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Green leaf volatiles (GLVs) play pivotal roles in plant anti-herbivore defense. This study investigated whether the rice 13-lipoxygense gene OsRCI-1 is involved in GLV production and plant defense in rice. The overexpression of OsRCI-1 (oeRCI lines) in rice resulted in increased wound-induced levels of two prominent GLVs, cis-3-hexen-1-ol and cis-3-hexenal. In a previous study, we found that the overexpression of OsRCI-1 reduced the colonization by the rice brown planthopper (BPH, Nilaparvata lugens) but increased the attractiveness to the egg parasitoid Anagrus nilaparvatae compared to wild-type (WT) plants. This study found that when cis-3-hexen-1-ol, but not cis-3-hexenal, was added to WT plants, it could change the BPH's colonization preference, i.e., more BPHs preferred to colonize the oeRCI lines. The exogenous application of cis-3-hexen-1-ol or cis-3-hexenal to BPH-infested WT plants could weaken or overturn the preference of A. nilaparvatae for oeRCI lines. However, field experiments revealed that only cis-3-hexenal was attractive to the parasitoid and increased the parasitism rates of BPH eggs. These results indicate that OsRCI-1 is involved in rice GLV production and therefore modulates both direct and indirect defense in rice. [ABSTRACT FROM AUTHOR]

The ATP-dependent caseinolytic protease (Clp) system has been reported to play an important role in plant growth, development, and defense against pathogens. However, whether the Clp system is involved in plant defense against herbivores remains largely unclear. We explore the role of the Clp system in rice defenses against brown planthopper (BPH) Nilaparvata lugens by combining chemical analysis, transcriptome, and molecular analyses, as well as insect bioassays. We found the expression of a rice Clp proteolytic subunit gene, OsClpP6, was suppressed by infestation of BPH gravid females and mechanical wounding. Silencing OsClpP6 enhanced the level of BPH-induced jasmonic acid (JA), JA-isoleucine (JA-Ile), and ABA, which in turn promoted the production of BPH-elicited rice volatiles and increased the resistance of rice to BPH. Field trials showed that silencing OsClpP6 decreased the population densities of BPH and WBPH. We also observed that silencing OsClpP6 decreased chlorophyll content in rice leaves at early developmental stages and impaired rice root growth and seed setting rate. These findings demonstrate that an OsClpP6-mediated Clp system in rice was involved in plant growth-defense trade-offs by affecting the biosynthesis of defense-related signaling molecules in chloroplasts. Moreover, rice plants, after recognizing BPH infestation, can enhance rice resistance to BPH by decreasing the Clp system activity. The work might provide a new way to breed rice varieties that are resistant to herbivores. [ABSTRACT FROM AUTHOR]

Chemical elicitors can increase plant defense against herbivorous insects and pathogens. The use of synthetic chemical elicitors is likely to be an alternative to traditional pesticides for crop pest control. However, only a few synthetic chemicals are reported to protect plants by regulating signaling pathways, increasing the levels of defense metabolites and interfering with insect feeding. Here, we found that the exogenous application of a phenoxycarboxylic compound, 4-chlorophenoxyacetic acid (4-CPA), can induce chemical defenses to protect rice plants from white-backed planthoppers (WBPH, Sogatella furcifera). Four-CPA was rapidly taken up by plant roots and degraded to 4-chlorophenol (4-CP). Four-CPA treatment modulated the activity of peroxidase (POD) and directly induced the deposition of lignin-like polymers using hydrogen peroxide (H2O2) as the electron acceptor. The polymers, which are thought to prevent the planthopper's stylet from reaching the phloem, were broken down by WBPH nymphs. Meanwhile, 4-CPA increased the levels of flavonoids and phenolamines (PAs). The increased flavonoids and PAs, together with the degradation product of the polymers, avoided nymphal feeding and prolonged the nymphal period for 1 day. These results indicate that 4-CPA has the potential to be used as a chemical elicitor to protect rice from planthoppers. Moreover, these findings also open a pathway for molecule structure design of phenoxycarboxylic compounds as chemical elicitors. [ABSTRACT FROM AUTHOR]

