Comparative transcriptome analyses provide novel insights into the differential response of Pigeonpea (Cajanus cajan L.) and its wild relative (Cajanus platycarpus (Benth.) Maesen) to herbivory by Helicoverpa armigera (Hübner)

Cucumber PGIP2 is involved in resistance to gray mold disease

Polygalacturonase inhibitor protein (PGIP) restricts fungal growth and colonization and functions in plant immunity. Gray mold in cucumber is a common fungal disease caused by Botrytis cinerea, and is widespread and difficult to control in cucumber (Cucumis sativus L.) production. In this study, Cucumis sativus polygalacturonase-inhibiting protein 2 (CsPGIP2) was found to be upregulated in response to gray mold in cucumber. CsPGIP2 was detected in the endoplasmic reticulum, cell membrane, and cell wall after transient transformation of protoplasts and tobacco. A possible interaction between Botrytis cinerea polygalacturonase 3 (BcPG3) and CsPGIP2 was supported by protein interaction prediction and BiFC analysis. Transgenic Arabidopsis plants expressing CsPGIP2 were constructed and exhibited smaller areas of gray mold infection compared to wild type (WT) plants after simultaneous inoculation. Evans blue dye (EBD) confirmed greater damage for WT plants, with more intense dyeing than for the transgenic Arabidopsis. Interestingly, compared to WT, transgenic Arabidopsis exhibited higher superoxide dismutase (AtSOD1) expression, antioxidant enzyme activities, lignin content, net photosynthetic rate (Pn), and photochemical activity. Our results suggest that CsPGIP2 stimulates a variety of plant defense mechanisms to enhance transgenic Arabidopsis resistance against gray mold disease.

Genome-wide identification and characterization of DIRIGENT gene family (CcDIR) in pigeonpea (Cajanus cajan L.) provide insights on their spatial expression pattern and relevance to stress response

This study is a thorough characterization of pigeonpea dirigent gene (CcDIR) family, an important component of the lignin biosynthesis pathway. Genome-wide analysis identified 25 CcDIR genes followed by a range of analytical approaches employed to unravel their structural and functional characteristics. Structural examination revealed a classic single exon and no intron arrangement in CcDIRs contributing to our understanding on evolutionary dynamics. Phylogenetic analysis elucidated evolutionary relationships among CcDIR genes with six DIR sub-families, while motif distribution analysis displayed and highlighted ten conserved protein motifs in CcDIRs. Promoter analyses of all the dirigent genes detected 18 stress responsive cis-acting elements offering insights into transcriptional regulation. While spatial expression analyses across six plant tissues showed preferential expression of CcDIR genes, exposure to salt (CcDIR2 and CcDIR9) and herbivory (CcDIR1, CcDIR2, CcDIR3 and CcDIR11), demonstrated potential roles of specific DIRs in plant defense. Interestingly, increased gene expression during herbivory, also correlated with increased lignin content authenticating the specific response. Furthermore, exogenous application of stress hormones, SA and MeJA on leaves significantly induced the expression of CcDIRs that responded to herbivory. Taken together, these findings contribute to a comprehensive understanding of CcDIR genes impacting development and stress response in the important legume pigeonpea.

The Key Role of Plant Hormone Signaling Transduction and Flavonoid Biosynthesis Pathways in the Response of Chinese Pine (Pinus tabuliformis) to Feeding Stimulation by Pine Caterpillar (Dendrolimus tabulaeformis)

