Elucidation of defense-related signaling responses to spot blotch infection in bread wheat (Triticum aestivum L.)

Multiple functions and regulatory networks of WRKY33 and its orthologs

Arabidopsis thaliana WRKY33 is currently one of the most studied members of the Group I WRKY transcription factor family. Research has confirmed that WRKY33 is involved in the regulation of various biological and abiotic stresses and occupies a central position in the regulatory network. The functional studies of orthologous genes of WRKY33 from other species are also receiving increasing attention. In this article, we summarized thirty-eight orthologous genes of AtWKRY33 from twenty-five different species. Their phylogenetic relationship and conserved WRKY domain were analyzed and compared. Similar to AtWKRY33, the well-studied orthologous gene members from rice and tomato also have multiple functions. In addition to playing important regulatory roles in responding to their specific pathogens, they are also involved in regulating various abiotic stresses and development. AtWKRY33 exerts its multiple functions through a complex regulatory network. Upstream transcription factors or other regulatory factors activate or inhibit the expression of AtWKRY33 at the chromatin and transcriptional levels. Interacting proteins affect the transcriptional activity of AtWKRY33 through phosphorylation, ubiquitination, SUMOylation, competition, or cooperation. The downstream genes are diverse and include three major categories: transcription factors, synthesis, metabolism, and signal transduction of various hormones, and disease resistance genes. In the regulatory network of AtWRKY33 orthologs, many conserved regulatory characteristics have been discovered, such as self-activation and phosphorylation by MAP kinases. This can provide a comparative reference for further studying the functions of other orthologous genes of AtWKRY33.

Carbohydrate elicitor-induced plant immunity: Advances and prospects

The perceived negative impacts of synthetic agrochemicals gave way to alternative, biological plant protection strategies. The deployment of induced resistance, comprising boosting the natural defense responses of plants, is one of those. Plants developed multi-component defense mechanisms to defend themselves against biotic and abiotic stresses. These are activated upon recognition of stress signatures via membrane-localized receptors. The induced immune responses enable plants to tolerate and limit the impact of stresses. A systemic cascade of signals enables plants to prime un-damaged tissues, which is crucial during secondary encounters with stress. Comparable stress tolerance mechanisms can be induced in plants by the application of carbohydrate elicitors such as chitin/chitosan, β-1,3-glucans, oligogalacturonides, cellodextrins, xyloglucans, alginates, ulvans, and carrageenans. Treating plants with carbohydrate-derived elicitors enable the plants to develop resistance appliances against diverse stresses. Some carbohydrates are also known to have been involved in promoting symbiotic signaling. Here, we review recent progresses on plant resistance elicitation effect of various carbohydrate elicitors and the molecular mechanisms of plant cell perception, cascade signals, and responses to cascaded cues. Besides, the molecular mechanisms used by plants to distinguish carbohydrate-induced immunity signals from symbiotic signals are discussed. The structure-activity relationships of the carbohydrate elicitors are also described. Furthermore, we forwarded future research outlooks that might increase the utilization of carbohydrate elicitors in agriculture in order to improve the efficacy of plant protection strategies.

Characterization of the Serine Protease TlSP1 from Trichoderma longibrachiatum T6 and Its Function in the Control of Heterodera avenae in Wheat

Serine protease is an extracellular protease secreted by biocontrol fungi that can effectively control nematode diseases by degrading nematode eggshells and enhancing plant resistance. Trichoderma longibrachiatum T6, an important biocontrol fungus, has been demonstrated to effectively parasitize and degrade Heterodera avenae cysts, eggs, and second-stage juveniles (J2s). However, the genes that encoding serine protease and their functions in T. longibrachiatum T6 have not been thoroughly investigated. In this study, we successfully cloned and sequenced the serine protease gene TlSP1 in T. longibrachiatum T6. Our results revealed that the expression level of the TlSP1 gene was induced and significantly increased in T. longibrachiatum T6 after inoculation with H. avenae cysts. The full-length sequence of the coding region (CDS) of TlSP1 gene was 1230 bp and encoded a protein consisting of 409 amino acids. Upon the transformation of the TlSP1 gene into Pichia pastoris X33, the purified recombinant TlSP1 protein exhibited optimal activity at a temperature of 50 °C and pH 8.0. Following 4-10-day of treatment with the purified recombinant TlSP1 protein, the eggshells and content were dissolved and exuded. The number of nematodes invading wheat roots was reduced by 38.43% in the group treated with both TlSP1 and eggs on one side (P1+N) compared to the control group, while the number of nematodes invading wheat roots was reduced by 30.4% in the TlSP1 and eggs two-sided treatment group (P1/N). Furthermore, both the P1+N and P1/N treatments significantly upregulated genes associated with defense enzymes (TaPAL, TaCAT, TaSOD, and TaPOD), genes involved in the lignin synthesis pathway (TaC4H, Ta4CL2, TaCAD1, and TaCAD12), and salicylic acid (SA)-responsive genes (TaNPR1, TaPR1, and TaPR2) and led to the high expression of jasmonic acid (JA)-responsive genes (TaPR4, TaOPR3, and TaAOS2). This study has highlighted the significant role of the TlSP1 gene in facilitating H. avenae eggshells' dissolution, preventing nematode invasion in the host plant, and boosting plant resistance in wheat.

