Isochorismate-based salicylic acid biosynthesis confers basal resistance to Fusarium graminearum in barley

The genetic orchestra of salicylic acid in plant resilience to climate change induced abiotic stress: critical review

Climate change, driven by human activities and natural processes, has led to critical alterations in varying patterns during cropping seasons and is a vital threat to global food security. The climate change impose several abiotic stresses on crop production systems. These abiotic stresses include extreme temperatures, drought, and salinity, which expose agricultural fields to more vulnerable conditions and lead to substantial crop yield and quality losses. Plant hormones, especially salicylic acid (SA), has crucial roles for plant resiliency under unfavorable environments. This review explores the genetics and molecular mechanisms underlying SA's role in mitigating abiotic stress-induced damage in plants. It also explores the SA biosynthesis pathways, and highlights the regulation of their products under several abiotic stresses. Various roles and possible modes of action of SA in mitigating abiotic stresses are discussed, along with unraveling the genetic mechanisms and genes involved in responses under stress conditions. Additionally, this review investigates molecular pathways and mechanisms through which SA exerts its protective effects, such as redox signaling, cross-talks with other plant hormones, and mitogen-activated protein kinase pathways. Moreover, the review discusses potentials of using genetic engineering approaches, such as CRISPR technology, for deciphering the roles of SA in enhancing plant resilience to climate change related abiotic stresses. This comprehensive analysis bridges the gap between genetics of SA role in response to climate change related stressors. Overall goal is to highlight SA's significance in safeguarding plants and by offering insights of SA hormone for sustainable agriculture under challenging environmental conditions.

Enhancing wheat regeneration and genetic transformation through overexpression of TaLAX1

In the realm of genetically transformed crops, the process of plant regeneration holds utmost significance. However, the low regeneration efficiency of several wheat varieties currently restricts the use of genetic transformation for gene functional analysis and improved crop production. This research explores overexpression of TaLAX PANICLE1 (TaLAX1), which markedly enhances regeneration efficiency, thereby boosting genetic transformation and genome editing in wheat. Particularly noteworthy is the substantial increase in regeneration efficiency of common wheat varieties previously regarded as recalcitrant to genetic transformation. Our study shows that increased expression of TaGROWTH-REGULATING FACTOR (TaGRF) genes, alongside that of their co-factor, TaGRF-INTERACTING FACTOR 1 (TaGIF1), enhances cytokinin accumulation and auxin response, which may play pivotal roles in the improved regeneration and transformation of TaLAX1-overexpressing wheat plants. Overexpression of TaLAX1 homologs also significantly increases the regeneration efficiency of maize and soybean, suggesting that both monocot and dicot crops can benefit from this enhancement. Our findings shed light on a gene that enhances wheat genetic transformation and elucidate molecular mechanisms that potentially underlie wheat regeneration.

The Emerging Role of 2OGDs as Candidate Targets for Engineering Crops with Broad-Spectrum Disease Resistance

Plant diseases caused by pathogens result in a marked decrease in crop yield and quality annually, greatly threatening food production and security worldwide. The creation and cultivation of disease-resistant cultivars is one of the most effective strategies to control plant diseases. Broad-spectrum resistance (BSR) is highly preferred by breeders because it confers plant resistance to diverse pathogen species or to multiple races or strains of one species. Recently, accumulating evidence has revealed the roles of 2-oxoglutarate (2OG)-dependent oxygenases (2OGDs) as essential regulators of plant disease resistance. Indeed, 2OGDs catalyze a large number of oxidative reactions, participating in the plant-specialized metabolism or biosynthesis of the major phytohormones and various secondary metabolites. Moreover, several 2OGD genes are characterized as negative regulators of plant defense responses, and the disruption of these genes via genome editing tools leads to enhanced BSR against pathogens in crops. Here, the recent advances in the isolation and identification of defense-related 2OGD genes in plants and their exploitation in crop improvement are comprehensively reviewed. Also, the strategies for the utilization of 2OGD genes as targets for engineering BSR crops are discussed.

Join the green team: Inducers of plant immunity in the plant disease sustainable control toolbox

BACKGROUND

Crops are constantly attacked by various pathogens. These pathogenic microorganisms, such as fungi, oomycetes, bacteria, viruses, and nematodes, threaten global food security by causing detrimental crop diseases that generate tremendous quality and yield losses worldwide. Chemical pesticides have undoubtedly reduced crop damage; however, in addition to increasing the cost of agricultural production, the extensive use of chemical pesticides comes with environmental and social costs. Therefore, it is necessary to vigorously develop sustainable disease prevention and control strategies to promote the transition from traditional chemical control to modern green technologies. Plants possess sophisticated and efficient defense mechanisms against a wide range of pathogens naturally. Immune induction technology based on plant immunity inducers can prime plant defense mechanisms and greatly decrease the occurrence and severity of plant diseases. Reducing the use of agrochemicals is an effective way to minimize environmental pollution and promote agricultural safety.

AIM OF REVIEW

The purpose of this workis to offer valuable insights into the current understanding and future research perspectives of plant immunity inducers and their uses in plant disease control, ecological and environmental protection, and sustainable development of agriculture.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this work, we have introduced the concepts of sustainable and environment-friendly concepts of green disease prevention and control technologies based on plant immunity inducers. This article comprehensively summarizes these recent advances, emphasizes the importance of sustainable disease prevention and control technologies for food security, and highlights the diverse functions of plant immunity inducers-mediated disease resistance. The challenges encountered in the potential applications of plant immunity inducers and future research orientation are also discussed.

Wheat cis-zeatin-O-glucosyltransferase cZOGT1 interacts with the Ca2+-dependent lipid binding protein TaZIP to regulate senescence

Premature senescence is an important factor affecting wheat yield and quality. Wheat yield can be increased by delaying senescence and prolonging the effective photosynthetic time. Previously, we found that the cis-zeatin-O-glucosyltransferase (cZOGT1) gene plays an important role in the stay-green wheat phenotype. In this study, cZOGT1-overexpressing lines exhibited a delayed senescence phenotype, despite a significant reduction in the total cytokinin content. Further, we found that cZOGT1 interacted with the Ca2+-dependent lipid binding protein TaZIP (cZOGT1-interacting protein), and that a high level of cZOGT1 expression led to the suppression of TaZIP expression, which in turn, reduced abscisic acid (ABA) content. The synergistic reduction in cytokinins and ABA levels eventually caused the stay-green phenotype in cZOGT1-overexpressing lines. This study provides a new theoretical basis to explain the mechanism underlying the wheat stay-green phenotype and provides a genetic resource for wheat molecular-design breeding.

Gamma-Aminobutyric Acid Supplementation Boosts the Phytohormonal Profile in 'Candidatus Liberibacter asiaticus'-Infected Citrus

The devastating citrus disease, Huanglongbing (HLB), is associated with 'Candidatus Liberibacter sp.' and transmitted by citrus psyllids. Unfortunately, HLB has no known sustainable cure yet. Herein, we proposed γ-aminobutyric acid (GABA) as a potential eco-friendly therapeutic solution to HLB. Herein, we used GC/MS-based targeted metabolomics combined with gene expression to investigate the role of GABA in citrus response against HLB and to better understand its relationship(s) with different phytohormones. GABA supplementation via root drench boosts the accumulation of endogenous GABA in the leaves of both healthy and 'Ca. L. asiaticus'-infected trees. GABA accumulation benefits the activation of a multi-layered defensive system via modulating the phytohormone levels and regulating the expression of their biosynthesis genes and some pathogenesis-related proteins (PRs) in both healthy and 'Ca. L. asiaticus'-infected plants. Moreover, our findings showed that GABA application stimulates auxin biosynthesis in 'Ca. L. asiaticus'-infected plants via the activation of the indole-3-pyruvate (I3PA) pathway, not via the tryptamine (TAM)-dependent pathway, to enhance the growth of HLB-affected trees. Likewise, GABA accumulation was associated with the upregulation of SA biosynthesis genes, particularly the PAL-dependent route, resulting in higher SA levels that activated CsPR1, CsPR2, CsPR5, and CsWRKY70, which are prominent to activation of the SA-mediated pathway. Additionally, higher GABA levels were correlated with an enhanced JA profile and linked with both CsPR3 and CsPR4, which activates the JA-mediated pathway. Collectively, our findings suggest that exogenous GABA application might be a promising alternative and eco-friendly strategy that helps citrus trees battle HLB.

Temporal and spatial transcriptional regulation of phytohormone metabolism during seed development in barley (Hordeum vulgare L.)

