Role of trichomes in defense against herbivores: comparison of herbivore response to woolly and hairless trichome mutants in tomato (Solanum lycopersicum)

Nitrogen input reduces the physical defense of rice plant against planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

Nitrogen has important effects on plant growth and defense. Although studies on the alternation in plant chemical defense by nitrogen fertilization have been extensively reported, how it affects physical defense is poorly understood. Two rice (Oryza sativa L.) (Poales: Poaceae) varieties (LDQ7 and YLY1) were applied with varying nitrogen regimes (0.90 and 180 kg ha-1) to study their physical defense against the brown planthopper (BPH) Nilaparvata lugens (Hemiptera: Delphacidae) in this study. Results of the electrical penetration graph showed that BPH searching and penetrating duration time was shortened with increasing nitrogen application. Also, the tubercle papicle of rice leaves decreased with increasing nitrogen application, while rice leaves' surface structure and waxy composition changed with increasing nitrogen application. In field experiments, BPH populations increased with the application of nitrogen fertilizer. These findings suggest that nitrogen input can affect plant-insect interactions by reducing the physical defense of plants, which provides new ideas for the organic combinations of yield increase and pest control in rice fields.

Cultivar-Specific Defense Responses in Wild and Cultivated Squash Induced by Belowground and Aboveground Herbivory

Plant domestication often alters plant traits, including chemical and physical defenses against herbivores. In squash, domestication leads to reduced levels of cucurbitacins and leaf trichomes, influencing interactions with insects. However, the impact of domestication on inducible defenses in squash remains poorly understood. Here, we investigated the chemical and physical defensive traits of wild and domesticated squash (Cucurbita argyrosperma), and compared their responses to belowground and aboveground infestation by the root-feeding larvae and the leaf-chewing adults of the banded cucumber beetle Diabrotica balteata (Coleoptera: Chrysomelidae). Wild populations contained cucurbitacins in roots and cotyledons but not in leaves, whereas domesticated varieties lacked cucurbitacins in all tissues. Belowground infestation by D. balteata larvae did not increase cucurbitacin levels in the roots but triggered the expression of cucurbitacin biosynthetic genes, irrespective of domestication status, although the response varied among different varieties. Conversely, whereas wild squash had more leaf trichomes than domesticated varieties, the induction of leaf trichomes in response to herbivory was greater in domesticated plants. Leaf herbivory varied among varieties but there was a trend of higher leaf damage on wild squash than domesticated varieties. Overall, squash plants responded to both belowground and aboveground herbivory by activating chemical defense-associated gene expression in roots and upregulating their physical defense in leaves, respectively. While domestication suppressed both chemical and physical defenses, our findings suggest that it may enhance inducible defense mechanisms by increasing trichome induction in response to herbivory.

The molecular dynamics between reactive oxygen species (ROS), reactive nitrogen species (RNS) and phytohormones in plant's response to biotic stress

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are critical for plant development as well as for its stress response. They can function as signaling molecules to orchestrate a well-defined response of plants to biotic stress. These responses are further fine-tuned by phytohormones, such as salicylic acid, jasmonic acid, and ethylene, to modulate immune response. In the past decades, the intricacies of redox and phytohormonal signaling have been uncovered during plant-pathogen interactions. This review explores the dynamic interplay of these components, elucidating their roles in perceiving biotic threats and shaping the plant's defense strategy. Molecular regulators and sites of oxidative burst have been explored during pathogen perception. Further, the interplay between various components of redox and phytohormonal signaling has been explored during bacterial, fungal, viral, and nematode infections as well as during insect pest infestation. Understanding these interactions highlights gaps in the current knowledge and provides insights into engineering crop varieties with enhanced resistance to pathogens and pests. This review also highlights potential applications of manipulating regulators of redox signaling to bolster plant immunity and ensure global food security. Future research should explore regulators of these signaling pathways as potential target to develop biotic stress-tolerant crops. Further insights are also needed into roles of endophytes and host microbiome modulating host ROS and RNS pool for exploiting them as biocontrol agents imparting resistance against pathogens in plants.

The genetic basis of leaf hair development in upland cotton (Gossypium hirsutum)

Trichomes, which originate from the epidermal cell of aerial organs, provide plants with defense and secretion functions. Although numerous genes have been implicated in trichome development, the molecular mechanisms underlying trichome cell formation in plants remain incompletely understood. Here, we using genome-wide association study (GWAS) across 1037 diverse accessions in upland cotton (Gossypium hirsutum) to identify three loci associated with leaf pubescence (hair) amount, located on chromosome A06 (LPA1), A08 (LPA2) and A11 (LPA3), respectively. GhHD1, a previously characterized candidate gene, was identified on LPA1 and encodes an HD-Zip transcription factor. For LPA2 and LPA3, we identified two candidate genes, GhGIR1 and GhGIR2, both encoding proteins with WD40 and RING domains that act as inhibitors of leaf hair formation. Expression analysis revealed that GhHD1 was predominantly expressed in hairy accessions, whereas GhGIR1 and GhGIR2 were expressed in hairless accessions. Silencing GhHD1 or overexpressing GhGIR1 in hairy accessions induced in a hairless phenotype, whereas silencing GhGIR2 in hairless accessions resulted in a hairy phenotype. We also demonstrated that GhHD1 interact with both GhGIR1 and GhGIR2, and GhGIR1 can interact with GhGIR2. Further investigation indicated that GhHD1 functions as a transcriptional activator, binding to the promoters of the GhGIR1 and GhGIR2 to active their expression, whereas GhGIR1 and GhGIR2 can suppress the transcriptional activation of GhHD1. Our findings shed light on the intricate regulatory network involving GhHD1, GhGIR1 and GhGIR2 in the initiation and development of plant epidermal hairs in cotton.

Combined Effects of Heavy Metal and Simulated Herbivory on Leaf Trichome Density in Sunflowers

Trichomes play a key role in both heavy metal tolerance and herbivory defense, and both stressors have been shown to induce increased trichome density. However, the combined effect of these stressors on trichome density in general, and specifically on metal-hyperaccumulating plants, has yet to be examined. The aim of this study was to test the effect of cadmium availability and herbivory on leaf trichome density and herbivore deterrence in the metal hyperaccumulator Helianthus annuus. To test this, H. Annuus plants were grown in control pots or pots inoculated with 10 mg/kg cadmium and were subjected to either no herbivory or simulated herbivory using mechanical damage and foliar jasmonic acid application. Herbivore deterrence was tested in a feeding assay using Spodoptera littoralis caterpillars. Interestingly, while the trichome density of H. annuus increased by 79% or 53.5% under high cadmium availability or simulated herbivory, respectively, it decreased by 26% when the stressors were combined. Furthermore, regardless of cadmium availability, simulated herbivory induced a 40% increase in deterrence of S. littoralis. These findings suggest that the combination of metal availability and herbivory might present excessive stress to hyperaccumulators. Moreover, they suggest that the risk of metal bioaccumulation in phytoremediation can be reduced by simulated herbivory.

Defects in Glabrous 3 (GL3) functionality underlie the absence of trichomes in Brassica napus

Previously, expression of the Arabidopsis thaliana GLABRA3 (GL3) induced trichome formation in Brassica napus. GL3 orthologues were examined from glabrous (B. oleracea), semi-glabrous (B. napus), moderately hirsute (B. rapa), and very hirsute (B. villosa) Brassica species. Ectopic expression of BnGL3, BrGL3 alleles, or BvGL3 induced trichome formation in glabrous B. napus with the effect on trichome number commensurate with density in the original accessions. Chimeric GL3 proteins in which the B. napus amino terminal region, which interacts with MYB proteins, or the middle region, which interacts with the WD40 protein TTG1, was exchanged with corresponding regions from A. thaliana were as stimulatory to trichome production as AtGL3. Exchange of the carboxy-terminal region containing a bHLH domain and an ACT domain did not alter the trichome stimulatory activity, although modeling of the ACT domain identified differences that could affect GL3 dimerization. B. napus A- and C-genomes orthologues differed in their abilities to form homo- and heterodimers. Modeling of the amino-terminal region revealed a conserved domain that may represent the MYB factor binding pocket. This region interacted with the MYB factors GL1, CPC, and TRY, as well as with JAZ8, which is involved in jasmonic acid-mediated regulation of MYC-like transcription factors. Protein interaction studies indicated that GL1 interaction with GL3 from B. napus and A. thaliana may underlie the difference in their respective abilities to induce trichome formation.

