Insect-resistant Plants Research Articles

Development of marker-free transgenic pigeon pea (Cajanus cajan) expressing a pod borer insecticidal protein

Pigeon pea, a grain legume of the semiarid tropics, is a rich source of high-quality protein. The productivity of this pulse is seriously affected by lepidopteron insect pests. To generate a sustainable insect-resistant plant, synthetically prepared bioactive key constituents of a crystal protein (Syn Cry1Ab) of Bacillus thuringiensis were expressed in pigeon pea under the guidance of a tissue-specific promoter of the RuBP carboxylase/oxygenase small subunit (rbcS) gene. Regenerated transgenic plants with the cry1Ab expression cassette (cry1Ab-lox-bar-lox) showed the optimum insect motility rate (90%) in an in vitro insect bioassay with second instar larvae, signifying the insecticidal potency of Syn Cry1Ab. In parallel, another plant line was also generated with a chimaeric vector harbouring a cre recombinase gene under the control of the CaMV 2 × 35S promoter. Crossing between T1 plants with a single insertion of cry1Ab-lox-bar-lox T-DNA and T1 plants with moderate expression of a cre gene with a linked hygromycin resistance (hptII) gene was performed to exclude the bialaphos resistance (bar) marker gene. Excision of the bar gene was achieved in T1F1 hybrids, with up to 35.71% recombination frequency. Insect-resistant pigeon pea plants devoid of selectable marker genes (syn Cry1Ab- bar and cre-hptII) were established in a consecutive generation (T1F2) through genetic segregation.

Response of Trichogramma pretiosum females (Hymenoptera: Trichogrammatidae) to herbivore-induced Bt maize volatiles

Parasitoids use herbivore-induced plant volatiles (HIPV´s) to locate their hosts. However, little is known about variations in HIPV´s production in genetically modified maize plants that are herbicide tolerant (singular event), insect resistant (Bt plants, singular event), or both herbicide tolerant and insect resistant, like staked events. We investigated the olfactory responses of the egg parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) to HIPV´s produced in maize (Zea mays) herbicide-tolerant and insect-resistant plants or their stacked events in response to damage caused by Spodoptera frugiperda during nighttime and daytime infestations. Real-time reverse-transcription PCR was used to assess whether the presence of one or more Bacillus thuringiensis (Bt) proteins and the time of induction of HIPV’s affected the expression of genes in plants under herbivore attack. The results showed that compounds were released during both nocturnal and diurnal infestations. However, some HIPV´s were released exclusively in infestations that started during the night by non-Bt plants and they were highly attractive to parasitoids. HIPV´s produced by non-Bt plants were more attractive to parasitoids than those released by Bt plants in infestations that started during the night. However, glyphosate-tolerant maize plants were more attractive to parasitoids than isogenic plants. The expression of the analyzed genes TPS10, TPS23, LOX10, and STC1 was higher in infestations that started during the night. In this study, we discuss the possible causes of the unresponsiveness of T. pretiosum females to HIPV´s produced by Bt maize.

An overview on transgenic plants for insect resistance

Insect-resistant plants may be created via plant genetic engineering, which involves introducing and producing entomopathogenic proteins in the plant. There have been two major approaches to investigating such plants.Plant genetic engineering allows for the development of insect-resistant plants via the insertion as well as expression of entomopathogenic proteins in planta. There are two major methods for obtaining such plants that have been investigated. The first includes the usage of delta-endotoxin coding sequences derived from Bacillus thuringiensis bacteria. Plant-derived genes, including those producing enzyme inhibitors and lectins, are used in the second method. Much effort is being put in across the globe to find plants of various kinds that express such genes and are resistant to insect pests. This overview discusses ongoing research initiatives as well as an evaluation of the status and issues faced on the path to commercialization of transgenic plants.

