Simulated herbivory in chickpea causes rapid changes in defense pathways and hormonal transcription networks of JA/ethylene/GA/auxin within minutes of wounding

Trichomes and unique gene expression confer insect herbivory resistance in Vitis labrusca grapevines

BACKGROUND

Grapevine (Vitis) is one of the world's most valuable fruit crops, but insect herbivory can decrease yields. Understanding insect herbivory resistance is critical to mitigating these losses. Vitis labrusca, a wild North American grapevine species, has been leveraged in breeding programs to generate hybrid grapevines with enhanced abiotic and biotic stress resistance, rendering it a valuable genetic resource for sustainable viticulture. This study assessed the resistance of V. labrusca acc. 'GREM4' and Vitis vinifera cv. 'PN40024' grapevines to Popillia japonica (Japanese beetle) herbivory and identified morphological and genetic adaptations underlying this putative resistance.

RESULTS

'GREM4' displayed greater resistance to beetle herbivory compared to 'PN40024' in both choice and no-choice herbivory assays spanning periods of 30 min to 19 h. 'GREM4' had significantly higher average leaf trichome densities than 'PN40024' and beetles preferred to feed on the side of leaves with fewer trichomes. When leaves from each species that specifically did not differ in trichome densities were fed on by beetles, significantly less leaf area was damaged in 'GREM4' (3.29mm2) compared to 'PN40024' (9.80mm2), suggesting additional factors beyond trichomes contributed to insect herbivory resistance in 'GREM4'. Comparative transcriptomic analyses revealed 'GREM4' exhibited greater constitutive (0 h) expression of defense response and secondary metabolite biosynthesis genes compared to 'PN40024', indicative of heightened constitutive defenses. Upon herbivory, 'GREM4' displayed a greater number of differentially expressed genes (690) compared to 'PN40024' (502), suggesting a broader response. Genes up-regulated in 'GREM4' were enriched in terpene biosynthesis, flavonoid biosynthesis, phytohormone signaling, and disease defense-related functions, likely contributing to heighted insect herbivory defense, while genes differentially expressed in 'PN40024' under herbivory were enriched in xyloglucan, cell wall formation, and calcium ion binding. The majority of genes implicated in insect herbivory defense were orthologs with specific expression patterns in 'GREM4' and 'PN40024', but some paralogous and genome-specific genes also likely contributed to conferring resistance.

CONCLUSIONS

Our findings suggest that 'GREM4' insect herbivory resistance was attributed to a combination of factors, including trichomes and unique constitutive and inducible expression of genes implicated in terpene, flavonoid, and phenylpropanoid biosynthesis, as well as pathogen defense.

The effects of Micro/Nano-plastics exposure on plants and their toxic mechanisms: A review from multi-omics perspectives

In recent years, plastic pollution has become a global environmental problem, posing a potential threat to agricultural ecosystems and human health, and may further exacerbate global food security problems. Studies have revealed that exposure to micro/nano-plastics (MPs/NPs) might cause various aspects of physiological toxicities, including plant biomass reduction, intracellular oxidative stress burst, photosynthesis inhibition, water and nutrient absorption reduction, cellular and genotoxicity, seed germination retardation, and that the effects were closely related to MP/NP properties (type, particle size, functional groups), exposure concentration, exposure duration and plant characteristics (species, tissue, growth stage). Based on a brief review of the physiological toxicity of MPs/NPs to plant growth, this paper comprehensively reviews the potential molecular mechanism of MPs/NPs on plant growth from perspectives of multi-omics, including transcriptome, metabolome, proteome and microbiome, thus to reveal the role of MPs/NPs in plant transcriptional regulation, metabolic pathway reprogramming, protein translational and post-translational modification, as well as rhizosphere microbial remodeling at multiple levels. Meanwhile, this paper also provides prospects for future research, and clarifies the future research directions and the technologies adopted.

A comprehensive investigation of lipid-transfer proteins from Cicer arietinum disentangles their role in plant defense against Helicoverpa armigera-infestation

Lipid Transfer Proteins (LTPs) play a crucial role in synthesizing lipid barrier polymers and are involved in defense signaling during pest and pathogen attacks. Although LTPs are conserved with multifaceted roles in plants, these are not yet identified and characterized in Cicer arietinum. In this study, a genome-wide analysis of LTPs was executed and their physiochemical properties, biochemical function, gene structure analysis, chromosomal localization, promoter analysis, gene duplication, and evolutionary analysis were performed using in silico tools. Furthermore, tissue-specific expression analysis and gene expression analysis during pest attack was also conducted for the LTPs. A total of 48 LTPs were identified and named as CaLTPs. They were predicted to be small unstable proteins with "Glycolipid transfer protein" and "Alpha-Amylase Inhibitors, Lipid Transfer and Seed Storage" domains, that are translocated to the extracellular region. CaLTPs were predicted to possess 3-4 introns and were located on all the eight chromosomes of chickpea with half of the CaLTPs being localized on chromosomes 4, 5, and 6, and found to be closely related to LTPs of Arabidopsis thaliana and Medicago trancatula. Gene duplication and synteny analysis revealed that most of the CaLTPs have evolved due to tandem or segmental gene duplication and were subjected to purifying selection during evolution. The promoters of CaLTPs had development-related, phytohormone-responsive, and abiotic and biotic stress-related cis-acting elements. A few CaLTP transcripts exhibited differential expression in diverse tissue types, while others showed no/very low expression. Out of 20 jasmonate-regulated CaLTPs, 14 exhibited differential expression patterns during Helicoverpa armigera-infestation, indicating their role in plant defense response. This study identified and characterized CaLTPs from an important legume, C. arietinum, and indicated their involvement in plant defense against H. armigera-infestation, which can be further utilized to explore lipid signaling during plant-pest interaction and pest management.