Plant terpenoid biosynthetic network and its multiple layers of regulation

Terpenoids constitute one of the largest and most chemically diverse classes of primary and secondary metabolites in nature with an exceptional breadth of functional roles in plants. Biosynthesis of all terpenoids begins with the universal five‑carbon building blocks, isopentenyl diphosphate (IPP) and its allylic isomer dimethylallyl diphosphate (DMAPP), which in plants are derived from two compartmentally separated but metabolically crosstalking routes, the mevalonic acid (MVA) and methylerythritol phosphate (MEP) pathways. Here, we review the current knowledge on the terpenoid precursor pathways and highlight the critical hidden constraints as well as multiple regulatory mechanisms that coordinate and homeostatically govern carbon flux through the terpenoid biosynthetic network in plants.

Compatibility of the fungus Beauveria bassiana and Trichoplusia ni SNPV against the cabbage looper Trichoplusia ni: crop plant matters

BACKGROUND

Microbial insecticides are an important weapon in insect pest management, but their use is still relatively limited. One approach for increasing their efficacy and use could be to combine different pathogens to increase pest mortality. However, little is known about whether increasing pathogen diversity will improve pest management. Here, we investigated the compatibility of two pathogens for the management of the cabbage looper, Trichoplusia ni, T. ni nucleopolyhedrovirus (TniSNPV) and the entomopathogenic fungus Beauveria bassiana, on two crops, tomato and broccoli. The pathogens were applied to individual plants using ultra low volume sprays, alone or in combination, either synchronously or asynchronously. Healthy third-instar T. ni larvae were introduced to the plants before application and collected by destructive sampling 24 h after the last pathogen application.

RESULTS

Combined applications did not result in an increase in larval mortality compared to TniSNPV alone, although mortality was generally high. B. bassiana was considerably less effective on broccoli compared to tomato. In both the combined treatments, virus-induced mortality was approximately 50% lower when applied together with the fungus, while fungus-induced mortality was not affected by the virus, even when the virus was introduced 24 h before the fungus.

CONCLUSION

While our results suggest that applying this combination of entomopathogens would not be beneficial for pest management, this study illustrates the need to consider the target crop as an important driver of the efficacy of both single and mixed pathogen applications in the field. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A large presence/absence variation in the promotor of the ClLOG gene determines trichome elongation in watermelon

KEY MESSAGE

The ClLOG gene encoding a cytokinin riboside 5'-monophosphate phosphoribohydrolase determines trichome length in watermelon, which is associated with its promoter variations. Trichomes, which are differentiated from epidermal cells, are special accessory structures that cover the above-ground organs of plants and possibly contribute to biotic and abiotic stress resistance. Here, a bulked segregant analysis (BSA) of an F2 population with significant variations in trichome length was undertaken. A 1.84-Mb candidate region on chromosome 10 was associated with trichome length. Resequencing and fine-mapping analyses indicated that a 12-kb structural variation in the promoter of Cla97C10G203450 (ClLOG) led to a significant expression difference in this gene in watermelon lines with different trichome lengths. In addition, a virus-induced gene silencing analysis confirmed that ClLOG positively regulated trichome elongation. These findings provide new information and identify a potential target gene for controlling multicellular trichome elongation in watermelon.

The chromosome-scale genome and the genetic resistance machinery against insect herbivores of the Mexican toloache, Datura stramonium

Plant resistance refers to the heritable ability of plants to reduce damage caused by natural enemies, such as herbivores and pathogens, either through constitutive or induced traits like chemical compounds or trichomes. However, the genetic architecture-the number and genome location of genes that affect plant defense and the magnitude of their effects-of plant resistance to arthropod herbivores in natural populations remains poorly understood. In this study, we aimed to unveil the genetic architecture of plant resistance to insect herbivores in the annual herb Datura stramonium (Solanaceae) through quantitative trait loci mapping. We achieved this by assembling the species' genome and constructing a linkage map using an F2 progeny transplanted into natural habitats. Furthermore, we conducted differential gene expression analysis between undamaged and damaged plants caused by the primary folivore, Lema daturaphila larvae. Our genome assembly resulted in 6,109 scaffolds distributed across 12 haploid chromosomes. A single quantitative trait loci region on chromosome 3 was associated with plant resistance, spanning 0 to 5.17 cM. The explained variance by the quantitative trait loci was 8.44%. Our findings imply that the resistance mechanisms of D. stramonium are shaped by the complex interplay of multiple genes with minor effects. Protein-protein interaction networks involving genes within the quantitative trait loci region and overexpressed genes uncovered the key role of receptor-like cytoplasmic kinases in signaling and regulating tropane alkaloids and terpenoids, which serve as powerful chemical defenses against D. stramonium herbivores. The data generated in our study constitute important resources for delving into the evolution and ecology of secondary compounds mediating plant-insect interactions.

The evolution of glandularity as a defense against herbivores in the tarweed clade

PREMISE

Glandular trichomes are implicated in direct and indirect defense of plants. However, the degree to which glandular and non-glandular trichomes have evolved as a consequence of herbivory remains unclear, because their heritability, their association with herbivore resistance, their trade-offs with one another, and their association with other functions are rarely quantified.

METHODS

We conducted a phylogenetic comparison of trichomes and herbivore resistance against the generalist caterpillar, Heliothis virescens, among tarweed species (Asteraceae: Madiinae) and a genetic correlation study comparing those same traits among maternal half-sibs of three tarweed species.

RESULTS

Within a tarweed species, we found no evidence that herbivore growth rate decreased on tarweed individuals or maternal sib groups with more glandularity or denser trichomes. However, tarweed species with more glandularity and fewer non-glandular trichomes resulted in slower-growing herbivores. Likewise, a trade-off between glandular and non-glandular trichomes was apparent among tarweed species, but not among individuals or sib groups within a species.

CONCLUSIONS

Our results suggest that this key herbivore does not select for trichomes as a direct defense in tarweed species. However, trichomes differed substantially among species and likely affect herbivore pressure on those species. Our results demonstrate that trade-offs among plant traits, as well as inference on the function of those traits, can depend on scale.

How plant traits respond to and affect vertebrate and invertebrate herbivores-Are measurements comparable across herbivore types?

Despite plants realistically being affected by vertebrate and invertebrate herbivores simultaneously, fundamental differences in the ecology and evolution of these two herbivore guilds often means their impacts on plants are studied separately. A synthesis of the literature is needed to understand the types of plant traits examined and their response to, and effect on (in terms of forage selection) vertebrate and invertebrate herbivory, and to identify associated knowledge gaps. Focusing on grassland systems and species, we found 138 articles that met our criteria: 39 invertebrate, 97 vertebrate and 2 focussed on both vertebrate and invertebrate herbivores. Our study identified invertebrate focussed research, research conducted in the Southern Hemisphere and research on nondomesticated herbivores was significantly underrepresented based on our search and should be a focus of future research. Differences in study focus (trait response or trait effect), along with differences in the types of traits examined, led to limited opportunity for comparison between the two herbivore guilds. This review therefore predominantly discusses the response and effect of plant traits to each herbivore guild separately. In future studies, we suggest this review be used as a guide for trait selection, to improve comparability and the broader significance of results.

Better Together: Volatile-Mediated Intraguild Effects on the Preference of Tuta absoluta and Trialeurodes vaporariorum for Tomato Plants

Plant-herbivore interactions have been extensively studied in tomato plants and their most common pests. Tomato plant chemical defenses, both constitutive and inducible, play a role in mediating these interactions. Damaged tomato plants alter their volatile profiles, affecting herbivore preferences between undamaged and damaged plants. However, previous studies on tomato volatiles and herbivore preferences have yielded conflicting results, both in the volatile chemistry itself as well as in the attraction/repellent herbivore response. This study revisits the volatile-mediated interactions between tomato plants and two of their main herbivores: the leafminer Tuta absoluta and the whitefly Trialeurodes vaporariorum. Tomato plant volatiles were analyzed before and after damage by each of these herbivores, and the preference for oviposition (T. absoluta) and settling (T. vaporariorum) on undamaged and damaged plants was assessed both after conspecific and heterospecific damage. We found that both insects consistently preferred damaged plants over undamaged plants. The emission of herbivore-induced plant volatiles (HIPVs) increased after T. absoluta damage but decreased after T. vaporariorum damage. While some of our findings are in line with previous reports, T. absoluta preferred to oviposit on plants damaged by conspecifics, which differs from earlier studies. A comparison of HIPVs emitted after damage by T. absoluta and T. vaporariorum revealed differences in up- or down-regulation, as well as significant variations in specific compounds (12 for T. absoluta and 26 for T. vaporariorum damaged-plants). Only two compounds, β-caryophyllene and tetradecane, significantly varied because of damage by either herbivore, in line with the overall variation of the HIPV blend. Differences in HIPVs and herbivore preferences may be attributed to the distinct feeding habits of both herbivores, which activate different defensive pathways in plants. The plant's challenge in simultaneously activating both defensive pathways may explain the preference for heterospecific damaged plants found in this study, which are also in line with our own observations in greenhouses.

