Silencing a Simple Extracellular Leucine-Rich Repeat Gene OsI-BAK1 Enhances the Resistance of Rice to Brown Planthopper Nilaparvata lugens.

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

Seasonal variation in defence compounds: A case study on pyrrolizidine alkaloids of clones of Jacobaea vulgaris, Jacobaea aquatica and their hybrids.

Concentration of plant secondary metabolites (SMs) show seasonal variations. However, it is still not well understood how these abiotic and biotic factors influence the seasonal variations of SMs. In addition, it is of interest to know if and how SMs are reallocated to the different plant organs, in particular whether SMs are reallocated to the remaining tissues when biomass is lost, e.g., during winter. Here we used Jacobaea vulgaris, Jacobaea aquatica, two F1 and four F2 hybrids that differed in their pyrrolizidine alkaloids (PAs) bouquet as a study system. A series of clones of these genotypes were investigated during their vegetative stage spanning 14 months in a semi-natural environment. We found that the total PA concentration in roots and shoots showed a gradual increase until the spring of the second year, whereafter it dropped substantially in shoots. The variation in PA composition due to seasonal changes was significant but relatively small. Senecionine-like PAs were the dominant PAs in roots, while jacobine-/erucifoline-like PAs were dominant in shoots. The variation of PA concentration was significantly correlated with temperature, day length, and plant age. A correlation analysis showed that PAs were not reallocated when biomass was lost in winter. Overall, our study showed that PA composition of each genotype changed over seasons in a different manner but seasonal variation did not overrule the differences in PA composition among genotypes.

Immunocapture of dsRNA-bound proteins provides insight into Tobacco rattle virus replication complexes and reveals Arabidopsis DRB2 to be a wide-spectrum antiviral effector.

Plant RNA viruses form organized membrane-bound replication complexes to replicate their genomes. This process requires virus- and host-encoded proteins and leads to the production of double-stranded RNA (dsRNA) replication intermediates. Here, we describe the use of Arabidopsis thaliana expressing GFP-tagged dsRNA-binding protein (B2:GFP) to pull down dsRNA and associated proteins in planta upon infection with Tobacco rattle virus (TRV). Mass spectrometry analysis of the dsRNA-B2:GFP-bound proteins from infected plants revealed the presence of viral proteins and numerous host proteins. Among a selection of nine host candidate proteins, eight showed relocalization upon infection, and seven of these colocalized with B2-labeled TRV replication complexes. Infection of A. thaliana T-DNA mutant lines for eight such factors revealed that genetic knockout of dsRNA-BINDING PROTEIN 2 (DRB2) leads to increased TRV accumulation and DRB2 overexpression caused a decrease in the accumulation of four different plant RNA viruses, indicating that DRB2 has a potent and wide-ranging antiviral activity. We propose B2:GFP-mediated pull down of dsRNA to be a versatile method to explore virus replication complex proteomes and to discover key host virus replication factors. Given the universality of dsRNA, development of this tool holds great potential to investigate RNA viruses in other host organisms.

Tuning Beforehand: A Foresight on RNA Interference (RNAi) and In Vitro-Derived dsRNAs to Enhance Crop Resilience to Biotic and Abiotic Stresses.

Crop yield is severely affected by biotic and abiotic stresses. Plants adapt to these stresses mainly through gene expression reprogramming at the transcriptional and post-transcriptional levels. Recently, the exogenous application of double-stranded RNAs (dsRNAs) and RNA interference (RNAi) technology has emerged as a sustainable and publicly acceptable alternative to genetic transformation, hence, small RNAs (micro-RNAs and small interfering RNAs) have an important role in combating biotic and abiotic stresses in plants. RNAi limits the transcript level by either suppressing transcription (transcriptional gene silencing) or activating sequence-specific RNA degradation (post-transcriptional gene silencing). Using RNAi tools and their respective targets in abiotic stress responses in many crops is well documented. Many miRNAs families are reported in plant tolerance response or adaptation to drought, salinity, and temperature stresses. In biotic stress, the spray-induced gene silencing (SIGS) provides an intelligent method of using dsRNA as a trigger to silence target genes in pests and pathogens without producing side effects such as those caused by chemical pesticides. In this review, we focus on the potential of SIGS as the most recent application of RNAi in agriculture and point out the trends, challenges, and risks of production technologies. Additionally, we provide insights into the potential applications of exogenous RNAi against biotic stresses. We also review the current status of RNAi/miRNA tools and their respective targets on abiotic stress and the most common responsive miRNA families triggered by stress conditions in different crop species.

