinase 4. The analysis also revealed a role for cytokinins interacting with mitogen-activated protein kinase 4 in CO2 -mediated stomatal regulation. Hence, oral secretions, while eliciting jasmonic acid-mediated defence responses, also elicit 12-oxo-phytodienoic acid-mediated changes in stomatal conductance and AC , an observation illustrating the complexity and economy of the signalling that regulates defence and carbon assimilation pathways in response to herbivore attack.
Asunto(s)
Carbono/metabolismo , Citocininas/metabolismo , Herbivoria/fisiología , Nicotiana/fisiología , Estomas de Plantas/fisiología , Animales , Ácidos Grasos Insaturados/metabolismo , Manduca/fisiología , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Fotosíntesis/fisiología , Hojas de la Planta/metabolismo , Proteínas de Plantas/metabolismo , Brotes de la Planta/genética , Brotes de la Planta/metabolismo , Plantas Modificadas Genéticamente , Ribulosa-Bifosfato Carboxilasa/metabolismoRESUMEN
Bacillus sp B55, a bacterium naturally associated with Nicotiana attenuata roots, promotes growth and survival of wild-type and, particularly, ethylene (ET)-insensitive (35)S-ethylene response1 (etr1) N. attenuata plants, which heterologously express the mutant Arabidopsis thaliana receptor ETR1-1. We found that the volatile organic compound (VOC) blend emitted by B55 promotes seedling growth, which is dominated by the S-containing compound dimethyl disulfide (DMDS). DMDS was depleted from the headspace during cocultivation with seedlings in bipartite Petri dishes, and (35)S was assimilated from the bacterial VOC bouquet and incorporated into plant proteins. In wild-type and (35)S-etr1 seedlings grown under different sulfate (SO(4)(-2)) supply conditions, exposure to synthetic DMDS led to genotype-dependent plant growth promotion effects. For the wild type, only S-starved seedlings benefited from DMDS exposure. By contrast, growth of (35)S-etr1 seedlings, which we demonstrate to have an unregulated S metabolism, increased at all SO(4)(-2) supply rates. Exposure to B55 VOCs and DMDS rescued many of the growth phenotypes exhibited by ET-insensitive plants, including the lack of root hairs, poor lateral root growth, and low chlorophyll content. DMDS supplementation significantly reduced the expression of S assimilation genes, as well as Met biosynthesis and recycling. We conclude that DMDS by B55 production is a plant growth promotion mechanism that likely enhances the availability of reduced S, which is particularly beneficial for wild-type plants growing in S-deficient soils and for (35)S-etr1 plants due to their impaired S uptake/assimilation/metabolism.
Asunto(s)
Bacillus/metabolismo , Disulfuros/metabolismo , Nicotiana/metabolismo , Azufre/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Bacillus/fisiología , Clorofila/metabolismo , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Glutatión/metabolismo , Interacciones Huésped-Patógeno , Redes y Vías Metabólicas/genética , Datos de Secuencia Molecular , Mutación , Enfermedades de las Plantas/genética , Enfermedades de las Plantas/microbiología , Raíces de Plantas/genética , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Plantas Modificadas Genéticamente , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Plantones/genética , Plantones/crecimiento & desarrollo , Plantones/metabolismo , Nicotiana/genética , Nicotiana/crecimiento & desarrollo , Compuestos Orgánicos Volátiles/metabolismoRESUMEN
Arabidopsis thaliana plants are less resistant to attack by the generalist lepidopteran herbivore Trichoplusia ni when plants and herbivores are entrained to opposite, versus identical diurnal cycles and tested under constant conditions. This effect is associated with circadian fluctuations in levels of jasmonic acid, the transcription factor MYC2, and glucosinolate contents in leaves. We tested whether a similar effect could be observed in a different plant-herbivore system: the wild tobacco Nicotiana attenuata and its co-evolved specialist herbivore, Manduca sexta. We measured larval growth on plants under both constant and diurnal conditions following identical or opposite entrainment, profiled the metabolome of attacked leaf tissue, quantified specific metabolites known to reduce M. sexta growth, and monitored M. sexta feeding activity under all experimental conditions. Entrainment did not consistently affect M. sexta growth or plant defense induction. However, both were reduced under constant dark conditions, as was M. sexta feeding activity. Our data indicate that the response induced by M. sexta in N. attenuata is robust to diurnal cues and independent of plant or herbivore entrainment. We propose that while the patterns of constitutive or general damage-induced defense may undergo circadian fluctuation, the orchestration of specific induced responses is more complex.