Mechanical wounding impacts the growth versus defense balance in tomato (Solanum lycopersicum)

Plants have evolved elaborate surveillance systems that allow them to perceive the attack by pests and pathogens and activate the appropriate defenses. Mechanical stimulation, such as mechanical wounding, represents one of the most reliable cues for the perception of potential herbivore aggressors. Here we demonstrate that mechanical wounding disturbs the growth versus defense balance in tomato, a physiological condition where growth reduction arises as a pleiotropic consequence of the activation of defense responses (or vice-versa). We observed that multiple lesions on tomato leaves impairs the formation of several growth-related traits, including shoot elongation, leaf expansion and time for flowering, while concomitantly activating the production of defense responses such as trichome formation and the upregulation of defense-related genes. We also provide genetic evidence that this wound-induced growth repression is possibly a consequence of tomato plants sensing the injuries via jasmonates (JAs), a class of plant hormones known to be master regulators of the plant growth versus defense balance. Besides providing a mechanistic explanation on how the growth and defense balance is shifted when plants are subjected to a specific type of mechanical stimulus, our results may offer a practical explanation for why tomato productivity is so negatively impacted by herbivore attack.

Comparative transcriptome-wide identification and differential expression of genes and lncRNAs in rice near-isogenic line (KW-Bph36-NIL) in response to BPH feeding

Brown planthopper (BPH) is the most devastating pest of rice in Asia, causing substantial yield losses and has become a challenging task to be controlled under field conditions. Although extensive measures have been taken over the past decades, which resulted in the evolution of new resistant BPH strains. Therefore, besides other possible approaches, equipping host plants with resistant genes is the most effective and environment-friendly technique for BPH control. Here, we systematically analyzed transcriptome changes in the susceptible rice variety Kangwenqingzhan (KW) and the resistant near-isogenic line (NIL) KW-Bph36-NIL, through RNA-seq, depicting the differential expression profiles of mRNAs and long non-coding RNAs (lncRNAs) in rice before and after BPH feeding. We observed a proportion of genes (1.48%) and (2.74%) were altered in KW and NIL, respectively, indicating different responses of rice strains against BPH feeding. Nevertheless, we characterized 384 differentially expressed long non-coding RNAs (DELs) that can be impacted by the two strains by alternatively changing the expression patterns of the respective coding genes, suggesting their certain involvement in response to BPH feeding. In BPH invasion, KW and NIL responded differently by modifying the synthesis, storage, and transformation of intracellular substances, adjusting the nutrient accumulation and utilization inside and outside the cells. In addition, NIL expressed stronger resistance by acutely up-regulating genes and other transcription factors related to stress resistance and plant immunity. Altogether, our study elaborates valuable insights into the genome-wide DEGs and DELs expression profiles of rice under BPH invasion by high throughput sequencing and further suggests that NILs can be utilized in BPH resistance breeding programs in developing high-resistance rice lines.

Environmental microplastics: Classification, sources, fates, and effects on plants

Microplastic (MP) pollution has become a global concern due to the generation of extensive plastic waste and products (370 million metric tons in 2020) that are difficult to biodegrade. Therefore, MPs have attracted a great deal of research attention, and many new findings regarding MPs (over 9000 papers published in the last 3 years) have been reported. MPs generally exert adverse effects on plants. As MPs accumulate in agricultural ecosystems, many studies have sought to understand the sources and fates of MPs and their effects on various plants. However, there have been few reviews of the properties of MPs, their effects on plants, and their interactions with other factors (e.g., drought, heat, ultraviolet light, plant hormones, heavy metals, and other pollutants) remain poorly understood. In this review, we performed scientometrics analyses of research papers (January 1, 2019, to September 30, 2022) in this field. We focused on the recent progress in the classification of MPs and their sources, circulation, and deposition in agricultural ecosystems. We review MP uptake and transport in plants, as well as factors (size, type, and environmental factors) that affect MP uptake, the positive and negative effects of MPs on plants, and the mechanisms of MP impacts on plants. We discuss current issues and future perspectives concerning research into plant interactions with MPs, along with some promising methods to manage the MP issue.

Wounding rapidly alters transcription factor expression, hormonal signaling, and phenolic compound metabolism in harvested sugarbeet roots

Injuries sustained by sugarbeet (Beta vulgaris L.) roots during harvest and postharvest operations seriously reduce the yield of white sugar produced from stored roots. Although wound healing is critically important to reduce losses, knowledge of these processes is limited for this crop as well as for roots in other species. To better understand the metabolic signals and changes that occur in wounded roots, dynamic changes in gene expression were determined by RNA sequencing and the activity of products from key genes identified in this analysis were determined in the 0.25 to 24 h following injury. Nearly five thousand differentially expressed genes that contribute to a wide range of cellular and molecular functions were identified in wounded roots. Highly upregulated genes included transcription factor genes, as well as genes involved in ethylene and jasmonic acid (JA) biosynthesis and signaling and phenolic compound biosynthesis and polymerization. Enzyme activities for key genes in ethylene and phenolic compound biosynthesis and polymerization also increased due to wounding. Results indicate that wounding causes a major reallocation of metabolism in sugarbeet taproots. Although both ethylene and JA are likely involved in triggering wound responses, the greater and more sustained upregulation of ethylene biosynthesis and signaling genes relative to those of JA, suggest a preeminence of ethylene signaling in wounded sugarbeet roots. Changes in gene expression and enzymes involved in phenolic compound metabolism additionally indicate that barriers synthesized to seal off wounds, such as suberin or lignin, are initiated within the first 24 h after injury.