Beyond skin-deep: targeting the plant surface for crop improvement

The above-ground plant surface is a well-adapted tissue layer that acts as an interface between the plant and its surrounding environment. As such, its primary role is to protect against desiccation and maintain the gaseous exchange required for photosynthesis. Further, this surface layer provides a barrier against pathogens and herbivory, while attracting pollinators and agents of seed dispersal. In the context of agriculture, the plant surface is strongly linked to post-harvest crop quality and yield. The epidermal layer contains several unique cell types adapted for these functions, while the non-lignified above-ground plant organs are covered by a hydrophobic cuticular membrane. This review aims to provide an overview of the latest understanding of the molecular mechanisms underlying crop cuticle and epidermal cell formation, with focus placed on genetic elements contributing towards quality, yield, drought tolerance, herbivory defence, pathogen resistance, pollinator attraction, and sterility, while highlighting the inter-relatedness of plant surface development and traits. Potential crop improvement strategies utilizing this knowledge are outlined in the context of the recent development of new breeding techniques.

Cannabinoids function in defense against chewing herbivores in Cannabis sativa L

In the decades since the first cannabinoids were identified by scientists, research has focused almost exclusively on the function and capacity of cannabinoids as medicines and intoxicants for humans and other vertebrates. Very little is known about the adaptive value of cannabinoid production, though several hypotheses have been proposed including protection from ultraviolet radiation, pathogens, and herbivores. To test the prediction that genotypes with greater concentrations of cannabinoids will have reduced herbivory, a segregating F2 population of Cannabis sativa was leveraged to conduct lab- and field-based bioassays investigating the function of cannabinoids in mediating interactions with chewing herbivores. In the field, foliar cannabinoid concentration was inversely correlated with chewing herbivore damage. On detached leaves, Trichoplusia ni larvae consumed less leaf area and grew less when feeding on leaves with greater concentrations of cannabinoids. Scanning electron and light microscopy were used to characterize variation in glandular trichome morphology. Cannabinoid-free genotypes had trichomes that appeared collapsed. To isolate cannabinoids from confounding factors, artificial insect diet was amended with cannabinoids in a range of physiologically relevant concentrations. Larvae grew less and had lower rates of survival as cannabinoid concentration increased. These results support the hypothesis that cannabinoids function in defense against chewing herbivores.

Tomato defences modulate not only insect performance but also their gut microbial composition

Plants protect their tissues from insect herbivory with specialized structures and chemicals, such as cuticles, trichomes, and metabolites contained therein. Bacteria inside the insect gut are also exposed to plant defences and can potentially modify the outcome of plant-insect interactions. To disentangle this complex multi-organism system, we used tomato mutants impaired in the production of plant defences (odorless-2 and jasmonic acid-insensitive1) and two cultivars (Ailsa Craig and Castlemart), exposed them to herbivory by the cabbage looper (Trichoplusia ni H.) and collected the insect frass for bacterial community analysis. While the epicuticular wax and terpene profiles were variable, the leaf fatty acid composition remained consistent among genotypes. Moreover, larval weight confirmed the negative association between plant defences and insect performance. The distinctive frass fatty acid profiles indicated that plant genotype also influences the lipid digestive metabolism of insects. Additionally, comparisons of leaf and insect-gut bacterial communities revealed a limited overlap in bacterial species between the two sample types. Insect bacterial community abundance and diversity were notably reduced in insects fed on the mutants, with Enterobacteriaceae being the predominant group, whereas putatively pathogenic taxa were found in wildtype genotypes. Altogether, these results indicate that plant defences can modulate insect-associated bacterial community composition.

Humic Substances Isolated from Recycled Biomass Trigger Jasmonic Acid Biosynthesis and Signalling

Intensive agriculture maintains high crop yields through chemical inputs, which are well known for their adverse effects on environmental quality and human health. Innovative technologies are required to reduce the risk generated by the extensive and harmful use of pesticides. The plant biostimulants made from humic substances isolated from recyclable biomass offer an alternative approach to address the need for replacing conventional agrochemicals without compromising the crop yield. The stimulatory effects of humic substances are commonly associated with plant hormones, particularly auxins. However, jasmonic acid (JA) is crucial metabolite in mediating the defence responses and governing plant growth and development. This work aimed to evaluate the changes in the biosynthesis and signalling pathway of JA in tomato seedlings treated with humic acids (HA) isolated from vermicompost. We use the tomato model system cultivar Micro-Tom (MT) harbouring a reporter gene fused to a synthetic promoter that responds to jasmonic acid (JERE::GUS). The transcript levels of genes involved in JA generation and activity were also determined using qRT-PCR. The application of HA promoted plant growth and altered the JA status, as revealed by both GUS and qRT-PCR assays. Both JA enzymatic synthesis (LOX, OPR3) and JA signalling genes (JAZ and JAR) were found in higher transcription levels in plants treated with HA. In addition, ethylene (ETR4) and auxin (ARF6) signalling components were positively modulated by HA, revealing a hormonal cross-talk. Our results prove that the plant defence system linked to JA can be emulated by HA application without growth inhibition.

Tomato Chemical Defenses Intensify Corn Earworm (Helicoverpa zea) Mortality from Opportunistic Bacterial Pathogens

Insect herbivores face multiple challenges to their ability to grow and reproduce. Plants can produce a series of defenses that disrupt and damage the herbivore digestive system, which are heightened upon injury by insect feeding. Additionally, insects face threats from virulent microorganisms that can incur their own set of potential costs to hosts. Microorganisms that invade through the digestive system may function in concert with defenses generated by plants, creating combined assailments on host insects. In our study, we evaluated how tomato defenses interact with an enteric bacterial isolate, Serratia marcescens, in the corn earworm (Helicoverpa zea). We performed bioassays using different tomato cultivars that were induced by methyl jasmonate and larvae orally inoculated with a S. marcescens isolate. Untreated corn earworm larval mortality was low on constitutive tomato, while larvae inoculated with S. marcescens exhibited > 50% mortality within 5 days. Induction treatments elevated both control mortality (~ 45%) and in combination with S. marcescens (> 95%). Larvae also died faster when encountering induced defenses and Serratia. Using a tomato mutant, foliar polyphenol oxidase activity likely had stronger impacts on S. marcescens-mediated larval mortality. Induction treatments also elevated the number of bacterial colony-forming units in the hemolymph of larvae inoculated with Serratia. Larval mortality by S. marcescens was low (< 10%) on artificial diets. Our results demonstrate that plant chemical defenses enhance larval mortality from an opportunistic gut microbe. We propose that the combined damage from both the plant and microbial agent overwhelm the herbivore to increase mortality rates and expedite host death.

Life-table analyses for the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae): effects of plant genotype

BACKGROUND

Host plant resistance plays an important role in integrated pest management programs. Crop resistance assessments commonly focus on only a single dependent variable, such as larval survival/plant damage, which limits the ability to appreciate the impact of host plants on pest populations in the full sense. Therefore, we performed life-table analyses for tomato leaf miner Tuta absoluta, on 19 Solanum lycopersicum genotypes and a wild Solanum habrochaites accession. These analyses assess the ability of the pest to attain a high population density on different tomato genotypes. Based on the resulting ranking of tomato resistance at the vegetative stage (45-day-old plants), we tested the resistance of six selected genotypes at the reproductive stage (4-month-old plants).

RESULTS

T. absoluta performance was significantly inferior on vegetative-stage S. habrochaites plants (LA 1777); time taken for the first instars to mine the leaves (5 ± 0.14 days), development time of early- and late-stage larvae (8.8 ± 0.2 and 4.2 ± 0.2 days, respectively), pupal period (11.2 ± 0.58 days), and total developmental time (29.4 ± 0.83 days) were significantly longer, fecundity was significantly lower (18.66 ± 7.24 days), and the highest total mortality (63.33%) also recorded compared with other genotypes, resulting in the lowest net reproductive rate (R₀ ) (11.20 ± 2.51). For the six selected genotypes, the ranking of plant resistance did not change between plants at the vegetative and reproductive stages.

CONCLUSION

This study suggested that of 20 screened tomato genotypes, LA 1777 and EC-620343 are the least suitable hosts for T. absoluta to establish fast-growing populations, and thus can be employed in integrated T. absoluta management. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Morphological characterization of intraspecific variation for trichome traits in tomato (Solanum lycopersicum)

Trichomes, the hairlike protuberances in plants, have been well known to act as the first line of defense against herbivores, and abiotic stresses, along with other structural defenses such as spines, thorns, and waxes. We previously reported the tremendous variation in trichome traits among different wild and cultivated Solanum species and demonstrated that trichomes types and density are traditionally miscalculated and often misnamed. However, intraspecific variation in trichome traits is poorly understood, although this has implications for stress tolerance and resistance breeding programs in economically important crop species and can also mediate ecological interactions at multiple trophic levels in their wild congeners. In this study, using tomato as a model, we characterized the trichomes from 10 commonly grown varieties using a minimal sample prep desktop scanning electron microscopy, and followed up with estimating their dimensions across the varieties and trichome types. We hypothesized that although trichome number may vary, the varieties will have similar trichome types, based on current literature. Our results show that there is significant variation for trichome number as well as dimensions of trichome types among these varieties. Furthermore, when we separately analyzed the number and dimensions of commonly found glandular and non-glandular trichomes, the results were consistent with broad assessment of trichomes, showing consistent variation among varieties, suggesting that trichome studies should not be limited to basic classification into glandular and non-glandular, and should accommodate the sub-types and their dimensions.