Comparative Transcriptome Analysis Reveals Genetic Mechanisms of Sugarcane Aphid Resistance in Grain Sorghum.

The sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae) (SCA), has become a major pest of grain sorghum since its appearance in the USA. Several grain sorghum parental lines are moderately resistant to the SCA. However, the molecular and genetic mechanisms underlying this resistance are poorly understood, which has constrained breeding for improved resistance. RNA-Seq was used to conduct transcriptomics analysis on a moderately resistant genotype (TAM428) and a susceptible genotype (Tx2737) to elucidate the molecular mechanisms underlying resistance. Differential expression analysis revealed differences in transcriptomic profile between the two genotypes at multiple time points after infestation by SCA. Six gene clusters had differential expression during SCA infestation. Gene ontology enrichment and cluster analysis of genes differentially expressed after SCA infestation revealed consistent upregulation of genes controlling protein and lipid binding, cellular catabolic processes, transcription initiation, and autophagy in the resistant genotype. Genes regulating responses to external stimuli and stress, cell communication, and transferase activities, were all upregulated in later stages of infestation. On the other hand, expression of genes controlling cell cycle and nuclear division were reduced after SCA infestation in the resistant genotype. These results indicate that different classes of genes, including stress response genes and transcription factors, are responsible for countering the physiological effects of SCA infestation in resistant sorghum plants.

Evaluating resistance of the soybean block technology cultivars to the Neotropical brown stink bug, Euschistus heros (F.).

Laboratory studies were conducted with the Neotropical brown stink bug, Euschistus heros (F.), to evaluate nymphal and adult biology on immature pods of soybean, Glycine max (L.) Merrill (Fabaceae), bearing the block technology (resistant to stink bug damage - cvs. BRS 391, BRS 543 RR and BRS 1003 IPRO) compared to a susceptible cultivar (BRS 5601 RR). Results indicated that nymphs' developmental time and survivorship were similar on all cultivars tested. The same was observed for adult survivorship and reproductive performance. However, data from electropenetrography (EPG) demonstrated that adults of E. heros spent significantly less time in feeding activities on resistant plants compared to the susceptible one. Large differences were observed in feeding activities on seeds; on resistant plants, the insects dedicated a shorter period of time to feed on seed endosperm than on BRS 5601. In addition, when bugs fed on seeds of block cultivars, the majority of probes were composed of only laceration/maceration activities (Eh3a waveform) without ingestion events of the cell contents (Eh3b waveform). In contrast, on the susceptible cultivar, Eh3a waveform events were repeated much more frequently (3-5X) with more probes also containing ingestion of seed contents. These results suggest that the soybean cultivars bearing the block technology presented a lower preference (antixenosis) by the bugs with fewer feeding activities, primarily in the seed endosperm, compared to the susceptible one tested.

Genomic signatures of the evolution of defence against its natural enemies in the poisonous and medicinal plant Datura stramonium (Solanaceae).

Tropane alkaloids and terpenoids are widely used in the medicine and pharmaceutic industry and evolved as chemical defenses against herbivores and pathogens in the annual herb Datura stramonium (Solanaceae). Here, we present the first draft genomes of two plants from contrasting environments of D. stramonium. Using these de novo assemblies, along with other previously published genomes from 11 Solanaceae species, we carried out comparative genomic analyses to provide insights on the genome evolution of D. stramonium within the Solanaceae family, and to elucidate adaptive genomic signatures to biotic and abiotic stresses in this plant. We also studied, in detail, the evolution of four genes of D. stramonium-Putrescine N-methyltransferase, Tropinone reductase I, Tropinone reductase II and Hyoscyamine-6S-dioxygenase-involved in the tropane alkaloid biosynthesis. Our analyses revealed that the genomes of D. stramonium show signatures of expansion, physicochemical divergence and/or positive selection on proteins related to the production of tropane alkaloids, terpenoids, and glycoalkaloids as well as on R defensive genes and other important proteins related with biotic and abiotic pressures such as defense against natural enemies and drought.