Ingenious characterization and assessment of lentil germplasm collection to aphid Acyrthosiphon pisum stress unveils distinct responses

Lentil cultivation is often hampered by aphid population outspreads with detrimental impacts to crop development and production, challenging food safety and agriculture sustainability. The pea aphid (Acyrthosiphon pisum) is a significant threat to lentil in the temperate zone rainfed systems. A set of management practices including resilient cultivars and application of insecticides have effectively controlled aphid infestation. However, the plant defense against insect pests is scantily dissected and limited to the individual components including antibiosis, antixenosis and tolerance that constitute a combination of plant stress responses. Utilizing a lentil germplasm collection, we assessed the antixenosis and aphid tolerance mechanisms in association to important morphological parameters. Physiological parameters including relative water content (RWC) measured at 24h and 48h post-aphid infestation revealed genotype-specific responses. The contents of key plant hormones including salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA) and indoleacetic acid (IAA) implicated in defense signal-transduction pathways were also determined in lentil accessions after aphid herbivory infestation. In parallel, the expression of hallmark defense genes governed by SA- and JA-signaling pathways at 24h and 48h post aphid herbivory revealed significant differentiation patterns among the accessions. An interplay of hormone crosstalk is unveiled that possibly governs defense responses and aphid resistance. Besides the metabolomic profiling of accessions under aphid herbivory indicated the indispensable role of key secondary metabolites accumulation such as flavonoids, alkaloids, phenolics and fatty acids as a front line of plant defense and a potential integration of hormone signaling pathways in metabolome reprogramming. Overall, the study presents a panorama of distinct lentil responses to aphids and a critical view of the molecular mechanisms implicated in lentil insect defense to further our insight and advance crop protection and breeding approaches in a climate changing environment.

Multi-omics analysis reveals the molecular responses of Torreya grandis shoots to nanoplastic pollutant

Micro/nanoplastic has become an emerging pollutant of global concern. At present, ecotoxic researches on micro/nanoplastics mostly focus on marine aquatic organisms and freshwater algae. Research on the ecological impacts of plastics on higher terrestrial plants, especially on forest plants, is relatively limited. Torreya grandis cv. Merrillii, a species of conifer in the family Taxaceae, is a unique and economically valuable tree species in China. The physiological and biochemical responses of T. grandis seedlings to polystyrene nanoplastics (PSNPs) with a diameter of 100 nm were systematically studied inthe present study. The results showed that nanoplastics enhanced the accumulation of the thiobarbituric acid reactive substance and the activities of catalase and peroxidase. The concentrations of iron, sulfur, and zinc were reduced after nanoplastic exposure. PSNP treatment had an important effect on a series of chemical and genetic indicators of T. grandis, includingantioxidants, small RNA, gene transcription, protein expressions, and metabolite accumulation. Multi-omic analysis revealed that PSNPs modulate terpenoid- and flavonoid-biosynthesis pathways by regulating small RNA transcription and protein expression. Our study provided novelty insights into the responses of forest plants to nanoplastic treatment.

The involvement of extracellular ATP in regulating the stunted growth of Arabidopsis plants by repeated wounding

BACKGROUND

Extracellular ATP (exATP) has been shown to act as a signal molecule for regulating growth, development, and responses of plants to the external environment.

RESULTS

In this study, we investigated the possible involvement of exATP in regulating the stunted growth caused by repeated wounding. The present work showed that the repeated wounding caused the decreases in leaf area, fresh weight, dry weight, and root length of Arabidopsis seedlings, while the exATP level was enhanced by the repeated wounding. Repeated application of exogenous ATP had similar effects on the plant growth, as the repeated wounding. Through the comparison of p2k1-3 mutant (in which T-DNA disrupted the gene coding P2K1, as exATP receptor) and wide type (WT) plants, it was found that the mutation in P2K1 decreased the sensitivity of plant growth to the repeated wounding and exogenous ATP application. Further works showed that the ibuprofen (IBU, an inhibitor of jasmonate biosynthesis) partially rescued the wound-induced growth degradation. In comparison, the P2K1 mutation partly rescued the wound-induced growth degradation, whereas this mutation failed to do so in the wounded seedlings treated with IBU, indicating that the role of exATP in regulating the growth degradation by repeated wounding could be linked to the JA signaling pathway.

CONCLUSIONS

In conclusion, these results indicate that exATP could be a regulator for the stunted growth of plants by repeated wounding.