Metabolomic analysis of methyl jasmonate treatment on phytocannabinoid production in Cannabis sativa

Cannabis sativa is a multi-use and chemically complex plant which is utilized for food, fiber, and medicine. Plants produce a class of psychoactive and medicinally important specialized metabolites referred to as phytocannabinoids (PCs). The phytohormone methyl jasmonate (MeJA) is a naturally occurring methyl ester of jasmonic acid and a product of oxylipin biosynthesis which initiates and regulates the biosynthesis of a broad range of specialized metabolites across a number of diverse plant lineages. While the effects of exogenous MeJA application on PC production has been reported, treatments have been constrained to a narrow molar range and to the targeted analysis of a small number of compounds. Using high-resolution mass spectrometry with data-dependent acquisition, we examined the global metabolomic effects of MeJA in C. sativa to explore oxylipin-mediated regulation of PC biosynthesis and accumulation. A dose-response relationship was observed, with an almost two-fold increase in PC content found in inflorescences of female clones treated with 15 mM MeJA compared to the control group. Comparison of the inflorescence metabolome across MeJA treatments coupled with targeted transcript analysis was used to elucidate key regulatory components contributing to PC production and metabolism more broadly. Revealing these biological signatures improves our understanding of the role of the oxylipin pathway in C. sativa and provides putative molecular targets for the metabolic engineering and optimization of chemical phenotype for medicinal and industrial end-uses.

Differential defensive and nutritional traits among cultivated tomato and its wild relatives shape their interactions with a specialist herbivore

Cultivated tomato presented lower constitutive volatiles, reduced morphological and chemical defenses, and increased leaf nutritional quality that affect its resistance against the specialist herbivore Tuta absoluta compared to its wild relatives. Plant domestication process has selected desirable agronomic attributes that can both intentionally and unintentionally compromise other important traits, such as plant defense and nutritional value. However, the effect of domestication on defensive and nutritional traits of plant organs not exposed to selection and the consequent interactions with specialist herbivores are only partly known. Here, we hypothesized that the modern cultivated tomato has reduced levels of constitutive defense and increased levels of nutritional value compared with its wild relatives, and such differences affect the preference and performance of the South American tomato pinworm, Tuta absoluta-an insect pest that co-evolved with tomato. To test this hypothesis, we compared plant volatile emissions, leaf defensive (glandular and non-glandular trichome density, and total phenolic content), and nutritional traits (nitrogen content) among the cultivated tomato Solanum lycopersicum and its wild relatives S. pennellii and S. habrochaites. We also determined the attraction and ovipositional preference of female moths and larval performance on cultivated and wild tomatoes. Volatile emissions were qualitatively and quantitatively different among the cultivated and wild species. Glandular trichomes density and total phenolics were lower in S. lycopersicum. In contrast, this species had a greater non-glandular trichome density and leaf nitrogen content. Female moths were more attracted and consistently laid more eggs on the cultivated S. lycopersicum. Larvae fed on S. lycopersicum leaves had a better performance reaching shorter larval developmental times and increasing the pupal weight compared to those fed on wild tomatoes. Overall, our study documents that agronomic selection for increased yields has altered the defensive and nutritional traits in tomato plants, affecting their resistance to T. absoluta.

A HD-ZIP transcription factor specifies fates of multicellular trichomes via dosage-dependent mechanisms in tomato

Hair-like structures are shared by most living organisms. The hairs on plant surfaces, commonly referred to as trichomes, form diverse types to sense and protect against various stresses. However, it is unclear how trichomes differentiate into highly variable forms. Here, we show that a homeodomain leucine zipper (HD-ZIP) transcription factor named Woolly controls the fates of distinct trichomes in tomato via a dosage-dependent mechanism. The autocatalytic reinforcement of Woolly is counteracted by an autoregulatory negative feedback loop, creating a circuit with a high or low Woolly level. This biases the transcriptional activation of separate antagonistic cascades that lead to different trichome types. Our results identify the developmental switch of trichome formation and provide mechanistic insights into the progressive fate specification in plants, as well as a path to enhancing plant stress resistance and the production of beneficial chemicals.

Negative Effects of Phthorimaea absoluta-Resistant Tomato Genotypes on the Zoophytophagous Biocontrol Agent, Orius laevigatus (Fieber) (Hemiptera: Anthocoridae)

Complex interactions between host plant resistance (HPR) and biological control agents, particularly omnivorous predators, can shape the outcome of an integrated pest management (IPM) program. However, such interactions are seldom explored during plant breeding programs. Therefore, in the present study, we compared the performance of the omnivorous biological control agent Orius laevigatus on six tomato genotypes with different levels of resistance to the tomato leaf miner Phthorimaea absoluta. We found that the O. laevigatus fitness components (i.e., egg deposition, egg hatching rate, and duration of egg, early nymphal, late nymphal stages, and their survival) were inferior on the wild resistant genotypes (LA 716 and LA 1777) in comparison to the resistant domesticated genotype EC 620343 and the susceptible genotypes (EC 705464 and EC 519819). It appears that the adverse effects of tomato genotypes on O. laevigatus are determined mainly by glandular and non-glandular trichome densities on the leaves. Comparison of O. laevigatus response to the tested tomato cultivars to that of P. absoluta revealed significant positive correlations in duration of the egg stages, development time of early and late larval stages, and overall immature mortality in both species. It appears, therefore, that defensive plant traits operate in a similar way on the pest and its predator in the system. Overall, the present study of the tomato-P. absoluta-O. laevigatus system provides experimental evidence for the need to optimize pest management by employing intermediate levels of crop resistance together with biological control agents.

PeVL1 Novel Elicitor Protein, from Verticillium lecanii 2, Enhances Systemic Resistance against Rice Leaf Roller (Marasmia ruralis Wlk.) in Rice (Oryza sativa L.)

The hazardous pest known as rice leaf roller (Marasmia ruralis Wlk.) (Lepidoptera: Pyralidae), which undermines rice (Oryza sativa L.) output globally, folds the leaves of the rice plant. Protein elicitors are thought to be biological elements that causes the rice to become resistant to herbivores. The potential for biocontrol of the emerging elicitor protein evaluated from Verticillium lecanii 2 (PeVL1) was evaluated against M. ruralis. To assess the impact of PeVL1 on immature development, survival, and lifetime, four different PeVL1 concentrations were allocated. Electrical penetration graphs (EPGs) against M. ruralis were used to evaluate adult reproductive efficiency and the interaction between the pest and the pathogen. Furthermore, the characterization of active substances in PeVL1 with multi-acting entomopathogenic effects looked into the direct interactions of PeVL1 with temperature and climatic change in rice (O. sativa) plants. PeVL1 treatments reduced the population increase of second and third generation M. ruralis compared to controls. In a test of host selection, M. ruralis colonized control plants more quickly than PeVL1-treated O. sativa plants. PeVL1 concentrations prolonged the M. ruralis larval stage. Similar to fecundity, PeVL1-treated seedlings produced fewer offspring than control seedlings. On PeVL1-treated leaves, trichomes and wax production created an unfavorable habitat for M. ruralis. PeVL1 changed the surface structure of the leaves, which inhibited colonization and decreased M. ruralis reproduction. The activation of pathways was another aspect of systemic defense activities including jasmonic acid (JA), salicylic acid (SA), and ethylene (ET). Based on these results against M. ruralis, the use of PeVL1 in the agroecosystem with integrated pest management and biocontrol seems appropriate. Our research provides a novel insight into a cutting-edge biocontrol method utilizing V. lecanii 2.

Anatomical inferences on aerial bud protection of three Eugenia shrub species from the Cerrado

Location and degree of protection of aerial buds are important functional traits in disturbance- or stress-prone environments since aerial buds ensure the development of new organs under favourable growing conditions. This study was carried out in a Brazilian Cerrado area under regeneration after long-term Pinus cultivation, where the trees were clear-cut in 2012 and the remaining material was burned in 2014. After the fire treatment, several species resprouted from belowground organs and their aboveground organs were directly exposed to full sunlight. We collected 15 terminal branches with fully expanded leaves from three individuals of each of three Eugenia species to investigate if those with well-developed belowground organs invest in bark for aboveground bud protection. The samples were analysed using light and electron microscopy. In addition to terminal and axillary buds, all species presented accessory buds, and the number varied according to the node analysed. None of the aerial buds were protected by bark, but all were well protected by cataphylls and densely pubescent leaf primordia. There were also inter- and intra-petiolar colleters that released a mucilaginous protein exudate. The distance between the shoot apical meristem and the outer surface was longer in the terminal bud than in axillary buds. The bud leaf primordia covering the shoot apical meristem had a thick cuticle, unicellular non-glandular trichomes that accumulate phenolic and lipophilic compounds, and secretory cavities. Our study shows that all three Eugenia species studied here had highly protected aerial buds allocated from belowground organs. These morphological traits may improve the chances of the species' persistence in areas subjected to frost events, low relative humidity, high irradiance and harmful UV levels.