Plant hormones play important roles in seed development; however, transcriptional regulation of their metabolism and levels of the respective bioactive forms during barley seed development is poorly understood. To this end, this study performed a comprehensive analysis of changes in the expression patterns phytohormone metabolism genes and levels of the respective bioactive forms in the embryo and endosperm tissues. Our study showed the presence of elevated levels of abscisic acid (ABA), bioactive forms of gibberellins (GAs), jasmonate (JA) and cytokinins (CKs), auxin and salicylic acid (SA) in the endosperm and embryo tissues at early stage of seed filling (SF). The levels of all hormones in both tissues, except that of ABA, decreased to low levels during SF. In contrast, embryonic ABA level increased during SF and peaked at physiological maturity (PM) while the endospermic ABA was maintained at a similar level observed during SF. Although its level decreased high amount of ABA was still present in the embryo during post-PM. We detected low levels of ABA in the endosperm and all the other hormones in both tissues during post-PM phase except the relatively higher levels of jasmonoyl-isoleucine and SA detected at late stage of post-PM. Our data also showed that spatiotemporal changes in the levels of plant hormones during barley seed development are mediated by the expression of specific genes involved in their respective metabolic pathways. These results indicate that seed development in barley is mediated by spatiotemporal modulation in the metabolism and levels of plant hormones.

Biologically synthesized zinc and copper oxide nanoparticles using Cannabis sativa L. enhance soybean (Glycine max) defense against fusarium virguliforme

In this study, zinc and copper oxide nanoparticles (NPs) were synthesized using hemp (Cannabis sativa L.) leaves (ZnONP-HL and CuONP-HL), and their antifungal potential was assessed against Fusarium virguliforme in soybean (Glycine max L.). Hemp was selected because it is known to contain large quantities of secondary metabolites that can potentially enhance the reactivity of NPs through surface property modification. Synthesizing NPs with biologically derived materials allows to avoid the use of harsh and expensive synthetic reducing and capping agents. The ZnONP-HL and CuONP-HL showed average grain/crystallite size of 13.51 nm and 7.36 nm, respectively. The biologically synthesized NPs compared well with their chemically synthesized counterparts (ZnONP chem, and CuONP chem; 18.75 nm and 10.05 nm, respectively), confirming the stabilizing role of hemp-derived biomolecules. Analysis of the hemp leaf extract and functional groups that were associated with ZnONP-HL and CuONP-HL confirmed the presence of terpenes, flavonoids, and phenolic compounds. Biosynthesized NPs were applied on soybeans as bio-nano-fungicides against F. virguliforme via foliar treatments. ZnONP-HL and CuONP-HL at 200 μg/mL significantly (p < 0.05) increased (∼ 50%) soybean growth, compared to diseased controls. The NPs improved the nutrient (e.g., K, Ca, P) content and enhanced photosynthetic indicators of the plants by 100-200%. A 300% increase in the expression of soybean pathogenesis related GmPR genes encoding antifungal and defense proteins confirmed that the biosynthesized NPs enhanced disease resistance against the fungal phytopathogen. The findings from this study provide novel evidence of systemic suppression of fungal disease by nanobiopesticides, via promoting plant defense mechanisms.

Sequencing trait-associated mutations to clone wheat rust-resistance gene YrNAM

Stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici (Pst), can significantly affect wheat production. Cloning resistance genes is critical for efficient and effective breeding of stripe rust resistant wheat cultivars. One resistance gene (Yr10CG) underlying the Pst resistance locus Yr10 has been cloned. However, following haplotype and linkage analyses indicate the presence of additional Pst resistance gene(s) underlying/near Yr10 locus. Here, we report the cloning of the Pst resistance gene YrNAM in this region using the method of sequencing trait-associated mutations (STAM). YrNAM encodes a non-canonical resistance protein with a NAM domain and a ZnF-BED domain. We show that both domains are required for resistance. Transgenic wheat harboring YrNAM gene driven by its endogenous promoter confers resistance to stripe rust races CYR32 and CYR33. YrNAM is an ancient gene and present in wild wheat species Aegilops longissima and Ae. sharonensis; however, it is absent in most wheat cultivars, which indicates its breeding value.

Untargeted Metabolomics Reveals a Multi-Faceted Resistance Response to Fusarium Head Blight Mediated by the Thinopyrum elongatum Fhb7E Locus Transferred via Chromosome Engineering into Wheat

The Thinopyrum elongatum Fhb7E locus has been proven to confer outstanding resistance to Fusarium Head Blight (FHB) when transferred into wheat, minimizing yield loss and mycotoxin accumulation in grains. Despite their biological relevance and breeding implications, the molecular mechanisms underlying the resistant phenotype associated with Fhb7E have not been fully uncovered. To gain a broader understanding of processes involved in this complex plant-pathogen interaction, we analysed via untargeted metabolomics durum wheat (DW) rachises and grains upon spike inoculation with Fusarium graminearum (Fg) and water. The employment of DW near-isogenic recombinant lines carrying or lacking the Th. elongatum chromosome 7E region including Fhb7E on their 7AL arm, allowed clear-cut distinction between differentially accumulated disease-related metabolites. Besides confirming the rachis as key site of the main metabolic shift in plant response to FHB, and the upregulation of defence pathways (aromatic amino acid, phenylpropanoid, terpenoid) leading to antioxidants and lignin accumulation, novel insights were revealed. Fhb7E conferred constitutive and early-induced defence response, in which specific importance of polyamine biosynthesis, glutathione and vitamin B6 metabolisms, along with presence of multiple routes for deoxynivalenol detoxification, was highlighted. The results suggested Fhb7E to correspond to a compound locus, triggering a multi-faceted plant response to Fg, effectively limiting Fg growth and mycotoxin production.

Transcriptome Dynamics Underlying Planticine®-Induced Defense Responses of Tomato (Solanum lycopersicum L.) to Biotic Stresses

The induction of natural defense mechanisms in plants is considered to be one of the most important strategies used in integrated pest management (IPM). Plant immune inducers could reduce the use of chemicals for plant protection and their harmful impacts on the environment. Planticine® is a natural plant defense biostimulant based on oligomers of α(1→4)-linked D-galacturonic acids, which are biodegradable and nontoxic. The aim of this study was to define the molecular basis of Planticine’s biological activity and the efficacy of its use as a natural plant resistance inducer in greenhouse conditions. Three independent experiments with foliar application of Planticine® were carried out. The first experiment in a climatic chamber (control environment, no pest pressure) subjected the leaves to RNA-seq analysis, and the second and third experiments in greenhouse conditions focused on efficacy after a pest infestation. The result was the RNA sequencing of six transcriptome libraries of tomatoes treated with Planticine® and untreated plants; a total of 3089 genes were found to be differentially expressed genes (DEGs); among them, 1760 and 1329 were up-regulated and down-regulated, respectively. DEG analysis indicated its involvement in such metabolic pathways and processes as plant-pathogen interaction, plant hormone signal transduction, MAPK signaling pathway, photosynthesis, and regulation of transcription. We detected up-regulated gene-encoded elicitor and effector recognition receptors (ELRR and ERR), mitogen-activated protein kinase (MAPKs) genes, and transcription factors (TFs), i.e., WRKY, ERF, MYB, NAC, bZIP, pathogenesis-related proteins (PRPs), and resistance-related metabolite (RRMs) genes. In the greenhouse trials, foliar application of Planticine® proved to be effective in reducing the infestation of tomato leaves by the biotrophic pathogen powdery mildew and in reducing feeding by thrips, which are insect herbivores. Prophylactic and intervention use of Planticine® at low infestation levels allows the activation of plant defense mechanisms.

Stress Management in Plants: Examining Provisional and Unique Dose-Dependent Responses

The purpose of this review is to critically evaluate the effects of different stress factors on higher plants, with particular attention given to the typical and unique dose-dependent responses that are essential for plant growth and development. Specifically, this review highlights the impact of stress on genome instability, including DNA damage and the molecular, physiological, and biochemical mechanisms that generate these effects. We provide an overview of the current understanding of predictable and unique dose-dependent trends in plant survival when exposed to low or high doses of stress. Understanding both the negative and positive impacts of stress responses, including genome instability, can provide insights into how plants react to different levels of stress, yielding more accurate predictions of their behavior in the natural environment. Applying the acquired knowledge can lead to improved crop productivity and potential development of more resilient plant varieties, ensuring a sustainable food source for the rapidly growing global population.