Asunto(s)
Ritmo Circadiano/fisiología , Herbivoria/fisiología , Manduca/fisiología , Nicotiana/fisiología , Nicotiana/parasitología , Animales , Ritmo Circadiano/efectos de la radiación , Larva/crecimiento & desarrollo , Luz , Metaboloma , Metabolómica , Hojas de la Planta/metabolismo , Hojas de la Planta/efectos de la radiación , Nicotiana/metabolismo , Nicotiana/efectos de la radiaciónRESUMEN
Herbivore attack elicits changes in cytokinins (CKs), but how these changes influence defense signaling remains poorly described. We investigated the influence of the CK pathway on the well-described inducible defense pathways of Nicotiana attenuata in response to wounding with and without elicitors from the specialist herbivore Manduca sexta. CK pathway manipulation often suffers from substantial side effects on plant growth and development. We therefore used multiple manipulation tools including spray application of CKs, chemically-inducible expression of the CK biosynthesis enzyme isopentenyltransferase, and transient and constitutive RNAi-mediated gene silencing of CK receptors to resolve the function of CKs in plant defense. The results demonstrated that CK concentrations in leaves and perception through CHASE-DOMAIN CONTAINING HIS KINASE 2 (NaCHK2) and NaCHK3 were important for the accumulation of jasmonic acid (JA) and phenolamides and proteinase inhibitor activity. By contrast, the CK pathway did not promote the accumulation of the active JA-isoleucine conjugate and negatively regulated the release of specific green leaf volatile esters. Interestingly, CK signaling also promotes the systemic phenolamide accumulation. We conclude that the CK pathway is an important regulator of herbivory-inducible defense signaling and chemistry, which expands its reported participation in adjusting a plant's physiology to abiotic and biotic stress responses.
Asunto(s)
Citocininas/metabolismo , Herbivoria , Nicotiana/inmunología , Nicotiana/fisiología , Transducción de Señal , Regulación de la Expresión Génica de las Plantas , Datos de Secuencia Molecular , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Nicotiana/genéticaRESUMEN
Cytokinins (CKs) are well-established as important phytohormonal regulators of plant growth and development. An increasing number of studies have also revealed the function of these hormones in plant responses to biotic and abiotic stresses. While the function of certain CK classes, including trans-zeatin and isopentenyladenine-type CKs, have been studied in detail, the role of cis-zeatin-type CKs (cZs) in plant development and in mediating environmental interactions is less well defined. Here we provide a comprehensive summary of the current knowledge about abundance, metabolism and activities of cZs in plants. We outline the history of their analysis and the metabolic routes comprising cZ biosynthesis and degradation. Further we provide an overview of changes in the pools of cZs during plant development and environmental interactions. We summarize studies that investigate the role of cZs in regulating plant development and defence responses to pathogen and herbivore attack and highlight their potential role as 'novel' stress-response markers. Since the functional roles of cZs remain largely based on correlative data and genetic manipulations of their biosynthesis, inactivation and degradation are few, we suggest experimental approaches using transgenic plants altered in cZ levels to further uncover their roles in plant growth and environmental interactions and their potential for crop improvement.