Jasmonic acid is involved in root cell wall phosphorus remobilization through the nitric oxide dependent pathway in rice

Jasmonic acid (JA) is involved in phosphorus (P) stress in plants, but its underlying molecular mechanisms are still elusive. In this study, we found root endogenous JA content in rice increased under P deficiency (-P), suggesting that JA might participate in P homeostasis in plants. This hypothesis was further confirmed through the addition of exogenous JA (+JA), as this could increase both the root and shoot soluble P content through regulating root cell wall P reutilization. In addition, -P+JA treatment significantly induced the expression of P transporter gene OsPT2, together with increased xylem P content, implying that JA is also important for P translocation from the root to the shoot in P-deficient rice. Furthermore, the accumulation of the molecular signal nitric oxide (NO) was enhanced under -P+JA treatment when compared with -P treatment alone, while the addition of c-PTIO, a scavenger of NO, could reverse the P-deficient phenotype alleviated by JA. Taken together, our results reveal a JA-NO-cell wall P reutilization pathway under P deficiency in rice.

Early wound-responsive cues regulate the expression of WRKY family genes in chickpea differently under wounded and unwounded conditions

Insect wounding activates a large number of signals that function coordinately to modulate gene expression and elicit defense responses. How each signal influences gene expression in absence of wounding is also important since it can shed light on changes occurring during the shift to wound response. Using simulated Helicoverpa armigera herbivory on chickpea, we had identified at least 14 WRKY genes that showed 5-50 fold increase in expression within 5-20 min of wounding. Our studies show that contrary to their collective effects upon wounding, individual chemical cues show distinct and often opposite effects in absence of wounding. In particular, jasmonic acid, a key early defense hormone, reduced transcripts of most WRKY genes by > 50% upon treatment of unwounded chickpea leaves as did salicylic acid. Neomycin (a JA biosynthesis inhibitor) delayed and also reduced early wound expression. H₂O₂ transiently activated several genes within 5-20 min by 5-8 fold while ethylene activated only a few WRKY genes by 2-5 fold. The summation of the individual effects of these chemical cues does not explain the strong increase in transcript levels upon wounding. Detailed studies of a 931 nt region of the CaWRKY41 promoter, show strong wound-responsive GUS expression in Arabidopsis even in presence of neomycin. Surprisingly its expression was lost in the coi1, ein2 and myc2myc3myc4 mutant backgrounds suggesting the requirement of intact ethylene and JA signaling pathways (dependent on MYCs) for wound-responsive expression. The studies highlight the complexity of gene regulation by different chemical cues in the presence and absence of wounding.

SUPPLEMENTARY INFORMATION

The online version contains Supplementary material available at 10.1007/s12298-022-01170-y.

Transcriptomics of tapping and healing process in frankincense tree during resin production

Frankincense tree (Boswellia sacra Fluek) has been poorly known on how it responds to tapping and wound-recovery process at molecular levels. Here, we used RNA-sequencing analysis to profile transcriptome of B. sacra after 30 min, 3 h and 6 h of post-tapping. Results showed 5525 differentially expressed genes (DEGs) that were related to terpenoid biosynthesis, phytohormonal regulation, cellular transport, and cell-wall synthesis. Plant-growth-regulators were applied exogenously which showed regulation of endogenous jasmonates and resulted in rapid recovery of cell-wall integrity by significantly up-regulated gene expression of terpenoid biosynthesis (germacrene-D synthase, B-amyrin synthase, and squalene epioxidase-1) and cell-wall synthesis (xyloglucan endotransglucosylase, cellulose synthase-A, and cell-wall hydrolase) compared to control. These findings suggest that tapping immediately activated several cell-developmental and regeneration processes, alongwith defense-induced terpenoid metabolism, to improve the healing process in epidermis. Exogenous growth regulators, especially jasmonic acid, can drastically help tree recovery from tissue degeneration and might help in tree conservation purposes.

Dynamics of Zea mays transcriptome in response to a polyphagous herbivore, Spodoptera litura

Zea mays defense response is well-crafted according to the physical and chemical weapons utilized by their invaders during the coevolutionary period. Maize plants employ diversified defense strategies and alter the spatiotemporal distribution of several classes of defensive compounds to affect insect herbivore performance. However, only little knowledge is available about the defense orchestration of maize in response to Spodoptera litura, a voracious Noctuidae pest. In order to decipher the defense status of Zea mays (African tall variety) against S. litura, a comparative feeding bioassay was executed, which revealed reduced performance of the herbivore on maize. In order to understand the molecular mechanism behind maize tolerance against S. litura, a microarray-based genome-wide expression analysis was performed. The comparative analysis displayed 792 differentially expressed genes (DEGs), wherein 357 genes were upregulated and 435 genes were downregulated at fold change ≥ 2 and p value ≤ 0.05. The upregulated genes were identified and categorized as defense-related, oxidative stress-related, transcription regulatory genes, protein synthesis genes, phytohormone-related, and primary and secondary metabolism-related. In contrast, downregulated genes were mainly associated with plant growth and development, indicating a balance of growth and defense response and utilization of a highly evolved C-diversion response were noticed. Maize plants showed better tolerance against herbivory and maintained its fitness using a combinatorial strategy. This peculiar response of Zea mays against S. litura offers an excellent possibility of managing polyphagous pests by spicing up the plant's defensive response with tolerance mechanism.