Genetic Modification of Plants: An Emerging Technology

Genetically modified (GM) plants can be created by adding specific DNA sequences obtained from the same plant species or different species. Which aims to achieve higher yields, disease and pest resistance, herbicide tolerance, production of antibodies, and other pharmaceutical molecules by manipulating gene expression to alter the protein properties. Insect resistant plants reduce the damage caused by pests and diseases. Herbicide glyphosate or glufosinate-tolerant GM plants gave promising results in combating weed. The properties of plants such as metal uptake, transport, accumulation, and detoxification of organic pollutants can be enhanced by genetically manipulating the fast-grown and introducing the responsible gene from the hyper accumulative species. GM plants can be used to produce cost-efficient and manageable drugs, vaccine, and biopharmaceuticals, if certain limitations are to be considered such as quality of final products, techniques for extraction and processing of biopharmaceuticals, and biosafety. Despite all these benefits, its adverse effects on the environment and human health have always been a matter of concern. The main limitation includes a horizontal transfer of the transgene to other species which may code for the specific antibiotic and herbicide resistance. It might be the possible transmission of resistance from the food products to the whole human population via intestinal bacteria. To address this several methods, need to be adopted to either keep away or eliminate marker genes from the transformed plants before growing in the field. Many scientists have come up with strategies to generate marker-free transgenic plants to give us safe and reliable GM technology.

Transgenic rice overexpressing insect endogenous microRNA csu-novel-260 is resistant to striped stem borer under field conditions.

RNA interference (RNAi) is a promising approach for developing insect-resistant crops. In the first two proof-of-concept studies, DNA fragments derived from essential insect genes were constructed into plant expression cassettes as inverted repeats, enabling long double-stranded RNAs (dsRNAs) to be transcribed in host plants (Baum et al., 2007; Mao et al., 2007). After ingestion, dsRNAs overexpressed in planta suppressed target gene expression via small interference RNA (siRNA)-mediated RNAi in western corn rootworm (Diabrotica virgifera virgifera) (Baum et al., 2007) and cotton bollworm (Helicoverpa armigera) (Mao et al., 2007), and thereby reduced their viability. Subsequent studies have mostly employed a similar approach and attempted to develop RNAi crops against various insect species (Liu et al., 2020). However, except for coleopterans that are generally susceptible to RNAi, most insects (e.g., lepidopterans, dipterans, hymenopterans, and hemipterans) exhibit unpredictable responses to dsRNA-induced RNAi, and this has become a hurdle for ubiquitous adaption of this strategy (Cooper et al., 2019). Potential factors influencing RNAi efficacy in insects involve dsRNA stability, cellular dsRNA absorption, core RNAi machinery integrity, systemic RNAi spread, and target gene amenability (Cooper et al., 2019).

Correlation of tea green leafhopper occurrence with leaf structure and biochemical components in different tea cultivars

Being one of the most disastrous pierce-sucking pests of tea plants [Camellia sinensis (L.) O. Kuntze], tea green leafhopper (Empoasca onukii Matsuda) greatly affects tea yield and quality. In this paper, correlations among leaf structure, biochemical components and tea green leafhopper occurrence in tea cultivars with larger planting area were deeply analyzed, aiming to find the key factor impacting the host selectivity of tea green leafhopper. Tea cultivar ‘Longjing 43’, together with ‘Shuchazao’, showed the most susceptibility to this pest with high tea polyphenols content. And the best resistant tea plant cultivar, ‘Caoxi No.1’, largely relied on the thicker leaf, epidermis (both upper and lower), cuticle and spongy tissue as revealed by principal component analysis. Here, we suggested that tea polyphenols were considered as a biochemical marker for determining the resistance ability to tea green leafhopper of different tea cultivars, along with leaf upper and lower structures as mechanical barriers, which can potentially be used to promote breeding of insect-resistant tea plants.

Conventional breeding of insect-resistant crop plants: still the best way to feed the world population.

Insect-resistant crops feed much of the world, using reduced carbon inputs and providing much greater economic returns on investment. Newer, more efficient efforts are urgently needed to speed development of insect-resistant plants before a projected 30% global population increase. Plant resistance researchers must employ genotyping by sequencing and high-throughput phenotyping to identify, map and track resistance genes. In contrast to maize, rice, vegetables and wheat, limited progress has occurred to develop meaningful levels of pest resistance in cassava, cowpea and pigeonpea - major sources of nutrition for nearly 1 billion people. A knowledge void exists about the effects of climate change (elevated CO2) on resistant plants, necessitating efforts to understand this stress. Collaborations with social scientists, extension specialists, economists, spatiotemporal modelers, ecologists, and virologists will be required to develop better ways to integrate insect resistant plants into integrated crop pest management programs.