Asunto(s)
Cadena Alimentaria , Regulación de la Expresión Génica de las Plantas , Reguladores del Crecimiento de las Plantas/metabolismo , Fenómenos Fisiológicos de las Plantas , Zeatina/metabolismo , Herbivoria , Desarrollo de la PlantaRESUMEN
Nearly half a century ago insect herbivores were found to induce the formation of green islands by manipulating cytokinin (CK) levels. However, the response of the CK pathway to attack by chewing insect herbivores remains unclear. Here, we characterize the CK pathway of Nicotiana attenuata (Torr. ex S. Wats.) and its response to wounding and perception of herbivore-associated molecular patterns (HAMPs). We identified 44 genes involved in CK biosynthesis, inactivation, degradation, and signaling. Leaf wounding rapidly induced transcriptional changes in multiple genes throughout the pathway, as well as in the levels of CKs, including isopentenyladenosine and cis-zeatin riboside; perception of HAMPs present in the oral secretions (OS) of the specialist herbivore Manduca sexta amplified these responses. The jasmonate pathway, which triggers many herbivore-induced processes, was not required for these HAMP-triggered changes, but rather suppressed the CK responses. Interestingly CK pathway changes were observed also in systemic leaves in response to wounding and OS application indicating a role of CKs in mediating long distance systemic processes in response to herbivory. Since wounding and grasshopper OS elicited similar accumulations of CKs in Arabidopsis thaliana L., we propose that CKs are integral components of wounding and HAMP-triggered responses in many plant species.
Asunto(s)
Citocininas/metabolismo , Herbivoria/fisiología , Nicotiana/fisiología , Transducción de Señal , Aminoácidos/metabolismo , Animales , Ciclopentanos/farmacología , Ácidos Grasos/metabolismo , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Genes de Plantas , Manduca/fisiología , Oxilipinas/farmacología , ARN Mensajero/genética , ARN Mensajero/metabolismo , Receptores de Reconocimiento de Patrones/metabolismo , Transducción de Señal/efectos de los fármacos , Transducción de Señal/genética , Nicotiana/genéticaRESUMEN
Field experiments with transgenic plants often reveal the functional significance of genetic traits that are important for the performance of the plants in their natural environments. Until now, only constitutive overexpression, ectopic expression and gene silencing methods have been used to analyze gene-related phenotypes in natural habitats. These methods do not allow sufficient control over gene expression for the study of ecological interactions in real time, of genetic traits that play essential roles in development, or of dose-dependent effects. We applied the sensitive dexamethasone (DEX)-inducible pOp6/LhGR expression system to the ecological model plant Nicotiana attenuata and established a lanolin-based DEX application method to facilitate ectopic gene expression and RNA interference-mediated gene silencing in the field and under challenging conditions (e.g. high temperature, wind and UV radiation). Fully established field-grown plants were used to silence phytoene desaturase and thereby cause photobleaching only in specific plant sectors, and to activate expression of the cytokinin (CK) biosynthesis gene isopentenyl transferase (ipt). We used ipt expression to analyze the role of CKs in both the glasshouse and the field to understand resistance to the native herbivore Tupiocoris notatus, which attacks plants at small spatial scales. By spatially restricting ipt expression and elevating CK levels in single leaves, damage by T. notatus increased, demonstrating the role of CKs in this plant-herbivore interaction at a small scale. As the arena of most ecological interactions is highly constrained in time and space, these tools will advance the genetic analysis of dynamic traits that matter for plant performance in nature.
Asunto(s)
Ecología/métodos , Técnicas Genéticas , Herbivoria , Plantas Modificadas Genéticamente , Interferencia de ARN , Transgenes , Animales , Dexametasona/farmacología , NicotianaRESUMEN
Although slugs and snails play important roles in terrestrial ecosystems and cause considerable damage on a variety of crop plants, knowledge about the mechanisms of plant immunity to molluscs is limited. We found slugs to be natural herbivores of Arabidopsis thaliana and therefore investigated possible resistance mechanisms of this species against several molluscan herbivores. Treating wounded leaves with the mucus residue ('slime trail') of the Spanish slug Arion lusitanicus increased wound-induced jasmonate levels, suggesting the presence of defence elicitors in the mucus. Plants deficient in jasmonate biosynthesis and signalling suffered more damage by molluscan herbivores in the laboratory and in the field, demonstrating that JA-mediated defences protect A. thaliana against slugs and snails. Furthermore, experiments using A. thaliana mutants with altered levels of specific glucosinolate classes revealed the importance of aliphatic glucosinolates in defending leaves and reproductive structures against molluscs. The presence in mollusc faeces of known and novel metabolites arising from glutathione conjugation with glucosinolate hydrolysis products suggests that molluscan herbivores actively detoxify glucosinolates. Higher levels of aliphatic glucosinolates were found in plants during the night compared to the day, which correlated well with the nocturnal activity rhythms of slugs and snails. Our data highlight the function of well-known antiherbivore defence pathways in resistance against slugs and snails and suggest an important role for the diurnal regulation of defence metabolites against nocturnal molluscan herbivores.