A New Catalog of Structural Variants in 1,301 A. thaliana Lines from Africa, Eurasia, and North America Reveals a Signature of Balancing Selection at Defense Response Genes.

Genomic variation in the model plant Arabidopsis thaliana has been extensively used to understand evolutionary processes in natural populations, mainly focusing on single-nucleotide polymorphisms. Conversely, structural variation has been largely ignored in spite of its potential to dramatically affect phenotype. Here, we identify 155,440 indels and structural variants ranging in size from 1 bp to 10 kb, including presence/absence variants (PAVs), inversions, and tandem duplications in 1,301 A. thaliana natural accessions from Morocco, Madeira, Europe, Asia, and North America. We show evidence for strong purifying selection on PAVs in genes, in particular for housekeeping genes and homeobox genes, and we find that PAVs are concentrated in defense-related genes (R-genes, secondary metabolites) and F-box genes. This implies the presence of a "core" genome underlying basic cellular processes and a "flexible" genome that includes genes that may be important in spatially or temporally varying selection. Further, we find an excess of intermediate frequency PAVs in defense response genes in nearly all populations studied, consistent with a history of balancing selection on this class of genes. Finally, we find that PAVs in genes involved in the cold requirement for flowering (vernalization) and drought response are strongly associated with temperature at the sites of origin.

Resistance to the wheat curl mite and mite-transmitted viruses: challenges and future directions.

Wheat curl mite (WCM) is the only known arthropod vector of four wheat viruses, the most important of which is Wheat streak mosaic virus (WSMV). Host resistance to WCM and WSMV is limited to a small number of loci, most of which are introgressed from wild relatives and are often associated with linkage drag and temperature sensitivity. Reports of virulent WCM populations and potential resistance-breaking WSMV isolates highlight the need for more diverse sources of resistance. Genome sequencing will be critical to fully characterize the genetic diversity in WCM and WSMV populations to better understand the incidence of WCM-transmitted viruses and to evaluate the potential stability of resistance genes. Characterizing host resistance genes will help build a mechanistic understanding of wheat-WCM-WSMV interactions and inform strategies to identify and engineer more durable resistance sources.

Long non-coding RNAs associate with jasmonate-mediated plant defence against herbivores.

Long non-coding RNA (lncRNA) are important regulators of many biological processes in plants, including defence against pathogens; whether lncRNAs mediate defence against herbivore attack is yet to be explored. With wild tobacco, Nicotiana attenuata, and its well-characterized interactions with herbivores, we identified a total of 1,290 significantly up- or down-regulated lncRNAs in response to a precise herbivore elicitation treatment. Of these, long intergenic non-coding RNAs (lincRNAs) were the most abundant. Based on their expression patterns, these up-regulated lincRNAs were classified as early (<1 hr) or late (>3 hr) responders. The early responding lincRNAs had accumulation patterns that tracked the herbivore-elicited burst of bioactive jasmonates (JAs) and the expression of regulator genes in JA signalling which regulate plant defences against herbivores. Silencing two of these early responders in N. attenuata (JAL1 and JAL3) significantly attenuated the accumulation of JAs, JA-mediated defensives and the plant's resistance to M. sexta attack, suggesting roles in regulating JA-mediated plant defence. By lincRNA sequencing of JA-deficient lines, many late responder lincRNAs were found to be transcriptionally regulated by JA signalling. This study uncovers a new role of lncRNAs in JA-mediated herbivore resistance.

Focused Identification of Germplasm Strategy (FIGS): polishing a rough diamond.

