How plants handle multiple stresses: hormonal interactions underlying responses to abiotic stress and insect herbivory

Genome-Wide Association Analysis Identifies Candidate Loci for Callus Induction in Rice (Oryza sativa L.)

Callus induction (CI) is a critical trait for transforming desirable genes in plants. A genome-wide association study (GWAS) analysis was conducted on the rice germplasms of 110 Indica rice accessions, in which three tissue culture media, B5, MS, and N6, were used for the CI of those rice panels' mature seeds. Seven quantitative trait loci (QTLs) on rice chromosomes 2, 6, 7, and 11 affected the CI percentage in the three media. For the B5 medium, one QTL (qCI-B5-Chr6) was identified on rice chromosome 6; for the MS medium, two QTLs were identified on rice chromosomes 2 and 6 (qCI-MS-Chr2 and qCI-MS-Chr6, respectively); for the N6 medium, four QTLs were identified on rice chromosomes 6, 7, and 11 (qCI-N6-Chr6.1 and qCI-N6-Chr6.2, qCI-N6-Chr7, and qCI-N6-Chr11, respectively). Fifty-five genes were identified within the haplotype blocks corresponding to these QTLs, thirty-one of which showed haplotypes associated with different CI percentages in those media. qCI-B5-Chr6 was located in the same region as qCI-N6-Chr6.2, and the Caleosin-related family protein was also identified in this region. Analysis of the gene-based haplotype revealed the association of this gene with different CI percentages in both B5 and N6 media, suggesting that the gene may play a critical role in the CI mechanism. Moreover, several genes, including those that encode the beta-tubulin protein, zinc finger protein, RNP-1 domain-containing protein, and lysophosphatidic acid acyltransferase, were associated with different CI percentages in the N6 medium. The results of this study provide insights into the potential QTLs and candidate genes for callus induction in rice that contribute to our understanding of the physiological and biochemical processes involved in callus formation, which is an essential tool in the molecular breeding of rice.

Heat stress reprograms herbivory-induced defense responses in potato plants

Climate change is predicted to increase the occurrence of extreme weather events such as heatwaves, which may thereby impact the outcome of plant-herbivore interactions. While elevated temperature is known to directly affect herbivore growth, it remains largely unclear if it indirectly influences herbivore performance by affecting the host plant they feed on. In this study, we investigated how transient exposure to high temperature influences plant herbivory-induced defenses at the transcript and metabolic level. To this end, we studied the interaction between potato (Solanum tuberosum) plants and the larvae of the potato tuber moth (Phthorimaea operculella) under different temperature regimes. We found that P. operculella larvae grew heavier on leaves co-stressed by high temperature and insect herbivory than on leaves pre-stressed by herbivory alone. We also observed that high temperature treatments altered phylotranscriptomic patterns upon herbivory, which changed from an evolutionary hourglass pattern, in which transcriptomic responses at early and late time points after elicitation are more variable than the ones in the middle, to a vase pattern. Specifically, transcripts of many herbivory-induced genes in the early and late defense stage were suppressed by HT treatment, whereas those in the intermediate stage peaked earlier. Additionally, we observed that high temperature impaired the induction of jasmonates and defense compounds upon herbivory. Moreover, using jasmonate-reduced (JA-reduced, irAOC) and -elevated (JA-Ile-elevated, irCYP94B3s) potato plants, we showed that high temperature suppresses JA signaling mediated plant-induced defense to herbivore attack. Thus, our study provides evidences on how temperature reprograms plant-induced defense to herbivores.

Far-red light increases maize volatile emissions in response to volatile cues from neighbouring plants

Plants perceive the presence and defence status of their neighbours through light and volatile cues, but how plants integrate both stimuli is poorly understood. We investigated if and how low Red to Far red light (R:FR) ratios, indicative of shading or canopy closure, affect maize (Zea mays) responses to herbivore-induced plant volatiles (HIPVs), including the green leaf volatile (Z)-3-hexenyl acetate. We modulated light signalling and perception by using FR supplementation and a phyB1phyB2 mutant, and we determined volatile release as a response readout. To gain mechanistic insights, we examined expression of volatile biosynthesis genes, hormone accumulation, and photosynthesis. Exposure to a full blend of HIPVs or (Z)-3-hexenyl acetate induced maize volatile release. Short-term FR supplementation increased this response. In contrast, prolonged FR supplementation or constitutive phytochrome B inactivation in phyB1phyB2 plants showed the opposite response. Short-term FR supplementation enhanced photosynthesis and stomatal conductance and (Z)-3-hexenyl acetate-induced JA-Ile levels. We conclude that a FR-enriched light environment can prompt maize plants to respond more strongly to HIPVs emitted by neighbours, which might be explained by changes in photosynthetic processes and phytochrome B signalling. Our findings reveal interactive responses to light and volatile cues with potentially important consequences for plant-plant and plant-herbivore interactions.

Integrated physiological, transcriptomic and metabolomic analyses provide insights into phosphorus-mediated cadmium detoxification in Salix caprea roots

Phosphorus (P) plays a crucial role in facilitating plant adaptation to cadmium (Cd) stress. However, the molecular mechanisms underlying P-mediated responses to Cd stress in roots remain elusive. This study investigates the effects of P on the growth, physiology, transcriptome, and metabolome of Salix caprea under Cd stress. The results indicate that Cd significantly inhibits plant growth, while sufficient P alleviates this inhibition. Under Cd exposure, P sufficiency resulted in increased Cd accumulation in roots, along with reduced oxidative stress levels (superoxide anion and hydrogen peroxide contents were reduced by 16.8% and 30.1%, respectively). This phenomenon can be attributed to the enhanced activities of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT), as well as increased levels of antioxidants including ascorbic acid (AsA) and flavonoids under sufficient P conditions. A total of 4208 differentially expressed genes (DEGs) and 552 differentially accumulated metabolites (DAMs) were identified in the transcriptomic and metabolomic analyses, with 2596 DEGs and 113 DAMs identified among treatments with different P levels under Cd stress, respectively. Further combined analyses reveal the potential roles of several pathways in P-mediated Cd detoxification, including flavonoid biosynthesis, ascorbate biosynthesis, and plant hormone signal transduction pathways. Notably, sufficient P upregulates the expression of genes including HMA, ZIP, NRAMP and CAX, all predicted to localize to the cell membrane. This may elucidate the heightened Cd accumulation under sufficient P conditions. These findings provide insights into the roles of P in enhancing plant resistance to Cd stress and improving of phytoremediation.

Strategies for Enhancing Plant Immunity and Resilience Using Nanomaterials for Sustainable Agriculture

Research on plant-nanomaterial interactions has greatly advanced over the past decade. One particularly fascinating discovery encompasses the immunomodulatory effects in plants. Due to the low doses needed and the comparatively low toxicity of many nanomaterials, nanoenabled immunomodulation is environmentally and economically promising for agriculture. It may reduce environmental costs associated with excessive use of chemical pesticides and fertilizers, which can lead to soil and water pollution. Furthermore, nanoenabled strategies can enhance plant resilience against various biotic and abiotic stresses, contributing to the sustainability of agricultural ecosystems and the reduction of crop losses due to environmental factors. While nanoparticle immunomodulatory effects are relatively well-known in animals, they are still to be understood in plants. Here, we provide our perspective on the general components of the plant's immune system, including the signaling pathways, networks, and molecules of relevance for plant nanomodulation. We discuss the recent scientific progress in nanoenabled immunomodulation and nanopriming and lay out key avenues to use plant immunomodulation for agriculture. Reactive oxygen species (ROS), the mitogen-activated protein kinase (MAPK) cascade, and the calcium-dependent protein kinase (CDPK or CPK) pathway are of particular interest due to their interconnected function and significance in the response to biotic and abiotic stress. Additionally, we underscore that understanding the plant hormone salicylic acid is vital for nanoenabled applications to induce systemic acquired resistance. It is suggested that a multidisciplinary approach, incorporating environmental impact assessments and focusing on scalability, can expedite the realization of enhanced crop yields through nanotechnology while fostering a healthier environment.