Asunto(s)
Arabidopsis/fisiología , Ciclopentanos/metabolismo , Glucosinolatos/metabolismo , Herbivoria , Moluscos , Oxilipinas/metabolismo , Animales , Arabidopsis/metabolismo , Moluscos/metabolismo , Periodicidad , Reguladores del Crecimiento de las Plantas/metabolismoRESUMEN
BACKGROUND: Induced defense responses to herbivores are generally believed to have evolved as cost-saving strategies that defer the fitness costs of defense metabolism until these defenses are needed. The fitness costs of jasmonate (JA)-mediated defenses have been well documented. Those of the early signaling units mediating induced resistance to herbivores have yet to be examined. Early signaling components that mediate herbivore-induced defense responses in Nicotiana attenuata, have been well characterized and here we examine their growth and fitness costs during competition with conspecifics. Two mitogen-activated protein kinases (MAPKs), salicylic acid (SA)-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) are rapidly activated after perception of herbivory and both kinases regulate herbivory-induced JA levels and JA-mediated defense metabolite accumulations. Since JA-induced defenses result in resource-based trade-offs that compromise plant productivity, we evaluated if silencing SIPK (irSIPK) and WIPK (irWIPK) benefits the growth and fitness of plants competiting with wild type (WT) plants, as has been shown for plants silenced in JA-signaling by the reduction of Lipoxygenase 3 (LOX3) levels. RESULTS: As expected, irWIPK and LOX3-silenced plants out-performed their competing WT plants. Surprisingly, irSIPK plants, which have the largest reductions in JA signaling, did not. Phytohormone profiling of leaves revealed that irSIPK plants accumulated higher levels of SA compared to WT. To test the hypothesis that these high levels of SA, and their presumed associated fitness costs of pathogen associated defenses in irSIPK plants had nullified the JA-deficiency-mediated growth benefits in these plants, we genetically reduced SA levels in irSIPK plants. Reducing SA levels partially recovered the biomass and fitness deficits of irSIPK plants. We also evaluated whether the increased fitness of plants with reduced SA or JA levels resulted from increased nitrogen or CO2 assimilation rates, and found no evidence that greater intake of these fitness-limiting resources were responsible. CONCLUSIONS: Signaling mediated by WIPK, but not SIPK, is associated with large fitness costs in competing N. attenuata plants, demonstrating the contrasting roles that these two MAPKs play in regulating the plants' growth-defense balance. We discuss the role of SIPK as an important regulator of plant fitness, possibly by modulating SA-JA crosstalk as mediated through ethylene signaling.
Asunto(s)
Ciclopentanos/metabolismo , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Nicotiana/enzimología , Nicotiana/crecimiento & desarrollo , Oxilipinas/metabolismo , Proteínas de Plantas/metabolismo , Ácido Salicílico/metabolismo , Transducción de Señal , Animales , Dióxido de Carbono/metabolismo , Silenciador del Gen , Herbivoria , Manduca/fisiología , Fotosíntesis , Reguladores del Crecimiento de las Plantas/metabolismo , Hojas de la Planta/metabolismo , Plantas Modificadas Genéticamente , Semillas/metabolismoRESUMEN
How plants perceive herbivory is not yet well understood. We investigated early responses of the model plant Arabidopsis (Arabidopsis thaliana) to attack from the generalist grasshopper herbivore, Schistocerca gregaria (Caelifera). When compared with wounding alone, S. gregaria attack and the application of grasshopper oral secretions (GS) to puncture wounds elicited a rapid accumulation of various oxylipins, including 13-hydroperoxy octadecatrienoic acid, 12-oxo-phytodienoic acid (OPDA), jasmonic acid, and jasmonic acid-isoleucine. Additionally, GS increased cytosolic calcium levels, mitogen-activated protein kinase (MPK3 and MPK6) activity, and ethylene emission but not the accumulation of hydrogen peroxide. Although GS contain caeliferin A16:0, a putative elicitor of caeliferan herbivores, treatment with pure, synthetic caeliferin A16:0 did not induce any of the observed responses. With mutant plants, we demonstrate that the observed changes in oxylipin levels are independent of MPK3 and MPK6 activity but that MPK6 is important for the GS-induced ethylene release. Biochemical and pharmacological analyses revealed that the lipase activity of GS plays a central role in the GS-induced accumulation of oxylipins, especially OPDA, which could be fully mimicked by treating puncture wounds only with a lipase from Rhizopus arrhizus. GS elicitation increased the levels of OPDA-responsive transcripts. Because the oral secretions of most insects used to study herbivory-induced responses in Arabidopsis rapidly elicit similar accumulations of OPDA, we suggest that lipids containing OPDA (arabidopsides) play an important role in the activation of herbivory-induced responses.