Differentiation and Propagation Potential of Arnica montana L. Achenes as a Consequence of the Morphological Diversity of Flowers and the Position of Flower Heads on the Plant

Arnica montana L. is a very important medicinal plant and simultaneously a European endemic endangered plant species. The morphological features and details of seed development and achene variability are poorly recognized. The aim of this study was to determine the impact of the achene position in the infructescence and the location of the inflorescence on the plant on the (i) morphological characteristics and germination ability of achenes, and (ii) recruitment of seedlings and their biometric features. Infructescences containing fully ripe achenes were randomly collected from A. montana individuals for the measurements and the germination experiment. Scanning electron microscopy, fluorescence microscopy, and light microscopy were used for characterization of flowers and achenes. The morphological traits of achenes and reproductive characteristics of A. montana were determined by the position of the achenes in the infructescence and the location of the inflorescence on the plant. The surface of arnica achenes is equipped with non-glandular and glandular trichomes, which is very rarely presented in species of the family Asteraceae. It is possible that the fluid-containing glandular trichomes are a source of essential oils. The peripherally located achenes were longer, thinner, and lighter. They were characterized by lower embryo weight, lower embryo/achene weight ratio, and lower germination capacity in comparison to the centrally located ones. The results presented in this article fill the gap in the knowledge of the morphology of achenes and the biology of the species, and provide information that can help in breeding programs, active protection, and field cultivation.

Biocontrol Potential of PeBL2, a Novel Entomopathogenic Bacterium from Brevibacillus laterosporus A60, Induces Systemic Resistance against Rice Leaf Folder Cnaphalocrocis exigua (Butler) in Rice (Oryza sativa L.)

The dangerous insect pest known as rice leaf folder Cnaphalocrocis exigua (Butler), which reduces rice output globally, twists and feeds on the young rice plant's leaves. Protein elicitors are hypothesized to be biological components that promote rice in becoming herbivore resistant. The evolving elicitor protein PeBL2, obtained from Brevibacillus laterosporus A60, was tested for biocontrol against C. exigua. Four distinct PeBL2 doses (74.23, 45.53, 22.26, and 11.13 μg mL^-1) were assigned to evaluate the impact of PeBL2 on immature growth, survivability, and lifespan. Adult reproductive efficiency and the interaction between the pest and the disease were assessed against C. exigua. Further, the assessment of active compounds in PeBL2 with multi-acting entomopathogenic effects investigated the direct correlations of PeBL2 with temperature and climatic change in plants of rice (Oryza sativa L.). When compared to controls, PeBL2 treatments reduced the growing population of second- and third-generation C. exigua. Cnaphalocrocis exigua colonized control plants faster than PeBL2-treated O. sativa plants in a host selection test. PeBL2 doses delayed the development of the larval stage of C. exigua. PeBL2-treated seedlings generated less offspring than control seedlings, identical to fecundity. Trichomes and wax formation on PeBL2-treated leaves generated an adverse environment for C. exigua. PeBL2 altered the surface topography of the leaves, preventing colonization and reducing C. exigua reproduction. PeBL2-treated O. sativa seedlings exhibited somewhat increased amounts of jasmonic acid (JA), salicylic acid (SA), and ethylene (ET). Systemic defensive processes also included the activation of pathways (JA, SA, and ET). Following these results versus C. exigua, the use of PeBL2 in an agroecosystem with integrated pest management and biocontrol appears to be reasonable. These findings shed new light on a cutting-edge biocontrol technique based on B. laterosporus A60.

Responses of Bunias orientalis to Short-term Fungal Infection and Insect Herbivory are Independent of Nutrient Supply

Plants have to allocate their resources in both growth and defense under different environmental challenges. Several plant species have become invasive particularly in disturbed fertile habitats, which may influence their resource allocation. We studied the effects of nitrate fertilization (low versus high) on various plant responses towards a pathogenic fungus, Alternaria brassicae, and a herbivorous insect species, Mamestra brassicae, in a population of Bunias orientalis, which is invasive in parts of central Europe. Aboveground biomass and leaf trichome density were enhanced in plants under high fertilization. In contrast, the short-term fungal infection and herbivory had no effect on aboveground biomass. Leaf water, nitrogen content and glucosinolate concentrations were neither affected by fertilization nor in response to antagonist attack. The total soluble sugar content, especially fructose, as well as leaf peroxidase activity increased significantly in leaves upon fungal infection, but independent of fertilization. Larval biomass gain and herbivore survival were likewise unaffected by fertilization. Our findings highlight that under conditions of high fertilization, B. orientalis plants allocate more resources into growth and morphological defenses than chemical defenses. In contrast, induced responses to short-term antagonist attack seem independent of nitrate availability in this population.

Adverse effects of inbreeding on the transgenerational expression of herbivore-induced defense traits in Solanum carolinense

In addition to directly inducing physical and chemical defenses, herbivory experienced by plants in one generation can influence the expression of defensive traits in offspring. Plant defense phenotypes can be compromised by inbreeding, and there is some evidence that such adverse effects can extend to the transgenerational expression of induced resistance. We explored how the inbreeding status of maternal Solanum carolinense plants influenced the transgenerational effects of herbivory on the defensive traits and herbivore resistance of offspring. Manduca sexta caterpillars were used to damage inbred and outbred S. carolinense maternal plants and cross pollinations were performed to produced seeds from herbivore-damaged and undamaged, inbred and outbred maternal plants. Seeds were grown in the greenhouse to assess offspring defense-related traits (i.e., leaf trichomes, internode spines, volatile organic compounds) and resistance to herbivores. We found that feeding by M. sexta caterpillars on maternal plants had a positive influence on trichome and spine production in offspring and that caterpillar development on offspring of herbivore-damaged maternal plants was delayed relative to that on offspring of undamaged plants. Offspring of inbred maternal plants had reduced spine production, compared to those of outbred maternal plants, and caterpillars performed better on the offspring of inbred plants. Both herbivory and inbreeding in the maternal generation altered volatile emissions of offspring. In general, maternal plant inbreeding dampened transgenerational effects of herbivory on offspring defensive traits and herbivore resistance. Taken together, this study demonstrates that inducible defenses in S. carolinense can persist across generations and that inbreeding compromises transgenerational resistance in S. carolinense.

Acoustic radiation force on a long cylinder, and potential sound transduction by tomato trichomes

Acoustic transduction by plants has been proposed as a mechanism to enable just-in-time up-regulation of metabolically expensive defensive compounds. Although the mechanisms by which this "hearing" occurs are unknown, mechanosensation by elongated plant hair cells known as trichomes is suspected. To evaluate this possibility, we developed a theoretical model to evaluate the acoustic radiation force that an elongated cylinder can receive in response to sounds emitted by animals, including insect herbivores, and applied it to the long, cylindrical stem trichomes of the tomato plant Solanum lycopersicum. Based on perturbation theory and validated by finite element simulations, the model quantifies the effects of viscosity and frequency on this acoustic radiation force. Results suggest that acoustic emissions from certain animals, including insect herbivores, may produce acoustic radiation force sufficient to trigger stretch-activated ion channels.

Type of Stress Induces Differential Responses in Acer rubrum (Red Maple), but Induced Responses Have No Effect on Herbivorous Pests

Plants thrive in dynamic environments requiring adaptive strategies in response to environmental stressors. Furthermore, insect herbivores may be attracted or deterred by the expression of these traits. This study examines growth, physiological, and phytochemical adaptations of maple trees in response to stressors and how these stressors effect herbivore feeding behavior within an agricultural production system. Agricultural systems are unique because plants experience environmental stressors unique to production such as herbicide sprays and girdling. Using four environmental stressors commonly observed in agricultural production (control, mechanical defoliation, chemical defoliation, and girdling), applied to two cultivars of red maple (Acer rubrum, ‘Brandywine’ and ‘Franksred’), this study analyzed differentiation of expressed traits in a production system. Responses varied depending on cultivar and stress treatment but had no effect on insect herbivore behavior. Understanding the ecological interactions within these systems will provide information for better plant production and pest management recommendations.