Arabidopsis Transcriptomics Reveals the Role of Lipoxygenase2 (AtLOX2) in Wound-Induced Responses

In wounded Arabidopsis thaliana leaves, four 13S-lipoxygenases (AtLOX2, AtLOX3, AtLOX4, AtLOX6) act in a hierarchical manner to contribute to the jasmonate burst. This leads to defense responses with LOX2 playing an important role in plant resistance against caterpillar herb-ivory. In this study, we sought to characterize the impact of AtLOX2 on wound-induced phytohormonal and transcriptional responses to foliar mechanical damage using wildtype (WT) and lox2 mutant plants. Compared with WT, the lox2 mutant had higher constitutive levels of the phytohormone salicylic acid (SA) and enhanced expression of SA-responsive genes. This suggests that AtLOX2 may be involved in the biosynthesis of jasmonates that are involved in the antagonism of SA biosynthesis. As expected, the jasmonate burst in response to wounding was dampened in lox2 plants. Generally, 1 h after wounding, genes linked to jasmonate biosynthesis, jasmonate signaling attenuation and abscisic acid-responsive genes, which are primarily involved in wound sealing and healing, were differentially regulated between WT and lox2 mutants. Twelve h after wounding, WT plants showed stronger expression of genes associated with plant protection against insect herbivory. This study highlights the dynamic nature of jasmonate-responsive gene expression and the contribution of AtLOX2 to this pathway and plant resistance against insects.

Harnessing Phytohormones: Advancing Plant Growth and Defence Strategies for Sustainable Agriculture

Phytohormones, pivotal regulators of plant growth and development, are increasingly recognized for their multifaceted roles in enhancing crop resilience against environmental stresses. In this review, we provide a comprehensive synthesis of current research on utilizing phytohormones to enhance crop productivity and fortify their defence mechanisms. Initially, we introduce the significance of phytohormones in orchestrating plant growth, followed by their potential utilization in bolstering crop defences against diverse environmental stressors. Our focus then shifts to an in-depth exploration of phytohormones and their pivotal roles in mediating plant defence responses against biotic stressors, particularly insect pests. Furthermore, we highlight the potential impact of phytohormones on agricultural production while underscoring the existing research gaps and limitations hindering their widespread implementation in agricultural practices. Despite the accumulating body of research in this field, the integration of phytohormones into agriculture remains limited. To address this discrepancy, we propose a comprehensive framework for investigating the intricate interplay between phytohormones and sustainable agriculture. This framework advocates for the adoption of novel technologies and methodologies to facilitate the effective deployment of phytohormones in agricultural settings and also emphasizes the need to address existing research limitations through rigorous field studies. By outlining a roadmap for advancing the utilization of phytohormones in agriculture, this review aims to catalyse transformative changes in agricultural practices, fostering sustainability and resilience in agricultural settings.

Defense strategies and associated phytohormonal regulation in Brassica plants in response to chewing and sap-sucking insects

Plants have evolved distinct defense strategies in response to a diverse range of chewing and sucking insect herbivory. While chewing insect herbivores, exemplified by caterpillars and beetles, cause visible tissue damage and induce jasmonic acid (JA)-mediated defense responses, sucking insects, such as aphids and whiteflies, delicately tap into the phloem sap and elicit salicylic acid (SA)-mediated defense responses. This review aims to highlight the specificity of defense strategies in Brassica plants and associated underlying molecular mechanisms when challenged by herbivorous insects from different feeding guilds (i.e., chewing and sucking insects). To establish such an understanding in Brassica plants, the typical defense responses were categorized into physical, chemical, and metabolic adjustments. Further, the impact of contrasting feeding patterns on Brassica is discussed in context to unique biochemical and molecular modus operandi that governs the resistance against chewing and sucking insect pests. Grasping these interactions is crucial to developing innovative and targeted pest management approaches to ensure ecosystem sustainability and Brassica productivity.

Overexpression of TaMPK3 enhances freezing tolerance by increasing the expression of ICE-CBF-COR related genes in the Arabidopsis thaliana

Mitogen-activated protein kinases (MAPKs) play important roles in plant stress response. As a major member of the MAPK family, MPK3 has been reported to participate in the regulation of chilling stress. However, the regulatory function of wheat (Triticum aestivum ) mitogen-activated protein kinase TaMPK3 in freezing tolerance remains unknown. Dongnongdongmai No.1 (Dn1) is a winter wheat variety with strong freezing tolerance; therefore, it is important to explore the mechanisms underlying this tolerance. In this study, the expression of TaMPK3 in Dn1 was detected under low temperature and hormone treatment. Gene cloning, bioinformatics and subcellular localisation analyses of TaMPK3 in Dn1 were performed. Overexpressed TaMPK3 in Arabidopsis thaliana was obtained, and freezing tolerance phenotype observations, physiological indices and expression levels of ICE-C-repeat binding factor (CBF)-COR -related genes were determined. In addition, the interaction between TaMPK3 and TaICE41 proteins was detected. We found that TaMPK3 expression responds to low temperatures and hormones, and the TaMPK3 protein is localised in the cytoplasm and nucleus. Overexpression of TaMPK3 in Arabidopsis significantly improves freezing tolerance. TaMPK3 interacts with the TaICE41 protein. In conclusion, TaMPK3 is involved in regulating the ICE-CBF-COR cold resistance module through its interaction with TaICE41, thereby improving freezing tolerance in Dn1 wheat.

Medicinal Plants Used by Oromo Community in Kofale District, West-Arsi Zone, Oromia Regional State, Ethiopia

Purpose

The purpose of this study was to record the utilization of medicinal plants by the Oromo people in the Kofale District, Oromia Regional State, Ethiopia, to control human and animal health problems.

Methods

Data regarding the use of medicinal plants were collected using ethnobotanical methods from 84 traditional medicine practitioners and 304 general informants sampled employing purposive and systematic random sampling methods, respectively, in the Kofale District. Data were analyzed using different indices, including a preference ranking exercise, informant consensus factor (ICF), fidelity level (FL) and relative popularity level (RPL).

Results

In the district, 106 medicinal plants were claimed to be used for the treatment of 43 human and 18 livestock illnesses, of which 75 (71%) were used to manage human health problems, 23 (21.5%) were used to treat both human and livestock ailments and eight (7.5%) were utilized to treat manage livestock health problems. Most (76.4%) plants were harvested from the wild. Leaves were the most commonly used plant part (55.6%) in remedy preparations. Skin diseases scored the highest ICF value (0.97), followed by gastrointestinal disorders (ICF = 0.95), cancer (ICF = 0.93), and hemorrhoids (ICF = 0.91). Medicinal plants that record the highest fidelity level (FL) (100%) and rank order priority (ROP) (100%) values included Justicia schimperiana, Embelia schimperi, Ekebergia capensis and Datura stramonium, which have been used to treat liver disorders, tapeworm infections, babesiosis, and rabies, respectively. There were significant differences (p<0.05) in the mean numbers of medicinal plants claimed by different social groups: older, illiterate, and traditional medicine practitioners reported higher mean numbers of medicinal plants than younger, literate, and general informants, respectively.

Conclusion

This study indicated the richness of medicinal plant species in Kofale District. Medicinal plants with the highest FL and ROP values and those used to treat disease categories with the highest ICF values should be prioritized in future phytochemical and pharmacological investigations.

Comparative analysis of defensive secondary metabolites in wild teosinte and cultivated maize under flooding and herbivory stress

Climate change is driving an alarming increase in the frequency and intensity of abiotic and biotic stress factors, negatively impacting plant development and agricultural productivity. To survive, plants respond by inducing changes in below and aboveground metabolism with concomitant alterations in defensive secondary metabolites. While plant responses to the isolated stresses of flooding and insect herbivory have been extensively studied, much less is known about their response in combination. Wild relatives of cultivated plants with robust stress tolerance traits provide an excellent system for comparing how diverse plant species respond to combinatorial stress, and provide insight into potential germplasms for stress-tolerant hybrids. In this study, we compared the below and aboveground changes in the secondary metabolites of maize (Zea mays) and a flood-tolerant wild relative Nicaraguan teosinte (Zea nicaraguensis) in response to flooding, insect herbivory, and their combination. Root tissue was analyzed for changes in belowground metabolism. Leaf total phenolic content and headspace volatile organic compound emission were analyzed for changes in aboveground secondary metabolism. Results revealed significant differences in the root metabolome profiles of teosinte and maize. Notably, the accumulation of the flavonoids apigenin, naringenin, and luteolin during flooding and herbivory differentiated teosinte from maize. Aboveground, terpenes, including trans-α-bergamotene and (E)-4,8-dimethylnona-1,3,7-triene, shaped compositional differences in their volatile profiles between flooding, herbivory, and their combination. Taken together, these results suggest teosinte may be more tolerant than maize due to dynamic metabolic changes during flooding and herbivory that help relieve stress and influence plant-insect interactions.