Asunto(s)
Arabidopsis/inmunología , Insectos/enzimología , Lipasa/metabolismo , Boca/enzimología , Animales , Arabidopsis/efectos de los fármacos , Arabidopsis/enzimología , Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Ciclopentanos/metabolismo , Etilenos/metabolismo , Ácidos Grasos Insaturados/farmacología , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Saltamontes/efectos de los fármacos , Saltamontes/enzimología , Insectos/efectos de los fármacos , Quinasas de Proteína Quinasa Activadas por Mitógenos/metabolismo , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Datos de Secuencia Molecular , Oxilipinas/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Especies Reactivas de Oxígeno/metabolismoRESUMEN
BACKGROUND: The optimal defence hypothesis (ODH) predicts that tissues that contribute most to a plant's fitness and have the highest probability of being attacked will be the parts best defended against biotic threats, including herbivores. In general, young sink tissues and reproductive structures show stronger induced defence responses after attack from pathogens and herbivores and contain higher basal levels of specialized defensive metabolites than other plant parts. However, the underlying physiological mechanisms responsible for these developmentally regulated defence patterns remain unknown. SCOPE: This review summarizes current knowledge about optimal defence patterns in above- and below-ground plant tissues, including information on basal and induced defence metabolite accumulation, defensive structures and their regulation by jasmonic acid (JA). Physiological regulations underlying developmental differences of tissues with contrasting defence patterns are highlighted, with a special focus on the role of classical plant growth hormones, including auxins, cytokinins, gibberellins and brassinosteroids, and their interactions with the JA pathway. By synthesizing recent findings about the dual roles of these growth hormones in plant development and defence responses, this review aims to provide a framework for new discoveries on the molecular basis of patterns predicted by the ODH. CONCLUSIONS: Almost four decades after its formulation, we are just beginning to understand the underlying molecular mechanisms responsible for the patterns of defence allocation predicted by the ODH. A requirement for future advances will be to understand how developmental and defence processes are integrated.
Asunto(s)
Desarrollo de la Planta/inmunología , Enfermedades de las Plantas/inmunología , Reguladores del Crecimiento de las Plantas/metabolismo , Inmunidad de la Planta , Plantas/inmunología , Transducción de Señal/genética , Herbivoria , Componentes Aéreos de las Plantas/genética , Componentes Aéreos de las Plantas/inmunología , Componentes Aéreos de las Plantas/metabolismo , Plantas/genética , Plantas/metabolismoRESUMEN
⢠SGT1 (suppressor of G-two allele of SKP1) is a conserved protein in all eukaryotes and is crucial for resisting pathogens in humans and plants. We studied whether SGT1 is involved in the induced defense response of a native tobacco (Nicotiana attenuata) to its natural herbivore, Manduca sexta. ⢠We diminished NaSGT1 transcription in N. attenuata using virus-induced gene silencing (VIGS) and analysed the induced defense responses after wounding and M. sexta elicitation. ⢠Silencing NaSGT1 highly attenuates wounding- and herbivory-induced amounts of jasmonic acid (JA) and JA-isoleucine but elevates the concentration of salicylic acid. Chemical profiling reveals that NaSGT1-silenced plants are also compromised in their ability to accumulate JA precursors produced in chloroplasts. We show that the reduced JA accumulation in NaSGT1-silenced plants is independent of the elevated salicylic acid levels. NaSGT1-silenced plants have decreased contents of defensive metabolites and have compromised resistance to M. sexta larvae. Transcript analyses after methyl jasmonate (MeJA) treatment revealed that NaSGT1 is important for the normal regulation of MeJA-induced transcriptional responses. ⢠This work demonstrates the importance of SGT1 in the regulatory network that deploys defense responses against herbivores, and highlights the significance of SGT1 in plants' responses to JA.