The pathway mediated by jasmonic acid (JA), biosynthesized via 13‐lipoxygenases (LOX), plays a central role in both plant development and defense. In rice, there are at least fourteen 13‐LOXs. Yet, only two 13‐LOXs have been known to be involved in the biosynthesis of JA and plant defenses in rice. Here we cloned a chloroplast‐localized 13‐LOX gene from rice, OsRCI‐1, whose transcripts were upregulated following infestation by brown planthopper (BPH, Nilaparvata lugens), one of the most important pests in rice. Overexpression of OsRCI‐1 (oeRCI lines) increased levels of BPH‐induced JA, jasmonate‐isoleucine, trypsin protease inhibitors and three volatile compounds, 2‐heptanone, 2‐heptanol and α‐thujene. BPHs showed a decreased colonization, fecundity and mass, and developed slowly on oeRCI plants compared with wild‐type (WT) plants. Moreover, BPH‐infested oeRCI plants were more attractive to the egg parasitoid of BPH, Anagrus nilaparvatae than equally treated WT plants. The decreased attractiveness to BPH and enhanced attractiveness to the parasitoid of oeRCI plants correlated with higher levels of BPH‐induced 2‐heptanone and 2‐heptanol, and 2‐heptanone, respectively. Compared with oeRCI plants, WT plants had higher plant height and 1000‐grain weight. These results indicate that OsRCI‐1 is involved in herbivore‐induced JA bursts and plays a role in plant defense and growth. We demonstrate that a chloroplast‐localized 13‐lipoxygenase gene OsRCI‐1 in rice, whose expression is induced by brown planthopper (BPH) infestation, is involved in BPH‐induced JA bursts and plays a role in plant defense and growth. [ABSTRACT FROM AUTHOR]

Summary: Phytohormone, particularly jasmonate (JA) and salicylate (SA) signaling, plays a central role in plant responses to herbivore and pathogen attack. Generally, SA mediates resistance responses against biotrophic pathogens and phloem‐feeding insects, while JA mediates responses against necrotrophic pathogens and chewing insects. The phytohormonal responses mediating rice resistance to a piercing‐sucking herbivore, the brown planthopper (BPH), remains unknown.Here, we combined transcriptome analysis, hormone measurements, genetic analysis and a field study to address this issue.Infestation by BPH adult females resulted in significant transcriptional reprograming. The upregulated genes were enriched in the JA signaling pathway. Consistently, the concentrations of JAs, but not SA, were dramatically increased in response to BPH attack. Two JA‐deficient lines (AOC and MYC2 knockout) and two SA‐deficient lines (nahG overexpression and NPR1 knockout) were constructed. BPH performed better on JA‐deficient lines than on wild‐type (WT) plants, but similarly on SA‐deficient and WT plants. During BPH attack, the accumulation of defensive secondary metabolites was attenuated in JA‐deficient lines compared with WT plants. Moreover, MYC2 mutants were more susceptible to planthoppers than WT plants in nature.This study reveals that JA signaling functions in rice defense against BPH. [ABSTRACT FROM AUTHOR]

DELLA proteins, negative regulators of the gibberellin (GA) pathway, play important roles in plant growth, development and pathogen resistance by regulating multiple phytohormone signals. Yet, whether and how they regulate plant herbivore resistance remain unknown. We found that the expression of the rice DELLA gene OsSLR1 was down-regulated by an infestation of female adults of the brown planthopper (BPH) Nilaparvata lugens. On one hand, OsSLR1 positively regulated BPH-induced levels of two mitogen-activated protein kinase and four WRKY transcripts, and of jasmonic acid, ethylene and H2O2. On the other hand, silencing OsSLR1 enhanced constitutive levels of defence-related compounds, phenolic acids, lignin and cellulose, as well as the resistance of rice to BPH in the laboratory and in the field. The increased resistance in rice with silencing of OsSLR1 is probably due to impaired JA and ethylene pathways, and, at least in part, to the increased lignin level and mechanical hardness of rice leaf sheaths. Our findings illustrate that OsSLR1, acting as an early negative regulator, plays an important role in regulating the resistance of rice to BPH by activating appropriate defence-related signalling pathways and compounds. Moreover, our data also provide new insights into relationships between plant growth and defence. [ABSTRACT FROM AUTHOR]