Integrative transcriptomics reveals association of abscisic acid and lignin pathways with cassava whitefly resistance

BACKGROUND

Whiteflies are a global threat to crop yields, including the African subsistence crop cassava (Manihot esculenta). Outbreaks of superabundant whitefly populations throughout Eastern and Central Africa in recent years have dramatically increased the pressures of whitefly feeding and virus transmission on cassava. Whitefly-transmitted viral diseases threaten the food security of hundreds of millions of African farmers, highlighting the need for developing and deploying whitefly-resistant cassava. However, plant resistance to whiteflies remains largely poorly characterized at the genetic and molecular levels. Knowledge of cassava-defense programs also remains incomplete, limiting characterization of whitefly-resistance mechanisms. To better understand the genetic basis of whitefly resistance in cassava, we define the defense hormone- and Aleurotrachelus socialis (whitefly)-responsive transcriptome of whitefly-susceptible (COL2246) and whitefly-resistant (ECU72) cassava using RNA-seq. For broader comparison, hormone-responsive transcriptomes of Arabidopsis thaliana were also generated.

RESULTS

Whitefly infestation, salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA) transcriptome responses of ECU72 and COL2246 were defined and analyzed. Strikingly, SA responses were largely reciprocal between the two cassava genotypes and we suggest candidate regulators. While susceptibility was associated with SA in COL2246, resistance to whitefly in ECU72 was associated with ABA, with SA-ABA antagonism observed. This was evidenced by expression of genes within the SA and ABA pathways and hormone levels during A. socialis infestation. Gene-enrichment analyses of whitefly- and hormone-responsive genes suggest the importance of fast-acting cell wall defenses (e.g., elicitor recognition, lignin biosynthesis) during early infestation stages in whitefly-resistant ECU72. A surge of ineffective immune and SA responses characterized the whitefly-susceptible COL2246's response to late-stage nymphs. Lastly, in comparison with the model plant Arabidopsis, cassava's hormone-responsive genes showed striking divergence in expression.

CONCLUSIONS

This study provides the first characterization of cassava's global transcriptome responses to whitefly infestation and defense hormone treatment. Our analyses of ECU72 and COL2246 uncovered possible whitefly resistance/susceptibility mechanisms in cassava. Comparative analysis of cassava and Arabidopsis demonstrated that defense programs in Arabidopsis may not always mirror those in crop species. More broadly, our hormone-responsive transcriptomes will also provide a baseline for the cassava community to better understand global responses to other yield-limiting pests/pathogens.

Excised leaves show limited and species-specific effects on photosynthetic parameters across crop functional types

Photosynthesis is increasingly becoming a recognized target for crop improvement. Phenotyping photosynthesis-related traits on field-grown material is a key bottleneck to progress here due to logistical barriers and short measurement days. Many studies attempt to overcome these challenges by phenotyping excised leaf material in the laboratory. To date there are no demonstrated examples of the representative nature of photosynthesis measurements performed on excised leaves relative to attached leaves in crops. Here, we tested whether standardized leaf excision on the day prior to phenotyping affected a range of common photosynthesis-related traits across crop functional types using tomato (C3 dicot), barley (C3 monocot), and maize (C4 monocot). Potentially constraining aspects of leaf physiology that could be predicted to impair photosynthesis in excised leaves, namely leaf water potential and abscisic acid accumulation, were not different between attached and excised leaves. We also observed non-significant differences in spectral reflectance and chlorophyll fluorescence traits between the treatments across the three species. However, we did observe some significant differences between traits associated with gas exchange and photosynthetic capacity across all three species. This study represents a useful reference for those who perform measurements of this nature and the differences reported should be considered in associated experimental design and statistical analyses.

Parasitic plant-host interaction between the holoparasite Cytinus hypocistis and the shrub Cistus albidus in their natural Mediterranean habitat: local and systemic hormonal effects

Mediterranean-type ecosystems provide a unique opportunity to study parasitic plant-host interactions, such as the relationship between the dominant shrub Cistus albidus L. and the root holoparasitic plant Cytinus hypocistis L. We examined this interaction (i) locally, by measuring the hormonal profiling of the interaction zone between the holoparasitic plant and the host, and (ii) systemically, by examining the hormonal profiling and physiological status of leaves from infested and uninfested plants. Furthermore, we explored how temporal variation (seasonal effects) and geographical location influenced the systemic hormonal and physiological response of leaves. Results shed light on tissue-related variations in hormones, suggesting the parasite exerted a sink effect, mainly influenced by cytokinins. Jasmonates triggered a defense response in leaves, far from the infestation point, and both jasmonates and abscisic acid (ABA) appeared to be involved in the tolerance to holoparasitism when plants were simultaneously challenged with summer drought. Parasitism did not have any major negative impact on the host, as indicated by physiological stress markers in leaves, thus indicating a high tolerance of the shrub C. albidus to the root holoparasitic plant C. hypocistis. Rather, parasitism seemed to exert a priming-like effect and some compensatory effects were observed (increased chlorophyll contents) in the host under mild climatic conditions. We conclude that (i) cytokinins, jasmonates and ABA play a role at the local and systemic levels in the response of C. albidus to the biotic stress caused by C. hypocistis, and that (ii) seasonal changes in environmental conditions and geographical location may impact holoparasitic plant-host interactions in the field, modulating the physiological response.

β-Cyclocitric acid enhances drought tolerance in peach (Prunus persica) seedlings

The β-cyclocitric acid (β-CCA) is a bioactive apocarotenoid previously shown to improve drought tolerance in annual plants. However, the underlying molecular mechanism of this process remains largely elusive. Moreover, the question about the activity of β-CCA in perennial fruit crops is still open. Here, we found that treatment of β-CCA enhances drought tolerance in peach seedlings. The application of β-CCA significantly increased the relative water content and root activity and reduced the electrolyte leakage of peach seedlings under drought stress. Moreover, treatment with β-CCA under drought stress increased chlorophyll fluorescence, indicating a positive effect on photosynthesis, while also enhancing superoxide dismutase and peroxidase activity and reducing reactive oxygen species (ROS) levels. Consistent with these alterations, transcriptome analysis revealed an up-regulation of photosynthesis and antioxidant-related genes upon the application of β-CCA under drought stress. We also detected an induction in genes related to detoxification, environmental adaptation, primary metabolism, phytohormone, phenylpropanoid and the biosynthesis of cutin, suberine and wax, which might contribute to the induction of drought resistance. Altogether, our study reveals that β-CCA positively modulates peach drought tolerance, which is mainly mediated by enhancing photosynthesis and reducing ROS, indicating the potential of utilizing β-CCA for drought control in peach and perhaps other fruit crops.

Silencing a dehydration-responsive element-binding gene enhances the resistance of plants to a phloem-feeding herbivore

Herbivore-induced plant defence responses share common components with plant responses to abiotic stresses. However, whether abiotic stress-responsive factors influence the resistance of plants to herbivores by regulating these components remains largely unknown. Here, we cloned a dehydration-responsive element-binding gene in rice, OsDREB1A, and investigated its role in the resistance of rice to the phloem-feeding herbivore, brown planthopper (BPH, Nilaparvata lugens), under normal and low temperatures. We found that OsDREB1A localized to the nucleus, and its transcripts in rice were up-regulated in response to BPH infestation, low temperatures and treatment with methyl jasmonate or salicylic acid. Silencing OsDREB1A changed transcript levels of two defence-related WRKY and two PLD genes, enhanced levels of jasmonic acid (JA), JA-isoleucine and abscisic acid, and decreased the ethylene level in rice; these changes subsequently enhanced the resistance of plants to BPH, especially at 17°C, by decreasing the hatching rate and delaying the development of BPH eggs. Moreover, silencing OsDREB1A increased the growth of rice plants. These findings suggest that OsDREB1A, which positively regulates the resistance of rice to abiotic stresses, negatively regulates the resistance of rice to BPH.

