Biomedical subjects

Rayko Halitschke

Publications and source records attributed to Rayko Halitschke.

11 recordsLinked to original sources

PubMed2006

Volatile signaling in plant-plant interactions: "talking trees" in the genomics era.

Plants may "eavesdrop" on volatile organic compounds (VOCs) released by herbivore-attacked neighbors to activate defenses before being attacked themselves. Transcriptome and signal cascade analyses of VOC-exposed plants suggest that plants eavesdrop to prime direct and indirect defenses and to hone competitive abilities. Advances in research on VOC biosynthesis and perception have facilitated the production of plants that are genetically "deaf" to particular VOCs or "mute" in elements of their volatile vocabulary. Such plants, together with advances in VOC analytical instrumentation, will allow researchers to determine whether fluency enhances the fitness of plants in natural communities.

Adaptation, Physiological↗

PubMed2006

Priming of plant defense responses in nature by airborne signaling between Artemisia tridentata and Nicotiana attenuata.

Plants release volatile organic compounds (VOCs) in response to wounding and herbivore attack, some of which trigger responses in neighboring unattacked plants in the laboratory under conditions that are not likely to occur in the real world. Whether plants 'eavesdrop' on the volatile emissions of their neighbors in nature is not known. The best documented field study of between-species signaling via above-ground VOCs involves increases in fitness parameters of native tobacco (Nicotiana attenuata) transplanted adjacent to clipped sagebrush (Artemesia tridentata tridentata). Clipped sagebrush releases many biologically active VOCs, including methyl jasmonate (MeJA), methacrolein and a series of terpenoid and green leaf VOCs, of which MeJA, while active under laboratory conditions, is not released in sufficient quantities to directly elicit induced resistance in the field. Here we demonstrate, with laboratory and field-based experiments, that priming (rather than direct elicitation) of native N. attenuata's induced chemical defenses by a sagebrush-released VOC bouquet can account for earlier findings. With microarrays enriched in N. attenuata herbivore-regulated genes, we found transcriptional responses in tobacco growing adjacent to clipped sagebrush foliage, but failed to detect the direct elicitation of defensive chemicals or proteins. However, we observed an accelerated production of trypsin proteinase inhibitors when Manduca sexta caterpillars fed on plants previously exposed to clipped sagebrush. This readying of a defense response, termed priming, results in lower total herbivore damage to plants exposed to clipped sagebrush and in a higher mortality rate of young Manduca caterpillars. Our study demonstrates priming of plant defense responses as a mechanism of plant-plant signaling in nature, and provides an example for the analysis of between-plant signaling under ecologically realistic conditions. Although we describe priming as a potential mechanism for signaling between plants in nature, we critically discuss the ecological relevance of the particular interaction.

Animals↗

PubMed2006

Using 'mute' plants to translate volatile signals.

When attacked by herbivores, plants release volatile organic compounds (VOCs) that attract natural enemies of the herbivores and function as indirect defenses. Whether or not neighboring plants 'eavesdrop' on these VOCs remains controversial because most studies use unrealistic experimental conditions and VOC exposures. In order to manipulate exposures of wild-type (WT) Nicotiana attenuata'receiver' plants, we elicited transformed 'emitter' plants, whose production of herbivore-induced C6 green leaf volatiles (GLVs) or terpenoid volatiles was genetically silenced, and placed them up-wind of WT 'receiver' plants in open-flow experimental chambers. We compared the transcriptional and secondary metabolite defense responses of WT receiver plants exposed to VOCs from these transgenic emitter plants with those of plants exposed to VOCs from WT emitter plants. No differences in the constitutive accumulation of defense metabolites and the signal molecule jasmonic acid (JA) were found. Additional elicitation of receiver plants revealed that exposure to WT, GLV-deficient and terpenoid-deficient volatile blends did not prime induced defenses, JA accumulation, or the expression of lipoxygenase 3 (NaLOX3), a gene involved in JA biosynthesis. However, exposure to wound- and herbivore-induced VOCs significantly altered the transcriptional patterns in receiver plants. We identified GLV-dependent genes by complementing the GLV-deficient volatile blend with a mixture of synthetic GLVs. Blends deficient in GLVs or cis-alpha-bergamotene regulated numerous genes in receiver plants that did not respond to the complete VOC blends of WT emitters, indicating a suppressive effect of GLVs and terpenoids. Whether these transcriptional responses translate into changes in plant fitness in nature remains to be determined.