Jasmonic acid (JA) and related metabolites play a key role in plant defense and growth. JA carboxyl methyltransferase (JMT) may be involved in plant defense and development by methylating JA to methyl jasmonate (MeJA) and thus influencing the concentrations of JA and related metabolites. However, no JMT gene has been well characterized in monocotyledon defense and development at the molecular level. After we cloned a rice JMT gene, OsJMT1, whose encoding protein was localized in the cytosol, we found that the recombinant OsJMT1 protein catalyzed JA to MeJA. OsJMT1 is up-regulated in response to infestation with the brown planthopper (BPH; Nilaparvata lugens). Plants in which OsJMT1 had been overexpressed (oe-JMT plants) showed reduced height and yield. These oe-JMT plants also exhibited increased MeJA levels but reduced levels of herbivore-induced JA and jasmonoyl-isoleucine (JA-Ile). The oe-JMT plants were more attractive to BPH female adults but showed increased resistance to BPH nymphs, probably owing to the different responses of BPH female adults and nymphs to the changes in levels of H2O2 and MeJA in oe-JMT plants. These results indicate that OsJMT1, by altering levels of JA and related metabolites, plays a role in regulating plant development and herbivore-induced defense responses in rice. [ABSTRACT FROM AUTHOR]

Green leaf volatiles (GLVs), the products of the hydroperoxide lyase (HPL) branch of the oxylipin pathway, play important roles in plant defense responses to both insect pests and pathogens. However, little is known about the role of GLVs in the defense responses of rice to the white-backed planthopper (WBPH, Sogatella furcifera (Horváth)). Here, we found that the rice HPL gene OsHPL3 was upregulated in response to infestation by WBPH adults and nymphs. Using an Agrobacterium-mediated transformation system, we obtained two homozygous lines with an antisense expression vector of OsHPL3 (as- hpl) and a single insertion that reduced the gene's expression by 48.31-52.56 %. Biochemical assays revealed that as- hpl lines had lower wound-induced GLV levels, mainly ( Z)-3-hexenal, ( Z)-3-hexen-1-ol, and ( E)-2-hexenal, but higher JA levels, compared to wild-type (WT) plants. Biological assays showed that WBPH adult females and nymphs preferred to settle and/or oviposit on WT plants, where they survived better than on as- hpl plants. In addition, both male and female WBPH nymphs fed on as- hpl plants performed less well: they developed more slowly, and pairs subsequently laid fewer eggs compared to pairs fed on WT plants. The enhanced resistance of as- hpl plants to WBPH infestation mainly correlated with lower levels of GLVs, especially ( Z)-3-hexenal. Collectively, these results indicated that WBPH infestation may enhance the susceptibility of rice by inducing the release of ( Z)-3-hexenal. [ABSTRACT FROM AUTHOR]

Xylanase inhibitors have been reported to play an important role in plant defense against fungal pathogens. However, little to nothing is known about their role in defense against herbivores. Here, we cloned a rice xylanase-inhibiting protein (XIP)-type gene OsHI-XIP whose encoding protein is located in the endoplasmic reticulum (ER). Transcriptional analysis revealed a low constitutive mRNA level of OsHI-XIP, while herbivore infestation, mechanical wounding, and treatment with jasmonic acid (JA), a signal that can be induced after infestation by the rice striped stem borer (SSB) Chilo suppressalis, result in an obvious increase in transcript levels. Overexpression of OsHI-XIP, which increased mRNA levels of the gene by 14.7- to 17.7-fold and 7.5- to 9.6-fold at 0 and 12 h, respectively, after SSB infestation, enhanced constitutive and SSB-induced xylanase inhibitor activity and reduced the larval performance of SSB. Moreover, overexpression of OsHI-XIP decreased the feeding and oviposion preferences of the rice brown planthopper (BPH) Nilaparvata lugens, but did not influence the growth and development of rice plants. The results suggest that the rice XIP-type xylanase inhibitor OsHI-XIP is involved in the resistance in rice to herbivores. [ABSTRACT FROM AUTHOR]