Metabolism and transcriptome profiling provides insight into the genes and transcription factors involved in monoterpene biosynthesis of borneol chemotype of Cinnamomum camphora induced by mechanical damage

Background

The borneol chemotype of Cinnamomum camphora (BCC), a monoterpene-rich woody plant species, is the sole source prescribed by the Chinese Pharmacopoeia for the production of natural D-borneol, a major monoterpene in BCC used for millennia as a topical analgesic in China. Nevertheless, the possible gene-regulatory roles of transcription factors (TFs) in BCC’s monoterpenoid biosynthesis remained unknown. Here, a joint analysis of the transcriptome and terpenoid metabolome of BCC induced by mechanical damage (MD) was used to comprehensively explore the interaction between TFs and terpene synthase (TPS) unigenes that might participate in monoterpene biosynthesis in BCC.

Results

Gas chromatography–mass spectrometry analysis detected 14 monoterpenes and seven sesquiterpenes. All but two monoterpenes underwent a significantly increased accumulation after the MD treatment. RNA sequencing data revealed that 10 TPS, 82 MYB, 70 AP2/ERF, 38 BHLH, 31 WRKY, and 29 bZIP unigenes responded to the MD treatment. A correlation analysis revealed that three monoterpene synthase genes (CcTPS1, CcTPS3, CcTPS4) highly correlated with multiple monoterpenes, namely D-borneol, camphor, and bornyl acetate, which could be responsible for monoterpenoid biosynthesis in BCC. Furthermore, five WRKY, 15 MYB, 10 ERF/AP2, five bZIP, and two BHLH genes had strong, positive correlations with CcTPS1 or CcTPS4, judging by their high coefficient values (R² > 0.8). The bioinformatics results were verified by quantitative real-time PCR.

Conclusion

This study provides insight into the genes involved in the biosynthesis and regulation of monoterpene in BCC and thus provides a pool of candidate genes for future mechanistic analyses of how monoterpenes accumulate in BCC.

Plant volatiles as cues and signals in plant communication

Volatile organic compounds are important mediators of mutualistic interactions between plants and their physical and biological surroundings. Volatiles rapidly indicate competition or potential threat before these can take place, and they regulate and coordinate adaptation responses in neighbouring plants, fine-tuning them to match the exact stress encountered. Ecological specificity and context-dependency of plant-plant communication mediated by volatiles represent important factors that determine plant performance in specific environments. In this review, we synthesise the recent progress made in understanding the role of plant volatiles as mediators of plant interactions at the individual and community levels, highlighting the complexity of the plant receiver response to diverse volatile cues and signals and addressing how specific responses shape plant growth and survival. Finally, we outline the knowledge gaps and provide directions for future research. The complex dialogue between the emitter and receiver based on either volatile cues or signals determines the outcome of information exchange, which shapes the communication pattern between individuals at the community level and determines their ecological implications at other trophic levels.

Influence of different elicitors on BIA production in Macleaya cordata

Sanguinarine (SAN) and chelerythrine (CHE) have been widely used as substitutes for antibiotics for decades. For a long time, SAN and CHE have been extracted from mainly Macleaya cordata, a plant species that is a traditional herb in China and belongs to the Papaveraceae family. However, with the sharp increase in demand for SAN and CHE, it is necessary to develop a new method to enhance the supply of raw materials. Here, we used methyl jasmonate (MJ), salicylic acid (SA) and wounding alone and in combination to stimulate aseptic seedlings of M. cordata at 0 h, 24 h, 72 h and 120 h and then compared the differences in metabolic profiles and gene expression. Ultimately, we found that the effect of using MJ alone was the best treatment, with the contents of SAN and CHE increasing by 10- and 14-fold, respectively. However, the increased SAN and CHE contents in response to combined wounding and MJ were less than those for induced by the treatment with MJ alone. Additionally, after MJ treatment, SAN and CHE biosynthetic pathway genes, such as those encoding the protopine 6-hydroxylase and dihydrobenzophenanthridine oxidase enzymes, were highly expressed, which is consistent with the accumulation of SAN and CHE. At the same time, we have also studied the changes in the content of synthetic intermediates of SAN and CHE after elicitor induction. This study is the first systematic research report about using elicitors to increase the SAN and CHE in Macleaya cordata.

Bruchid beetle ovipositioning mediated defense responses in black gram pods

BACKGROUND

Black gram [Vigna mungo (L)] seeds are a rich source of digestible protein and dietary fibre, both for human and animal consumption. However, the quality and quantity of the Vigna seeds are severely affected by bruchid beetles during storage. Therefore, analyses of the expression of the bruchid induced transcript dynamics in black gram pods would be helpful to understand the underlying defense mechanism against bruchid oviposition.

RESULTS

We used the RNAseq approach to survey the changes in transcript profile in the developing seeds of a moderately resistant cultivar IC-8219 against bruchid oviposition using a susceptible cultivar T-9 as a control. A total of 96,084,600 and 99,532,488 clean reads were generated from eight (4 each) samples of IC-8219 and T-9 cultivar, respectively. Based on the BLASTX search against the NR database, 32,584 CDSs were generated of which 31,817 CDSs were significantly similar to Vigna radiata, a close relative of Vigna mungo. The IC-8219 cultivar had 630 significantly differentially expressed genes (DEGs) of which 304 and 326 genes up and down-regulated, respectively. However, in the T-9 cultivar, only 168 DEGs were identified of which 142 and 26 genes up and down-regulated, respectively. The expression analyses of 10 DEGs by qPCR confirmed the accuracy of the RNA-Seq data. Gene Ontology and KEGG pathway analyses helped us to better understand the role of these DEGs in oviposition mediated defense response of black gram. In both the cultivars, the most significant transcriptomic changes in response to the oviposition were related to the induction of defense response genes, transcription factors, secondary metabolites, enzyme inhibitors, and signal transduction pathways. It appears that the bruchid ovipositioning mediated defense response in black gram is induced by SA signaling pathways and defense genes such as defensin, genes for secondary metabolites, and enzyme inhibitors could be potential candidates for resistance to bruchids.