In nature, plants have developed a series of resistance mechanisms to face various external stresses. As understanding of the molecular mechanisms underlying plant resistance continues to deepen, exploring endogenous resistance in plants has become a hot topic in this field. Despite the multitude of studies on plant-induced resistance, how plants respond to stress under natural conditions remains relatively unclear. To address this gap, we investigated Chinese pine (Pinus tabuliformis) using pine caterpillar (Dendrolimus tabulaeformis) under natural conditions. Healthy Chinese pine trees, approximately 10 years old, were selected for studying induced resistance in Huangtuliangzi Forestry, Pingquan City, Chengde City, Hebei Province, China. Pine needles were collected at 2 h and 8 h after feeding stimulation (FS) via 10 pine caterpillars and leaf clipping control (LCC), to simulate mechanical damage caused by insect chewing for the quantification of plant hormones and transcriptome and metabolome assays. The results show that the different modes of treatments significantly influence the contents of JA and SA in time following treatment. Three types of differentially accumulated metabolites (DAMs) were found to be involved in the initial response, namely phenolic acids, lipids, and flavonoids. Weighted gene co-expression network analysis indicated that 722 differentially expressed genes (DEGs) are positively related to feeding stimulation and the specific enriched pathways are plant hormone signal transduction and flavonoid biosynthesis, among others. Two TIFY transcription factors (PtTIFY54 and PtTIFY22) and a MYB transcription factor (PtMYB26) were found to be involved in the interaction between plant hormones, mainly in the context of JA signal transduction and flavonoid biosynthesis. The results of this study provide an insight into how JA activates, serving as a reference for understanding the molecular mechanisms of resistance formation in conifers responding to mandibulate insects.

Integrating genomics and genome editing for orphan crop improvement: a bridge between orphan crops and modern agriculture system

Domestication of orphan crops could be explored by editing their genomes. Genome editing has a lot of promise for enhancing agricultural output, and there is a lot of interest in furthering breeding in orphan crops, which are sometimes plagued with unwanted traits that resemble wild cousins. Consequently, applying model crop knowledge to orphan crops allows for the rapid generation of targeted allelic diversity and innovative breeding germplasm. We explain how plant breeders could employ genome editing as a novel platform to accelerate the domestication of semi-domesticated or wild plants, resulting in a more diversified base for future food and fodder supplies. This review emphasizes both the practicality of the strategy and the need to invest in research that advances our understanding of plant genomes, genes, and cellular systems. Planting more of these abandoned orphan crops could help alleviate food scarcities in the challenge of future climate crises.

The plant specialized metabolite epicatechin- 3-gallate (EC3G) perturbs lipid metabolism and attenuates fat accumulation in pigeonpea pod borer, Helicoverpa armigera

Control of pod borer Helicoverpa armigera, a notorious polyphagous pest requires paramount attention with focus on environment-friendly management approaches. Overproduction of catechins (epigallocatechin-EGC and epicatechin-3-gallate-EC3G) in the pod borer-resistant pigeonpea wild relative, Cajanus platycarpus during continued herbivory prodded us to assess their underlying molecular effect on H. armigera. Significant reduction in larval and pupal growth parameters was observed when reared on artificial diet incorporated with 100 ppm EC3G vis a vis 100 ppm EGC and EGC + EC3G. Comparative RNAseq analyses of larvae that fed on normal and EC3G-incorporated diet revealed 62 differentially expressed genes dominated by detoxification and lipid metabolism. While lipase and fatty acid-binding protein 2-like were up-regulated, delta9-FADS-like involved in fatty acid synthesis was downregulated, indicating effect of EC3G on fat metabolism. Validation of RNAseq data by qPCR; midgut glutathione-S-transferase and esterase assays depicted increased lipolysis and reduced lipogenesis in EC3G-fed larvae. Additionally, differential accumulation of stearic acid and oleic acid in EC3G-fed and control larvae/adults ascertained perturbation in lipogenesis. Supported by modelling, molecular docking and simulations, we demonstrate the possible involvement of the insect adipokinetic hormone receptor (AKHR) in the EC3G-mediated response. The study demonstrates plant specialized metabolite EC3G as a potential candidate for H. armigera control.

Helicoverpa armigera preference and performance on three cultivars of short-duration pigeonpea (Cajanus cajan): the importance of whole plant assays

BACKGROUND

Helicoverpa armigera is a major pest of pigeonpea (Cajanus cajan). Efforts to develop pigeonpea varieties resistant to H. armigera attack have been met with limited success, despite reports of high levels of resistance to H. armigera in wild relatives of pigeonpea and reports of low to moderate levels of resistance in cultivated varieties. Here we examined H. armigera oviposition preference and larval performance on whole plants of three cultivars of short-duration pigeonpea: a susceptible control (ICPL 87) and two cultivars with purported host-plant resistance (ICPL 86012 and ICPL 88039).