Host-derived artificial miRNA-mediated silencing of ecdysone receptor gene provides enhanced resistance to Helicoverpa armigera in tomato

Helicoverpa armigera causes huge crop losses due to its polyphagous nature. The present study demonstrates the use of artificial microRNA (amiRNA) mediated gene silencing approach to generate insect resistant tomato plants. Ecdysone receptor (HaEcR) gene of the target pest, H. armigera, which is involved in the regulation of all developmental stages of the insect life cycle, was silenced by sequence-specific amiRNA (amiRNA-HaEcR). Continuous feeding on detached tomato leaves expressing the amiRNA-319a-HaEcR resulted in reduced target gene transcripts and affected the overall growth and survival of H. armigera. Not only the target gene was down-regulated but, the feeding also affected the expression of down-stream genes involved in the ecdysone signaling pathway. The resistant trait was also observed in T1 generation of tomato transgenic lines. These results further established the role of EcR as a master regulator in insect development and effectiveness of amiRNA technology for efficient control of H. armigera.

INFLUENCE OF TRANSGENIC MAIZE ON BEHAVIOR OF ADULT FEMALE OF Spodoptera frugiperda (J. E. SMITH) (LEPIDOPTERA: NOCTUIDAE)

It is known that genetic manipulation of plants can cause pleiotropic effects or mutations originated from the incorporation of an exogenous gene, which may interfere with foraging of herbivores. Little is known about how herbicide-tolerant plants (singular event), insect-resistant plants (singular event), and herbicide-tolerant plus insect-resistant plants (stacked event) affect foraging of Spodoptera frugiperda. The objective of this study was to evaluate if singular and stacked maize events interfere with the quantity and quality of S. frugiperda eggs. The hybrids DKB390 (VTPRO, VTPRO2, VTPRO3), DKB390 (isogenic) and Ag 3700 RR2 were evaluated. Choice and non-choice tests for oviposition preference of S. frugiperda, in plants with and without injuries, were performed in a greenhouse. The size of egg masses and the number of hatched larvae were evaluated. Larger egg masses and higher number of hatched larvae per plant were found in transgenic plants. The conclusion was that S. frugiperda females modify their oviposition behavior in the presence of transgenic and non-transgenic maize hybrids, especially when they are injured. However, the females do not discriminate between singular or stacked hybrid for oviposition.

A new method for evaluating the effects of insecticidal proteins expressed by transgenic plants on ectoparasitoid of target pest

Transgenic Bt insect-resistant plants are highly resistant to Lepidoptera stockpile pest Indian meal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae), a storage pest. Habrobracon hebetor (Say) (Hymenoptera: Braconidae), which is an ectoparasitic wasp of Indian meal moth, may be exposed to the Bt protein through the food chain. In the current study, high dose of Cry1C protein was injected into the hemolymph of P. interpunctella by microinjection, and the hemolymph was used as the carrier to deliver Bt protein to the H. hebetor. Using this method, we developed a new Tier-1 risk assessment system for ectoparasitoid, successfully avoided "host/prey quality-mediated effect," and improve the accuracy of safety evaluation. Results showed that injected Cry1C was stable and bioactive in the hemolymph of P. interpunctella parasitized by H. hebetor, and high dose of Cry1C has no negative impacts on egg hatching rate, developmental duration from egg to adult, survival egg to adult, pupa weight, adults weight (male and female), adult longevity and reproduction, and activity of stress-related enzymes of H. hebetor. However, the hemolymph of P. interpunctella injected into Galanthus nivalis L. agglutinin (the positive control) had significant negative impact on these biological parameters of H. hebetor. The results indicate that H. hebetor are not sensitive to Cry1C protein at the tested concentration and there were no detrimental effects of Cry1C protein on any biological parameters tested in the present study. More importantly, we constructed a new efficient and simple system for the biosafety assessment on the larvae of ectoparasitoid of target pest.

Full-length transcriptome and targeted metabolome analyses provide insights into defense mechanisms of Malus sieversii against Agrilus mali.