In vivo surface-enhanced Raman scattering nanosensor for the real-time monitoring of multiple stress signalling molecules in plants

When under stress, plants release molecules to activate their defense system. Detecting these stress-related molecules offers the possibility to address stress conditions and prevent the development of diseases. However, detecting endogenous signalling molecules in living plants remains challenging due to low concentrations of these analytes and interference with other compounds; additionally, many methods currently used are invasive and labour-intensive. Here we show a non-destructive surface-enhanced Raman scattering (SERS)-based nanoprobe for the real-time detection of multiple stress-related endogenous molecules in living plants. The nanoprobe, which is placed in the intercellular space, is optically active in the near-infrared region (785 nm) to avoid interferences from plant autofluorescence. It consists of a Si nanosphere surrounded by a corrugated Ag shell modified by a water-soluble cationic polymer poly(diallyldimethylammonium chloride), which can interact with multiple plant signalling molecules. We measure a SERS enhancement factor of 2.9 × 10⁷ and a signal-to-noise ratio of up to 64 with an acquisition time of ~100 ms. To show quantitative multiplex detection, we adopted a binding model to interpret the SERS intensities of two different analytes bound to the SERS hot spot of the nanoprobe. Under either abiotic or biotic stress, our optical nanosensors can successfully monitor salicylic acid, extracellular adenosine triphosphate, cruciferous phytoalexin and glutathione in Nasturtium officinale, Triticum aestivum L. and Hordeum vulgare L.-all stress-related molecules indicating the possible onset of a plant disease. We believe that plasmonic nanosensor platforms can enable the early diagnosis of stress, contributing to a timely disease management of plants.

The N-terminus of a Fusarium graminearum-secreted protein enhances broad-spectrum disease resistance in plants

Fusarium head blight is a destructive disease caused by Fusarium species. Little is known about the pathogenic molecular weapons of Fusarium graminearum. The gene encoding a small secreted protein, Fg02685, in F. graminearum was found to be upregulated during wheat head infection. Knockout mutation of Fg02685 reduced the growth and development of Fusarium in wheat spikes. Transient expression of Fg02685 or recombinant protein led to plant cell death in a BAK1- and SOBIR1-independent system. Fg02685 was found to trigger plant basal immunity by increasing the deposition of callose, the accumulation of reactive oxygen species (ROS), and the expression of defence-related genes. The Fg02685 signal peptide was required for the plant's apoplast accumulation and induces cell death, indicating Fg02685 is a novel conserved pathogen-associated molecular pattern. Moreover, its homologues are widely distributed in oomycetes and fungal pathogens and induced cell death in tobacco. The conserved α-helical motif at the N-terminus was necessary for the induction of cell death. Moreover, a 32-amino-acid peptide, Fg02685 N-terminus peptide 32 (FgNP32), was essential for the induction of oxidative burst, callose deposition, and mitogen-activated protein kinase signal activation in plants. Prolonged exposure to FgNP32 enhanced the plant's resistance to Fusarium and Phytophthora. This study provides new approaches for an environment-friendly control strategy for crop diseases by applying plant immune inducers to strengthen broad-spectrum disease resistance in crops.

Extensive cross-talk among stress-regulated protective metabolites, biogenic-amines and phytohormone-signalling, co-ordinated by dopamine-mediated seed-priming, governs tolerance against fluoride stress in rice

Seed priming with dopamine reduced fluoride bioaccumulation, induced endogenous dopamine level, thereby orchestrating phytohormone homeostasis and biogenic amine metabolism, and modulating osmolyte and antioxidant machinery to enhance fluoride tolerance in rice. The aim of this study was to decipher the efficacy of seed priming with dopamine in curtailing the adverse impacts of fluoride toxicity in rice seedlings. Fluoride-stressed seedlings exhibited severe growth retardation, high fluoride bioaccumulation, electrolyte leakage and marked cellular injuries. Dopamine priming stimulated the overall physiological growth parameters during stress, via reduced formation of H₂O₂, malondialdehyde and methylglyoxal, due to lesser fluoride-accumulation. Fluoride stress-induced endogenous dopamine level was further induced upon dopamine priming, marked by the up regulated DOPA decarboxylase expression. Additionally, dopamine treatment led to escalated activity of catalase, superoxide dismutase and glutathione peroxidase in the stressed seedlings, concomitant with altered CAT, SOD and GPX expression. The higher accumulation of protective osmolytes (proline and total amino acids) and non-enzymatic antioxidants (phenolics, flavonoids, anthocyanins, glutathione and carotenoids), upon dopamine priming, during fluoride stress, could be linked with the altered expression pattern of the respective genes. Dopamine promoted active utilization of the biogenic amine (polyamines and ϒ-amino butyric acid) pools for toxicity mitigation, correlated with the modulation of the concerned enzyme activity and gene expression. Dopamine stimulated the accumulation of phytohormones like gibberellin and salicylic acid, via inducing the biosynthetic genes like gibberellin-3-oxidase (GA3ox) and isochorismate synthase (ICS), respectively, while depreciating the abscisic acid and melatonin level during fluoride stress. To our knowledge, this is the first documented report for the remedial role of dopamine priming against fluoride stress in any plant species. This study will open new arenas in sustainable agriculture for the exploitation of this pulsating biomolecule against fluoride stress.

Barley Resistance to Fusarium graminearum Infections: From Transcriptomics to Field with Food Safety Concerns

Global climate change and the urgency to transform food crops require substantial breeding efforts to meet the food security challenges. Barley, an important cereal, has remained a preferential host of phytotoxic diseases caused by the Fusarium graminearum that not only severely reduces the crop yield but also compromises its food quality due to the accumulation of mycotoxins. To develop resistance against Fusarium infections, a better understanding of the host-pathogen interaction is inevitable and could be tracked through molecular insights. Here, we focused precisely on the potential gene targets that are exclusive to this devastating pathosystem and could be harnessed for fast breeding of barley. We also discuss the eco-friendly applications of nanobio hybrid and the CRISPR technology for barley protection. This review covers the critical information gaps within the subject and may be useful for the sustainable improvement of barley from the perspective of food and environmental safety concerns.

A R2R3 MYB Transcription Factor, TaMYB391, Is Positively Involved in Wheat Resistance to Puccinia striiformis f. sp. tritici

A biotrophic fungus, Puccinia striiformis f.sp. tritici (Pst), which causes stripe rust disease in wheat is the most yield-limiting factor in wheat production. Plants have complex defense mechanisms against invading pathogens. Hypersensitive response (HR), a kind of programmed cell death (PCD) at the infection site, is among these defense mechanisms. Transcription factors (TFs) play a crucial role in plant defense response against invading pathogens. Myeloblastosis (MYB) TFs are among the largest TFs families that are involved in response to both biotic and abiotic stresses. However, little is known about the mechanisms of MYB TFs during the interaction between wheat and the stripe rust fungus. Here, we identified an R2R3 MYB TF from wheat, designated as TaMYB391, and characterized its functional role during wheat-Pst interaction. Our data indicated that TaMYB391 is induced by Pst infection and exogenous application of salicylic acid (SA) and abscisic acid (ABA). TaMYB391 is localized in the nucleus of both wheat and Nicotiana benthamiana. Transient overexpression of TaMYB391 in N. benthamiana triggered HR-related PCD accompanied by increased electrolyte leakage, high accumulation of reactive oxygen species (ROS), and transcriptional accumulation of SA defense-related genes and HR-specific marker genes. Overexpression of TaMYB391 in wheat significantly enhanced wheat resistance to stripe rust fungus through the induction of pathogenesis-related (PR) genes, ROS accumulation and hypersensitive cell death. On the other hand, RNAi-mediated silencing of TaMYB391 decreased the resistance of wheat to Pst accompanied by enhanced growth of the pathogen. Together our findings demonstrate that TaMYB391 acts as a positive regulator of HR-associated cell death and positively contributes to the resistance of wheat to the stripe rust fungus by regulating certain PR genes, possibly through SA signaling pathways.

Role of reactive oxygen species in lesion mimic formation and conferred basal resistance to Fusarium graminearum in barley lesion mimic mutant 5386

This study investigated the barley lesion mimic mutant (LMM) 5386, evidenced by a leaf brown spot phenotype localized on the chromosome 3H, and its conferred basal resistance to Fusarium graminearum. RNA-seq analysis identified 1453 genes that were differentially expressed in LMM 5386 compared to those in the wild type. GO and KEGG functional annotations suggested that lesion mimic formation was mediated by pathways involving oxidation reduction and glutathione metabolism. Additionally, reactive oxygen species (ROS) accumulation in brown spots was substantially higher in LMM 5386 than in the wild-type plant; therefore, antioxidant competence, which is indicated by ROS accumulation, was significantly lower in LMM 5386. Furthermore, the reduction of glycine in LMM 5386 inhibited glutathione biosynthesis. These results suggest that the decrease in antioxidant competence and glutathione biosynthesis caused considerable ROS accumulation, leading to programmed cell death, which eventually reduced the yield components in LMM 5386.