RESULTS

In our no-choice oviposition experiment, H. armigera laid similar numbers of eggs on all three cultivars tested, but under choice conditions moths laid slightly more eggs on ICPL 88039. Larval growth and development were affected by cultivar, and larvae grew to the largest size (weight) and developed fastest on ICPL 86012. Moths laid most of their eggs on floral structures, sites where subsequent early instar larvae overwhelmingly fed. Experimentally placing neonate larvae at different locations on plants demonstrated that larvae placed on flowers experienced greater survival, faster development, and greater weight gain than those placed on leaves. The type and density of trichomes (a potential resistance trait) differed among cultivars and plant structures, but larvae selected to feed at sites where trichomes were absent.

CONCLUSION

Future work examining host-plant resistance against H. armigera should incorporate the behavioural preference of moths and larvae in experiments using whole plants as opposed to bioassays of excised plant parts in Petri dishes. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Cajanus platycarpus Flavonoid 3'5' Hydroxylase_2 (CpF3'5'H_2) Confers Resistance to Helicoverpa armigera by Modulating Total Polyphenols and Flavonoids in Transgenic Tobacco

Pod borer Helicoverpa armigera, a polyphagus herbivorous pest, tremendously incurs crop damage in economically important crops. This necessitates the identification and utility of novel genes for the control of the herbivore. The present study deals with the characterization of a flavonoid 3'5' hydroxylase_2 (F3'5'H_2) from a pigeonpea wild relative Cajanus platycarpus, possessing a robust chemical resistance response to H. armigera. Though F3'5'H_2 displayed a dynamic expression pattern in both C. platycarpus (Cp) and the cultivated pigeonpea, Cajanus cajan (Cc) during continued herbivory, CpF3'5'H_2 showed a 4.6-fold increase vis a vis 3-fold in CcF3'5'H_2. Despite similar gene copy numbers in the two Cajanus spp., interesting genic and promoter sequence changes highlighted the stress responsiveness of CpF3'5'H_2. The relevance of CpF3'5'H_2 in H. armigera resistance was further validated in CpF3'5'H_2-overexpressed transgenic tobacco based on reduced leaf damage and increased larval mortality through an in vitro bioassay. As exciting maiden clues, CpF3'5'H_2 deterred herbivory in transgenic tobacco by increasing total flavonoids, polyphenols and reactive oxygen species (ROS) scavenging capacity. To the best of our knowledge, this is a maiden attempt ascertaining the role of F3'5'H_2 gene in the management of H. armigera. These interesting leads suggest the potential of this pivotal branch-point gene in biotic stress management programs.

CRISPR-Cas Genome Editing for Insect Pest Stress Management in Crop Plants

Global crop yield and food security are being threatened by phytophagous insects. Innovative methods are required to increase agricultural output while reducing reliance on hazardous synthetic insecticides. Using the revolutionary CRISPR-Cas technology to develop insect-resistant plants appears to be highly efficient at lowering production costs and increasing farm profitability. The genomes of both a model insect, Drosophila melanogaster, and major phytophagous insect genera, viz. Spodoptera, Helicoverpa, Nilaparvata, Locusta, Tribolium, Agrotis, etc., were successfully edited by the CRISPR-Cas toolkits. This new method, however, has the ability to alter an insect’s DNA in order to either induce a gene drive or overcome an insect’s tolerance to certain insecticides. The rapid progress in the methodologies of CRISPR technology and their diverse applications show a high promise in the development of insect-resistant plant varieties or other strategies for the sustainable management of insect pests to ensure food security. This paper reviewed and critically discussed the use of CRISPR-Cas genome-editing technology in long-term insect pest management. The emphasis of this review was on the prospective uses of the CRISPR-Cas system for insect stress management in crop production through the creation of genome-edited crop plants or insects. The potential and the difficulties of using CRISPR-Cas technology to reduce pest stress in crop plants were critically examined and discussed.