Chemical ecology in conservation biocontrol: new perspectives for plant protection

Threats to food security require novel sustainable agriculture practices to manage insect pests. One strategy is conservation biological control (CBC), which relies on pest control services provided by local populations of arthropod natural enemies. Research has explored manipulative use of chemical information from plants and insects that act as attractant cues for natural enemies (predators and parasitoids) and repellents of pests. In this review, we reflect on past strategies using chemical ecology in CBC, such as herbivore-induced plant volatiles and the push-pull technique, and propose future directions, including leveraging induced plant defenses in crop plants, repellent insect-based signaling, and genetically engineered crops. Further, we discuss how climate change may disrupt CBC and stress the importance of context dependency and yield outcomes.

Irrigation Strategies with Controlled Water Deficit in Two Production Cycles of Cotton

Water scarcity is one of the main abiotic factors that limit agricultural production. In this sense, the identification of genotypes tolerant to water deficit associated with irrigation management strategies is extremely important. In this context, the objective of this study was to evaluate the morphology, production, water consumption, and water use efficiency of colored fiber cotton genotypes submitted to irrigation strategies with a water deficit in the phenological phases. Two experiments were conducted in succession. In the first experiment, a randomized block design was used in a 3 × 7 factorial scheme, corresponding to three colored cotton genotypes (BRS Rubi, BRS Jade, and BRS Safira) in seven irrigation management strategies with 40% of the real evapotranspiration (ETr) varying the phenological stages. In the second experiment, the same design was used in a 3 × 10 factorial arrangement (genotypes × irrigation management strategies). The water deficit in the vegetative phase can be used in the first year of cotton cultivation. Among the genotypes, 'BRS Jade' is the most tolerant to water deficit in terms of phytomass accumulation and fiber production.

Organ-specific responses during acclimation of mycorrhizal and non-mycorrhizal tomato plants to a mild water stress reveal differential local and systemic hormonal and nutritional adjustments

MAIN CONCLUSION

Tomato plant acclimation to a mild water stress implied tissue-specific hormonal and nutrient adjustments, being the root one of the main modulators of this response. Phytohormones are key regulators of plant acclimation to water stress. However, it is not yet clear if these hormonal responses follow specific patterns depending on the plant tissue. In this study, we evaluated the organ-specific physiological and hormonal responses to a 14 day-long mild water stress in tomato plants (Solanum lycopersicum cv. Moneymaker) in the presence or absence of the arbuscular mycorrhizal fungus Rhizoglomus irregulare, a frequently used microorganism in agriculture. Several physiological, production, and nutritional parameters were evaluated throughout the experiments. Additionally, endogenous hormone levels in roots, leaves, and fruits at different developmental stages were quantified by ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Water deficit drastically reduced shoot growth, while it did not affect fruit production. In contrast, fruit production was enhanced by mycorrhization regardless of the water treatment. The main tissue affected by water stress was the root system, where huge rearrangements in different nutrients and stress-related and growth hormones took place. Abscisic acid content increased in every tissue and fruit developmental stage, suggesting a systemic response to drought. On the other hand, jasmonate and cytokinin levels were generally reduced upon water stress, although this response was dependent on the tissue and the hormonal form. Finally, mycorrhization improved plant nutritional status content of certain macro and microelements, specially at the roots and ripe fruits, while it affected jasmonate response in the roots. Altogether, our results suggest a complex response to drought that consists in systemic and local combined hormonal and nutrient responses.

Seed Priming with MeJa Prevents Salt-Induced Growth Inhibition and Oxidative Damage in Sorghum bicolor by Inducing the Expression of Jasmonic Acid Biosynthesis Genes

Salinity is one of the major detrimental abiotic stresses at the forefront of deterring crop productivity globally. Although the exogenous application of phytohormones has formerly proven efficacious to plants, their effect on the moderately stress-tolerant crop "Sorghum bicolor" remains elusive. To investigate this, S. bicolor seeds primed with methyl jasmonate (0; 10 and 15 μM MeJa) were exposed to salt (200 mM NaCl) stress, and their morpho-physiological, biochemical, and molecular attributes were measured. Salt stress significantly decreased shoot length and fresh weight by 50%, whereas dry weight and chlorophyll content were decreased by more than 40%. Furthermore, salt-stress-induced oxidative damage was evident by the formation of brown formazan spots (indicative of H₂O₂ production) on sorghum leaves and a more than 30% increase in MDA content. However, priming with MeJa improved growth, increased chlorophyll content, and prevented oxidative damage under salt stress. While 15 µM MeJa maintained proline content to the same level as the salt-stressed samples, total soluble sugars were maintained under 10 µM MeJa, indicating a high degree of osmotic adjustment. Shriveling and thinning of the epidermis and xylem tissues due to salt stress was prevented by MeJa, followed by a more than 70% decrease in the Na⁺/K⁺ ratio. MeJa also reversed the FTIR spectral shifts observed for salt-stressed plants. Furthermore, salt stress induced the expression of the jasmonic acid biosynthesis genes; linoleate 92-lipoxygenase 3, allene oxide synthase 1, allene oxide cyclase, and 12-oxophytodienoate reductase 1. In MeJa-primed plants, their expression was reduced, except for the 12-oxophytodienoate reductase 1 transcript, which further increased by 67%. These findings suggest that MeJa conferred salt-stress tolerance to S. bicolor through osmoregulation and synthesis of JA-related metabolites.

Bringing Fundamental Insights of Induced Resistance to Agricultural Management of Herbivore Pests

In response to herbivory, most plant species adjust their chemical and morphological phenotype to acquire induced resistance to the attacking herbivore. Induced resistance may be an optimal defence strategy that allows plants to reduce metabolic costs of resistance in the absence of herbivores, allocate resistance to the most valuable plant tissues and tailor its response to the pattern of attack by multiple herbivore species. Moreover, plasticity in resistance decreases the potential that herbivores adapt to specific plant resistance traits and need to deal with a moving target of variable plant quality. Induced resistance additionally allows plants to provide information to other community members to attract natural enemies of its herbivore attacker or inform related neighbouring plants of pending herbivore attack. Despite the clear evolutionary benefits of induced resistance in plants, crop protection strategies to herbivore pests have not exploited the full potential of induced resistance for agriculture. Here, we present evidence that induced resistance offers strong potential to enhance resistance and resilience of crops to (multi-) herbivore attack. Specifically, induced resistance promotes plant plasticity to cope with multiple herbivore species by plasticity in growth and resistance, maximizes biological control by attracting natural enemies and, enhances associational resistance of the plant stand in favour of yield. Induced resistance may be further harnessed by soil quality, microbial communities and associational resistance offered by crop mixtures. In the transition to more sustainable ecology-based cropping systems that have strongly reduced pesticide and fertilizer input, induced resistance may prove to be an invaluable trait in breeding for crop resilience.

Identification of Green-Leaf Volatiles Released from Cabbage Palms (Sabal palmetto) Infected with the Lethal Bronzing Phytoplasma

Lethal bronzing (LB) is a fatal infection that affects over 20 species of palms (Arecaceae) and is caused by the phytoplasma 'Candidatus Phytoplasma aculeata'. This pathogen causes significant economic losses to landscape and nursery companies in Florida, USA. Recently, the vector was determined to be the planthopper Haplaxius crudus, which was more abundant on LB-infected palms. Herein, the volatile chemicals emitted from LB-infected palms were characterized using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME/GC-MS). Infected Sabal palmetto were identified and confirmed as positive for LB via quantitative PCR. Healthy controls of each species were selected for comparison. All infected palms exhibited elevated levels of hexanal and E-2-hexenal. Threatened palms showed high releasing concentrations of 3-hexenal and Z-3-hexen-1-ol. The volatiles characterized herein are common green-leaf volatiles (GLVs) emitted by plants under stress. This study considers the first documented case of GLVs in palms attributed to phytoplasma infection. Due to the apparent attraction of LB-infected palms to the vector, one or several of the GLVs identified in this study could serve as a lure for the vector and supplement management programs.