Malus sieversii is the wild progenitor for many cultivars of domesticated apple and an important germplasm resource for breeding. However, this valuable species faces a significant threat in the areas north of the Tianshan Mountains in China, by the invasion of Agrilus mali, a destructive pest of apple trees belonging to the family Buprestidae. Our preliminary study has has shown that there may be resistance to this insect in M. sieversii plants in the field, but the corresponding molecular mechanisms remain unclear. In this study, we compared the response of insect-resistant and insect-susceptible plants of M. sieversii to insect feeding using full-length transcriptome and targeted metabolome. 112,103 non-chimeric full-length reads (FLNC) totaling 10.52 Gb of data were generating with Pacific Biosciences SingleMolecule, Real-Time (PacBio SMRT) sequencing. A total of 130.06 Gb data of long reads were acquired with an Illumina HiSeq. Function annotation indicated that the different expressed genes (DEGs) were mainly involved in signal transduction pathway of plant hormones and in the synthesis of compounds such as terpenes, quinones, flavonoids, and jasmonic acid. Through targeted metabolome analysis resistant strains showed higher levels of trans-cinnamic acid, caffeine and ferulic acid after pest infestation. This study helps to decipher the transcriptional changes and related signaling paths in M. sieversii after an insect feeding, which lays a foundation for further research on molecular mechanisms of insect resistance in apples.

Does Singular and Stacked Corn Affect Choice Behavior for Oviposition and Feed in Spodoptera frugiperda (Lepidoptera: Noctuidae)?

Little is known about the effects of genetically modified corn plants on the foraging of Spodoptera frugiperda (J.E. Smith). Therefore, this study examines whether singular herbicide-tolerant and insect-resistant plants and their stacked events interfere with food preference and oviposition of S. frugiperda. Two non-Bt corn hybrids and three Bt-hybrids, some of them with glyphosate tolerance (GT), were evaluated. Food preference of larvae and biological parameters were assessed. Oviposition preference bioassays involved choice and no choice condition in plants uninfested and previously infested by larvae in a greenhouse and in the field. The results indicate that there is no relationship between preference of larvae and adult moths. Adult females selected preferentially transgenic hybrids, while larvae selected non-Bt hybrid. Fall armyworm larvae avoid Bt-toxin-expressing leaf tissues, survived only on the non-Bt leaf tissues, and showed minor differences in other life-history traits reared on GT and non-transgenic corn leaf tissues. Female moths showed preference for transgenic plants to lay eggs, but with variable output between previously infested and uninfested plants with larvae. The fact that moths preferred Ag 3700RR2 and non-Bt hybrids for oviposition supports the refuge's strategy aiming at producing susceptible individuals. The use of this hybrid must be integrated with a program of control. The results showed also the importance of correct hybrid selection as part of insect resistance management to Bt-plants. The implications of these findings for understanding the impacts of plant-mediated cues on pest behavior in transgenic crop systems are discussed.

Influence of Heat Processing on DNA Degradation and PCR-Based Detection of Wild-Type and Transgenic Maize

Reliable detection of genetically modified (GM) maize is significant for food authenticity, labelling, quality, and safety assessment. This study aims to evaluate the factors influencing degradation and polymerase chain reaction (PCR) amplification of DNA from the wild type and transgenic maize (events Bt-176 and MON810) during thermal treatment at 100°C and 121°C. A new PCR method was developed targeting the Cry1Ab gene to detect insect-resistant GM plants. The yield of genomic DNAs extracted by the DNeasy plant mini kit dramatically decreased while DNAs obtained by cetyltrimethyl ammonium bromide- (CTAB-) based method did not show any visible changes in the yield by the time of processing. Treatment at 100°C did not significantly affect either genomic DNAs or amplicons. Heating at 121°C induced time-dependent degradation of genomic DNAs and exogenous Cry1Ab gene; however, it did not have any considerable influence on the exogenous 141 bp amplicons or endogenous amplicons in the range of 102 bp to 226 bp with the exception of the event MON810 extracted by the DNeasy plant mini kit. More yield was observed at 226 bp than 140 bp fragment of the invertase gene. The 141 bp fragment of the transgenic CaMV 35S promoter exhibited the highest thermal stability of all the examined amplicons. Analysis of foodstuffs demonstrated 102 bp amplicons specific for the zein gene as the effective marker to detect maize in the processed foods. The obtained results demonstrate that PCR-based detection of the wild type and transgenic maize is dependent on the combination of different parameters of crucial factors such as temperature and duration of exposure, transgenic event, DNA extraction method, DNA marker, and size and location of amplicons.