Integrated Transcriptome and Metabolome Analysis to Identify Sugarcane Gene Defense against Fall Armyworm (Spodoptera frugiperda) Herbivory

Sugarcane is the most important sugar crop, contributing ≥80% to total sugar production around the world. Spodoptera frugiperda is one of the main pests of sugarcane, potentially causing severe yield and sugar loss. The identification of key defense factors against S. frugiperda herbivory can provide targets for improving sugarcane resistance to insect pests by molecular breeding. In this work, we used one of the main sugarcane pests, S. frugiperda, as the tested insect to attack sugarcane. Integrated transcriptome and metabolomic analyses were performed to explore the changes in gene expression and metabolic processes that occurred in sugarcane leaf after continuous herbivory by S. frugiperda larvae for 72 h. The transcriptome analysis demonstrated that sugarcane pest herbivory enhanced several herbivory-induced responses, including carbohydrate metabolism, secondary metabolites and amino acid metabolism, plant hormone signaling transduction, pathogen responses, and transcription factors. Further metabolome analysis verified the inducement of specific metabolites of amino acids and secondary metabolites by insect herbivory. Finally, association analysis of the transcriptome and metabolome by the Pearson correlation coefficient method brought into focus the target defense genes against insect herbivory in sugarcane. These genes include amidase and lipoxygenase in amino acid metabolism, peroxidase in phenylpropanoid biosynthesis, and pathogenesis-related protein 1 in plant hormone signal transduction. A putative regulatory model was proposed to illustrate the sugarcane defense mechanism against insect attack. This work will accelerate the dissection of the mechanism underlying insect herbivory in sugarcane and provide targets for improving sugarcane variety resistance to insect herbivory by molecular breeding.

MnASI1 Mediates Resistance to Botrytis cinerea in Mulberry (Morus notabilis)

Six α-amylase/subtilisin inhibitor genes (MnASIs) were identified from mulberry (Morus notabilis). In this study, bioinformatics and expression pattern analysis of six MnASIs were performed to determine their roles in resistance to B. cinerea. The expression of all six MnASIs was significantly increased under Botrytis cinerea infection. MnASI1, which responded strongly to B. cinerea, was overexpressed in Arabidopsis and mulberry. The resistance of Arabidopsis and mulberry overexpressing MnASI1 gene to B. cinerea was significantly improved, the catalase (CAT) activity was increased, and the malondialdehyde (MDA) content was decreased after inoculation with B. cinerea. At the same time, H₂O₂ and O₂⁻ levels were reduced in MnASI1 transgenic Arabidopsis, reducing the damage of ROS accumulation to plants. In addition, MnASI1 transgenic Arabidopsis increased the expression of the salicylic acid (SA) pathway-related gene AtPR1. This study provides an important reference for further revealing the function of α-amylase/subtilisin inhibitors.

Reactive oxygen species in plants: an invincible fulcrum for biotic stress mitigation

Climate change-associated environmental vagaries have amplified the incidence of pests and pathogens on plants, thus imparting the increased quest for management strategies. Plants respond to stresses through intricate signaling networks that regulate diverse cellular mechanisms. Reactive oxygen species (ROS) are cardinal towards the maintenance of normal plant activities as well as improving stress management. Plants that exhibit a fine balance between ROS levels and its management apparently mitigate stresses better. There have been very many compendiums on signaling and management of ROS during several abiotic stresses. However, expansion of knowledge related to ROS induction and homeostasis during biotic stresses is pertinent. Hence, considering its importance, we provide insights in this review on how plants signal and manage ROS upon an oxidative burst during their interaction with pathogens and herbivores. Substantial degree of molecular changes and pivotal roles of ROS have been detected during phyto-pathogen/herbivore interactions, opening novel platforms to understand signaling/management of events under varied biotic stresses. It is interesting to know that, though plants react to biotic stresses through oxidative burst, receptors and elicitors involved in the signal transduction differ across stresses. The review provides explicit details about the specific signaling of ROS production in plants under pathogen and herbivore attack. Furthermore, we also provide an update about tackling the accumulated ROS under biotic stresses as another pivotal step. ROS signaling and homeostasis can be exploited as critical players and a fulcrum to tackle biotic stresses, thus paving the way for futuristic combinatorial stress management strategies. KEY POINTS: • The review is a comprehension of redox signaling and management in plants during herbivory and pathogen infection • Reactive oxygen species (ROS) is an important factor during normal plant activities as well as in their response to stresses. Diverse modes of ROS signaling and management have been observed during both biotic stresses independently • Exploration of plant biology in multi-stress resistant plants like the crop wild relatives could pave the way for combinatorial management of stress for a better tomorrow.