Effects of Salicylic Acid Concentration and Post-Treatment Time on the Direct and Systemic Chemical Defense Responses in Maize (Zea mays L.) Following Exogenous Foliar Application

Salicylic acid (SA) plays a critical role in allergic reactions of plants to pathogens and acquired systemic resistance. Thus far, although some research has been conducted on the direct effects of different concentrations of SA on the chemical defense response of treated plant parts (leaves) after at multiple post-treatments times, few research has reported on the systematic effects of non-treated parts (roots). Therefore, we examined direct and systemic effects of SA concentration and time following foliar application on chemical defense responses in maize variety 5422 with two fully expanded leaves. In the experiments, maize leaves were treated with different SA concentrations of 0.1, 0.5, 1.0, 2.5, 5.0 mM, and then, the presence of defense chemicals and enzymes in treated leaves and non-treated roots was measured at different time points of 3, 12, 24, 48, 72 h following SA foliar application. The results showed that direct and systemic effects of SA treatment to the leaf on chemical defense responses were related to SA concentration and time of measurement after spraying SA. In treated leaves, total phenolics content increased directly by 28.65% at the time point of 12 h following foliar application of 0.5 mM SA. DIMBOA (2,4-dihydroxy-7-methoxy-2H, 1, 4-benzoxazin-3 (4H)-one) content was directly enhanced by 80.56~551.05% after 3~72 h following 0.5~5.0 mM SA treatments. Polyphenol oxidase and superoxide dismutase activities were directly enhanced after 12~72 h following 0.5~5.0 mM SA treatments, whereas peroxidase and catalase activities were increased after 3~24 h following application of 1.0~5.0 mM SA. In non-treated roots, DIMBOA content and polyphenol oxidase activity were enhanced systematically after 3~48 h following 1.0~5.0 mM SA foliar treatments. Superoxide dismutase activities were enhanced after 3~24 h following 0.5~2.5 mM SA applications, but total phenolics content, peroxidase and catalase activity decreased in some particular concentrations or at the different times of measurement in the SA treatment. It can be concluded that SA foliar application at 1.0 and 2.5 mM produces strong chemical defense responses in maize, with the optimal induction time being 24 h following the foliar application.

Opposing effects of MYZUS PERSICAE-INDUCED LIPASE 1 and jasmonic acid influence the outcome of Arabidopsis thaliana-Fusarium graminearum interaction

Fusarium graminearum (Fg) is an important fungal pathogen of small grain cereals that can also infect Arabidopsis thaliana. In Arabidopsis, jasmonic acid (JA) signalling involving JASMONATE RESISTANT 1 (JAR1), which synthesizes JA-isoleucine, a signalling form of JA, promotes susceptibility to Fg. Here we show that Arabidopsis MYZUS PERSICAE-INDUCED LIPASE 1 (MPL1), via its influence on limiting JA accumulation, restricts Fg infection. MPL1 expression was up-regulated in response to Fg infection, and MPL1-OE plants, which overexpress MPL1, exhibited enhanced resistance against Fg. In comparison, disease severity was higher on the mpl1 mutant than the wild type. JA content was lower in MPL1-OE and higher in mpl1 than in the wild type, indicating that MPL1 limits JA accumulation. Pharmacological experiments confirmed the importance of MPL1-determined restriction of JA accumulation on curtailment of Fg infection. Methyl-JA application attenuated the MPL1-OE-conferred resistance, while the JA biosynthesis inhibitor ibuprofen enhanced resistance in mpl1. Also, the JA biosynthesis-defective opr3 mutant was epistatic to mpl1, resulting in enhanced resistance in mpl1 opr3 plants. In comparison, JAR1 was not essential for the mpl1-conferred susceptibility to Fg. Considering that methyl-JA promotes Fg growth in culture, we suggest that in part MPL1 curtails disease by limiting the availability of a plant-derived Fg growth-promoting factor.

Lactic Acid Bacteria as Potential Biocontrol Agents for Fusarium Head Blight Disease of Spring Barley

Fusarium head blight (FHB) is a devastating disease encountered by spring-grown barley. Traditionally, synthetic chemicals have been used to control this disease on small grain cereals. A move toward biological control agents as part of sustainable agriculture is pertinent due to the evolutionary mechanisms employed by fungal diseases to circumvent current protection strategies. This study evaluated the effect of six lactic acid bacteria isolates on the development of FHB under in vitro and glasshouse conditions. The relative expression of Fusarium marker genes and transcription factors under Fusarium infection was examined. Dual-culture assays observed inhibition zones of up to 10 and 17% of total plate area for L. amylovorus FST 2.11 and L. brevis R2Δ, respectively. Detached leaf assays validated the antifungal activity and showed the potential of all test isolates to significantly inhibit sporulation of Fusarium culmorum and Fusarium graminearum strains. Spray inoculation of lactic acid bacteria to barley spikelets prior to Fusarium spore application significantly reduced disease severity for five candidates (P < 0.05) under glasshouse conditions. Mycotoxin analysis revealed the ability of L. amylovorus DSM20552 to significantly reduce deoxynivalenol content in spikelets (P < 0.05). A preliminary gene expression study showed the positive influence of lactic acid bacteria on the expression of important defense-related marker genes and transcription factors upon FHB. These results indicate the potential of lactic acid bacteria to be included as part of an integrated pest management strategy for the management of FHB disease. This strategy will reduce FHB severity and deoxynivalenol (DON) contamination of spring barley, leading to high acceptance in the grain market.

The high concentrations of abscisic, jasmonic, and salicylic acids produced under long days do not accelerate flowering in Chenopodium ficifolium 459

The survival and adaptation of angiosperms depends on the proper timing of flowering. The weedy species Chenopodium ficifolium serves as a useful diploid model for comparing the transition to flowering with the important tetraploid crop Chenopodium quinoa due to the close phylogenetic relationship. The detailed transcriptomic and hormonomic study of the floral induction was performed in the short-day accession C. ficifolium 459. The plants grew more rapidly under long days but flowered later than under short days. The high levels of abscisic, jasmonic, and salicylic acids at long days were accompanied by the elevated expression of the genes responding to oxidative stress. The increased concentrations of stress-related phytohormones neither inhibited the plant growth nor accelerated flowering in C. ficifolium 459 at long photoperiods. Enhanced content of cytokinins and the stimulation of cytokinin and gibberellic acid signaling pathways under short days may indicate the possible participation of these phytohormones in floral initiation. The accumulation of auxin metabolites suggests the presence of a dynamic regulatory network in C. ficifolium 459.

The Black Necrotic Lesion Enhanced Fusarium graminearum Resistance in Wheat

Fusarium head blight, mainly incited by Fusarium graminearum, is a devastating wheat disease worldwide. Diverse Fusarium head blight (FHB) resistant sources have been reported, but the resistance mechanisms of these sources remain to be investigated. FHB-resistant wheat germplasm often shows black necrotic lesions (BNLs) around the infection sites. To determine the relationship between BNL and FHB resistance, leaf tissue of a resistant wheat cultivar Sumai 3 was inoculated with four different F. graminearum isolates. Integrated metabolomic and transcriptomic analyses of the inoculated samples suggested that the phytohormone signaling, phenolamine, and flavonoid metabolic pathways played important roles in BNL formation that restricted F. graminearum extension. Exogenous application of flavonoid metabolites on wheat detached leaves revealed the possible contribution of flavonoids to BNL formation. Exogenous treatment of either salicylic acid (SA) or methyl jasmonate (MeJA) on wheat spikes significantly reduced the FHB severity. However, exogenous MeJA treatment prevented the BNL formation on the detached leaves of FHB-resistant wheat Sumai 3. SA signaling pathway influenced reactive oxygen species (ROS) burst to enhance BNL formation to reduce FHB severity. Three key genes in SA biosynthesis and signal transduction pathway, TaICS1, TaNPR1, and TaNPR3, positively regulated FHB resistance in wheat. A complex temporal interaction that contributed to wheat FHB resistance was detected between the SA and JA signaling pathways. Knowledge of BNLs extends our understanding of the molecular mechanisms of FHB resistance in wheat and will benefit the genetic improvement of wheat FHB resistance.

Immunomodulatory Molecular Mechanisms of Luffa cylindrica for Downy Mildews Resistance Induced by Growth-Promoting Endophytic Fungi

Downy mildew (DM), caused by P. cubensis, is harmful to cucurbits including luffa, with increased shortcomings associated with its control through cultural practices, chemical fungicides, and resistant cultivars; there is a prompt need for an effective, eco-friendly, economical, and safe biocontrol approach. Current research is therefore dealt with the biocontrol of luffa DM1 through the endophytic fungi (EF) consortium. Results revealed that T. harzianum (ThM9) and T. virens (TvA1) showed pathogen-dependent inducible metabolic production of squalene and gliotoxins by higher gene expression induction of SQS1/ERG9 (squalene synthase) and GliP (non-ribosomal peptide synthetase). Gene expression of lytic enzymes of EF was also induced with subsequently higher enzyme activities upon confrontation with P. cubensis. EF-inoculated luffa seeds showed efficient germination with enhanced growth potential and vigor of seedlings. EF-inoculated plants showed an increased level of growth-promoting hormone GA with higher gene expression of GA2OX8. EF-pre-inoculated seedlings were resistant to DM and showed an increased GSH content and antioxidant enzyme activities (SOD, CAT, POD). The level of MDA, H₂O_2, REL, and disease severity was reduced by EF. ACC, JA, ABA, and SA were overproduced along with higher gene expression of LOX, ERF, NCED2, and PAL. Expression of defense-marker genes (PPO, CAT2, SOD, APX, PER5, LOX, NBS-LRR, PSY, CAS, Ubi, MLP43) was also modulated in EF-inoculated infected plants. Current research supported the use of EF inoculation to effectively escalate the systemic immunity against DM corresponding to the significant promotion of induced systemic resistance (ISR) and systemic acquired resistance (SAR) responses through initiating the defense mechanism by SA, ABA, ET, and JA biosynthesis and signaling pathways in luffa.