Comparative transcriptome analysis reveals key pathways and genes involved in trichome development in tea plant (Camellia sinensis)

Trichomes, which develop from epidermal cells, are considered one of the important characteristics of the tea plant [Camellia sinensis (L.) O. Kuntze]. Many nutritional and metabolomic studies have indicated the important contributions of trichomes to tea products quality. However, understanding the regulation of trichome formation at the molecular level remains elusive in tea plants. Herein, we present a genome-wide comparative transcriptome analysis between the hairless Chuyeqi (CYQ) with fewer trichomes and the hairy Budiaomao (BDM) with more trichomes tea plant genotypes, toward the identification of biological processes and functional gene activities that occur during trichome development. In the present study, trichomes in both cultivars CYQ and BDM were unicellular, unbranched, straight, and soft-structured. The density of trichomes was the highest in the bud and tender leaf periods. Further, using the high-throughput sequencing method, we identified 48,856 unigenes, of which 31,574 were differentially expressed. In an analysis of 208 differentially expressed genes (DEGs) encoding transcription factors (TFs), five may involve in trichome development. In addition, on the basis of the Gene Ontology (GO) annotation and the weighted gene co-expression network analysis (WGCNA) results, we screened several DEGs that may contribute to trichome growth, including 66 DEGs related to plant resistance genes (PRGs), 172 DEGs related to cell wall biosynthesis pathway, 29 DEGs related to cell cycle pathway, and 45 DEGs related to cytoskeleton biosynthesis. Collectively, this study provided high-quality RNA-seq information to improve our understanding of the molecular regulatory mechanism of trichome development and lay a foundation for additional trichome studies in tea plants.

Co-Transcriptomic Analysis of the Maize-Western Corn Rootworm Interaction

The Western corn rootworm (WCR; Diabrotica virgifera virgifera) is an economically important belowground pest of maize. Belowground feeding by WCR is damaging because it weakens the roots system, diminishes nutrient uptake, and creates entry points for fungal and bacterial pathogens and increases lodging, all of which can significantly suppress maize yields. Previously, it was demonstrated that belowground herbivory can trigger plant defense responses in the roots and the shoots, thereby impacting intraplant communication. Although several aspects of maize-WCR interactions have been reported, co-transcriptomic remodeling in the plant and insect are yet to be explored. We used a maize genotype, Mp708, that is resistant to a large guild of herbivore pests to study the underlying plant defense signaling network between below and aboveground tissues. We also evaluated WCR compensatory transcriptome responses. Using RNA-seq, we profiled the transcriptome of roots and leaves that interacted with WCR infestation up to 5 days post infestation (dpi). Our results suggest that Mp708 shoots and roots had elevated constitutive and WCR-feeding induced expression of genes related to jasmonic acid and ethylene pathways, respectively, before and after WCR feeding for 1 and 5 days. Similarly, extended feeding by WCR for 5 days in Mp708 roots suppressed many genes involved in the benzoxazinoid pathway, which is a major group of indole-derived secondary metabolites that provides resistance to several insect pests in maize. Furthermore, extended feeding by WCR on Mp708 roots revealed several genes that were downregulated in WCR, which include genes related to proteolysis, neuropeptide signaling pathway, defense response, drug catabolic process, and hormone metabolic process. These findings indicate a dynamic transcriptomic dialog between WCR and WCR-infested maize plants.

The dual function of elicitors and effectors from insects: reviewing the 'arms race' against plant defenses

This review provides an overview, analysis, and reflection on insect elicitors and effectors (particularly from oral secretions) in the context of the 'arms race' with host plants. Following injury by an insect herbivore, plants rapidly activate induced defenses that may directly or indirectly affect the insect. Such defense pathways are influenced by a multitude of factors; however, cues from the insect's oral secretions are perhaps the most well studied mediators of such plant responses. The relationship between plants and their insect herbivores is often termed an 'evolutionary arms race' of strategies for each organism to either overcome defenses or to avoid attack. However, these compounds that can elicit a plant defense response that is detrimental to the insect may also benefit the physiology or metabolism of an insect species. Indeed, several insect elicitors of plant defenses (such as the fatty acid-amino acid conjugate, volicitin) are known to enhance an insect's ability to obtain nutritionally important compounds from plant tissue. Here we re-examine the well-known elicitors and effectors from chewing insects to demonstrate not only our incomplete understanding of the specific biochemical and molecular cascades involved in these interactions but also to consider the role of these compounds for the insect species itself. Finally, this overview discusses opportunities for research in the field of plant-insect interactions by utilizing tools such as genomics and proteomics to integrate the future study of these interactions through ecological, physiological, and evolutionary disciplines.

Leaf trait association in relation to herbivore defense, drought resistance, and economics in a tropical invasive plant

PREMISE

Exploring how functional traits vary and covary is important to understand plant responses to environmental change. However, we have limited understanding of the ways multiple functional traits vary and covary within invasive species.

METHODS

We measured 12 leaf traits of an invasive plant Chromolaena odorata, associated with plant or leaf economics, herbivore defense, and drought resistance on 10 introduced populations from Asia and 12 native populations from South and Central America, selected across a broad range of climatic conditions, and grown in a common garden.

RESULTS

Species' range and climatic conditions influenced leaf traits, but trait variation across climate space differed between the introduced and native ranges. Traits that confer defense against herbivores and drought resistance were associated with economic strategy, but the patterns differed by range. Plants from introduced populations that were at the fast-return end of the spectrum (high photosynthetic capacity) had high physical defense traits (high trichome density), whereas plants from native populations that were at the fast-return end of the spectrum had high drought escape traits (early leaf senescence and high percentage of withered shoots).

CONCLUSIONS

Our results indicate that invasive plants can rapidly adapt to novel environmental conditions. Chromolaena odorata showed multiple different functional trait covariation patterns and clines in the native and introduced ranges. Our results emphasize that interaction between multiple traits or functions should be considered when investigating the adaptive evolution of invasive plants.

Hrip1 Induces Systemic Resistance against Bean Aphid (Megoura japonica Matsumura) in Common Beans (Phaseolus vulgaris L.)

The emerging elicitor protein Hrip1 was evaluated for sublethal effects and biocontrol potential in the common bean Phaseolus vulgaris. In Megoura japonica Matsumura, purified elicitor protein Hrip1 was investigated for impacts on endurance, life expectancy, juvenile expansion, fully grown procreative performance, and pathogen–pest interface. The multi-acting entomopathogenic effects of the active compounds of Alternaria tenuissima active on Hrip1 in common bean (Phaseolus vulgaris L.) plants were also investigated. Megoura japonica population expansion was reduced by Hrip1 treatments (second and third generations). In a host selection test, control plants colonized quicker than Hrip1-treated P. vulgaris plants. Hrip1 influenced the longevity, development, and fertility of insects. Hrip1-elicitor protein concentrations aided M. japonica nymph development. Similarly, seedlings treated with Hrip1 generated fewer offspring than seedlings not treated with Hrip1. Hrip1 altered plant height and leaf surface structure, reducing M. japonica reproduction and colonization. Hrip1-treated P. vulgaris seedlings exhibited somewhat increased amounts of jasmonic acid, salicylic acid, and ethylene (ET). The integrated management of insect pests and biocontrol with Hrip1 in the agroecosystem appears to be suitable against M. japonica based on these findings.

Tomato Defense against Whiteflies under Drought Stress: Non-Additive Effects and Cultivar-Specific Responses

Two of the main causes of losses in tomato production are the greenhouse whitefly, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae), and drought, which is becoming a central problem in agriculture due to global climate change. The separate effects of whitefly infestation and drought have been amply studied in many crop systems. However, less is known about their combined effects. To evaluate whether drought stress (DS) affects plant defense against whiteflies, we assessed the joint effects of whitefly infestation and DS on plant vegetative and reproductive performance in four tomato cultivars, and assessed the effects of DS on plant resistance and tolerance (compensatory ability) to whiteflies in a greenhouse experiment. Generally, we found negative effects of DS and whiteflies on plant performance, but the combined effects of DS and herbivory were not worse than those of either stress alone. In fact, plant performance under the combined effect of both stresses was usually similar to that in the presence of whiteflies without DS. Plants growing under DS had greater trichome density. However, plant resistance—as measured by whitefly population growth—decreased under DS in two cultivars and was unaffected in the other two. Compensatory ability decreased under DS in all but one cultivar. These cultivar-specific responses suggest genetic variation in resistance and tolerance to whiteflies and could be associated with differences in drought tolerance among cultivars. Our findings underscore the difficulty in predicting the combined effects of DS and herbivory and point to the need for a better understanding of the mechanisms underlying plant responses to both stresses at the molecular, cellular, and organismal levels.