Improved abiotic stress tolerance in Arabidopsis by constitutive active form of a banana DREB2 type transcription factor, MaDREB20.CA, than its native form, MaDREB20

Banana is grown as one of the important fruit crops in tropical and subtropical regions of the world. In this study, we report induced expression of a dehydration responsive element binding 2 (DREB2) gene (MaDREB20) under individual heat, drought, and combined drought and heat stress in root of two banana genotypes Grand Nain (GN) and Hill Banana (HB). Motif analysis of MaDREB20 protein demonstrated the presence of a negative regulatory domain (NRD) or PEST motif between 150 and 184 amino acids. Transgenic Arabidopsis overexpressing MaDREB20 gene showed more survival rate, above-ground biomass, seed yield, leaf relative water content, and proline content but less ion leakage and malonaldehyde content, revealing improved tolerance against heat and drought as well as their combination than the wild-type. Overexpression of MaDREB20.CA (constitutive active form of MaDREB20 after removal of PEST region) showed better abiotic stress tolerance in Arabidopsis than its native form (MaDREB20). Transgenic Arabidopsis overexpressing MaDREB20 and MaDREB20.CA genes appeared to be associated with reduced stomatal densities under normal condition, better regulation of stomatal aperture under drought than in wild-type plants, and differential regulation of downstream target (AtTCH4 and AtIAA1) genes under heat, drought, and combined stress. Taken together, our findings revealed important functions of MaDREB20 in abiotic stress responses in transgenic Arabidopsis and could form a basis for CRISPR/Cas9-mediated removal of its NRD to enhance stress tolerance in banana.

Water availability and plant-herbivore interactions

Water is essential to plant growth and drives plant evolution and interactions with other organisms such as herbivores. However, water availability fluctuates, and these fluctuations are intensified by climate change. How plant water availability influences plant-herbivore interactions in the future is an important question in basic and applied ecology. Here we summarize and synthesize the recent discoveries on the impact of water availability on plant antiherbivore defense ecology and the underlying physiological processes. Water deficit tends to enhance plant resistance and escape traits (i.e. early phenology) against herbivory but negatively affects other defense strategies, including indirect defense and tolerance. However, exceptions are sometimes observed in specific plant-herbivore species pairs. We discuss the effect of water availability on species interactions associated with plants and herbivores from individual to community levels and how these interactions drive plant evolution. Although water stress and many other abiotic stresses are predicted to increase in intensity and frequency due to climate change, we identify a significant lack of study on the interactive impact of additional abiotic stressors on water-plant-herbivore interactions. This review summarizes critical knowledge gaps and informs possible future research directions in water-plant-herbivore interactions.

JA-induced TaMPK6 enhanced the freeze tolerance of Arabidopsis thaliana through regulation of ICE-CBF-COR module and antioxidant enzyme system

Mitogen-activated protein kinases (MAPKs) play important roles in the stress response of plants. However, the function of MPK proteins in freeze-resistance in wheat remains unclear. Dongnongdongmai No.1 (Dn1) is a winter wheat variety with a strong freezing resistance at extremely low temperature. In this study, we demonstrated that TaMPK6 is induced by JA signaling and is involved in the modulation of Dn1 freeze resistance. Overexpression of TaMPK6 in Arabidopsis increased the survival rate of plant at -10 ℃. The scavenging ability of reactive oxygen species (ROS) and the expression of cold-responsive genes CBFs and CORs were significantly enhanced in TaMPK6-overexpressed Arabidopsis, suggesting a role of TaMPK6 in activating the ICE-CBF-COR module and antioxidant enzyme system to resist freezing stress. Furthermore, TaMPK6 is localized in the nucleus and TaMPK6 interacts with TaICE41, TaCBF14, and TaMYC2 proteins, the key components in JA signaling and the ICE-CBF-COR pathway. These results suggest that JA-induced TaMPK6 may regulate freezing-resistance in wheat by interacting with the TaICE41, TaCBF14, and TaMYC2 proteins, which in turn enhances the ICE-CBF-COR pathway. Our study revealed the molecular mechanism of TaMPK6 involvement in the cold resistance pathway in winter wheat under cold stress, which provides a basis for enriching the theory of wheat cold resistance.

Host Resistance to Parasitic Plants-Current Knowledge and Future Perspectives

Parasitic flowering plants represent a diverse group of angiosperms, ranging from exotic species with limited distribution to prominent weeds, causing significant yield losses in agricultural crops. The major damage caused by them is related to the extraction of water and nutrients from the host, thus decreasing vegetative growth, flowering, and seed production. Members of the root parasites of the Orobanchaceae family and stem parasites of the genus Cuscuta are among the most aggressive and damaging weeds, affecting both monocotyledonous and dicotyledonous crops worldwide. Their control and eradication are hampered by the extreme seed longevity and persistence in soil, as well as their taxonomic position, which makes it difficult to apply selective herbicides not damaging to the hosts. The selection of resistant cultivars is among the most promising approaches to deal with this matter, although still not widely employed due to limited knowledge of the molecular mechanisms of host resistance and inheritance. The current review aims to summarize the available information on host resistance with a focus on agriculturally important parasitic plants and to outline the future perspectives of resistant crop cultivar selection to battle the global threat of parasitic plants.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

Impact of heat priming on heat shock responses in Origanum vulgare: Enhanced foliage photosynthetic tolerance and biphasic emissions of volatiles

Climate change enhances the frequency of heatwaves that negatively affect photosynthesis and can alter constitutive volatile emissions and elicit emissions of stress volatiles, but how pre-exposure to mildly warmer temperatures affects plant physiological responses to subsequent severe heat episodes remains unclear, especially for aromatic plants with high and complex volatile defenses. We studied the impact of heat shock (45 °C/5 min) applied alone and after exposure to moderate heat stress (35 °C/1 h, priming) on foliage photosynthesis and volatile emissions in the aromatic plant Origanum vulgare through 72 h recovery period. Heat stress decreased photosynthesis rates and stomatal conductance, whereas the reductions in photosynthesis were primarily due to non-stomatal factors. In non-primed plants, heat shock-induced reductions in photosynthetic activity were the greatest, but photosynthetic activity completely recovered by the end of the experiment. In primed plants, a certain inhibition of photosynthetic activity remained, suggesting a sustained priming effect. Heat shock enhanced the emissions of volatiles including lipoxygenase pathway volatiles, long-chained fatty acid-derived compounds, mono- and sesquiterpenes, geranylgeranyl diphosphate pathway volatiles, and benzenoids, whereas different heat treatments resulted in unique emission blends. In non-primed plants, stress-elicited emissions recovered at 72 h. In primed plants, volatile emissions were multiphasic, the first phase, between 0.5 and 10 h, reflected the primary stress response, whereas the secondary rise, between 24 and 72 h, indicated activations of different defense metabolic pathways. Our results demonstrate that exposure to mild heat leads to a sustained physiological stress memory that enhances plant resistance to subsequent severe heat stress episodes.

Comparison of Tomato Transcriptomic Profiles Reveals Overlapping Patterns in Abiotic and Biotic Stress Responses

Until a few years ago, many studies focused on the transcriptomic response to single stresses. However, tomato cultivations are often constrained by a wide range of biotic and abiotic stress that can occur singularly or in combination, and several genes can be involved in the defensive mechanism response. Therefore, we analyzed and compared the transcriptomic responses of resistant and susceptible genotypes to seven biotic stresses (Cladosporium fulvum, Phytophthora infestans, Pseudomonas syringae, Ralstonia solanacearum, Sclerotinia sclerotiorum, Tomato spotted wilt virus (TSWV) and Tuta absoluta) and five abiotic stresses (drought, salinity, low temperatures, and oxidative stress) to identify genes involved in response to multiple stressors. With this approach, we found genes encoding for TFs, phytohormones, or participating in signaling and cell wall metabolic processes, participating in defense against various biotic and abiotic stress. Moreover, a total of 1474 DEGs were commonly found between biotic and abiotic stress. Among these, 67 DEGs were involved in response to at least four different stresses. In particular, we found RLKs, MAPKs, Fasciclin-like arabinogalactans (FLAs), glycosyltransferases, genes involved in the auxin, ET, and JA pathways, MYBs, bZIPs, WRKYs and ERFs genes. Detected genes responsive to multiple stress might be further investigated with biotechnological approaches to effectively improve plant tolerance in the field.