Asunto(s)
Ciclopentanos/metabolismo , Conducta Alimentaria/fisiología , Inmunidad Innata , Manduca/fisiología , Nicotiana/parasitología , Oxilipinas/metabolismo , Enfermedades de las Plantas/inmunología , Proteínas de Plantas/metabolismo , Animales , Ciclopentanos/farmacología , Conducta Alimentaria/efectos de los fármacos , Silenciador del Gen/efectos de los fármacos , Inmunidad Innata/efectos de los fármacos , Manduca/efectos de los fármacos , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Modelos Biológicos , Oxilipinas/farmacología , Enfermedades de las Plantas/parasitología , Ácido Salicílico/metabolismo , Nicotiana/efectos de los fármacos , Nicotiana/enzimología , Nicotiana/genética , Transcripción Genética/efectos de los fármacosRESUMEN
Salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) are activated by Manduca sexta attack and elicitors to mediate defense signaling in Nicotiana attenuata. Here, the ecological consequences of SIPK and WIPK silencing for N. attenuata's resistance to M. sexta and its other native herbivores were analyzed. Stably transformed plants with reduced expression of NaSIPK (irNaSIPK) and NaWIPK(irNaWIPK) were generated and characterized in field and glasshouse experiments. Both irNaSIPK and irNaWIPK plants had reduced direct and indirect defenses but were not particularly susceptible in nature. In the glasshouse, M. sexta larvae consumed less and gained the same mass on irNaSIPK and irNaWIPK as on wild-type (WT) plants. Green leaf volatile (GLV) emission was highly attenuated in irNaSIPK and irNaWIPK plants, and complementation with synthetic GLVs increased M. sexta performance. To test the hypothesis that reduced GLV emissions account for the lack of herbivory phenotype, GLV emissions were attenuated by silencing NaHPL in jasmonate-deficient plants (asNaLOX3), which are highly susceptible to herbivores. Reducing GLV emissions in asNaLOX3 plants 'rescued' these plants from being heavily damaged by M. sexta. GLV emissions in irNaSIPK and irNaWIPK plants may compensate for the impaired defenses of NaSIPK- and NaWIPK-silenced plants in nature by reducing their apparency to herbivores.
Asunto(s)
Regulación de la Expresión Génica de las Plantas , Expresión Génica , Silenciador del Gen , Manduca , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Nicotiana/enzimología , Proteínas de Plantas/metabolismo , Animales , Ciclopentanos/farmacología , Conducta Alimentaria , Proteínas Quinasas Activadas por Mitógenos/genética , Nicotina , Aceites Volátiles , Oxilipinas/farmacología , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Nicotiana/genéticaRESUMEN
Endophytic insects provide the textbook examples of herbivores that manipulate their host plant's physiology, putatively altering source/sink relationships by transferring cytokinins (CK) to create 'green islands' that increase the nutritional value of infested tissues. However, unambiguous demonstrations of CK transfer are lacking. Here we show that feeding by the free-living herbivore Tupiocoris notatus on Nicotiana attenuata is characterized by stable nutrient levels, increased CK levels and alterations in CK-related transcript levels in attacked leaves, in striking similarity to endophytic insects. Using 15N-isotope labeling, we demonstrate that the CK N6-isopentenyladenine (IP) is transferred from insects to plants via their oral secretions. In the field, T. notatus preferentially attacks leaves with transgenically increased CK levels; plants with abrogated CK-perception are less tolerant of T. notatus feeding damage. We infer that this free-living insect uses CKs to manipulate source/sink relationships to increase food quality and minimize the fitness consequences of its feeding.