CONCLUSION

We generated a transcript profile of immature black gram pods upon bruchid ovipositioning by de novo assembly and studied the underlying defense mechanism of a moderately resistant cultivar.

Functional characterisation of the transcriptome from leaf tissue of the fluoroacetate-producing plant, Dichapetalum cymosum, in response to mechanical wounding

Dichapetalum cymosum produces the toxic fluorinated metabolite, fluoroacetate, presumably as a defence mechanism. Given the rarity of fluorinated metabolites in nature, the biosynthetic origin and function of fluoroacetate have been of particular interest. However, the mechanism for fluorination in D. cymosum was never elucidated. More importantly, there is a severe lack in knowledge on a genetic level for fluorometabolite-producing plants, impeding research on the subject. Here, we report on the first transcriptome for D. cymosum and investigate the wound response for insights into fluorometabolite production. Mechanical wounding studies were performed and libraries of the unwounded (control) and wounded (30 and 60 min post wounding) plant were sequenced using the Illumina HiSeq platform. A combined reference assembly generated 77,845 transcripts. Using the SwissProt, TrEMBL, GO, eggNOG, KEGG, Pfam, EC and PlantTFDB databases, a 69% annotation rate was achieved. Differential expression analysis revealed the regulation of 364 genes in response to wounding. The wound responses in D. cymosum included key mechanisms relating to signalling cascades, phytohormone regulation, transcription factors and defence-related secondary metabolites. However, the role of fluoroacetate in inducible wound responses remains unclear. Bacterial fluorinases were searched against the D. cymosum transcriptome but transcripts with homology were not detected suggesting the presence of a potentially different fluorinating enzyme in plants. Nevertheless, the transcriptome produced in this study significantly increases genetic resources available for D. cymosum and will assist with future research into fluorometabolite-producing plants.

An overview of the transcriptional responses of two tolerant and susceptible sugarcane cultivars to borer (Diatraea saccharalis) infestation

Diatraea saccharalis constitutes a threat to the sugarcane productivity, and obtaining borer tolerant cultivars is an alternative method of control. Although there are studies about the relationship between the interaction of D. saccharalis with sugarcane, little is known about the molecular and genomic basis of defense mechanisms that confer tolerance to sugarcane cultivars. Here, we analyzed the transcriptional profile of two sugarcane cultivars in response to borer attack, RB867515 and SP80-3280, which are considered tolerant and sensitive to the borer attack, respectively. A sugarcane genome and transcriptome were used for read mapping. Differentially expressed transcripts and genes were identified and termed to as DETs and DEGs, according to the sugarcane database adopted. A total of 745 DETs and 416 DEGs were identified (log₂|ratio| > 0.81; FDR corrected P value ≤ 0.01) after borer infestation. Following annotation of up- and down-regulated DETs and DEGs by similarity searches, the sugarcane cultivars demonstrated an up-regulation of jasmonic acid (JA), ethylene (ET), and defense protein genes, as well as a down-regulation of pathways involved in photosynthesis and energy metabolism. The expression analysis also highlighted that RB867515 cultivar is possibly more transcriptionally activated after 12 h from infestation than SP80-3280, which could imply in quicker responses by probably triggering more defense-related genes and mediating metabolic pathways to cope with borer attack.

Defense Response in Chickpea Pod Wall due to Simulated Herbivory Unfolds Differential Proteome Profile

The pod wall of legumes is known to protect the developing seeds from pests and pathogens. However, the mechanism of conferring defense against insects has not yet been deciphered. Here, we have utilized 2-dimensional gel electrophoresis (2D-GE) coupled with mass spectrometry (MS/MS) to identify over expressed proteins in the pod wall of two different cultivars (commercial cultivar: JG 11 and tolerant cultivar: ICC 506-EB) of chickpea after 12 h of application of Helicoverpa armigera oral secretions (simulated herbivory). The assays were performed with a view that larvae are a voracious feeder and cause substantial damage to the pod within 12 h. A total of 600 reproducible protein spots were detected on gels, and the comparative analysis helped identify 35 (12 up-regulated, 23 down-regulated) and 20 (10 up-regulated, 10 down-regulated) differentially expressed proteins in JG 11 and ICC 506-EB, respectively. Functional classification of protein spots of each cultivar after MS/MS indicated that the differentially expressed proteins were associated with various metabolic activities. Also, stress-related proteins such as mannitol dehydrogenase (MADH), disease resistance-like protein-CSA1, serine/threonine kinase (D6PKL2), endoglucanase-19 etc. were up-regulated due to simulated herbivory. The proteins identified with a possible role in defense were further analyzed using the STRING database to advance our knowledge on their interacting partners. It decoded the involvement of several reactive oxygen species (ROS) scavengers and other proteins involved in cell wall reinforcement. The biochemical analysis also confirmed the active role of ROS scavengers during simulated herbivory. Thus, our study provides valuable new insights on chickpea-H.armigera interactions at the protein level.