Different vegetal protein hydrolysates distinctively alleviate salinity stress in vegetable crops: A case study on tomato and lettuce

Plants have evolved diverse plant-species specific tolerance mechanisms to cope with salt stress. However, these adaptive strategies often inefficiently mitigate the stress related to increasing salinity. In this respect, plant-based biostimulants have gained increasing popularity since they can alleviate deleterious effects of salinity. Hence, this study aimed to evaluate the sensitivity of tomato and lettuce plants grown under high salinity and the possible protective effects of four biostimulants based on vegetal protein hydrolysates. Plants were set in a 2 × 5 factorial experimental design completely randomized with two salt conditions, no salt (0 mM) and high salt (120 mM for tomato or 80 mM for lettuce), and five biostimulant treatments (C: Malvaceae-derived, P: Poaceae-derived, D: Legume-derived commercial 'Trainer^®', H: Legume-derived commercial 'Vegamin^®', and Control: distilled water). Our results showed that both salinity and biostimulant treatments affected the biomass accumulation in the two plant species, albeit to different extents. The salinity stress induced a higher activity of antioxidant enzymes (e.g., catalase, ascorbate peroxidase, guaiacol peroxidase and superoxide dismutase) and the overaccumulation of osmolyte proline in both lettuce and tomato plants. Interestingly, salt-stressed lettuce plants showed a higher accumulation of proline as compared to tomato plants. On the other hand, the treatment with biostimulants in salt-stressed plants caused a differential induction of enzymatic activity depending on the plant and the biostimulant considered. Overall, our results suggest that tomato plants were constitutively more tolerant to salinity than lettuce plants. As a consequence, the effectiveness of biostimulants in alleviating high salt concentrations was more evident in lettuce. Among the four biostimulants tested, P and D showed to be the most promising for the amelioration of salt stress in both the plant species, thereby suggesting their possible application in the agricultural practice.

Gene-by-environment interactions in plants: Molecular mechanisms, environmental drivers, and adaptive plasticity

Plants demonstrate a broad range of responses to environmental shifts. One of the most remarkable responses is plasticity, which is the ability of a single plant genotype to produce different phenotypes in response to environmental stimuli. As with all traits, the ability of plasticity to evolve depends on the presence of underlying genetic diversity within a population. A common approach for evaluating the role of genetic variation in driving differences in plasticity has been to study genotype-by-environment interactions (G × E). G × E occurs when genotypes produce different phenotypic trait values in response to different environments. In this review, we highlight progress and promising methods for identifying the key environmental and genetic drivers of G × E. Specifically, methodological advances in using algorithmic and multivariate approaches to understand key environmental drivers combined with new genomic innovations can greatly increase our understanding about molecular responses to environmental stimuli. These developing approaches can be applied to proliferating common garden networks that capture broad natural environmental gradients to unravel the underlying mechanisms of G × E. An increased understanding of G × E can be used to enhance the resilience and productivity of agronomic systems.

Interplay of Methodology and Conceptualization in Plant Abiotic Stress Signaling

Characterizing the mechanisms of plant sensitivity and reactivity to physicochemical cues related to abiotic stresses is of utmost importance for understanding plant-environment interactions, adaptations of the sessile lifestyle, and the evolutionary dynamics of plant species and populations. Moreover, plant communities are confronted with an environmental context of global change, involving climate changes, planetary pollutions of soils, waters and atmosphere, and additional anthropogenic changes. The mechanisms through which plants perceive abiotic stress stimuli and transduce stress perception into physiological responses constitute the primary line of interaction between the plant and the environment, and therefore between the plant and global changes. Understanding how plants perceive complex combinations of abiotic stress signals and transduce the resulting information into coordinated responses of abiotic stress tolerance is therefore essential for devising genetic, agricultural, and agroecological strategies that can ensure climate change resilience, global food security, and environmental protection. Discovery and characterization of sensing and signaling mechanisms of plant cells are usually carried out within the general framework of eukaryotic sensing and signal transduction. However, further progress depends on a close relationship between the conceptualization of sensing and signaling processes with adequate methodologies and techniques that encompass biochemical and biophysical approaches, cell biology, molecular biology, and genetics. The integration of subcellular and cellular analyses as well as the integration of in vitro and in vivo analyses are particularly important to evaluate the efficiency of sensing and signaling mechanisms in planta. Major progress has been made in the last 10-20 years with the caveat that cell-specific processes and in vivo processes still remain difficult to analyze and with the additional caveat that the range of plant models under study remains rather limited relatively to plant biodiversity and to the diversity of stress situations.

Damage of brown planthopper (BPH) Nilaparvata lugens and rice leaf folder (LF) Cnaphalocrocis medinalis in parent plants lead to distinct resistance in ratoon rice

Herbivore-induced defense responses are often specific, whereas plants could induce distinct defense responses corresponding to infestation by different herbivorous insects. Brown plant hopper (BPH) Nilaparvata lugens, a phloem-feeding insect, and rice leaf folder (LF) Cnaphalocrocis medinalis, a chewing insect, are both specialist herbivores on rice. To characterize the distinct resistance primed by prior damage to these two specialist herbivores, we challenged rice plants with two herbivores during vegetative growth of parent plants and assessed plant resistance in subsequent ratoons. Here, we show that LF and BPH induce different suites of defense responses in parent rice plants, LF induced higher level of JA accumulation and OsAOS, OsCOI1 transcripts, while BPH induced higher accumulation of SA and OsPAL1 transcripts. Moreover, an apparent loss of LF resistance was observed in OsAOS, OsCOI1 RNAi lines. Ratoon plants generated from parents receiving prior LF infestation exhibited higher jasmonic acid (JA) levels and elevated levels of transcripts of defense-related genes associated with JA signaling, while ratoon generated from parents receiving prior BPH infestation exhibited higher salicylic acid (SA) levels and elevated levels of transcripts of defense-related genes associated with SA signaling. Moreover, previous LF infestation obviously elevated ratoons resistance to LF, while previous infestation by BPH led to enhanced resistance in ratoons to BPH. Pre-priming of ratoons defense to LF was significantly reduced in OsAOS and OsCOI1 RNAi plant, but silencing OsAOS and OsCOI1 did not attenuate ratoons resistance to BPH. These results suggest that infestation of two specialist herbivores with different feeding styles in parent crop led to distinct defense responses in subsequent rations, and the acquired resistance to LF in ratoons is associated with priming of jasmonic acid-dependent defense responses.

Investigating soil properties and vegetation parameters in different biochar-amended vegetated soil at large suction for application in bioengineered structures

Bioengineered structures, such as landfill cover, vegetated slopes or embankments, green roof and turf are comprised of soil and vegetation where vegetation imparts stability and protection through root reinforcement and hydrologic action. Soil in bioengineered structures often compacted and subjected to prolong drying due to irregular irrigation which necessitates the investigation of soil properties and vegetation growth in biochar-amended soil (BAS) under large suction range and it is scarce in the literature. In the present study, the effect of different biochar types on soil properties, and the vegetation growth in compacted soil and under large suction range was investigated for application in bioengineered structures. The results revealed that the biochar amendment decreased the dry density (5-32%) and increased the water retention capacity (θ_s by 15-104%, θ₁₅₀₀ by 82-445% and plant available water content (PAWC) by 22-55%), pH (28-77%) and cation exchange capacity (CEC, 16-723%) of the soil. Further, the vegetation growth i.e., vegetation density, dry root mass and shoot mass increased by 8-13%, 33-108% and 4-157% respectively after biochar amendment. The vegetation wilting was started at a higher suction (~ 900 kPa) relative to bare soil (800 kPa), the permanent wilting point (PWP) increased (by 3-35%) and the complete photosynthetic activity remained unchanged at a higher suction (1600 kPa) relative to bare soil (1050 kPa) after biochar amendment. Among the biochar types i.e., Sugarcane Bagasse biochar (SBB), Mesquite biochar (MB) and Water Hyacinth biochar (WHB) tested, the MB showed the best performance i.e., the suitable vegetation growth and health status. The improved water retention due to increased porosity, specific surface area (SSA) and presence of hydrophilic functional groups, and the higher pH, CEC and lower dry density in BAS attributed to the higher vegetation growth. The findings of the present study suggest the application of BAS in bioengineered structures.

Abiotic and Herbivory Combined Stress in Tomato: Additive, Synergic and Antagonistic Effects and Within-Plant Phenotypic Plasticity

Background: Drought, N deficiency and herbivory are considered the most important stressors caused by climate change in the agro- and eco-systems and varied in space and time shaping highly dynamic and heterogeneous stressful environments. This study aims to evaluate the tomato morpho-physiological and metabolic responses to combined abiotic and herbivory at different within-plant spatial levels and temporal scales. Methods: Leaf-level morphological, gas exchange traits and volatile organic compounds (VOCs) profiles were measured in tomato plants exposed to N deficiency and drought, Tuta absoluta larvae and their combination. Additive, synergistic or antagonistic effects of the single stress when combined were also evaluated. Morpho-physiological traits and VOCs profile were also measured on leaves located at three different positions along the shoot axes. Results: The combination of the abiotic and biotic stress has been more harmful than single stress with antagonistic and synergistic but non-additive effects for the morpho-physiological and VOCs tomato responses, respectively. Combined stress also determined a high within-plant phenotypic plasticity of the morpho-physiological responses. Conclusions: These results suggested that the combined stress in tomato determined a “new stress state” and a higher within-plant phenotypic plasticity which could permit an efficient use of the growth and defense resources in the heterogeneous and multiple stressful environmental conditions.