Plant Nutrition Influences Resistant Maize Defense Responses to the Fall Armyworm (Spodoptera frugiperda)

Plants are often confronted by different groups of herbivores, which threaten their growth and reproduction. However, they are capable of mounting defenses against would-be attackers which may be heightened upon attack. Resistance to insects often varies among plant species, with different genotypes exhibiting unique patterns of chemical and physical defenses. Within this framework, plant access to nutrients may be critical for maximal functioning of resistance mechanisms and are likely to differ among plant genotypes. In this study, we aimed to test the hypothesis that access to nutrition would alter the expression of plant resistance to insects and alter insect performance in a manner consistent with fertilization regime. We used two maize (Zea mays) genotypes possessing different levels of resistance and the fall armyworm (Spodoptera frugiperda) as model systems. Plants were subjected to three fertilization regimes prior to assessing insect-mediated responses. Upon reaching V4 stage, maize plants were separated into two groups, one of which was infested with fall armyworm larvae to induce plant defenses. Plant tissue was collected and used in insect bioassays and to measure the expression of defense-related genes and proteins. Insect performance differed between the two plant genotypes substantially. For each genotype, fertilization altered larval performance, where lower fertilization rates hindered larval growth. Induction of plant defenses by prior herbivory substantially reduced naïve fall armyworm growth in both genotypes. The effects between fertilization and induced defenses were complex, with low fertilization reducing induced defenses in the resistant maize. Gene and protein expression patterns differed between the genotypes, with herbivory often increasing expression, but differing between fertilization levels. The soluble protein concentrations did not change across fertilization levels but was higher in the susceptible maize genotype. These results demonstrate the malleability of plant defenses and the cascading effects of plant nutrition on insect herbivory.

Biocontrol Potential of Novel Emerging Multiacting Bacterium Bacillus amyloliquefaciens NC6 against Brevicoryne brassicae in Brassica rapa ssp. Pekinensis

The emerging elicitor protein PeBA1, extracted from Bacillus amyloliquefaciens NC6, was tested against the cabbage aphid (Brevicoryne brassicae) for its biocontrol potential. Its effects on the survival, lifespan, immature development, adult reproductive performance, and pest–pathogen interaction were assessed using electrical penetration graphs (EPGs) against B. brassicae. Furthermore, the direct effects of PeBA1 with temperature and climate change in Brassica rapa ssp. Pekinensis plants were investigated by the characterization of active compounds in B. amyloliquefaciens with multi-acting entomopathogenic effects. Compared with controls, PeBA1 treatments decreased (second- and third-generation) B. brassicae population growth rates. In a host selection test, control plants were colonized faster by B. brassicae than PeBA1-treated B. rapa plants. The B. brassicae nymphal development was extended by PeBA1 concentrations. Likewise, fecundity was reduced in PeBA1-treated seedlings compared with control, with fewer offspring produced. The trichomes and wax production on PeBA1-treated leaves resulted in a hostile environment for B. brassicae. PeBA1 altered the surface structure of the leaves, reducing B. brassicae reproduction and preventing colonization. Systemic defensive processes also included the activation of pathways (JA, SA, and ET). Based on these findings against B. brassicae, integrated pest management and bio control with PeBA1 in the agroecosystem appears to be suitable.

Cyanogenesis in the Sorghum Genus: From Genotype to Phenotype

Domestication has resulted in a loss of genetic diversity in our major food crops, leading to susceptibility to biotic and abiotic stresses linked with climate change. Crop wild relatives (CWR) may provide a source of novel genes potentially important for re-gaining climate resilience. Sorghum bicolor is an important cereal crop with wild relatives that are endemic to Australia. Sorghum bicolor is cyanogenic, but the cyanogenic status of wild Sorghum species is not well known. In this study, leaves of wild species endemic in Australia are screened for the presence of the cyanogenic glucoside dhurrin. The direct measurement of dhurrin content and the potential for dhurrin-derived HCN release (HCNp) showed that all the tested Australian wild species were essentially phenotypically acyanogenic. The unexpected low dhurrin content may reflect the variable and generally nutrient-poor environments in which they are growing in nature. Genome sequencing of six CWR and PCR amplification of the CYP79A1 gene from additional species showed that a high conservation of key amino acids is required for correct protein function and dhurrin synthesis, pointing to the transcriptional regulation of the cyanogenic phenotype in wild sorghum as previously shown in elite sorghum.

Methyl jasmonate treatment, aphid resistance assay, and transcriptomic analysis revealed different herbivore defensive roles between tobacco glandular and non-glandular trichomes

KEY MESSAGE

Methyl jasmonate treatment and aphid resistance assays reveal different roles in herbivore defensive responses between tobacco glandular and non-glandular trichomes. These roles correlate with trichome gene expression patterns. In plants, trichomes greatly contribute to biotic stress resistance. To better understand the different defensive functions between glandular and non-glandular trichomes, we used Nicotiana tabacum as a model. This species bears three types of trichomes: long and short stalk glandular trichomes (LGT and SGT, respectively), and non-glandular trichomes (NGT). Tobacco accession T.I.1068 (lacking NGT) and T.I.1112 (lacking LGT) were used for the experiment. After methyl jasmonate (MeJA) treatment, LGT formation was promoted not only in T.I.1068, but also in T.I.1112, whereas NGT remained absent in T.I.1068, and was slightly reduced in T.I.1112. Diterpenoids, which play important roles in herbivore resistance, accumulated abundantly in T.I.1068 and were elevated by MeJA; however, they were not found in T.I.1112 but became detectable after MeJA treatment. The aphid resistance of T.I.1068 was higher than that of T.I.1112, and both were enhanced by MeJA, which was closely correlated with LGT density. Trichomes detached from T.I.1068 and T.I.1112 were used for RNA-Seq analysis, the results showed that pentose phosphate, photosynthesis, and diterpenoid biosynthesis genes were much more expressed in T.I.1068 than in T.I.1112, which was consistent with the vigorous diterpenoid biosynthesis in T.I.1068. In T.I.1112, citrate cycle, propanoate, and glyoxylate metabolism processes were enriched, and some defensive protein genes were expressed at higher levels than those in T.I.1068.These results suggested that LGT plays a predominant role in aphid resistance, whereas NGT could strengthen herbivore resistance by accumulating defensive proteins, and the roles of LGT and NGT are associated with their gene expression patterns.

Epidermis-Specific Metabolic Engineering of Sesquiterpene Formation in Tomato Affects the Performance of Potato Aphid Macrosiphum euphorbiae

Tomato produces a number of terpenes in their glandular trichomes that contribute to host plant resistance against pests. While glandular trichomes of cultivated tomato Solanum lycopersicum primarily accumulate a blend of monoterpenes, those of the wild tomato species Solanum habrochaites produce various sesquiterpenes. Recently, we have identified two groups of sesquiterpenes in S. habrochaites accessions that negatively affect the performance and choice behavior of the potato aphid (Macrosiphum euphorbiae). Aphids are piercing-sucking herbivores that use their mouthpart to penetrate and probe plant tissues in order to ultimately access vascular tissue and ingest phloem sap. Because secondary metabolites produced in glandular trichomes can affect the initial steps of the aphid feeding behavior, introducing the formation of defensive terpenes into additional plant tissues via metabolic engineering has the potential to reduce tissue penetration by aphids and in consequence virus transmission. Here, we have developed two multicistronic expression constructs based on the two sesquiterpene traits with activity toward M. euphorbiae previously identified in S. habrochaites. Both constructs are composed of sequences encoding a prenyl transferase and a respective S. habrochaites terpene synthase, as well as enhanced green fluorescent protein as a visible marker. All three coding sequences were linked by short nucleotide sequences encoding the foot-and-mouth disease virus 2A self-processing oligopeptide which allows their co-expression under the control of one promoter. Transient expression of both constructs under the epidermis-specific Arabidopsis CER5-promoter in tomato leaves demonstrated that formation of the two sets of defensive sesquiterpenes, β-caryophyllene/α-humulene and (-)-endo-α-bergamotene/(+)-α-santalene/(+)-endo-β-bergamotene, can be introduced into new tissues in tomato. The epidermis-specific transgene expression and terpene formation were verified by fluorescence microscopy and tissue fractionation with subsequent analysis of terpene profiles, respectively. In addition, the longevity and fecundity of M. euphorbiae feeding on these engineered tomato leaves were significantly reduced, demonstrating the efficacy of this novel aphid control strategy.

Morphological characterization of trichomes shows enormous variation in shape, density and dimensions across the leaves of 14 Solanum species

Trichomes are the epidermal appendages commonly observed on plant surfaces including leaves, stem and fruits. Plant trichomes have been well studied as a structural plant defence designed to protect plants against abiotic and biotic stressors such as UV rays, temperature extremities and herbivores. Trichomes are primarily classified into glandular and non-glandular trichomes, based on the presence or absence of a glandular head. The plant genus Solanum is the largest genus of family Solanaceae that houses ~3500 species of ecological and economic importance have a diverse set of trichomes that vary in density and morphology. However, due to the incomplete and contradictory classification system, trichomes have subjective names and have been largely limited to be grouped into glandular or non-glandular types. Through this study, we did a complete workup to classify and characterize trichomes on both adaxial and abaxial leaf surface of 14 wild and domesticated species of the genus Solanum. Using electron microscopy, statistical analyses and artistic rendition, we examined finer details of trichomes and measured their density and dimensions to compile a detailed data set which can be of use for estimating the variation in trichome types, and their density, with consequences for understanding their functional roles. Our study is the first of its kind that provides us with a better and well-defined classification, density and dimension analysis to complete the morphological classification of trichomes on both leaf surfaces of a diverse range of members in Solanum genus.