Asunto(s)
Citocininas/metabolismo , Endófitos/crecimiento & desarrollo , Endófitos/metabolismo , Insectos/crecimiento & desarrollo , Insectos/metabolismo , Nicotiana/efectos de los fármacos , Nicotiana/parasitología , Animales , Transporte Biológico , Perfilación de la Expresión Génica , Interacciones Huésped-Parásitos , Isopenteniladenosina/metabolismo , Marcaje Isotópico , Isótopos de Nitrógeno/análisis , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/parasitologíaRESUMEN
Plant genetic diversity structures animal communities and affects plant population productivity. However, few studies have investigated which traits are involved and the mechanisms mediating these effects. We studied the consequences of varying the expression of a single biosynthetic gene in jasmonate (JA) defense hormones, which are essential for defense against herbivores but constrain plant growth, in experimental mesocosm populations of wild tobacco (Nicotiana attenuata) plants under attack from three native herbivores. Empoasca leafhoppers preferentially attack JA-deficient N. attenuata plants in nature, and the specialist Tupiocoris notatus mirids avoid Empoasca-damaged plants. However, in experimental mesocosm populations having equal numbers of wild-type (WT) and JA-deficient plants that are silenced in the expression of the biosynthetic gene lipoxygenase 3 (LOX3), Empoasca sp. attacked both genotypes. Empoasca sp. damage, rather than JA, determined T. notatus damage, which was reduced in mixed populations. The growth of specialist Manduca sexta larvae was reduced on WT vs. asLOX3 monocultures, but differed in mixtures depending on caterpillar density. However, seed capsule number remained similar for WT and asLOX3 plants in mixtures, not in monocultures, in two experimental scenarios reflecting high and low caterpillar attack. At high caterpillar density, WT plants growing in mixtures produced more seed capsules than those growing in monocultures while seed production of asLOX3 plants did not differ by population type. However, at low caterpillar density, asLOX3 plants growing in mixed populations produced more seed capsules than those growing in monoculture, while seed capsule production did not differ for WT by population type. Thus, mixed populations had a more stable output of seed capsules under the two scenarios. This may result from a balance between JA-mediated herbivore defense and plant competitive ability in mixed populations.
Asunto(s)
Hemípteros/fisiología , Herbivoria , Lipooxigenasa , Manduca/fisiología , Nicotiana , Proteínas de Plantas , Animales , Larva/fisiología , Lipooxigenasa/genética , Lipooxigenasa/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Nicotiana/enzimología , Nicotiana/genética , Nicotiana/crecimiento & desarrolloRESUMEN
The jasmonate hormones are essential regulators of plant defense against herbivores and include several dozen derivatives of the oxylipin jasmonic acid (JA). Among these, the conjugate jasmonoyl isoleucine (JA-Ile) has been shown to interact directly with the jasmonate co-receptor complex to regulate responses to jasmonate signaling. However, functional studies indicate that some aspects of jasmonate-mediated defense are not regulated by JA-Ile. Thus, it is not clear whether JA-Ile is best characterized as the master jasmonate regulator of defense, or if it regulates more specific aspects. We investigated possible functions of JA-Ile in anti-herbivore resistance of the wild tobacco Nicotiana attenuata, a model system for plant-herbivore interactions. We first analyzed the soluble and volatile secondary metabolomes of irJAR4xirJAR6, asLOX3, and WT plants, as well as an RNAi line targeting the jasmonate co-receptor CORONATINE INSENSITIVE 1 (irCOI1), following a standardized herbivory treatment. irJAR4xirJAR6 were the most similar to WT plants, having a ca. 60% overlap in differentially regulated metabolites with either asLOX3 or irCOI1. In contrast, while at least 25 volatiles differed between irCOI1 or asLOX3 and WT plants, there were few or no differences in herbivore-induced volatile emission between irJAR4xirJAR6 and WT plants, in glasshouse- or field-collected samples. We then measured the susceptibility of jasmonate-deficient vs. JA-Ile-deficient plants in nature, in comparison to wild-type (WT) controls, and found that JA-Ile-deficient plants (irJAR4xirJAR6) are much better defended even than a mildly jasmonate-deficient line (asLOX3). The differences among lines could be attributed to differences in damage from specific herbivores, which appeared to prefer either one or the other jasmonate-deficient phenotype. We further investigated the elicitation of one herbivore-induced volatile known to be jasmonate-regulated and to mediate resistance to herbivores: (E)-α-bergamotene. We found that JA was a more potent elicitor of (E)-α-bergamotene emission than was JA-Ile, and when treated with JA, irJAR4xirJAR6 plants emitted 20- to 40-fold as much (E)-α-bergamotene than WT. We conclude that JA-Ile regulates specific aspects of herbivore resistance in N. attenuata. This specificity may allow plants flexibility in their responses to herbivores and in managing trade-offs between resistance, vs. growth and reproduction, over the course of ontogeny.