A novel transcription factor, ScAIL1, modulates plant defense responses by targeting DELLA and regulating gibberellin and jasmonic acid signaling in sugarcane

DELLA proteins are important repressors of gibberellin signaling, regulating plant development and defense responses through crosstalk with various phytohormones. Sugarcane ScGAI encodes a DELLA protein that regulates culm development. However, it is unclear which transcription factors mediate the transcription of ScGAI. Here, we identified two different ScGAI promoter sequences that cooperatively regulate ScGAI transcription. We also identified a nuclear-localized AP2 family transcription factor, ScAIL1, which inhibits the transcription of ScGAI by directly binding to two ScGAI promoters. ScAIL1 was expressed in all sugarcane tissues tested and was induced by gibberellin and various stressors, including NaCl, polyethylene glycol, and pathogenic fungi and bacteria. Overexpression of ScAIL1 in rice significantly improved resistance to bacterial blight and rice blast, while reducing growth and development. In addition, several genes associated with stress responses were significantly up-regulated in transgenic rice overexpressing ScAIL1. Endogenous phytohormone content and expression analysis further revealed that ScAIL1-overexpressing lines improved resistance to bacterial blight and rice blast instead of promoting growth, and that this response was associated with increased jasmonic acid synthesis and gibberellin inactivation. These results provide molecular evidence that the role of ScAIL1 in the plant defense response is related to jasmonic acid and gibberellin signaling.

The Effects of High CO2 and Strigolactones on Shoot Branching and Aphid-Plant Compatibility Control in Pea

Elevated atmospheric CO2 concentrations (eCO2) regulate plant architecture and susceptibility to insects. We explored the mechanisms underpinning these responses in wild type (WT) peas and mutants defective in either strigolactone (SL) synthesis or signaling. All genotypes had increased shoot height and branching, dry weights and carbohydrate levels under eCO2, demonstrating that SLs are not required for shoot acclimation to eCO2. Since shoot levels of jasmonic acid (JA) and salicylic acid (SA) tended to be lower in SL signaling mutants than the WT under ambient conditions, we compared pea aphid performance on these lines under both CO2 conditions. Aphid fecundity was increased in the SL mutants compared to the WT under both ambient and eCO2 conditions. Aphid infestation significantly decreased levels of JA, isopentenyladenine, trans-zeatin and gibberellin A4 and increased ethylene precursor ACC, gibberellin A1, gibberellic acid (GA3) and SA accumulation in all lines. However, GA3 levels were increased less in the SL signaling mutants than the WT. These studies provide new insights into phytohormone responses in this specific aphid/host interaction and suggest that SLs and gibberellins are part of the network of phytohormones that participate in host susceptibility.

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

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

Transcriptome profiling of Toona ciliata young stems in response to Hypsipyla robusta Moore

Toona ciliata is a traditional woody plant that can be used as a medicinal material in China. The extracts of its roots, stems, leaves, and flowers all have a wide range of bioactive compounds. However, T. ciliata has been facing an unresolved pest problem caused by Hypsipyla robusta Moore (HRM), which seriously affects its growth and development. In this study, the expression level of TcMYB3 gene reached the maximum (28-fold) at 12 h and transcriptome sequencing of young stems eaten by HRM for 0, 3, 12, and 21 h were performed. A large number of differentially expressed genes (DEGs) were identified including jointly up-regulated genes (263) and down-regulated genes (378). JA synthesis and signaling transduction, terpene biosynthesis, and MAPKs signaling pathway were analyzed in depth and found that TcOPR3, TcJAR1, TcJAZs, and TcTPS9 genes possessed anti-insect potential. Moreover, MYB and ERF transcription factor (TF) families were significantly strengthened to the point that they may participate in induced defense mechanisms in T. ciliata. These data not only provide insights into the molecular mechanisms in resistance of T. ciliata to HRM but also helps to explore the new biocontrol strategies against insects in eco-friendly woody plants.

Whole genome sequencing reveals footprints of adaptive genetic variation in populations of Eruca sativa

Populations of Eruca sativa (Brassicaceae) derived from arid and Mediterranean habitats exhibit ecotypic differentiation. Here, pooled DNA sequencing was used to assess adaptive genome differentiation in the two ecotypes. Differentiated SNP loci were scanned with the empirical FST outlier method and by correlating allele frequencies with environmental parameters. Genetic diversity values were relatively higher in the pooled arid genome, whereas the pooled Mediterranean genome exhibited stronger directional selection, indicating the impact of climatic conditions on genetic diversity. GO enrichment analysis categorized the annotated differentiated loci according to biological processes, revealing a large set of candidate genes related to abiotic and biotic stress responses. Allelic variation was detected in regulatory elements and coding regions (synonymous and non-synonymous mutations) of genes belonging to different transcription factors and phytohormone signaling, suggesting adaptation to both abiotic and biotic conditions. Furthermore, SNP mutations were also found in genic regions belonging to the synthesis of secondary metabolites, including aliphatic glucosinolates and their hydrolyzed bioactive compounds, among others. The results of this eco-genomic study demonstrate the role of divergent abiotic and biotic selection factors in evolutionary processes leading to adaptive ecotypic differentiation.

Application of 2,4-Epibrassinolide Improves Drought Tolerance in Tobacco through Physiological and Biochemical Mechanisms

Drought stress is a major abiotic stress that hinders plant growth and development. Brassinosteroids (BR), including 2,4-epibrassinolide (EBR), play important roles in plant growth, development, and responses to abiotic stresses, including drought stress. This work investigates exogenous EBR application roles in improving drought tolerance in tobacco. Tobacco plants were divided into three groups: WW (well-watered), DS (drought stress), and DSB (drought stress + 0.05 mM EBR). The results revealed that DS decreased the leaf thickness (LT), whereas EBR application upregulated genes related to cell expansion, which were induced by the BR (DWF4, HERK2, and BZR1) and IAA (ARF9, ARF6, PIN1, SAUR19, and ABP1) signaling pathway. This promoted LT by 28%, increasing plant adaptation. Furthermore, EBR application improved SOD (22%), POD (11%), and CAT (5%) enzyme activities and their related genes expression (FeSOD, POD, and CAT) along with a higher accumulation of osmoregulatory substances such as proline (29%) and soluble sugars (14%) under DS and conferred drought tolerance. Finally, EBR application augmented the auxin (IAA) (21%) and brassinolide (131%) contents and upregulated genes related to drought tolerance induced by the BR (BRL3 and BZR2) and IAA (YUCCA6, SAUR32, and IAA26) signaling pathways. These results suggest that it could play an important role in improving mechanisms of drought tolerance in tobacco.

Modelling Waterlogging Impacts on Crop Growth: A Review of Aeration Stress Definition in Crop Models and Sensitivity Analysis of APSIM

Currently, crop physiological responses to waterlogging are considered only in a few crop models and in a limited way. Here, we examine the process bases of seven contemporary models developed to model crop growth in waterlogged conditions. The representation of plant recovery in these models is over-simplified, while plant adaptation or phenotypic plasticity due to waterlogging is often not considered. Aeration stress conceptualisation varies from the use of simple multipliers in equations describing transpiration and biomass to complex linkages of aeration-deficit factors with root growth, transpiration and nitrogen fixation. We recommend further studies investigating more holistic impacts and multiple stresses caused by plant behaviours driven by soils and climate. A sensitivity analysis using one model (a developer version of APSIM) with default parameters showed that waterlogging has the greatest impact on photosynthesis, followed by phenology and leaf expansion, suggesting a need for improved equations linking waterlogging to carbon assimilation. Future studies should compare the ability of multiple models to simulate real and in situ effects of waterlogging stress on crop growth using consistent experimental data for initialisation, calibration and validation. We conclude that future experimental and modelling studies must focus on improving the extent to which soil porosity, texture, organic carbon and nitrogen and plant-available water affect waterlogging stress, physiological plasticity and the ensuing temporal impacts on phenology, growth and yield.