Deciphering of Pod Borer [Helicoverpa armigera (Hübner)] Resistance in Cajanus platycarpus (Benth.) Offers Novel Insights on the Reprogramming and Role of Flavonoid Biosynthesis Pathway

Management of pod borer, Helicoverpa armigera in pigeonpea (Cajanus cajan L.), an important legume crop, has been a pertinent endeavor globally. As with other crops, wild relatives of pigeonpea are bestowed with various resistance traits that include the ability to deter the H. armigera. Understanding the molecular basis of pod borer resistance could provide useful leads for the management of this notorious herbivore. Earlier studies by our group in deciphering the resistance response to herbivory through multiomics approaches in the pigeonpea wild relative, Cajanus platycarpus, divulged the involvement of the flavonoid biosynthesis pathway, speculating an active chemical response of the wild relative to herbivory. The present study is a deeper understanding of the chemical basis of pod borer (H. armigera) resistance in, C. platycarpus, with focus on the flavonoid biosynthesis pathway. To substantiate, quantification of transcripts in H. armigera-challenged C. platycarpus (8 h, 24 h, 48 h, 96 h) showed dynamic upregulation (up to 11-fold) of pivotal pathway genes such as chalcone synthase, dihydroflavonol-4-reductase, flavonoid-3'5'-hydroxylase, flavonol synthase, leucoanthocyanidin reductase, and anthocyanidin synthase. Targeted LC-MS analyses demonstrated a concomitant increase (up to 4-fold) in naringenin, kaempferol, quercetin, delphinidin, cyanidin, epigallocatechin, and epicatechin-3-gallate. Interestingly, H. armigera diet overlaid with the over-produced flavonoids (100 ppm) showed deleterious effects on growth leading to a prolonged larval period demonstrating noteworthy coherence between over-accumulation of pathway transcripts/metabolites. The study depicts novel evidence for the directed metabolic reprogramming of the flavonoid biosynthesis pathway in the wild relative to pod borer; plant metabolic potential is worth exploiting for pest management.

Identification of dynamic microRNA associated with systemic defence against Helicoverpa armigera infestation in Cajanus scarabaeoides

BACKGROUND

Helicoverpa armigera is a major insect pest of several crop plants, including pigeonpea. Resistant gene sources are not available in the cultivated gene pool, but resistance has been observed in its crop wild relative, Cajanus scarabaeoides. Gene regulatory mechanisms governing the systemic immune response of this plant to pod borer infestation have not yet been deciphered. MicroRNA (miRNA) profiles of H. armigera-infested and undamaged adjacent leaves of C. scarabaeoides were compared to gain an insight into the plant-insect interactions and to identify dynamic miRNA molecules potentially acting as mediators of systemic defence responses.

RESULTS

A total of 211 conserved, temporally dynamic miRNA were identified in the unfed adjacent leaves, out of which 98 were found to be differentially expressed in comparison to control leaves. On further analysis, most of the miRNA detected in the adjacent leaves was found to target genes involved in the defence pathways and plant immune response. An overlap of the differentially expressing miRNAs was observed between insect-fed and adjacent unfed leaves, indicating the transmission of signal from the site of infestation to the undamaged parts of the plant, indicative of induction of a systemic defence response.