Multi-Omics Analysis Reveals a Regulatory Network of ZmCCT During Maize Resistance to Gibberella Stalk Rot at the Early Stage

Gibberella stalk rot (GSR) caused by Fusarium graminearum is one of the most devastating diseases in maize; however, the regulatory mechanism of resistance to GSR remains largely unknown. We performed a comparative multi-omics analysis to reveal the early-stage resistance of maize to GSR. We inoculated F. graminearum to the roots of susceptible (Y331) and resistant (Y331-ΔTE) near-isogenic lines containing GSR-resistant gene ZmCCT for multi-omics analysis. Transcriptome detected a rapid reaction that confers resistance at 1-3 hpi as pattern-triggered immunity (PTI) response to GSR. Many key properties were involved in GSR resistance, including genes in photoperiod and hormone pathways of salicylic acid and auxin. The activation of programmed cell death-related genes and a number of metabolic pathways at 6 hpi might be important to prevent further colonization. This is consistent with an integrative analysis of transcriptomics and proteomics that resistant-mediated gene expression reprogramming exhibited a dynamic pattern from 3 to 6 hpi. Further metabolomics analysis revealed that the amount of many chemical compounds was altered in pathways associated with the phenylpropanoid biosynthesis and the phenylalanine metabolism, which may play key roles to confer the GSR resistance. Taken together, we generated a valuable resource to interpret the defense mechanism during early GSR resistance.

Control of Early Blight Fungus (Alternaria alternata) in Tomato by Boric and Phenylboronic Acid

Finding a suitable alternative to the small pool of existing antifungal agents is a vital task in contemporary agriculture. Therefore, intensive research has been conducted globally to uncover environmentally friendly and efficient agents that can suppress pathogens resistant to the currently used antimycotics. Here, we tested the activity of boric acid (BA) and its derivative phenylboronic acid (PBA) in controlling the early blight symptoms in tomato plants infected with pathogenic fungus Alternaria alternata. By following the appearance and intensity of the lesions on leaves of the tested plants, as well as by measuring four selected physiological factors that reflect plant health, we have shown that both BA and PBA act prophylactically on fungal infection. They did it by reducing the amount and severity of early blight symptoms, as well as by preventing deterioration of the physiological traits, occurring upon fungal inoculation. Phenylboronic acid was more efficient in suppressing the impact of A. alternata infection. Therefore, we conclude that BA, and even more so PBA, may be used as agents for controlling early blight on tomato plants, as they are both quite effective and environmentally friendly.

Monitoring of Host Suitability and Defense-Related Genes in Wheat to Bipolaris sorokiniana

Spot blotch caused by Bipolaris sorokiniana is a destructive disease of wheat worldwide. This study investigated the aggressiveness of B. sorokiniana isolates from different wheat-growing areas of Bolu province in Turkey on the cultivar Seri-82. Host susceptibility of 55 wheat cultivars was evaluated against the most aggressive isolate. Our results indicated that the cultivars Anafarta and Koç-2015 were the most resistant. A specific and sensitive qPCR assay was developed for detecting the pathogen in plant tissues and evaluating wheat plants with different resistance levels. Three primer sets, BsGAPDHF/BsGAPDHR, BsITSF/BsITSR, and BsSSUF/BsSSUR, were designed based on glyceraldehyde-3-phosphate dehydrogenase, internal transcribed spacers, and 18S rRNA loci of B. sorokiniana with detection limits of 1, 0.1, and 0.1 pg of pathogen DNA, respectively. The qPCR assay was highly sensitive and did not amplify DNA from the other closely related fungal species and host plants. The protocol differentiated wheat plants with varying degrees of resistance. The assay developed a useful tool for the quantification of the pathogen in the early stages of infection and may provide a significant contribution to a more efficient selection of wheat genotypes in breeding studies. In the present study, expression levels of PR proteins, phenylalanine ammonia-lyase, catalase, ascorbate peroxidase, and superoxide dismutase enzymes were upregulated in Anafarta (resistant) and Nenehatun (susceptible) cultivars at different post-infection time points, but more induced in the susceptible cultivar. The results showed considerable variation in the expression levels and timing of defense genes in both cultivars.

Barley transcription factor HvNLP2 mediates nitrate signaling and affects nitrogen use efficiency

Plants have evolved complex mechanisms to adapt to the changing nitrogen levels in the environment. In Arabidopsis, more than a dozen nitrate signaling regulatory genes have been characterized, including the NODULE INCEPTION-LIKE PROTEIN (AtNLP) genes, which play essential roles in nitrate signaling. However, whether NLP genes in the Triticeae crops are involved in nitrate regulation and nitrogen use efficiency (NUE) remains unknown. Here, we isolated a barley (Hordeum vulgare L.) mutant, hvnlp2-1, from a TILLING (Targeting Local Lesions IN Genomes) population and constructed two RNAi lines, hvnlp2-2 and hvnlp2-3, to study the function of HvNLP2. The expression of the nitrate-responsive genes was substantially inhibited after nitrate treatment in the hvnlp2 mutants, indicating that HvNLP2 controls nitrate signaling. Nitrate content was significantly higher in the hvnlp2 mutants, which may result from the decreased assimilation of nitrogen caused by reduced nitrate reductase activity and expression of nitrate assimilatory genes. HvNLP2 is localized to the nucleus in the presence of nitrate. Further investigation showed that HvNLP2 binds to and activates the nitrate-responsive cis-elements. Moreover, hvnlp2 exhibited reduced biomass, seed yield, and NUE. Therefore, HvNLP2 controls nitrate signaling and plays an important role in NUE.

The elemental defense effect of cadmium on Alternaria brassicicola in Brassica juncea

BACKGROUND

The elemental defense hypothesis states a new defensive strategy that hyperaccumulators defense against herbivores or pathogens attacks by accumulating heavy metals. Brassica juncea has an excellent ability of cadmium (Cd) accumulation. However, the elemental defense effect and its regulation mechanism in B. juncea remain unclear.

RESULTS

In this study, we profiled the elemental defense effect and the molecular regulatory mechanism in Cd-accumulated B. juncea after Alternaria brassicicola infection. B. juncea treated with 180 mg Kg^- 1 DW CdCl₂ 2.5H₂O exhibited obvious elemental defense effect after 72 h of infection with A. brassicicola. The expression of some defense-related genes including BjNPR1, BjPR12, BjPR2, and stress-related miRNAs (miR156, miR397, miR398a, miR398b/c, miR408, miR395a, miR395b, miR396a, and miR396b) were remarkably elevated during elemental defense in B. juncea.

CONCLUSIONS

The results indicate that Cd-accumulated B. juncea may defend against pathogens by coordinating salicylic acid (SA) and jasmonic acid (JA) mediated systemic acquired resistance (SAR) and elemental defense in a synergistic joint effect. Furthermore, the expression of miRNAs related to heavy metal stress response and disease resistance may regulate the balance between pathogen defense and heavy metal stress-responsive in B. juncea. The findings provide experimental evidence for the elemental defense hypothesis in plants from the perspectives of phytohormones, defense-related genes, and miRNAs.

Regulation of plant biotic interactions and abiotic stress responses by inositol polyphosphates

Inositol pyrophosphates (PP-InsPs), derivatives of inositol hexakisphosphate (phytic acid, InsP₆) or lower inositol polyphosphates, are energy-rich signaling molecules that have critical regulatory functions in eukaryotes. In plants, the biosynthesis and the cellular targets of these messengers are not fully understood. This is because, in part, plants do not possess canonical InsP₆ kinases and are able to synthesize PP-InsP isomers that appear to be absent in yeast or mammalian cells. This review will shed light on recent discoveries in the biosynthesis of these enigmatic messengers and on how they regulate important physiological processes in response to abiotic and biotic stresses in plants.