Plant defense strategies against attack by multiple herbivores

Plants may effectively tailor defenses by recognizing their attackers and reprogramming their physiology. Although most plants are under attack by a large diversity of herbivores, surprisingly little is known about the physiological capabilities of plants to deal with attack by multiple herbivores. Studies on dual herbivore attack identified that defense against one attacker may cause energetic and physiological constraints to deal with a second attacker. How these constraints shape plant plasticity in defense to their full community of attackers is a major knowledge gap in plant science. Here, we provide a framework for plant defense to multiherbivore attack by defining the repertoire of plastic defense strategies that may allow plants to optimize their defenses against a multitude of stressors.

Molecular communication network and its applications in crop sciences

Plant molecular biology and bacterial behaviour research in the future could focus on using genetically engineered bacteria as a sensor, hormonal/disease detector, and target gene expression, as well as establishing a bioluminescence feedback communication system. Over the last two decades, understanding plant signal transduction pathways of plant hormones has become an active research field to understand plant behavior better. To accomplish signal transduction, plants use a variety of hormones for inter- and intra-communication, and biotic or abiotic stressors activate those. Signal transduction pathways refer to the use of various communication methods by effectors to elicit a response at the molecular level. Research methodologies such as inter-kingdom signaling have been introduced to study signal transduction and communication pathways, or what we can term plant molecular communication. However, stochastic qualities are inherent in most technologies used to monitor these biological processes. Molecular communication (MC) is a new research topic that uses the natural features of biological organisms to communicate and aims to manipulate their stochastic nature to achieve the desired results. MC is a multidisciplinary research field inspired by the use of molecules to store, spread, and receive information between biological organisms known as "Biological Nanomachines." It has been used to demonstrate how biological entities may be characterised, modelled, and engineered as communication devices in the same manner as traditional communication technologies are. We attempted to link MC and PLANT'S MC in this study and we believe that reasonable combined efforts may be made to use the functional applications of MC for detecting and understanding molecular-level activities such as signaling transduction pathways in crops.

Plant Water Stress Reduces Aphid Performance: Exploring Mechanisms Driven by Water Stress Intensity

Drought alters plant traits in ways that affect herbivore performance. However, we lack a comprehensive understanding of the plant-derived mechanisms that mediate insect responses to drought. Water stress occurs along gradients of intensity, and the impacts of drought intensity on plant-insect interactions is understudied. Here, we assessed aphid performance on wheat plants exposed to a gradient of water stress and measured plant nutrients and phytohormones that may mediate aphid response to drought. We show that water stress reduced aphid performance, and the negative effect grew stronger as the magnitude of water stress increased. The plant response to water limitation was not consistent across the stress gradient and was reliant on the trait measured. Water limitation did not affect whole-plant nitrogen; however, water limitation did reduce amino acid concentration and increase sugars, but only under high stress intensity. The phytohormones abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA), and the expression of their associated gene transcripts, were also differentially affected by water stress intensity. In well-watered conditions, aphid feeding increased concentrations of the defense-related hormones SA and JA over time; however, any amount of water limitation prevented aphid induction of JA. Although aphids may experience a reprieve from JA-related defenses in stressed conditions, SA levels remain high in response to aphid feeding, indicating aphids are still vulnerable to SA-related defenses. Any level of water stress also increased the expression of a callose-associated gene transcript, a physical defense that impairs feeding. Thus, poor aphid performance on mildly-stressed plants was correlated with increased plant defenses, whereas poor performance on highly-stressed plants was correlated with stronger plant defense induction and reduced plant nutritional quality. Understanding the mechanisms driving aphid and plant performance under water stress conditions can improve our ability to predict how aphid populations will respond to climate change.

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

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

Measuring SERVQUAL dimensions and their importance for customer-satisfaction using online reviews: a text mining approach

Purpose

The extant literature has utilized the SERVQUAL scale to measure service quality dimensions and their importance towards customer-satisfaction using close-ended survey-based questions and not open-ended questions and/or user-generated qualitative responses. On the other hand, while measuring customer-satisfaction drivers from user-generated content (UGC), extant studies have majorly used overall or aspect-wise evaluations and not evaluations specific to SERVQUAL dimensions. In this study, the authors try to bridge the gap.

Design/methodology/approach

The authors suggest a methodology consisting of text mining, machine learning and econometric techniques that can measure consumer evaluations of SERVQUAL dimensions. The authors used qualitative and quantitative UGC obtained from 27,052 online reviews on 362 airlines by reviewers of 158 nationalities for our analysis.

Findings

The authors established a unique method which combines qualitative and qualitative UGC to measure service quality. The authors have also uncovered the comparative importance of such dimensions in creating customer-satisfaction and recommendation in the context of the airline industry.

Originality/value

The paper is one of the pioneering studies that try to find measures of SERVQUAL dimensions from online consumer reviews and their influence on customer satisfaction.

Proline, a multifaceted signalling molecule in plant responses to abiotic stress: understanding the physiological mechanisms

Abiotic stresses have a detrimental impact on plant growth and productivity and are a major threat to sustainable crop production in rapidly changing environments. Proline, an important amino acid, plays an important role in maintaining the metabolism and growth of plants under abiotic stress conditions. Many insights indicate a positive relationship between proline accumulation and tolerance of plants to various abiotic stresses. Because of its metal chelator properties, it acts as a molecular chaperone, an antioxidative defence molecule that scavenges reactive oxygen species (ROS), as well as having signalling behaviour to activate specific gene functions that are crucial for plant recovery from stresses. It also acts as an osmoprotectant, a potential source to acquire nitrogen as well as carbon, and plays a significant role in the flowering and development of plants. Overproduction of proline in plant cells contributes to maintaining cellular homeostasis, water uptake, osmotic adjustment and redox balance to restore the cell structures and mitigate oxidative damage. Many reports reveal that transgenic plants, particularly those overexpressing genes tailored for proline accumulation, exhibit better adaptation to abiotic stresses. Therefore, this review aims to provide a comprehensive update on proline biosynthesis and accumulation in plants and its putative regulatory roles in mediating plant defence against abiotic stresses. Additionally, the current and future directions in research concerning manipulation of proline to induce gene functions that appear promising in genetics and genomics approaches to improve plant adaptive responses under changing climate conditions are also highlighted.

Poplar's Waterlogging Resistance Modeling and Evaluating: Exploring and Perfecting the Feasibility of Machine Learning Methods in Plant Science

Floods, as one of the most common disasters in the natural environment, have caused huge losses to human life and property. Predicting the flood resistance of poplar can effectively help researchers select seedlings scientifically and resist floods precisely. Using machine learning algorithms, models of poplar's waterlogging tolerance were established and evaluated. First of all, the evaluation indexes of poplar's waterlogging tolerance were analyzed and determined. Then, significance testing, correlation analysis, and three feature selection algorithms (Hierarchical clustering, Lasso, and Stepwise regression) were used to screen photosynthesis, chlorophyll fluorescence, and environmental parameters. Based on this, four machine learning methods, BP neural network regression (BPR), extreme learning machine regression (ELMR), support vector regression (SVR), and random forest regression (RFR) were used to predict the flood resistance of poplar. The results show that random forest regression (RFR) and support vector regression (SVR) have high precision. On the test set, the coefficient of determination (R²) is 0.8351 and 0.6864, the root mean square error (RMSE) is 0.2016 and 0.2780, and the mean absolute error (MAE) is 0.1782 and 0.2031, respectively. Therefore, random forest regression (RFR) and support vector regression (SVR) can be given priority to predict poplar flood resistance.

Farming Households' Satisfaction With Quality of Agricultural Extension Services: A Case Study of Quang Binh Province, Vietnam

Agriculture is an important sector of Vietnam, in which agricultural extension (AE) is a long-standing activity but was officially institutionalized in 1993 when Vietnam reformed its economic model. The AE system in Vietnam is organized quite closely from the central to local levels with various forms of AE. This study assesses the satisfaction of farmers with AE services in Quang Binh province, Vietnam. The results of a survey of 455 farmers show a positive relationship between quality and satisfaction. Factors such as assurance, reliability, and sympathy are important factors in AE service quality. The study also provides recommendations to strengthen AE services, including updating technical information, organizing demonstration models, and stronger investment in AE systems at all levels.