Background: The brown planthopper (BPH), Nilaparvata lugens (Stål), a destructive rice pest in Asia, can quickly overcome rice resistance by evolving new virulent populations. Herbivore saliva plays an important role in plant–herbivore interactions, including in plant defense and herbivore virulence. However, thus far little is known about BPH saliva at the molecular level, especially its role in virulence and BPH–rice interaction. Methodology/Principal Findings: Using cDNA amplification in combination with Illumina short-read sequencing technology, we sequenced the salivary-gland transcriptomes of two BPH populations with different virulence; the populations were derived from rice variety TN1 (TN1 population) and Mudgo (M population). In total, 37,666 and 38,451 unigenes were generated from the salivary glands of these populations, respectively. When combined, a total of 43,312 unigenes were obtained, about 18 times more than the number of expressed sequence tags previously identified from these glands. Gene ontology annotations and KEGG orthology classifications indicated that genes related to metabolism, binding and transport were significantly active in the salivary glands. A total of 352 genes were predicted to encode secretory proteins, and some might play important roles in BPH feeding and BPH–rice interactions. Comparative analysis of the transcriptomes of the two populations revealed that the genes related to ‘metabolism,’ ‘digestion and absorption,’ and ‘salivary secretion’ might be associated with virulence. Moreover, 67 genes encoding putative secreted proteins were differentially expressed between the two populations, suggesting these genes may contribute to the change in virulence. Conclusions/Significance: This study was the first to compare the salivary-gland transcriptomes of two BPH populations having different virulence traits and to find genes that may be related to this difference. Our data provide a rich molecular resource for future functional studies on salivary glands and will be useful for elucidating the molecular mechanisms underlying BPH feeding and virulence differences. [ABSTRACT FROM AUTHOR]

As important signal molecules, jasmonates (JAs) and green leaf volatiles (GLVs) play diverse roles in plant defense responses against insect pests and pathogens. However, how plants employ their specific defense responses by modulating the levels of JA and GLVs remains unclear. Here, we describe identification of a role for the rice HPL3 gene, which encodes a hydroperoxide lyase (HPL), OsHPL3/CYP74B2, in mediating plant-specific defense responses. The loss-of-function mutant hpl3-1 produced disease-resembling lesions spreading through the whole leaves. A biochemical assay revealed that OsHPL3 possesses intrinsic HPL activity, hydrolyzing hydroperoxylinolenic acid to produce GLVs. The hpl3-1 plants exhibited enhanced induction of JA, trypsin proteinase inhibitors and other volatiles, but decreased levels of GLVs including ( Z)-3-hexen-1-ol. OsHPL3 positively modulates resistance to the rice brown planthopper [BPH, Nilaparvata lugens (Stål)] but negatively modulates resistance to the rice striped stem borer [SSB, Chilo suppressalis (Walker)]. Moreover, hpl3-1 plants were more attractive to a BPH egg parasitoid, Anagrus nilaparvatae, than the wild-type, most likely as a result of increased release of BPH-induced volatiles. Interestingly, hpl3-1 plants also showed increased resistance to bacterial blight ( Xanthomonas oryzae pv. oryzae). Collectively, these results indicate that OsHPL3, by affecting the levels of JA, GLVs and other volatiles, modulates rice-specific defense responses against different invaders. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

Many plant proteins with extracellular leucine-rich repeat (eLRR) domains play an important role in plant immunity. However, the role of one class of eLRR plant proteins—the simple eLRR proteins—in plant defenses against herbivores remains largely unknown. Here, we found that a simple eLRR protein OsI-BAK1 in rice localizes to the plasma membrane. Its expression was induced by mechanical wounding, the infestation of gravid females of brown planthopper (BPH) Nilaparvata lugens or white-backed planthopper Sogatella furcifera and treatment with methyl jasmonate or abscisic acid. Silencing OsI-BAK1 (ir-ibak1) in rice enhanced the BPH-induced transcript levels of three defense-related WRKY genes (OsWRKY24, OsWRKY53 and OsWRKY70) but decreased the induced levels of ethylene. Bioassays revealed that the hatching rate was significantly lower in BPH eggs laid on ir-ibak1 plants than wild-type (WT) plants; moreover, gravid BPH females preferred to oviposit on WT plants over ir-ibak1 plants. The exogenous application of ethephon on ir-ibak1 plants eliminated the BPH oviposition preference between WT and ir-ibak1 plants but had no effect on the hatching rate of BPH eggs. These findings suggest that OsI-BAK1 acts as a negative modulator of defense responses in rice to BPH and that BPH might exploit this modulator for its own benefit. [ABSTRACT FROM AUTHOR]