Chitosan Nanoparticles Inactivate Alfalfa Mosaic Virus Replication and Boost Innate Immunity in Nicotiana glutinosa Plants

Plant viral infection is one of the most severe issues in food security globally, resulting in considerable crop production losses. Chitosan is a well-known biocontrol agent against a variety of plant infections. However, research on combatting viral infections is still in its early stages. The current study investigated the antiviral activities (protective, curative, and inactivation) of the prepared chitosan/dextran nanoparticles (CDNPs, 100 µg mL-1) on Nicotiana glutinosa plants. Scanning electron microscope (SEM) and dynamic light scattering analysis revealed that the synthesized CDNPs had a uniform, regular sphere shapes ranging from 20 to 160 nm in diameter, with an average diameter of 91.68 nm. The inactivation treatment was the most effective treatment, which resulted in a 100% reduction in the alfalfa mosaic virus (AMV, Acc# OK413670) accumulation level. On the other hand, the foliar application of CDNPs decreased disease severity and significantly reduced viral accumulation levels by 70.43% and 61.65% in protective and curative treatments, respectively, under greenhouse conditions. Additionally, the induction of systemic acquired resistance, increasing total carbohydrates and total phenolic contents, as well as triggering the transcriptional levels of peroxidase, pathogen-related protein-1, and phenylalanine ammonia-lyase were observed. In light of the results, we propose that the potential application of CDNPs could be an eco-friendly approach to enhance yield and a more effective therapeutic elicitor for disease management in plants upon induction of defense systems.

MAMP and DAMP signaling contributes resistance to Fusarium graminearum in Arabidopsis

Plants perceive externally produced microbe-associated molecular patterns (MAMPs) and endogenously produced danger-associated molecular patterns (DAMPs) to activate inducible immunity. While several inducible immune responses have been observed during Fusarium graminearum infection, the identity of the signaling pathways involved is only partly known. We screened 227 receptor kinase and innate immune response genes in Arabidopsis to identify nine genes with a role in F. graminearum resistance. Resistance-promoting genes included the chitin receptors LYK5 and CERK1, and the reactive oxygen species (ROS)-producing NADPH oxidase RbohF, which were required for full inducible immune responses during infection. Two of the genes identified in our screen, APEX and the PAMP-induced peptide 1 (PIP1) DAMP receptor RLK7, repressed F. graminearum resistance. Both RbohF and RLK7 were required for full chitin-induced immune responses and PIP1 precursor expression was induced by chitin and F. graminearum infection. Together, this indicates that F. graminearum resistance is mediated by MAMP and DAMP signaling pathways and that chitin-induced signaling is enhanced by PIP1 perception and ROS production.

Benzoic Acid and Its Hydroxylated Derivatives Suppress Early Blight of Tomato (Alternaria solani) via the Induction of Salicylic Acid Biosynthesis and Enzymatic and Nonenzymatic Antioxidant Defense Machinery

Tomato early blight, caused by Alternaria solani, is a destructive foliar fungal disease. Herein, the potential defensive roles of benzoic acid (BA) and two of its hydroxylated derivatives, ρ-hydroxybenzoic acid (HBA), and protocatechuic acid (PCA) against A. solani were investigated. All tested compounds showed strong dose-dependent fungistatic activity against A. solani and significantly reduced the disease development. Benzoic acid, and its hydroxylated derivatives, enhanced vegetative growth and yield traits. Moreover, BA and its derivatives induce the activation of enzymatic (POX, PPO, CAT, SlAPXs, and SlSODs) and non-enzymatic (phenolics, flavonoids, and carotenoids) antioxidant defense machinery to maintain reactive oxygen species (ROS) homeostasis within infected leaves. Additionally, BA and its hydroxylated derivatives induce the accumulation of salicylic acid (SA) and its biosynthetic genes including isochorismate synthase (SlICS), aldehyde oxidases (SlAO1 and SlAO2), and phenylalanine ammonia-lyases (SlPAL1, SlPAL2, SlPAL3, SlPAL5, and SlPAL6). Higher SA levels were associated with upregulation of pathogenesis-related proteins (SlPR-1, SlPR1a2, SlPRB1-2, SlPR4, SlPR5, SlPR6), nonexpressor of pathogenesis-related protein 1 (SlNPR1), and salicylic acid-binding protein (SlSABP2). These findings outline the potential application of BA and its hydroxylated derivatives as a sustainable alternative control strategy for early blight disease and also deciphering the physiological and biochemical mechanisms behind their protective role.

Production of purple Ma bamboo (Dendrocalamus latiflorus Munro) with enhanced drought and cold stress tolerance by engineering anthocyanin biosynthesis

Overexpression of the leaf color (Lc) gene in Ma bamboo substantially increased the accumulation level of anthocyanin, and improved plant tolerance to cold and drought stresses, probably due to the increased antioxidant capacity. Most bamboos, including Ma bamboo (Dendrocalamus latiflorus Munro), are naturally evergreen and sensitive to cold and drought stresses, while it's nearly impossible to make improvements through conventual breeding due to their long and irregular flowering habit. Moreover, few studies have reported bamboo germplasm innovation through genetic engineering as bamboo genetic transformation remains difficult. In this study, we have upregulated anthocyanin biosynthesis in Ma bamboo, to generate non-green Ma bamboo with increased abiotic stress tolerance. By overexpressing the maize Lc gene, a bHLH transcription activator involved in the anthocyanin biosynthesis in Ma bamboo, we generated purple bamboos with increased anthocyanin levels including cyanidin-3-O-rutinoside, peonidin 3-O-rutinoside, and an unknown cyanidin pentaglycoside derivative. The expression levels of 9 anthocyanin biosynthesis genes were up-regulated. Overexpression of the Lc gene improved the plant tolerance to cold and drought stress, probably due to increased antioxidant capacity. The levels of the cold- and drought-related phytohormone jasmonic acid in the transgenic plants were also enhanced, which may also contribute to the plant stress-tolerant phenotypes. High anthocyanin accumulation level did not affect plant growth. Transcriptomic analysis showed higher expressions of genes involved in the flavonoid pathway in Lc transgenic bamboos compared with those in wild-type ones. The anthocyanin-rich bamboos generated here provide an example of ornamental and multiple agronomic trait improvements by genetic engineering in this important grass species.

Transcriptome Alterations of an in vitro-Selected, Moderately Resistant, Two-Row Malting Barley in Response to 3ADON, 15ADON, and NIV Chemotypes of Fusarium graminearum

Fusarium head blight caused by Fusarium graminearum is a devastating disease of malting barley. Mycotoxins associated with contaminated grain can be transferred from malt to beer and pose a health risk to consumers. In western Canada, F. graminearum has undergone an adaptive shift from 15ADON constituency to dominance by virulent 3ADON-producers; likewise, NIV-producers have established in regions of southern United States. Lack of adapted resistance sources with adequate malting quality has promoted the use of alternative breeding methodologies, such as in vitro selection. We studied the low-deoxynivalenol characteristic of in vitro selected, two-row malting barley variety "Norman" by RNAseq in contrast to its parental line "CDC Kendall," when infected by 15ADON-, 3ADON-, and NIV-producing isolates of F. graminearum. The current study documents higher mycotoxin accumulation by 3ADON isolates, thereby representing increased threat to barley production. At 72-96-h post infection, significant alterations in transcription patterns were observed in both varieties with pronounced upregulation of the phenylpropanoid pathway and detoxification gene categories (UGT, GST, CyP450, and ABC), particularly in 3ADON treatment. Defense response was multitiered, where differential expression in "Norman" associated with antimicrobial peptides (thionin 2.1, defensing, non-specific lipid-transfer protein) and stress-related proteins, such as late embryogenesis abundant proteins, heat-shock, desiccation related, and a peroxidase (HvPrx5). Several gene targets identified in "Norman" would be useful for application of breeding varieties with reduced deoxynivalenol content.

PAL-mediated SA biosynthesis pathway contributes to nematode resistance in wheat

The pathogen cereal cyst nematode (CCN) is deleterious to Triticeae crops and is a threat to the global crop yield. Accession no. 1 of Aegilops variabilis, a relative of Triticum aestivum (bread wheat), is highly resistant to CCN. Our previous study demonstrated that the expression of the phenylalanine ammonia lyase (PAL) gene AevPAL1 in Ae. variabilis is strongly induced by CCN. PAL, the first enzyme of phenylpropanoid metabolism, is involved in abiotic and biotic stress responses. However, its role in plant-CCN interaction remains unknown. In the present study, we proved that AevPAL1 helps to confer CCN resistance through affecting the synthesis of salicylic acid (SA) and downstream secondary metabolites. The silencing of AevPAL1 increased the incidence of CCN infection in roots and decreased the accumulation of SA and phenylalanine (Phe)-derived specialized metabolites. The exogenous pre-application of SA also improved CCN resistance. Additionally, the functions of PAL in phenylpropanoid metabolism correlated with tryptophan decarboxylase (TDC) functioning in tryptophan metabolism pathways. The silencing of either AevPAL1 or AevTDC1 exhibited a concomitant reduction in the expression of both genes and the contents of metabolites downstream of PAL and TDC. These results suggested that AevPAL1, possibly in coordination with AevTDC1, positively contributes to CCN resistance by altering the downstream secondary metabolites and SA content in Ae. variabilis. Moreover, AevPAL1 overexpression significantly enhanced CCN resistance in bread wheat and did not exhibit significant negative effects on yield-related traits, suggesting that AevPAL1 is valuable for the genetic improvement of CCN resistance in bread wheat.