CONCLUSION

The miRNA response in the unfed leaves had the signatures of induced changes in metabolism and signal transduction for induction of defence pathway genes. This study reveals the participation of miRNAs in imparting pod borer resistance and mounting a systemic defence response against pod borer infestation in C. scarabaeoides. © 2022 Society of Chemical Industry.

Relevance of methionine sulfoxide reductase(s) (MSR) as candidate proteins in redox homeostasis-mediated resistance response to Helicoverpa armigera (Hübner) in the pigeonpea wild relative Cajanus platycarpus (Benth.) Maesen

Pod borer, Helicoverpa armigera, a polyphagus herbivore causes extensive economic losses to crops, including pigeonpea. Exploitation of pod borer resistance in wild relatives is pertinent due to the absence of resistance sources in cultivated pigeonpea and crossing-incompatibility with the resistant wild relatives. We present leads obtained in deeper understanding of pod borer resistance mechanism in Cajanus platycarpus, a pigeonpea wild relative. Surge in cellular ROS during herbivory leads to redox-PTMs (post translational modifications) of methionine-rich proteins including antioxidant enzymes, causing oxidative damage. Plants then officiate methionine sulfoxide reductases (MSRs), that maintain the redox status of methionine and hence homeostasis. We demonstrate functionality of MSRs (MSRA and MSRB) in the resistance response of the wild relative to pod borer. Among 5 MSRA and 3 MSRB genes, CpMSRA2 and CpMSRB1 were herbivore-responsive based on expression during herbivory. Clues about the stress-responsiveness were obtained upon analyses of cis-elements and co-expressing genes. Apparently, the wild relative followed a non-canonical mode of redox management, as divulged by antioxidant enzymes and the scavenging capacity. Differential lipid peroxidation as an early response provided evidences for an effective redox management in the wild relative. This is the first report signifying redox homeostasis in the resistance response towards herbivory.

Comparative analysis of herbivory responsive miRNAs to delineate pod borer (Helicoverpa armigera) resistance mechanisms in Cajanus cajan and its wild relative Cajanus scarabaeoides

Comparative analysis of herbivory responsive miRNAs between pod borer susceptible C. cajan and its resistant Crop Wild Relative (CWR) C. scarabaeoides revealed miRNA-based regulation of defense genes and plant-insect interactions. Gram pod borer (Helicoverpa armigera) is one of most devastating pests of pigeon pea (Cajanus cajan) worldwide, responsible for huge losses in crop productivity. The lack of genes conferring resistance to pod borer in pigeon pea has proven to be a bottleneck for its improvement. One of its CWR, C. scarabaeoides has demonstrated resistance to this pest and can be exploited for developing pest resistant crop varieties. Differences in expression patterns of herbivory responsive microRNAs in the susceptible C. cajan and resistant C. scarabaeoides after different time duration of pod borer infestation (2 h, 8 h and 18 h) were identified, characterized and functionally validated to understand their role in insect defense response. A total of 462 conserved and 449 novel miRNAs and 273 conserved and 185 novel miRNAs, were identified in C. cajan and C. scarabaeoides, respectively. Among the identified miRNAs, 65, 68 and 65 miRNAs were found to be differentially expressing between the C. scarabaeoides and C. cajan libraries 2 h, 8 h and 18 h post infestation, respectively. These miRNAs were found to target genes involved in a number of pathways contributing to defense and acquired resistance in C. scarabaeoides against pod borer, indicating miRNA-based regulation of defense pathways. Expression patterns of eight of these miRNAs were validated by qRT-PCR. This study provides novel insights into the miRNA-mediated plant-insect interactions and the mechanisms of regulatory pathways involved in insect defense. These findings can be utilized for further exploring the mechanism of herbivore defense in plant systems.

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.