β-Glucosidase has been reported to induce the production of herbivore-induced plant volatiles. However, how it works remains unclear. Here, we investigated the levels of salicylic acid (SA), jasmonic acid (JA), ethylene, and H2O2, all of which are known signaling molecules that play important roles in induced plant defense in rice plants treated with β-gIucosidase, and compared these to levels in plants infested by the rice brown planthopper Nilaparvata lugens (Stål). Results showed that wounding and treatment by β-glucosidase increased the levels of SA, ethylene, and H2O2, but not JA, in all plants compared to control plants. The signaling pathways activated by β-gIucosidase treatment are similar to those activated by an infestation by N. lugens, although the magnitude and timing of the signals elicited by the two treatments are different. This may explain why both treatments have similar volatile profiles and are equally attractive to the parasitoid Anagrus nhlaparvatae Pang et Wang. [ABSTRACT FROM AUTHOR]

The phytohormone jasmonate (JA) plays a central role in plant defenses against biotic stressors. However, our knowledge of the JA signaling pathway in rice (Oryza sativa) remains incomplete. Here, we integrated multiomic data from three tissues to characterize the functional modules involved in organizing JA-responsive genes. In the core regulatory sector, MYC2 transcription factor transcriptional cascades are conserved in different species but with distinct regulators (e.g. bHLH6 in rice), in which genes are early expressed across all tissues. In the feedback sector, MYC2 also regulates the expression of JA repressor and catabolic genes, providing negative feedback that truncates the duration of JA responses. For example, the MYC2-regulated NAC (NAM, ATAF1/2, and CUC2) transcription factor genes NAC1, NAC3, and NAC4 encode proteins that repress JA signaling and herbivore resistance. In the tissue-specific sector, many late-expressed genes are associated with the biosynthesis of specialized metabolites that mediate particular defensive functions. For example, the terpene synthase gene TPS35 is specifically induced in the leaf sheath and TPS35 functions in defense against oviposition by brown planthoppers and the attraction of this herbivore's natural enemies. Thus, by characterizing core, tissue-specific, and feedback sectors of JA-elicited defense responses, this work provides a valuable resource for future discoveries of key JA components in this important crop. Jasmonate-mediated defense responses in rice can be divided into the core regulatory sector, the local tissue-specific sector, and the negative feedback sector. [ABSTRACT FROM AUTHOR]

The pentose phosphate pathway (PPP) plays an important role in plant growth and development, and plant responses to biotic and abiotic stresses. Yet, whether the PPP regulates plant defenses against herbivorous insects remains unclear. In this study, we cloned a rice cytosolic 6-phosphogluconate dehydrogenase gene, Os6PGDH1, which encodes the key enzyme catalyzing the third step in the reaction involving the oxidative phase of the PPP, and explored its role in rice defenses induced by brown planthopper (BPH) Nilaparvata lugens. Levels of Os6PGDH1 transcripts were detected in all five examined tissues, with the highest in outer leaf sheaths and lowest in inner leaf sheaths. Os6PGDH1 expression was strongly induced by mechanical wounding, infestation of gravid BPH females, and jasmonic acid (JA) treatment. Overexpressing Os6PGDH1 (oe6PGDH) decreased the height of rice plants and the mass of the aboveground part of plants, but slightly increased the length of plant roots. In addition, the overexpression of Os6PGDH1 enhanced levels of BPH-induced JA, jasmonoyl-isoleucine (JA-Ile), and H2O2, but decreased BPH-induced levels of ethylene. Bioassays revealed that gravid BPH females preferred to feed and lay eggs on wild-type (WT) plants over oe6PGDH plants; moreover, the hatching rate of BPH eggs raised on oe6PGDH plants and the fecundity of BPH females fed on these were significantly lower than the eggs and the females raised and fed on WT plants. Taken together, these results indicate that Os6PGDH1 plays a pivotal role not only in rice growth but also in the resistance of rice to BPH by modulating JA, ethylene, and H2O2 pathways. [ABSTRACT FROM AUTHOR]

Plant defense against herbivores is costly and often associated with growth repression. The phytohormone jasmonate (JA) plays a central role in prioritizing defense over growth during herbivore attack, but the underlying mechanisms remain unclear. When brown planthoppers (BPH, Nilaparvata lugens) attack rice (Oryza sativa), growth is dramatically suppressed. BPH infestation also increases inactive gibberellin (GA) levels and transcripts of GA 2-oxidase (GA2ox) genes, 2 (GA2ox3 and GA2ox7) of which encode enzymes that catalyze the conversion of bioactive GAs to inactive GAs in vitro and in vivo. Mutation of these GA2oxs diminishes BPH-elicited growth restriction without affecting BPH resistance. Phytohormone profiling and transcriptome analyses revealed that GA2ox-mediated GA catabolism was enhanced by JA signaling. The transcript levels of GA2ox3 and GA2ox7 were significantly attenuated under BPH attack in JA biosynthesis (allene oxide cyclase [aoc]) or signaling-deficient (myc2) mutants. In contrast, GA2ox3 and GA2ox7 expression was increased in MYC2 overexpression lines. MYC2 directly binds to the G-boxes in the promoters of both GA2ox genes to regulate their expression. We conclude that JA signaling simultaneously activates defense responses and GA catabolism to rapidly optimize resource allocation in attacked plants and provides a mechanism for phytohormone crosstalk. Jasmonate-mediated gibberellin catabolism is partially responsible for brown planthopper–elicited growth inhibition in rice. [ABSTRACT FROM AUTHOR]