Overexpression of isochorismate synthase enhances salt tolerance in barley

Isochorismate synthase (ICS) is a key enzyme for the synthesis of salicylic acid (SA) in plants. SA plays an important role in the response of plants to abiotic stress. In this study, transgenic barley was constructed to evaluate the function of ICS under salt stress. ICS_OE lines showed obvious salt stress tolerance, this results from the increased outward Na⁺ flux and inward K⁺ flux in roots, thereby maintaining a lower cytosolic Na⁺/K⁺ ratio under salt stress. Overexprssion of ICS also improved Na⁺ sequestration in shoots under salt stress. In addition, ICS_OE lines displayed less accumulation of reactive oxygen species and oxidative damage, accompanied by higher activity of antioxidant enzymes. The improved Na⁺/K⁺ ratio, Na⁺ sequestration, and antioxidative competence play an important role in the enhanced salt tolerance of ICS_OE lines. These findings help to elucidate the abiotic stress resistance of the ICS pathway in barley.

Overexpression of isochorismate synthase enhances drought tolerance in barley

Isochorismate synthase (ICS) is a key enzyme for the synthesis of salicylic acid (SA) in plants. SA mediates plant responses to both biotic and abiotic stresses. In previous studies, we found that overexpression of ICS (ICS_OE) or suppression of ICS (ICS_RNAi) affected the host response to Fusarium graminearum in barley. However, whether the barley ICS gene plays a role in adapting to abiotic stresses remains to be determined. In the present study, expression of the ICS gene was upregulated when treated with 20 % PEG6000, and ICS_OE lines were more drought tolerant than wild type (WT) and ICS_RNAi. In addition, the abscisic acid (ABA) levels in the ICS_OE lines were higher than those in the WT and ICS_RNAi lines under drought stress. High ABA levels significantly reduced Gs and E, which may impact water retention under drought stress. Under drought conditions, the activity of antioxidant enzymes was significantly higher in the ICS_OE lines, correlating with a lower levels of reactive oxygen species (ROS) and malondialdehyde (MDA). Enhanced antioxidant competence also contributed to drought tolerance in ICS_OE lines. These findings help elucidate the abiotic stress resistance of the ICS pathway in barley.

Salicylic Acid Accumulation Controlled by LSD1 Is Essential in Triggering Cell Death in Response to Abiotic Stress

Salicylic acid (SA) is well known hormonal molecule involved in cell death regulation. In response to a broad range of environmental factors (e.g., high light, UV, pathogens attack), plants accumulate SA, which participates in cell death induction and spread in some foliar cells. LESION SIMULATING DISEASE 1 (LSD1) is one of the best-known cell death regulators in Arabidopsis thaliana. The lsd1 mutant, lacking functional LSD1 protein, accumulates SA and is conditionally susceptible to many biotic and abiotic stresses. In order to get more insight into the role of LSD1-dependent regulation of SA accumulation during cell death, we crossed the lsd1 with the sid2 mutant, caring mutation in ISOCHORISMATE SYNTHASE 1(ICS1) gene and having deregulated SA synthesis, and with plants expressing the bacterial nahG gene and thus decomposing SA to catechol. In response to UV A+B irradiation, the lsd1 mutant exhibited clear cell death phenotype, which was reversed in lsd1/sid2 and lsd1/NahG plants. The expression of PR-genes and the H2O2 content in UV-treated lsd1 were significantly higher when compared with the wild type. In contrast, lsd1/sid2 and lsd1/NahG plants demonstrated comparability with the wild-type level of PR-genes expression and H2O2. Our results demonstrate that SA accumulation is crucial for triggering cell death in lsd1, while the reduction of excessive SA accumulation may lead to a greater tolerance toward abiotic stress.

Nicotinamide Mononucleotide Potentiates Resistance to Biotrophic Invasion of Fungal Pathogens in Barley

Nicotinamide mononucleotide (NMN), a precursor of nicotinamide adenine dinucleotide (NAD), induces disease resistance to the Fusarium head blight fungus Fusarium graminearum in Arabidopsis and barley, but it is unknown at which stage of the infection it acts. Since the rate of haustorial formation of an obligate biotrophic barley powdery mildew fungus Blumeria graminis f. sp. hordei (Bgh) was significantly reduced in NMN-treated coleoptile epidermal cells, the possibility that NMN induces resistance to the biotrophic stage of F. graminearum was investigated. The results show that NMN treatment caused the wandering of hyphal growth and suppressed the formation of appressoria-like structures. Furthermore, we developed an experimental system to monitor the early stage of infection in real-time and analyzed the infection behavior. We observed that the hyphae elongated windingly by NMN treatment. These results suggest that NMN potentiates resistance to the biotrophic invasion of F. graminearum as well as Bgh.

Integrated metabolo-transcriptomics and functional characterization reveals that the wheat auxin receptor TIR1 negatively regulates defense against Fusarium graminearum

Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe (teleomorph Gibberella zeae (Schw.) Perch) results in large yield losses in annual global wheat production. Although studies have identified a number of wheat FHB resistance genes, a deeper understanding of the mechanisms underlying host plant resistance to F. graminearum is required for the control of FHB. Here, an integrated metabolomics and transcriptomics analysis of infected wheat plants (Triticum aestivum L.) enabled identification of 789 differentially accumulated metabolites, including flavonoids, phenolamides, tryptamine derivatives, and phytohormones, and revealed altered expression of more than 100 genes that function in the biosynthesis or regulation of these pathways. Our data regarding the effects of F. graminearum infection on flavonoids and auxin signaling led to follow-up experiments that showed that exogenous kaempferide and apigenin application on spikes increased wheat resistance to FHB, while exogenous auxin treatment increased FHB susceptibility. RNAi-mediated knockdown of the gene encoding the auxin receptor, TaTIR1, increased FHB resistance. Our data supported the use of TaTIR1 knockdown in controlling FHB. Our study provides insights on the wheat response to F. graminearum infection and its FHB resistance mechanisms while illustrating the potential of TaTIR1 knockdown in increasing FHB resistance during crop improvement programs.

The role of signal production and transduction in induced resistance of harvested fruits and vegetables

Postharvest diseases are the primary reason causing postharvest loss of fruits and vegetables. Although fungicides show an effective way to control postharvest diseases, the use of fungicides is gradually being restricted due to safety, environmental pollution, and resistance development in the pathogen. Induced resistance is a new strategy to control postharvest diseases by eliciting immune activity in fruits and vegetables with exogenous physical, chemical, and biological elicitors. After being stimulated by elicitors, fruits and vegetables respond immediately against pathogens. This process is actually a continuous signal transduction, including the generation, transduction, and interaction of signal molecules. Each step of response can lead to corresponding physiological functions, and ultimately induce disease resistance by upregulating the expression of disease resistance genes and activating a variety of metabolic pathways. Signal molecules not only mediate defense response alone, but also interact with other signal transduction pathways to regulate the disease resistance response. Among various signal molecules, the second messenger (reactive oxygen species, nitric oxide, calcium ions) and plant hormones (salicylic acid, jasmonic acid, ethylene, and abscisic acid) play an important role in induced resistance. This article summarizes and reviews the research progress of induced resistance in recent years, and expounds the role of the above-mentioned signal molecules in induced resistance of harvested fruits and vegetables, and prospects for future research.