Organic Chemicals↗

PubMed2004

Nicotine's defensive function in nature.

Plants produce metabolites that directly decrease herbivore performance, and as a consequence, herbivores are selected for resistance to these metabolites. To determine whether these metabolites actually function as defenses requires measuring the performance of plants that are altered only in the production of a certain metabolite. To date, the defensive value of most plant resistance traits has not been demonstrated in nature. We transformed native tobacco(Nicotiana attenuata) with a consensus fragment of its two putrescine N-methyl transferase (pmt) genes in either antisense or inverted-repeat (IRpmt) orientations. Only the latter reduced (by greater than 95%) constitutive and inducible nicotine. With D(4)-nicotinic acid (NA), we demonstrate that silencing pmt inhibits nicotine production, while the excess NA dimerizes to form anatabine. Larvae of the nicotine-adapted herbivore Manduca sexta (tobacco hornworm) grew faster and, like the beetle Diabrotica undecimpunctata, preferred IRpmt plants in choice tests. When planted in their native habitat, IRpmt plants were attacked more frequently and, compared to wild-type plants, lost 3-fold more leaf area from a variety of native herbivores, of which the beet armyworm, Spodoptera exigua, and Trimerotropis spp. grasshoppers caused the most damage. These results provide strong evidence that nicotine functions as an efficient defense in nature and highlights the value of transgenic techniques for ecological research.

Animals↗

PubMed2004

Silencing the jasmonate cascade: induced plant defenses and insect populations.

We transformed the native tobacco, Nicotiana attenuata, to silence its lipoxygenase, hydroperoxide lyase, and allene oxide synthase genes in order to inhibit oxylipin signaling, known to mediate the plant's direct and indirect defenses. When planted into native habitats, lipoxygenase-deficient plants were more vulnerable to N. attenuata's adapted herbivores but also attracted novel herbivore species, which fed and reproduced successfully. In addition to highlighting the value of genetically silencing plants to study ecological interactions in nature, these results show that lipoxygenase-dependent signaling determines host selection for opportunistic herbivores and that induced defenses influence herbivore community composition.

Acetates↗

PubMed2004

Individual variability in herbivore-specific elicitors from the plant's perspective.

Lepidopteran larvae oral secretions and regurgitant (R), which contain a plethora of potential elicitors, are known to dramatically change a plant's wound response. We demonstrate, with a detailed microarray and secondary metabolite analysis, that the two most abundant fatty acid-amino acid conjugates (FACs) in the R of the specialist herbivore Manduca sexta (Lepidoptera, Sphingidae) can account for all measured direct (trypsin proteinase inhibitor: TPI) and indirect (cis-alpha-bergamotene) defences, the endogenous jasmonic acid burst that elicits them, and 86% of the induced transcriptional changes (89% up and 83% down) in its native host Nicotiana attenuata and hence are necessary and sufficient for the Manduca-specific modulation of the wound response. FACs were not found in eggs, but detected in larvae of all instars after their first meal. FACs were found in all regions of the alimentary canal and in the frass, but did not occur in salivary or mandibular glands, extracts of which were not active in any assay. Individual larvae differed substantially in their FAC composition and two FAC chemotypes were discernible: N-linolenoyl-L-glutamine biased R and N-linolenoyl-L-glutamate biased R. We created synthetic blends of FACs to mimic these chemical phenotypes and determined whether plants respond differently to the different R chemotypes. Micorarray and TPI analysis revealed that plants do not differentiate. N. attenuata plants use FACs from feeding caterpillars to tailor their wound responses but do not use the variability in FAC ratios to recognize attack from an individual caterpillar.