Global status of the regulation of genome editing technologies.

Abstract Innovations affect societies in various ways. For example, the latest innovations in cell phones and electronics are readily adopted without hesitation. However, many innovations regarding the breeding of plants, the production of food crops and the processing of food products, can be met with fear and trepidation by some societies. Europe, the foundation of the Industrial Revolution, has developed strong adversity to agricultural innovations that involve innovative genome editing methods in general and to genetically modified (GM) crops in particular. While much of the industrial world models their regulatory frameworks for plant agriculture on the science-based risk assessment framework developed through the efforts of the Organisation for Economic Cooperation and Development, the European Union's regulatory framework for GM crops is based on the precautionary principle, approving but a single GM crop variety for production in the twenty-first century. As any field of science and technology advances, so has the breeding of GM crops. GM crop varieties were developed through the insertion of a gene or genes from a different species, such as the insertion of the trait for insect resistance in plants that originally came from a soil bacterium. Crop varieties are now being developed through a group of targeted, site-directed mutation technologies, known as genome editing, where some of this group of technologies results in no foreign genes being transferred into new varieties. While technologically viewed as a significant advancement in the development of new plant varieties, some jurisdictions have chosen to regulate genome editing as equivalent to GM crops, thereby establishing a de facto ban on the application of the technology. Yet other jurisdictions have chosen to embrace the technology, announcing that some applications of genome editing will face no regulatory oversight. This paper provides a global overview of the various regulatory frameworks for genome editing.

Screening the variability in oilseed rape resistance to pollen beetle attacks in the field and assessment of biochemical biomarkers

The pollen beetle (Brassicogethes aeneus) is one of the main insect pests affecting oilseed rape crops. Efficiency of insecticides used to control this pest is decreasing due to the development of resistance to compounds such as pyrethroids in many populations. Breeding oilseed rape for resistance to pollen beetle attacks could be an interesting strategy to find alternative control methods but has not been really developed in this crop yet. However, screening plants for insect resistance remains complicated as it often involves field tests on large genotype collections which are complicated to carry out without biases. Current knowledge on the chemical ecology of interactions between oilseed rape and pollen beetles could help finding biochemical markers of this resistance and bypass this problematic field screening phase, thus allowing an indirect breeding approach. Previous laboratory tests have shown that variations in attack levels among a small set of oilseed genotypes could be explained by the biochemistry of bud tissues. The present study aimed at validating this link under field conditions. For that purpose, we conducted a multi-site experiment in France with 19 genotypes exposed to pollen beetle attacks. We phenotyped pollen beetle damage and sampled buds in the field to assess their chemical composition. Large variability in pollen beetle attacks was observed over the genotypes. These attack levels were consistent between locations. Bud chemistry was highly variable, but most compounds were well correlated between locations. Potential biomarkers previously identified in laboratory experiments were not confirmed to be correlated with resistance to pollen beetles in the field, but new compounds which may be considered interesting markers for resistance screening against the pollen beetle emerged.

English

Continue climatic changes in the world enhance the emergence of invasive agricultural insect pests. Tuta absoluta is one of the most devastating tomato leafminer and it spreads extensively in almost all parts of the world. It is a serious threat for tomato production and it results in highest damage. T. absoluta has fast growth rate with developmental stages of egg, larvae, pupa, and adult and it adapts to different environmental conditions. A larva is the most destructive one that consumes preferably leaves, stems and fruits of the tomato plant by hiding within mesophyll of the plant tissues. Although different environmentally hazardous pesticides are used against T. absoluta, none of the insecticides give full control due to the resistance development. This problem calls an urgent search for eco-friendly alternatives to control this invasive insect. Recent investigations are focused on different environmental friendly approaches that inclusively termed as IPM strategies. These are cultural practices, biopesticides, and biological using parasitoids, predators, microbial cells, microbial products, RNAi, inheritance sterility development in insect and pest resistant plant cultivar production are considered as promising alternatives to control T. absoluta. Therefore, this review briefly describes the current status of these methods used to design suitable and sustainable management strategies against T. absoluta. Key words: Tomato leafminer, insecticide resistances, biopesticides, biological control.