PGPR-induced OsASR6 improves plant growth and yield by altering root auxin sensitivity and the xylem structure in transgenic Arabidopsis thaliana

Plant-growth-promoting rhizobacteria (PGPR) improve plant growth by altering the root architecture, although the mechanisms underlying this alteration have yet to be unravelled. Through microarray analysis of PGPR-treated rice roots, a large number of differentially regulated genes were identified. Ectopic expression of one of these genes, OsASR6 (ABA STRESS RIPENING6), had a remarkable effect on plant growth in Arabidopsis. Transgenic lines over-expressing OsASR6 had larger leaves, taller inflorescence bolts and greater numbers of siliques and seeds. The most prominent effect was observed in root growth, with the root biomass increasing four-fold compared with the shoot biomass increase of 1.7-fold. Transgenic OsASR6 over-expressing plants showed higher conductance, transpiration and photosynthesis rates, leading to an ˜30% higher seed yield compared with the control. Interestingly, OsASR6 expression led to alterations in the xylem structure, an increase in the xylem vessel size and altered lignification, which correlated with higher conductance. OsASR6 is activated by auxin and, in turn, increases auxin responses and root auxin sensitivity, as observed by the increased expression of auxin-responsive genes, such as SAUR32 and PINOID, and the key auxin transcription factor, ARF5. Collectively, these phenomena led to an increased root density. The effects of OsASR6 expression largely mimic the beneficial effects of PGPRs in rice, indicating that OsASR6 activation may be a key factor governing PGPR-mediated changes in rice. OsASR6 is a potential candidate for the manipulation of rice for improved productivity.

A strong early acting wound-inducible promoter, RbPCD1pro, activates cryIAc expression within minutes of wounding to impart efficient protection against insects

The expression of insecticidal proteins under constitutive promoters in transgenic plants is fraught with problems like developmental abnormalities, yield drag, expression in unwanted tissues, and seasonal changes in expression. RbPCD1pro, a rapid, early acting wound-inducible promoter from rose that is activated within 5 min of wounding, was isolated and characterized. Wounding increased transcript levels up to 150 and 500 folds within 5 and 20 min coupled with high translation as seen by histochemical GUS enzyme activity within 5-20 min. RbPCD1pro was activated by both sucking and chewing insects and showed wound-inducible expression in various aerial tissues of plants representing commercially important dicot and monocot families. The promoter showed no expression in any vegetative tissue except upon wounding. Functionality of RbPCD1pro was tested by its ability to drive expression of the insecticidal protein gene cryIAc in transgenic Arabidopsis and tomato. Strong wound-inducible CryIAc expression was observed in both plants that increased 100-350 fold (Arabidopsis) and 280-600 fold (tomato) over the unwounded background within 5 min and over 1000-1600 fold within 20 min. The unwounded background level was just 3-6% of the CaMV35S promoter while wound-induced expression was 5-27 folds higher than the best CaMV35S line in just 5 min and 80-fold higher in 20 min. Transgenic plants showed strong resistance even to larger fourth instar larvae of H. armigera and no abnormalities in development and general plant growth. This is one of the earliest acting promoters with wide biotechnological application across monocot and dicot plants.

An effector from cotton bollworm oral secretion impairs host plant defense signaling

Insects have evolved effectors to conquer plant defense. Most known insect effectors are isolated from sucking insects, and examples from chewing insects are limited. Moreover, the targets of insect effectors in host plants remain unknown. Here, we address a chewing insect effector and its working mechanism. Cotton bollworm (Helicoverpa armigera) is a lepidopteran insect widely existing in nature and severely affecting crop productivity. We isolated an effector named HARP1 from H. armigera oral secretion (OS). HARP1 was released from larvae to plant leaves during feeding and entered into the plant cells through wounding sites. Expression of HARP1 in Arabidopsis mitigated the global expression of wounding and jasmonate (JA) responsive genes and rendered the plants more susceptible to insect feeding. HARP1 directly interacted with JASMONATE-ZIM-domain (JAZ) repressors to prevent the COI1-mediated JAZ degradation, thus blocking JA signaling transduction. HARP1-like proteins have conserved function as effectors in noctuidae, and these types of effectors might contribute to insect adaptation to host plants during coevolution.

RNA-Seq analysis reveals transcript diversity and active genes after common cutworm (Spodoptera litura Fabricius) attack in resistant and susceptible wild soybean lines

BACKGROUND

Common cutworm (CCW) is highly responsible for destabilizing soybean productivity. Wild soybean is a resource used by breeders to discover elite defensive genes.