RESUMEN
Although many established tools for cytokinin (CK) pathway manipulations are well suitable for the analysis of molecular interactions, their use on a whole plant scale is often limited by the induction of severe developmental defects. To circumvent this problem, different methods were developed that allow for a more precise manipulation of the CK pathway. Here we present one of these systems, the pOp6/LhGR system for chemically inducible gene expression. This system allows regulation on a spatial, temporal, and quantitative scale and therefore provides a superior tool for analyzing the role of CKs in the interactions of plants with their environment. The pOp6/LhGR system was tested for RNAi-mediated gene silencing and heterologous gene expression and was successfully used for CK pathway manipulations in different model organisms (Arabidopsis thaliana, Nicotiana tabaccum, Nicotiana attenuata, Citrus sinensis × C. trifoliate). Here we describe specific aspects of the screening procedure and present an experimental setup that can not only be used in the laboratory but is also applicable under field conditions.
Asunto(s)
Citocininas/metabolismo , Ingeniería Genética , Plantas/genética , Plantas/metabolismo , Transducción de Señal , Regulación de la Expresión Génica de las Plantas , Pruebas Genéticas , Herbivoria , Fenotipo , Plantas Modificadas GenéticamenteRESUMEN
BACKGROUND: Although leaf herbivory-induced changes in allocation of recently assimilated carbon between the shoot and below-ground tissues have been described in several species, it is still unclear which part of the root system is affected by resource allocation changes and which signalling pathways are involved. We investigated carbon partitioning in root tissues following wounding and simulated leaf herbivory in young Nicotiana attenuata plants. RESULTS: Using 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG), which was incorporated into disaccharides in planta, we found that simulated herbivory reduced carbon partitioning specifically to the root tips in wild type plants. In jasmonate (JA) signalling-deficient COI1 plants, the wound-induced allocation of [(18)F]FDG to the roots was decreased, while more [(18)F]FDG was transported to young leaves, demonstrating an important role of the JA pathway in regulating the wound-induced carbon partitioning between shoots and roots. CONCLUSIONS: Our data highlight the use of [(18)F]FDG to study stress-induced carbon allocation responses in plants and indicate an important role of the JA pathway in regulating wound-induced shoot to root signalling.
Asunto(s)
Carbono/metabolismo , Fluorodesoxiglucosa F18/metabolismo , Nicotiana/metabolismo , Hojas de la Planta/metabolismo , Raíces de Plantas/metabolismo , Animales , Autorradiografía , Ciclopentanos/metabolismo , Disacáridos/biosíntesis , Herbivoria , Especificidad de Órganos , Oxilipinas/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Radiofármacos/metabolismo , Transducción de Señal , Estrés FisiológicoRESUMEN
Slugs and snails specifically secrete mucus to aid their locomotion. This mucus is the contact material between molluscan herbivores and plants. We have recently shown that the locomotion mucus of the slug Deroceras reticulatum contains salicylic acid (SA).(1) When applied to wounded leaves of Arabidopsis thaliana this mucus induces the activity of the SA-responsive pathogenesis related 1 (PR1) promotor1. Here we analyzed PR1 promotor activity in response to treatments with locomotion mucus of eight slugs and snails. Although none of the mucus contained SA, their application still elicited PR1 promotor activity. These data provide further insights into the complex interactions between molluscan herbivores and plants.