Inhibition of Fusarium solani in transgenic insect-resistant cotton plants treated with silver nanoparticles from Prosopis glandulosa and Pluchea sericea

The phytosynthesis of nanoparticles is a green chemistry approach that combines nanotechnology and bioactive compounds of plants. The aim of this study was to evaluate the effect of silver nanoparticles (AgNPs) from Prosopis glandulosa and Pluchea sericea, respectively, on the control of Fusarium solani previously inoculated in the rhizosphere of transgenic insect-resistant cotton plants. The results showed that the weekly application of AgNPs from P. glandulosa and P. sericea caused a diminution of fungal propagules in the soil after 30 days of treatment. In this sense, the AgNPs from P. glandulosa were more efficient in the reduction of infection points in the roots of the plants infected with F. solani compared with AgNPs from P. sericea. Additionally, the application of AgNPs from both plants showed a significant increase of optimum quantum yield (Fv/Fm), stomata conductance (gs), and the number of lateral roots in transgenic insect-resistant cotton plants after 30 days of exposure when compared to the control. Based on our results, AgNPs from P. glandulosa and P. sericea could inhibit growth of Fusarium solani. However, more extensive and elaborate studies are needed to explain the different mechanisms that participate in the inhibition of growth of fungus using nanoparticles from these plants.

Post-ingestive effects of flavonoids in the midgut epithelium of Anticarsia gemmatalis (Hübner 1818) (Lepidoptera: Erebidae) larvae

An alternative control to soybean caterpillar has been the use of insect resistant plants that present phenolic flavonoids. The midgut is the main access pathway of food and chemical substances ingested. The present study examined morphological alterations in the midgut epithelium of the soybean caterpillar, after the ingestion of soybean genotypes containing the flavonoids rutin and genistin. The caterpillars and genotypes (BRS 257 - control, BR 16, Dowling, PI 229358, IAC 100 and PI 227687) were obtained from the insect rearing facility at the Embrapa Soja. The midguts were collected, fixed in Karnovsky, processed and analyzed under a light microscope. All treatments caused alterations in the midgut epithelial cells. These alterations in the columnar cells were more assiduous than the on other cell types, showing an increase of cytoplasmic protrusions and vacuoles. The goblet cells showed few changes for all genotypes tested, while the regenerative cells presented alterations mainly for the Dowling and PI 227687 treatments. The peritrophic membrane was absent for genotypes IAC100 and PI 227687. We conclude that the Dowling and PI 227687 genotypes were effective and promoted great morphological alterations in the midgut of the soybean caterpillars, being able to be very effective for the control of this plague.

Comparison of RNAi Sequences in Insect-Resistant Plants to Expressed Sequences of a Beneficial Lady Beetle: A Closer Look at Off-Target Considerations.

Sequences obtained from transcriptomes of the lady beetle Coleomegilla maculata were compared to those designed for incorporation into crops. Searches of the transcriptomes identified sequences as the most likely to be closely similar to the sequences described in RNAi plant incorporated products. Some proposed prime RNAi pest management targets were also used to identify predicted orthologs from C. maculata. The lady beetle sequences were aligned with sequences from corn rootworms and Colorado potato beetles and, as appropriate in the case of targets, regions of similarity were compared with the genetic model organism for beetles, Tribolium castaneum. Some high levels of nucleotide identity were identified, particularly with an actin-derived sequence from Colorado potato beetle. This actin-derived sequence shared identical sequences with the lady beetle and a parasitic wasp.

Jasmonate response decay and defense metabolite accumulation contributes to age-regulated dynamics of plant insect resistance

Immunity deteriorates with age in animals but comparatively little is known about the temporal regulation of plant resistance to herbivores. The phytohormone jasmonate (JA) is a key regulator of plant insect defense. Here, we show that the JA response decays progressively in Arabidopsis. We show that this decay is regulated by the miR156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE9 (SPL9) group of proteins, which can interact with JA ZIM-domain (JAZ) proteins, including JAZ3. As SPL9 levels gradually increase, JAZ3 accumulates and the JA response is attenuated. We provide evidence that this pathway contributes to insect resistance in young plants. Interestingly however, despite the decay in JA response, older plants are still comparatively more resistant to both the lepidopteran generalist Helicoverpa armigera and the specialist Plutella xylostella, along with increased accumulation of glucosinolates. We propose a model whereby constitutive accumulation of defense compounds plays a role in compensating for age-related JA-response attenuation during plant maturation.