RESULTS

The transcriptomes of two wild accessions (W11 and W99) with different resistance to CCW were analyzed at early- and late-induction time points. After induction, the susceptible accession W11 differentially expressed 1268 and 508 genes at the early and late time points, respectively. Compared with W11, the resistant accession W99 differentially expressed 1270 genes at the early time point and many more genes (2308) at the late time point. In total, 3836 non-redundant genes were identified in both lines. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that the differentially expressed genes (DEGs) in W99 at the late time point were mostly associated with specific processes and pathways. Among the non-redundant genes, 146 genes were commonly up-regulated in the treatment condition compared with the control condition at the early- and late-induction time points in both accessions used in this experiment. Approximately 40% of the common DEGs were related to secondary metabolism, disease resistance, and signal transduction based on their putative function. Excluding the common DEGs, W99 expressed more unique DEGs than W11. Further analysis of the 3836 DEGs revealed that the induction of CCW not only up-regulated defense-related genes, including 37 jasmonic acid (JA)-related genes, 171 plant-pathogen-related genes, and 17 genes encoding protease inhibitors, but also down-regulated growth-related genes, including 35 photosynthesis-related genes, 48 nutrition metabolism genes, and 28 auxin metabolism genes. Therefore, representative defense-related and growth-related genes were chosen for binding site prediction via co-expression of transcription factors (TFs) and spatial expression pattern analyses. In total, 53 binding sites of 28 TFs were identified based on 3 defense-related genes and 3 growth-related genes. Phosphate transporter PT1, which is a representative growth-related gene, was transformed into soybean, and the transgenic soybean plants were susceptible to CCW.

CONCLUSIONS

In summary, we described transcriptome reprograming after herbivore induction in wild soybean, identified the susceptibility of growth-related genes, and provided new resources for the breeding of herbivore-resistant cultivated soybeans.

MicroR408 regulates defense response upon wounding in sweet potato

MiRNAs play diverse roles in plant development and defense responses by binding to their mRNA targets based on sequence complementarity. Here, we investigated a wound-related miR408 and its target genes in sweet potato (Ipomoea batatas) by small RNA deep sequencing and transcriptome analysis. The expression patterns of miR408 and the miR408 precursor were significantly repressed by wounding and jasmonate (JA). In contrast, expression of the putative target genes IbKCS (3-ketoacyl-CoA synthase 4), IbPCL (plantacyanin), and IbGAUT (galacturonosyltransferase 7-like) of miR408 was increased following wounding, whereas only IbKCS was increased after JA treatment. Target cleavage site mapping and Agrobacterium-mediated transient assay demonstrated that IbKCS, IbPCL, and IbGAUT were the targets of miR408. The expression of miR408 target genes was repressed in transgenic sweet potatoes overexpressing miR408. These data indicated a relationship between miR408 and its target genes. Notably, miR408-overexpressing plants showed a semi-dwarf phenotype and attenuated resistance to insect feeding, while transgenic plants overexpressing IbKCS exhibited more insect resistance than plants overexpressing only the empty vector. Collectively, sweet potato reduces the abundance of miR408 upon wounding to elevate the expression of IbKCS, IbPCL, and IbGAUT. The expression of IbKCS enhances the defense system against herbivore wounding.

Glyphosate induced toxicity to chickpea plants and stress alleviation by herbicide tolerant phosphate solubilizing Burkholderia cepacia PSBB1 carrying multifarious plant growth promoting activities

In this study, strain PSBB1 isolated from Vicia faba rhizosphere was identified as Burkholderia cepacia, by 16S rDNA sequence analysis and characterized. Strain PSBB1 tolerated glyphosate up to 3200 μg ml-1 and produced IAA (81.6 μg ml-1), ACC deaminase (69.3 mg-1 protein h-1), SA (39.3 μg ml-1) and 2,3-DHBA (26.6 μg ml-1), solubilized insoluble P (50.8 μg ml-1) and secreted 29.4 μg ml-1 exopolysaccharides, which decreased with increasing concentrations of glyphosate. Cell damage following glyphosate application was visible under SEM and CLSM. The phytotoxicity of glyphosate on chickpea was variable but significant. B. cepacia mitigated toxicity and enhanced the size, dry matter, symbiosis, seed attributes and nutritional contents of chickpea. Further, B. cepacia strain PSBB1 declined the levels of CAT, POD, APX and GPX and MDA contents at 4332 μg kg-1 soil glyphosate. Proline also increased under glyphosate stress but declined in B. cepacia inoculated plants. The ability to tolerate higher concentration of glyphosate, the capacity to secrete plant growth regulators even under herbicide stress and potential to reduce the level of proline and antioxidant enzymes makes B. cepacia as an interesting choice for enhancing chickpea production in soils contaminated even with herbicides.

Altering Plant Defenses: Herbivore-Associated Molecular Patterns and Effector Arsenal of Chewing Herbivores

Chewing herbivores, such as caterpillars and beetles, while feeding on the host plant, cause extensive tissue damage and release a wide array of cues to alter plant defenses. Consequently, the cues can have both beneficial and detrimental impacts on the chewing herbivores. Herbivore-associated molecular patterns (HAMPs) are molecules produced by herbivorous insects that aid them to elicit plant defenses leading to impairment of insect growth, while effectors suppress plant defenses and contribute to increased susceptibility to subsequent feeding by chewing herbivores. Besides secretions that originate from glands (e.g., saliva) and fore- and midgut regions (e.g., oral secretions) of chewing herbivores, recent studies have shown that insect frass and herbivore-associated endosymbionts also play a critical role in modulating plant defenses. In this review, we provide an update on a growing body of literature that discusses the chewing insect HAMPs and effectors and the mechanisms by which they modulate host defenses. Novel "omic" approaches and availability of new tools will help researchers to move forward this discipline by identifying and characterizing novel insect HAMPs and effectors and how these herbivore-associated cues are perceived by host plant receptors.