Comparative TMT Proteomic Analysis Unveils Unique Insights into Helicoverpa armigera (Hübner) Resistance in Cajanus scarabaeoides (L.) Thouars

Pigeonpea [Cajanus cajan (L.) Millspaugh] is an economically important legume playing a crucial role in the semi-arid tropics. Pigeonpea is susceptible to Helicoverpa armigera (Hübner), which causes devastating yield losses. This pest is developing resistance to many commercially available insecticides. Therefore, crop wild relatives of pigeonpea, are being considered as potential sources of genes to expand the genetic base of cultivated pigeonpea to improve traits such as host plant resistance to pests and pathogens. Quantitative proteomic analysis was conducted using the tandem mass tag platform to identify differentially abundant proteins between IBS 3471 and ICPL 87 tolerant accession and susceptible variety to H. armigera, respectively. Leaf proteome were analysed at the vegetative and flowering/podding growth stages. H. armigera tolerance in IBS 3471 appeared to be related to enhanced defence responses, such as changes in secondary metabolite precursors, antioxidants, and the phenylpropanoid pathway. The development of larvae fed on an artificial diet with IBS 3471 lyophilised leaves showed similar inhibition with those fed on an artificial diet with quercetin concentrations with 32 mg/25 g of artificial diet. DAB staining (3,3'-diaminobenzidine) revealed a rapid accumulation of reactive oxygen species in IBS 3471. We conclude that IBS 3471 is an ideal candidate for improving the genetic base of cultivated pigeonpea, including traits for host plant resistance.

Characterization and in planta validation of a CHI4 chitinase from Cajanus platycarpus (Benth.) Maesen for its efficacy against pod borer, Helicoverpa armigera (Hübner)

BACKGROUND

Pigeonpea, Cajanus cajan is one of the economically important legume food crops and a major source of dietary proteins. Management of pod borer, Helicoverpa armigera has been prominent among crop improvement programs. Lack of resistance sources in the cultivated germplasm and crossing incompatibility with pod borer-resistant wild relatives have prompted biotechnological interventions. Identification and exploitation of genes from pigeonpea wild relatives in host plant resistance towards the pod borer assumes pertinence. Dynamic transcriptome analysis of the wild relative vis a vis cultivated pigeonpea identified a CHI4 chitinase as one of the putative insect resistance genes.

RESULTS

The study presents variations in important amino acids in CHI4 chitinases from C. cajan and its wild relative C. platycarpus. Comparative protein modeling and docking analysis of the two proteins demonstrated differences in substrate binding efficacy of the chitinase from C. platycarpus which resulted in a minimum binding energy of -8.7 kcal mol^-1 . Furthermore, we successfully evaluated the insecticidal activity of the chitinase from C. platycarpus against H. armigera challenge through heterologous expression in tobacco. Molecular characterization of transgenic plants confirmed that their efficacy against H. armigera was a result of the integration of CHI4 from C. platycarpus.

CONCLUSION

Docking analysis demonstrated effective substrate interaction as a possible reason for efficacy against pod borer in the chitinase from C. platycarpus. This was authenticated by successful overexpression and bioefficacy assessment against H. armigera in tobacco. The CHI4 gene from C. platycarpus can be useful in the mitigation of H. armegira in pigeonpea as well as in other crops. © 2021 Society of Chemical Industry.

Transcriptional Responses of Resistant and Susceptible Wheat Exposed to Wheat Curl Mite

(1) Background: The wheat curl mite (Aceria tosichella Keifer) is a key pest of wheat (Triticum aestivum L.) worldwide. While a number of wheat cultivars resistant to the mites have been employed to minimize the impact on the yield and quality of grain, little is known regarding the mechanisms underlying host plant resistance. Therefore, the goal of this study was to explore changes in transcriptome of resistant and susceptible wheat in order to quantify the molecular changes that drive host plant resistance. (2) Methods: Two varieties, wheat curl mite-susceptible (Karl 92) and wheat curl mite-resistant (TAM112) wheat, both at 2-week postemergence, were used in this study. Half of the plants were exposed to wheat curl mite herbivory and half remained mite-free and served as controls. Transcriptome changes were quantified using RNA-seq and compared among treatments to identify genes and pathways affected by herbivores. (3) Results: We identified a number of genes and pathways involved in plant defenses against pathogens, herbivores, and abiotic stress that were differentially expressed in the resistant wheat exposed to wheat curl mite herbivory but were unaffected in the susceptible wheat. (4) Conclusions: Our outcomes indicated that resistant wheat counteracts wheat curl mite exposure through effective induction of genes and pathways that enhance its defense responses.