SlHair2 Regulates the Initiation and Elongation of Type I Trichomes on Tomato Leaves and Stems

Trichomes are hair-like structures that are essential for abiotic and biotic stress responses. Tomato Hair (H), encoding a C2H2 zinc finger protein, was found to regulate the multicellular trichomes on stems. Here, we characterized Solyc10g078990 (hereafter Hair2, H2), its closest homolog, to examine whether it was involved in trichome development. The H2 gene was highly expressed in the leaves, and its protein contained a single C2H2 domain and was localized to the nucleus. The number and length of type I trichomes on the leaves and stems of knock-out h2 plants were reduced when compared to the wild-type, while overexpression increased their number and length. An auto-activation test with various truncated forms of H2 using yeast two-hybrid (Y2H) suggested that H2 acts as a transcriptional regulator or co-activator and that its N-terminal region is important for auto-activation. Y2H and pull-down analyses showed that H2 interacts with Woolly (Wo), which regulates the development of type I trichomes in tomato. Luciferase complementation imaging assays confirmed that they had direct interactions, implying that H2 and Wo function together to regulate the development of trichomes. These results suggest that H2 has a role in the initiation and elongation of type I trichomes in tomato.

Aboveground Herbivory Influences Belowground Defense Responses in Maize

The European corn borer (ECB; Ostrinia nubilalis) is an economically damaging insect pest of maize (Zea mays L.), an important cereal crop widely grown globally. Among inbred lines, the maize genotype Mp708 has shown resistance to diverse herbivorous insects, although several aspects of the defense mechanisms of Mp708 plants are yet to be explored. Here, the changes in root physiology arising from short-term feeding by ECB on the shoot tissues of Mp708 plants was evaluated directly using transcriptomics, and indirectly by monitoring changes in growth of western corn rootworm (WCR; Diabrotica virgifera virgifera) larvae. Mp708 defense responses negatively impacted both ECB and WCR larval weights, providing evidence for changes in root physiology in response to ECB feeding on shoot tissues. There was a significant downregulation of genes in the root tissues following short-term ECB feeding, including genes needed for direct defense (e.g., proteinase inhibitors and chitinases). Our transcriptomic analysis also revealed specific regulation of the genes involved in hormonal and metabolite pathways in the roots of Mp708 plants subjected to ECB herbivory. These data provide support for the long-distance signaling-mediated defense in Mp708 plants and suggest that altered metabolite profiles of roots in response to ECB feeding of shoots likely negatively impacted WCR growth.

PeaT1 and PeBC1 Microbial Protein Elicitors Enhanced Resistance against Myzus persicae Sulzer in Chili Capsicum annum L

The green peach aphid (Myzus persicae Sulzer), a major and harmful chili aphid usually managed using chemical pesticides, is responsible for massive annual agricultural losses. The efficacy of two protein elicitors, PeaT1 and PeBC1, to stimulate a defensive response against M. persicae in chili was studied in this study. When compared to positive (water) and negative (buffer, 50 mM Tris-HCl, pH 8.0) controls, the rates of population growth (intrinsic rate of increase) of M. persicae (second and third generations) were lower with PeaT1- and PeBC1-treated chilli seedlings. M. persicae demonstrated a preference for colonizing control (12.18 ± 0.06) plants over PeaT1- (7.60 ± 0.11) and PeBC1 (6.82 ± 0.09) treated chilli seedlings in a host selection assay. Moreover, PeaT1- and PeBC1-treated chilli seedlings, the nymphal development period of the M. persicae was extended. Similarly, fecundity was lowered in the PeaT1- and PeBC1-treated chilli seedlings, with fewer offspring produced compared to the positive (water) and negative controls (50 mM Tris-HCl, pH 8.0). The trichomes and wax production on the PeaT1 and PeBC1-treated chilli leaves created a disadvantageous surface environment for M. persicae. Compared to control (30.17 ± 0.16 mm^-2), PeaT1 (56.23 ± 0.42 mm^-2) and PeBC1 (52.14 ± 0.34 mm^-2) had more trichomes. The levels of jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) were significantly higher in the PeaT1- and PeBC1-treated chili seedlings, indicating considerable accumulation. PeaT1 and PeBC1 significantly affected the height of the chili plant and the surface structure of the leaves, reducing M. persicae reproduction and preventing colonization, according to the data. The activation of pathways was also part of the defensive response (JA, SA, and ET). This present research findings established an evidence of biocontrol for the utilization of PeaT1 and PeBC1 in the defence of chili plants against M. persicae.

Determining relevant traits for selecting landrace accessions of Phaseolus lunatus L. for insect resistance

Plant-insect interactions are a determining factor for sustainable crop production. Although plants can resist or tolerate herbivorous insects to varying degrees, even with the use of pesticides, insects can reduce plant net productivity by as much as 20%, so sustainable strategies for pest control with less dependence on chemicals are needed. Selecting plants with optimal resistance and photosynthetic traits can help minimize damage and maintain productivity. Here, 27 landrace accessions of lima beans, Phaseolus lunatus L., from the Yucatan Peninsula were evaluated in the field for morphological resistance traits, photosynthetic characteristics, insect damage and seed yield. Variation was found in physical leaf traits (number, area, and dry mass of leaves; trichome density, specific leaf thickness and hardness) and in physiological traits (photosynthetic rate, stomatal conductance, intercellular carbon, water-use efficiency, and transpiration). Five accessions (JMC1325, JMC1288, JMC1339, JMC1208 and JMC1264) had the lowest index for cumulative damage with the highest seed yield, although RDA analysis uncovered two accessions (JMC1339, JMC1288) with strong positive association of seed yield and the cumulative damage index with leaf production, specific leaf area (SLA) and total leaf area. Leaf traits, including SLA and total leaf area are important drivers for optimizing seed yield. This study identified 12 important morphological and physiological leaf traits for selecting landrace accessions of P. lunatus for high yields (regardless of damage level) to achieve sustainable, environmentally safe crop production.

Advances in the Regulation of Epidermal Cell Development by C2H2 Zinc Finger Proteins in Plants

Plant epidermal cells, such as trichomes, root hairs, salt glands, and stomata, play pivotal roles in the growth, development, and environmental adaptation of terrestrial plants. Cell fate determination, differentiation, and the formation of epidermal structures represent basic developmental processes in multicellular organisms. Increasing evidence indicates that C2H2 zinc finger proteins play important roles in regulating the development of epidermal structures in plants and plant adaptation to unfavorable environments. Here, we systematically summarize the molecular mechanism underlying the roles of C2H2 zinc finger proteins in controlling epidermal cell formation in plants, with an emphasis on trichomes, root hairs, and salt glands and their roles in plant adaptation to environmental stress. In addition, we discuss the possible roles of homologous C2H2 zinc finger proteins in trichome development in non-halophytes and salt gland development in halophytes based on bioinformatic analysis. This review provides a foundation for further study of epidermal cell development and abiotic stress responses in plants.

Tomato transcriptomic response to Tuta absoluta infestation

BACKGROUND

The South America pinworm, Tuta absoluta, is a destructive pest of tomato that causes important losses worldwide. Breeding of resistant/tolerant tomato cultivars could be an effective strategy for T. absoluta management but, despite the economic importance of tomato, very limited information is available about its response to this treat. To elucidate the defense mechanisms to herbivore feeding a comparative analysis was performed between a tolerant and susceptible cultivated tomato at both morphological and transcriptome level to highlight constitutive leaf barriers, molecular and biochemical mechanisms to counter the effect of T. absoluta attack.

RESULTS

The tolerant genotype showed an enhanced constitutive barrier possibly as result of the higher density of trichomes and increased inducible reactions upon mild infestation thanks to the activation/repression of key transcription factors regulating genes involved in cuticle formation and cell wall strength as well as of antinutritive enzymes, and genes involved in the production of chemical toxins and bioactive secondary metabolites.

CONCLUSIONS

Overall, our findings suggest that tomato resilience to the South America pinworm is achieved by a combined strategy between constitutive and induced defense system. A well-orchestrated modulation of plant transcription regulation could ensure a trade-off between defense needs and fitness costs. Our finding can be further exploited for developing T. absoluta tolerant cultivars, acting as important component of integrated pest management strategy for more sustainable production.