Animals↗

PubMed2004

Silencing of hydroperoxide lyase and allene oxide synthase reveals substrate and defense signaling crosstalk in Nicotiana attenuata.

The fatty acid hydroperoxide (HP) substrates required for the biosynthesis of jasmonic acid (JA) and green leaf volatiles (GLVs) are supplied by separate lipoxygenases (LOX). We silenced the expression of two genes downstream of the LOX: allene oxide synthase (AOS) and HP lyase (HPL) by antisense expression of endogenous genes (NaAOS, NaHPL) in Nicotiana attenuata, in which the biosynthesis of JA is amplified by herbivore-specific elicitors. We report that these elicitors also amplify wound-induced GLV releases, but suppress the wound-induced increase of NaHPL transcripts, suggesting that substrate flux controls GLV biosynthesis. As expected, silencing of NaHPL and NaAOS reduced GLV release and JA accumulation, respectively. Surprisingly, HPL- and AOS-silenced plants had enhanced JA and GLV responses, suggesting substrate 'crosstalk' between these two oxylipin cascades. Plants with depleted GLVs (as-hpl) were less attractive than wild type (WT) or empty vector control plants in choice-tests with native lepidopteran herbivores. In feeding trials, Manduca sexta larvae developed slower on as-hpl plants. The reduced larval consumption and performance, which was not caused by increases in defense responses in as-hpl plants, could be restored to WT levels by the addition of synthetic GLVs, demonstrating that GLVs function as feeding stimulants. Gene expression profiling by cDNA microarray analysis and characterization of several induced defenses in herbivore-elicited as-hpl and as-aos plants revealed differential involvement of JA and GLVs in defense signaling. Elicitation of volatile terpenoids (an indirect defense) requires JA signaling, where as trypsin protease inhibitor elicitation (a direct defense) requires both functional JA and GLV cascades.

Aldehyde-Lyases↗

PubMed2003

Antisense LOX expression increases herbivore performance by decreasing defense responses and inhibiting growth-related transcriptional reorganization in Nicotiana attenuata.

Inhibition of jasmonic acid (JA) signaling has been shown to decrease herbivore resistance, but the responsible mechanisms are largely unknown because insect resistance is poorly understood in most model plant systems. We characterize three members of the lipoxygenase (LOX) gene family in the native tobacco plant Nicotiana attenuata and manipulate, by antisense expression, a specific, wound- and herbivory-induced isoform (LOX3) involved in JA biosynthesis. In three independent lines, antisense expression reduced wound-induced JA accumulation but not the release of green leaf volatiles (GLVs). The impaired JA signaling reduced two herbivore-induced direct defenses, nicotine and trypsin protease inhibitors (TPI), as well as the potent indirect defense, the release of volatile terpenes that attract generalist predators to feeding herbivores. All these defenses could be fully restored by methyl-JA (MeJA) treatment, with the exception of the increase in TPI activity, which was partially restored, suggesting the involvement of additional signals. The impaired ability to produce chemical defenses resulted in lower resistance to Manduca sexta attack, which could also be restored by MeJA treatment. Expression analysis using a cDNA microarray, specifically designed to analyze M. sexta-induced gene expression in N. attenuata, revealed a pivotal role for LOX3-produced oxylipins in upregulating defense genes (protease inhibitor, PI; xyloglucan endotransglucosylase/hydrolase, XTH; threonine deaminase, TD; hydroperoxide lyase, HPL), suppressing both downregulated growth genes (RUBISCO and photosystem II, PSII) and upregulated oxylipin genes (alpha-dioxygenase, alpha-DOX). By genetically manipulating signaling in a plant with a well-characterized ecology, we demonstrate that the complex phenotypic changes that mediate herbivore resistance are controlled by a specific part of the oxylipin cascade.

Animals↗

PubMed2003

Molecular interactions between the specialist herbivore Manduca sexta (lepidoptera, sphingidae) and its natural host Nicotiana attenuata. VI. Microarray analysis reveals that most herbivore-specific transcriptional changes are mediated by fatty acid-amino acid conjugates.