Genome Editing for Resistance to Insect Pests: An Emerging Tool for Crop Improvement

Plants are challenged incessantly by several biotic and abiotic stresses during their entire growth period. As with other biotic stress factors, insect pests have also posed serious concerns related to yield losses due to which agricultural productivity is at stake. In plants, trait modification for crop improvement was initiated with breeding approaches followed by genetic engineering. However, stringent regulatory policies for risk assessment and lack of social acceptance for genetically modified crops worldwide have incited researchers toward alternate strategies. Genome engineering or genome editing has emerged as a new breeding technique with the ability to edit the genomes of plants, animals, microbes, and human beings. Several gene editing strategies are being executed with continuous emergence of variants. The scientific community has unraveled the utility of various editing tools from endonucleases to CRISPR/Cas in several aspects related to plant growth, development, and mitigation of stresses. The categorical focus on the development of tools and techniques including designing of binary vectors to facilitate ease in genome engineering are being pursued. Through this Review, we embark upon the conglomeration of various genome editing strategies that can be and are being used to design insect pest resistance in plants. Case studies and novel crop-based approaches that reiterate the successful use of these tools in insects as well as in plants are highlighted. Further, the Review also provides implications for the requirement of a specific regulatory framework and risk assessment of the edited crops. Genome editing toward insect pest management is here to stay, provided uncompromising efforts are made toward the identification of amiable target genes.

Exploring the application of wild species for crop improvement in a changing climate

Modern agriculture is currently facing challenges from a burgeoning population and changing climate, which requires improved crops with adaptation to climate and elite yield and quality traits. While there is a breeding bottleneck caused by intensive selection, gene banks containing conserved wild relatives and landraces can be used as breeding resources. However, with limited genetic information available on these wild relatives, the application has been hindered. With the development of both genomics and bioinformatics techniques, it is now easier to identify the genetic variation in wild species, which can be utilized for the introgression of elite traits. These wild species can therefore play an important role in food security and breeding sustainability.

Unraveling the proteomic changes involved in the resistance response of Cajanus platycarpus to herbivory by Helicoverpa armigera

The pigeonpea wild relative Cajanus platycarpus is resistant to Helicoverpa armigera, one of the major pests responsible for yield losses in Cajanus cajan. Deciphering the molecular mechanism underlying host plant resistance is pertinent to identify proteins that aid in the mitigation of the insect pest. The present study adopted comparative proteomics as a tool to interpret the resistance mechanism(s) in C. platycarpus vis-à-vis C. cajan during continued herbivory (up to 96 h). Over-representation analysis of the differentially expressed proteins implicated a multi-dimensional resistance response accomplished by both physical and chemical barriers in C. platycarpus. While the chemical basis for resistance was depicted by the upregulation of proteins playing a rate limiting role in the phenylpropanoid pathway, the physical basis was provided by the regulation of proteins involved in microtubule assembly and synthesis of lignins. Upregulation of proteins in the polyamine pathway indicated the role of metabolite conjugates to be negatively affecting herbivore growth. Reallocation of resources and diversion of metabolic flux to support the production of secondary metabolites could be the probable approach in the wild relative against herbivory. Our study provided deeper insights into the pod borer resistance mechanism in C. platycarpus for utility in crop improvement. KEY POINTS: • Pod borer resistance in Cajanus platycarpus is multi-dimensional. • Pod borer resistance has been arbitrated to cell wall rigidity and secondary metabolites. • Phenylpropanoid pathway derivatives apparently shaped the plant chemical defense against pod borer.