Focused Identification of Germplasm Strategy (FIGS) has been advocated as an efficient approach to predict and harness variation in adaptive traits in genebanks or wild populations of plants. However, a weakness of the current FIGS approach is that it only utilizes a priori knowledge of one evolutionary factor: natural selection. Further optimization is needed to capture elusive traits, and this review shows that nonadaptive evolutionary processes (gene flow and genetic drift) should be incorporated to increase precision. Focusing on plant resistance to insect herbivores, we also note that historic selection pressures can be difficult to disentangle, and provide suggestions for successful mining based on eco-evolutionary theory. We conclude that with such refinement FIGS has high potential for enhancing breeding efforts and hence sustainable plant production.

Genetic and molecular understanding of host rice resistance and Nilaparvata lugens adaptation.

The variability of brown planthopper (BPH) populations and diversity of the host rice germplasm provide an ideal model for exploring the genetic and molecular basis of insect-plant interactions. During the long-term evolutionary arms race, complicated feeding and defense strategies have developed in BPH and rice. Nine major BPH resistance genes have been cloned and the exploration of BPH resistance genes medicated mechanism against BPH shed a light on the molecular basis of the rice-BPH interaction. This short review provides an update on our current understanding of the genetic and molecular mechanism for rice resistance and BPH adaptation. Understanding the interactions between BPH and rice will provide novel insights for sustainable control of this pest.

Identification of candidate genes conferring tolerance to aluminum stress in Pinus massoniana inoculated with ectomycorrhizal fungus.

BACKGROUND: Pinus massoniana Lamb. is an important afforestation tree species with high economic, ecological and medicinal values. Aluminum (Al) toxicity driven by soil acidification causes dieback of P. massoniana plantations. Previous studies showed that ectomycorrhizal fungi alleviate Al stress damages in Pinus, but the underlying molecular mechanisms and key genes induced by ectomycorrhizal fungi inoculation under Al stress in Pinus have not been explored. Herein, we applied Al stress for 60 days to P. massoniana seedlings inoculated with Suillus luteus (SL) and those non-inoculated. Then, we compared their growth parameters and transcriptome in order to detect candidate genes induced by SL conferring Al tolerance in P. massoniana. RESULT: Our results showed that SL inoculation confers Al stress tolerance in P. massoniana through improved growth performance, strong antioxidant enzyme activities and reduced malondialdehyde accumulation as compared to non-inoculated seedlings. Transcriptome sequencing further supported these findings as very few genes (51 genes) were transcriptionally altered by Al in SL inoculated plants as compared to non-inoculated plants (2140 genes). We identified three core genes (cox1, cox3 and Nd1) that were strongly up-regulated by Al in the SL inoculated plants but were down-regulated in the non-inoculated plants. We also identified 42 genes specifically regulated by SL inoculated plants under Al stress, which are involved in a wide range of biological processes such as antioxidative response, transporters, hormone signaling and plant pathogen infection responses. CONCLUSIONS: Altogether, our data suggest that SL inoculation induces priming of key stress response pathways and triggers specific genes that efficiently alleviate Al stress effects in P. massoniana. The candidate genes resources generated in this study are of utmost importance for functional characterization and molecular studies aiming at improving Al tolerance in plants.

Genomic and chemical evidence for local adaptation in resistance to different herbivores in Datura stramonium.

Because most species are collections of genetically variable populations distributed to habitats differing in their abiotic/biotic environmental factors and community composition, the pattern and strength of natural selection imposed by species on each other's traits are also expected to be highly spatially variable. Here, we used genomic and quantitative genetic approaches to understand how spatially variable selection operates on the genetic basis of plant defenses to herbivores. To this end, an F2 progeny was generated by crossing Datura stramonium (Solanaceae) parents from two populations differing in their level of chemical defense. This F2 progeny was reciprocally transplanted into the parental plants' habitats and by measuring the identity by descent (IBD) relationship of each F2 plant to each parent, we were able to elucidate how spatially variable selection imposed by herbivores operated on the genetic background (IBD) of resistance to herbivory, promoting local adaptation. The results highlight that plants possessing the highest total alkaloid concentrations (sum of all alkaloid classes) were not the most well-defended or fit. Instead, specific alkaloids and their linked loci/alleles were favored by selection imposed by different herbivores. This has led to population differentiation in plant defenses and thus, to local adaptation driven by plant-herbivore interactions.