Evidence is accumulating that insect-specific plant responses are mediated by constituents in the oral secretions and regurgitants (R) of herbivores, however the relative importance of the different potentially active constituents remains unclear. Fatty acid-amino acid conjugates (FACs) are found in the R of many insect herbivores and have been shown to be necessary and sufficient to elicit a set of herbivore-specific responses when the native tobacco plant Nicotiana attenuata is attacked by the tobacco hornworm, Manduca sexta. Attack by this specialist herbivore results in a large transcriptional reorganization in N. attenuata, and 161 genes have been cloned from previous cDNA differential display-polymerase chain reaction and subtractive hybridization with magnetic beads analysis. cDNAs of these genes, in addition to those of 73 new R-responsive genes identified by cDNA-amplified fragment-length polymorphism display of R-elicited plants, were spotted on polyepoxide coated glass slides to create microarrays highly enriched in Manduca spp.- and R-induced genes. With these microarrays, we compare transcriptional responses in N. attenuata treated with R from the two most damaging lepidopteran herbivores of this plant in nature, M. sexta and Manduca quinquemaculata, which have very similar FAC compositions in their R, and with the two most abundant FACs in Manduca spp. R. More than 68% of the genes up- and down-regulated by M. sexta R were similarly regulated by M. quinquemaculata R. A majority of genes up-regulated (64%) and down-regulated (49%) by M. sexta R were similarly regulated by treatment with the two FACs. In contrast, few genes showed similar transcriptional changes after H(2)O(2)- and R-treatment. These results demonstrate that the two most abundant FACs in Manduca spp. R can account for the majority of Manduca spp.-induced alterations of the wound response of N. attenuata.

Amino Acids↗

PubMed2002

Volatile signaling in plant-plant-herbivore interactions: what is real?

Plants release volatiles after herbivore attack in a highly regulated fashion. These compounds attract natural enemies and function as indirect defenses. Whether neighboring plants 'eavesdrop' on these volatile signals and tailor their defenses accordingly remains controversial. Recent laboratory studies have identified transcriptional changes that occur in plants in response to certain volatiles. These changes occur under conditions that enhance the probability of signal perception and response. Field studies have demonstrated repeatable increases in the herbivore resistance of plants growing downwind of damaged plants.

Animals↗

PubMed2002

A knock-out mutation in allene oxide synthase results in male sterility and defective wound signal transduction in Arabidopsis due to a block in jasmonic acid biosynthesis.

Recent studies on jasmonic acid (JA) biosynthetic mutants have shown that jasmonates play essential roles in pollen maturation and dehiscence and wound-induced defence against biotic attacks. To better understand the biosynthetic mechanisms of this essential plant hormone, we isolated an Arabidopsis knock-out mutant defective in the JA biosynthetic gene CYP74A (allene oxide synthase, AOS) using reverse genetics screening methods. This enzyme catalyses dehydration of the hydroperoxide to an unstable allene oxide in the JA biosynthetic pathway. Endogenous JA levels, which increase 100-fold 1 h after wounding in wild-type plants, do not increase after wounding in the aos mutant. In addition, the mutant showed severe male sterility due to defects in anther and pollen development. The male-sterile phenotype was completely rescued by exogenous application of methyl jasomonate and by complementation with constitutive expression of the AOS gene. RT-PCR analysis showed that the induction of transcripts for vegetative storage protein and lipoxygenase genes, previously shown to be inducible by wound and jasmonate application in the wild-type, was absent in the aos mutant. In transgenic plants constitutively expressing AOS, wound-induced JA levels were 50-100% higher compared to wild-type plants. Taken together with JA deficiency in the aos mutant, our results show that AOS is critical for the biosynthesis of all biologically active jasmonates. Our results also suggest that AOS expression is limiting JA levels in wounded plants, but that the AOS hydroperoxide substrate levels, controlled by upstream enzymes (lipoxygenase and phospholipase), determine JA levels in unwounded plants.

Arabidopsis↗