The heavy metal, cadmium (Cd), has become a new threat to rice production in paddy fields. Cd is absorbed by rice roots and translocated to shoots, where it accumulates in different tissues. Rice is also commonly attacked by insect herbivores, but the effects of low-level Cd exposure on the performance of rice pests and the underlying mechanisms remain unexplored. We investigated brown planthopper (BPH) performance on Cd-exposed rice in the laboratory and field. Low-level Cd exposure did not significantly affect rice growth but decreased hatching rate and extended hatching duration of BPH eggs. No direct toxic effect of low Cd exposure on BPH eggs were found in in vitro developmental rate assays. By transcriptome analysis, a total of 747 rice genes were differentially expressed in Cd-exposed plants under BPH attack. Interestingly, BPH-elicited jasmonate (JA) and phenylpropanoid pathway genes were up-regulated by Cd exposure. Consistently, the levels of JAs and JA-mediated phenylpropanoid derivatives were also increased. Furthermore, Cd exposure did not affect BPH performance on mutant plants impaired in JA biosynthesis (aoc-2) and signaling (myc2–5), suggesting that JA is required to influence BPH performance under Cd exposure. In the field, herbivore populations were reduced on Cd-treated plants compared with control plants. This study revealed that low-level Cd exposure primes JA-mediated defense responses in rice and thereby affects herbivore performance. • Low-level Cd exposure enhanced rice resistance to BPH in the laboratory and field. • BPH-elicited JA and phenylpropanoid levels were primed by low-level Cd exposure. • JA signaling is required for enhanced BPH resistance under Cd exposure. [ABSTRACT FROM AUTHOR]

It is increasingly evident that plants interact with their outside world through the production of volatile organic compounds, 1–5 but whether the volatiles have evolved to serve in plant defense is still a topic of considerable debate. 3,6–8 Unharmed leaves constitutively release small amounts of volatiles, but when the leaves are damaged by herbivorous arthropods, they emit substantially more volatiles. These herbivore-induced plant volatiles (HIPVs) attract parasitoids and predators that kill insect herbivores, 9–12 and this can benefit the plants. 13,14 As yet, however, there is no tangible evolutionary evidence that this tritrophic interplay contributes to the selection forces that have shaped the volatile emissions of plants. 2,3,5–8,15 With this in mind, we investigated the evolutionary changes in volatile emissions in invasive common ragwort and the respective defensive roles of its constitutive and inducible volatiles. This Eurasian plant has invaded other continents, where it evolved for many generations in the absence of specialized herbivores and their natural enemies. We found that, compared to native ragworts, invasive plants release higher levels of constitutive volatiles but considerably lower levels of herbivore-induced volatiles. As a consequence, invasive ragwort is more attractive to a specialist moth but avoided by an unadapted generalist moth. Importantly, conforming to the indirect defense hypothesis, a specialist parasitoid was much more attracted to caterpillar-damaged native ragwort, which was reflected in higher parasitism rates in a field trial. The evolution of foliar volatile emissions appears to be indeed driven by their direct and indirect roles in defenses against insects. [Display omitted] • The evolution of invasive plants can provide insight into the function of volatiles • Invasive ragwort releases more constitutive but fewer inducible volatiles • The invader is more attractive to a specialist herbivore but less to its parasitoid • The evolution of volatiles from invasive ragwort supports their defensive function Lin et al. compare constitutive and herbivore-induced volatiles emitted by ragwort plants from native and invasive areas. The observed differences and the corresponding behavioral responses of a specialist and a generalist herbivore as well as of a parasitic wasp support the hypothesis that volatiles evolved as plant defenses. [ABSTRACT FROM AUTHOR]