The 13-lipoxygenase MSD2 and the ω-3 fatty acid desaturase MSD3 impact Spodoptera frugiperda resistance in Sorghum.

MAIN CONCLUSION: Linolenic acid produced by the ω-3 fatty acid desaturase MSD3 in sorghum is used for insect-induced jasmonic acid production and is important for resistance against Spodoptera frugiperda. Jasmonic acid (JA) is a phytohormone that regulates both plant development and stress responses. In sorghum (Sorghum bicolor), the ω-3 fatty acid desaturase Multiseeded3 (MSD3) and the 13-lipoxygenase Multiseeded2 (MSD2) are important for producing JA to regulate panicle development and spikelet fertility, but their function in plant defense remains unknown. In this study, we examined whether these genes are important for the production of JA in response to herbivory by the insect pest Spodoptera frugiperda. Compared to wild-type controls, the msd3 mutant accumulated less JA in leaves of both infested and uninfested plants, revealing that MSD3 is involved in stress-induced JA production. In contrast, herbivore-induced JA production in the msd2 mutant was indistinguishable from wild type, indicating that MSD2 does not function in herbivore-induced JA production. An increase of S. frugiperda growth was observed on both the msd3 and msd2 mutants, hinting at roles for both JA and additional oxylipins in sorghum's defense responses.

Spectroscopic Investigation of the Kinetic Mechanism Involved in the Association of Potyviral VPg with the Host Plant Translation Initiation Factor eIF4E.

The infectious cycle of potyviruses requires the formation of a complex between the viral genome-linked protein VPg and the host eukaryotic translation initiation factor 4E, eIF4E. Mutations associated with plant resistance to potyviruses were previously mapped at the eIF4E surface, while on the virus side, mutations leading to plant resistance breaking were identified within the VPg. In the present study, fluorescence spectroscopy was used to probe the contribution of the VPg intrinsically disordered region bearing amino acids determinant of the resistance breaking, to the VPg-eIF4E binding mechanism. Synthetic peptides encompassing the VPg88-120 central region were found to tightly bind to eIF4E. Fluorescence energy transfer experiments show that, upon binding to eIF4E, the N and C termini of the VPg88-111 fragment move closer to one another, at a distance compatible with a α-helix folding. When the VPg112-120 region, which contains amino acids associated with resistance breakdown, is appended to VPg88-111, the complex formation with eIF4E switches from a single-step to a two-step kinetic model. This study revisits a recent investigation of the VPg-eIF4E complex by specifying the contribution of the VPg central helix and its appended disordered region to VPg association with eIF4E.

Improved host-plant resistance to Phytophthora rot and powdery mildew in soybean (Glycine max (L.) Merr.).

Soybean is an important oilseed cum vegetable crop, susceptible to various biotic stresses which is attributed to recent decline in crop productivity. The emergence of virulent biotypes/strains of different plant pathogens necessitates the development of new crop varieties with enhanced host resistance mechanisms. Pyramiding of multiple disease-resistant genes is one of the strategies employed to develop durable disease-resistant cultivars to the prevailing and emerging biotypes of pathogens. The present study, reports the successful introgression of two major R-genes, including Rps2 (Phytophthora rot resistance), Rmd-c (complete-powdery mildew resistance) and effective nodulating gene (rj2) through functional Marker-Assisted Backcross Breeding (MABB) in the genetic background of well-adapted and high yielding soybean varieties, CO 3 and JS 335. We have identified several promising introgressed lines with enhanced resistance to Phytophthora rot and powdery mildew. The improved soybean lines have exhibited medium to high level of resistance against powdery mildew and Phytophthora rot as well as displayed effective nodulation capacity. Our study has proven the generation of resistant genotypes to realize the potential of MABB for achieving host plant resistance in soybean. The improved lines developed can greatly assist the soybean breeding programs in India and other soybean growing countries for evolving disease-resistant varieties.