Exogenous salicylic acid mitigates the accumulation of some pesticides in cucumber seedlings under different cultivation methods

Salicylic acid (SA) is a crucial signal molecule and phytohormone, regulating the biotic and abiotic stress responses as well as plant development. In this research, we comparatively examined the effects of exogenous SA on the behaviors of thiamethoxam (THIM), hymexazol (HMI) and chlorantraniliprole (CAP) in cucumber planting systems under soil pot and hydroponic cultivation. The cucumber seedlings were transplanted into soil or nutrient solution containing a target pesticide (1 mg/kg) or a target pesticide with SA (1 mg/kg) after the fourth leaf emerged. We examined the behaviors of pesticides both the SA treated and nontreated plants by analyzing cucumber root, stem and leaf samples taken on the 0-21 days following the root treatment. The root concentration factor (RCF), bioconcentration factor (BCF) and translocation factors (TF_stem and TF_leaf) were calculated for the comparison of the differences in the behaviors of pesticides. We found that the accumulation behaviors of pesticides in planting systems were related to the physicochemical properties of pesticides, exogenous SA and cultivation methods. Exogenous SA had a certain promoting effect on the degradation of pesticides in soil and nutrient solution, resulting in reduced half-lives. SA was able to block the accumulation of pesticides in roots and leaves and alleviated the accumulation ability of roots, the bioconcentration ability of plants, and the translocation ability from roots to leaves. Interestingly, SA had more distinct effects on the behaviors of pesticides under hydroponic experiments than under soil pot experiments. Furthermore, the behaviors of clothianidin (CLO), the main metabolite of THIM, were also assessed, indicating that THIM was mainly metabolized to CLO in leaves and stems, and SA facilitated this process. Our findings suggest that SA has a certain regulatory effect on the accumulation of pesticides in plants, and SA-blocked pesticide accumulation is practically rewarding for improving food safety.

Germplasms, genetics and genomics for better control of disastrous wheat Fusarium head blight

Fusarium head blight (FHB), or scab, for its devastating nature to wheat production and food security, has stimulated worldwide attention. Multidisciplinary efforts have been made to fight against FHB for a long time, but the great progress has been achieved only in the genomics era of the past 20 years, particularly in the areas of resistance gene/QTL discovery, resistance mechanism elucidation and molecular breeding for better resistance. This review includes the following nine main sections, (1) FHB incidence, epidemic and impact, (2) causal Fusarium species, distribution and virulence, (3) types of host resistance to FHB, (4) germplasm exploitation for FHB resistance, (5) genetic control of FHB resistance, (6) fine mapping of Fhb1, Fhb2, Fhb4 and Fhb5, (7) cloning of Fhb1, (8) omics-based gene discovery and resistance mechanism study and (9) breeding for better FHB resistance. The advancements that have been made are outstanding and exciting; however, judged by the complicated nature of resistance to hemi-biotrophic pathogens like Fusarium species and lack of immune germplasm, it is still a long way to go to overcome FHB.

An update on salicylic acid biosynthesis, its induction and potential exploitation by plant viruses

Salicylic acid (SA) is a plant hormone essential for effective resistance to viral and non-viral pathogens. SA biosynthesis increases rapidly in resistant hosts when a dominant host resistance gene product recognizes a pathogen. SA stimulates resistance to viral replication, intercellular spread and systemic movement. However, certain viruses stimulate SA biosynthesis in susceptible hosts. This paradoxical effect limits virus titer and prevents excessive host damage, suggesting that these viruses exploit SA-induced resistance to optimize their accumulation. Recent work showed that SA production in plants does not simply recapitulate bacterial SA biosynthetic mechanisms, and that the relative contributions of the shikimate and phenylpropanoid pathways to the SA pool differ markedly between plant species.

Salicylic Acid Biosynthesis in Plants

Salicylic acid (SA) is an important plant hormone that is best known for mediating host responses upon pathogen infection. Its role in plant defense activation is well established, but its biosynthesis in plants is not fully understood. SA is considered to be derived from two possible pathways; the ICS and PAL pathway, both starting from chorismate. The importance of both pathways for biosynthesis differs between plant species, rendering it hard to make generalizations about SA production that cover the entire plant kingdom. Yet, understanding SA biosynthesis is important to gain insight into how plant pathogen responses function and how pathogens can interfere with them. In this review, we have taken a closer look at how SA is synthesized and the importance of both biosynthesis pathways in different plant species.

MdWRKY15 improves resistance of apple to Botryosphaeria dothidea via the salicylic acid-mediated pathway by directly binding the MdICS1 promoter

Isochorismate synthase (ICS) plays an essential role in the accumulation of salicylic acid (SA) and plant disease resistance. Diseases caused by Botryosphaeria dothidea affect apple yields. Thus, it is important to understand the role of ICS1 in disease resistance to B. dothidea in apple. In this study, SA treatment enhanced the resistance to B. dothidea. MdICS1 was induced by B. dothidea and enhanced the resistance to B. dothidea. MdICS1 promoter analysis indicated that the W-box was vital for the response to B. dothidea treatment. MdWRKY15 was found to interact with the W-box using yeast one-hybrid screening. Subsequently, the interaction was confirmed by EMSA, yeast one-hybrid, ChIP-PCR, and quantitative PCR assays. Moreover, luciferase and GUS analysis further indicated that MdICS1 was transcriptionally activated by MdWRKY15. Finally, we found the function of MdWRKY15 in the resistance to B. dothidea was partially dependent on MdICS1 from the phenotype of transgenic apples and calli. In summary, we revealed that MdWRKY15 activated the transcription of MdICS1 by directly binding to its promoter to increase the accumulation of SA and the expression of disease-related genes, thereby resulting in the enhanced resistance to B. dothidea in the SA biosynthesis pathway.

NbWRKY40 Positively Regulates the Response of Nicotiana benthamiana to Tomato Mosaic Virus via Salicylic Acid Signaling

WRKY transcription factors play important roles in plants, including responses to stress; however, our understanding of the function of WRKY genes in plant responses to viral infection remains limited. In this study, we investigate the role of NbWRKY40 in Nicotiana benthamiana resistance to tomato mosaic virus (ToMV). NbWRKY40 is significantly downregulated by ToMV infection, and subcellular localization analysis indicates that NbWRKY40 is targeted to the nucleus. In addition, NbWRKY40 activates W-box-dependent transcription in plants and shows transcriptional activation in yeast cells. Overexpressing NbWRKY40 (OEWRKY40) inhibits ToMV infection, whereas NbWRKY40 silencing confers susceptibility. The level of salicylic acid (SA) is significantly higher in OEWRKY40 plants compared with that of wild-type plants. In addition, transcript levels of the SA-biosynthesis gene (ICS1) and SA-signaling genes (PR1b and PR2) are dramatically higher in OEWRKY40 plants than in the control but lower in NbWRKY40-silenced plants than in the control. Furthermore, electrophoretic mobility shift assays show that NbWRKY40 can bind the W-box element of ICS1. Callose staining reveals that the plasmodesmata is decreased in OEWRKY40 plants but increased in NbWRKY40-silenced plants. Exogenous application of SA also reduces viral accumulation in NbWRKY40-silenced plants infected with ToMV. RT-qPCR indicates that NbWRKY40 does not affect the replication of ToMV in protoplasts. Collectively, our findings suggest that NbWRKY40 likely regulates anti-ToMV resistance by regulating the expression of SA, resulting in the deposition of callose at the neck of plasmodesmata, which inhibits viral movement.

Stable Isotope-Assisted Plant Metabolomics: Investigation of Phenylalanine-Related Metabolic Response in Wheat Upon Treatment With the Fusarium Virulence Factor Deoxynivalenol

The major Fusarium mycotoxin deoxynivalenol (DON) is a virulence factor in wheat and has also been shown to induce defense responses in host plant tissue. In this study, global and tracer labeling with 13C were combined to annotate the overall metabolome of wheat spikes and to evaluate the response of phenylalanine-related pathways upon treatment with DON. At anthesis, spikes of resistant and susceptible cultivars as well as two related near isogenic wheat lines (NILs) differing in the presence/absence of the major resistance QTL Fhb1 were treated with 1 mg DON or water (control), and samples were collected at 0, 12, 24, 48, and 96 h after treatment (hat). A total of 172 Phe-derived wheat constituents were detected with our untargeted approach employing 13C-labeled phenylalanine and subsequently annotated as flavonoids, lignans, coumarins, benzoic acid derivatives, hydroxycinnamic acid amides (HCAAs), as well as peptides. Ninety-six hours after the DON treatment, up to 30% of the metabolites biosynthesized from Phe showed significantly increased levels compared to the control samples. Major metabolic changes included the formation of precursors of compounds implicated in cell wall reinforcement and presumed antifungal compounds. In addition, also dipeptides, which presumably are products of proteolytic degradation of truncated proteins generated in the presence of the toxin, were significantly more abundant upon DON treatment. An in-depth comparison of the two NILs with correlation clustering of time course profiles revealed some 70 DON-responsive Phe derivatives. While several flavonoids had constitutively different abundance levels between the two NILs differing in resistance, other Phe-derived metabolites such as HCAAs and hydroxycinnamoyl quinates were affected differently in the two NILs after treatment with DON. Our results suggest a strong activation of the general phenylpropanoid pathway and that coumaroyl-CoA is mainly diverted towards HCAAs in the presence of Fhb1, whereas the metabolic route to monolignol(-conjugates), lignans, and lignin seems to be favored in the absence of the Fhb1 resistance quantitative trait loci.