Effects of the cucumber mosaic virus 2a protein on aphid-plant interactions in Arabidopsis thaliana.

The cucumber mosaic virus (CMV) 2a RNA-dependent RNA polymerase protein has an additional function in Arabidopsis thaliana, which is to stimulate feeding deterrence (antixenosis) against aphids. Antixenosis is thought to increase the probability that aphids, after acquiring CMV particles from brief probes of an infected plant's epidermal cells, will be discouraged from settling and instead will spread inoculum to neighbouring plants. The amino acid sequences of 2a proteins encoded by a CMV strain that induces antixenosis in A. thaliana (Fny-CMV) and one that does not (LS-CMV) were compared to identify residues that might determine the triggering of antixenosis. These data were used to design reassortant viruses comprising Fny-CMV RNAs 1 and 3, and recombinant CMV RNA 2 molecules encoding chimeric 2a proteins containing sequences derived from LS-CMV and Fny-CMV. Antixenosis induction was detected by measuring the mean relative growth rate and fecundity of aphids (Myzus persicae) confined on infected and on mock-inoculated plants. An amino acid sequence determining antixenosis induction by CMV was found to reside between 2a protein residues 200 and 300. Subsequent mutant analysis delineated this to residue 237. We conjecture that the Fny-CMV 2a protein valine-237 plays some role in 2a protein-induced antixenosis.

A Genome-Wide View of Transcriptional Responses during Aphis glycines Infestation in Soybean.

Soybean aphid (Aphis glycines Matsumura) is one of the major limiting factors in soybean production. The mechanism of aphid resistance in soybean remains enigmatic as little information is available about the different mechanisms of antibiosis and antixenosis. Here, we used genome-wide gene expression profiling of aphid susceptible, antibiotic, and antixenotic genotypes to investigate the underlying aphid-plant interaction mechanisms. The high expression correlation between infested and non-infested genotypes indicated that the response to aphid was controlled by a small subset of genes. Plant response to aphid infestation was faster in antibiotic genotype and the interaction in antixenotic genotype was moderation. The expression patterns of transcription factor genes in susceptible and antixenotic genotypes clustered together and were distant from those of antibiotic genotypes. Among them APETALA 2/ethylene response factors (AP2/ERF), v-myb avian myeloblastosis viral oncogene homolog (MYB), and the transcription factor contained conserved WRKYGQK domain (WRKY) were proposed to play dominant roles. The jasmonic acid-responsive pathway was dominant in aphid-soybean interaction, and salicylic acid pathway played an important role in antibiotic genotype. Callose deposition was more rapid and efficient in antibiotic genotype, while reactive oxygen species were not involved in the response to aphid attack in resistant genotypes. Our study helps to uncover important genes associated with aphid-attack response in soybean genotypes expressing antibiosis and antixenosis.

Ethylene Is Not Essential for R-Gene Mediated Resistance but Negatively Regulates Moderate Resistance to Some Aphids in Medicago truncatula.

Ethylene is important for plant responses to environmental factors. However, little is known about its role in aphid resistance. Several types of genetic resistance against multiple aphid species, including both moderate and strong resistance mediated by R genes, have been identified in Medicago truncatula. To investigate the potential role of ethylene, a M. truncatula ethylene- insensitive mutant, sickle, was analysed. The sickle mutant occurs in the accession A17 that has moderate resistance to Acyrthosiphon kondoi, A. pisum and Therioaphis trifolii. The sickle mutant resulted in increased antibiosis-mediated resistance against A. kondoi and T. trifolii but had no effect on A. pisum. When sickle was introduced into a genetic background carrying resistance genes, AKR (A. kondoi resistance), APR (A. pisum resistance) and TTR (T. trifolii resistance), it had no effect on the strong aphid resistance mediated by these genes, suggesting that ethylene signaling is not essential for their function. Interestingly, for the moderate aphid resistant accession, the sickle mutant delayed leaf senescence following aphid infestation and reduced the plant biomass losses caused by both A. kondoi and T. trifolii. These results suggest manipulation of the ethylene signaling pathway could provide aphid resistance and enhance plant tolerance against aphid feeding.