The diversity of endophytic fungi in Tartary buckwheat (Fagopyrum tataricum) and its correlation with flavonoids and phenotypic traits

Tartary buckwheat (Fagopyrum tataricum) is a significant medicinal crop, with flavonoids serving as a crucial measure of its quality. Presently, the artificial cultivation of Tartary buckwheat yields low results, and the quality varies across different origins. Therefore, it is imperative to identify an effective method to enhance the yield and quality of buckwheat. Endophytic fungi reside within plants and form a mutually beneficial symbiotic relationship, aiding plants in nutrient absorption, promoting host growth, and improving secondary metabolites akin to the host. In this study, high-throughput sequencing technology was employed to assess the diversity of endophytic fungi in Tartary buckwheat. Subsequently, a correlation analysis was performed between fungi and metabolites, revealing potential increases in flavonoid content due to endophytic fungi such as Bipolaris, Hymenula, and Colletotrichum. Additionally, a correlation analysis between fungi and phenotypic traits unveiled the potential influence of endophytic fungi such as Bipolaris, Buckleyzyma, and Trichosporon on the phenotypic traits of Tartary buckwheat. Notably, the endophytic fungi of the Bipolaris genus exhibited the potential to elevate the content of Tartary buckwheat metabolites and enhance crop growth. Consequently, this study successfully identified the resources of endophytic fungi in Tartary buckwheat, explored potential functional endophytic fungi, and laid a scientific foundation for future implementation of biological fertilizers in improving the quality and growth of Tartary buckwheat.

Heat and Wheat: Adaptation strategies with respect to heat shock proteins and antioxidant potential; an era of climate change

Extreme changes in weather including heat-wave and high-temperature fluctuations are predicted to increase in intensity and duration due to climate change. Wheat being a major staple crop is under severe threat of heat stress especially during the grain-filling stage. Widespread food insecurity underscores the critical need to comprehend crop responses to forthcoming climatic shifts, pivotal for devising adaptive strategies ensuring sustainable crop productivity. This review addresses insights concerning antioxidant, physiological, molecular impacts, tolerance mechanisms, and nanotechnology-based strategies and how wheat copes with heat stress at the reproductive stage. In this study stress resilience strategies were documented for sustainable grain production under heat stress at reproductive stage. Additionally, the mechanisms of heat resilience including gene expression, nanomaterials that trigger transcription factors, (HSPs) during stress, and physiological and antioxidant traits were explored. The most reliable method to improve plant resilience to heat stress must include nano-biotechnology-based strategies, such as the adoption of nano-fertilizers in climate-smart practices and the use of advanced molecular approaches. Notably, the novel resistance genes through advanced molecular approach and nanomaterials exhibit promise for incorporation into wheat cultivars, conferring resilience against imminent adverse environmental conditions. This review will help scientific communities in thermo-tolerance wheat cultivars and new emerging strategies to mitigate the deleterious impact of heat stress.

Assessment of Tunisian Trichoderma Isolates on Wheat Seed Germination, Seedling Growth and Fusarium Seedling Blight Suppression

Beneficial microorganisms, including members of the Trichoderma genus, are known for their ability to promote plant growth and disease resistance, as well as being alternatives to synthetic inputs in agriculture. In this study, 111 Trichoderma strains were isolated from the rhizospheric soil of Florence Aurore, an ancient wheat variety that was cultivated in an organic farming system in Tunisia. A preliminary ITS analysis allowed us to cluster these 111 isolates into three main groups, T. harzianum (74 isolates), T. lixii (16 isolates) and T. sp. (21 isolates), represented by six different species. Their multi-locus analysis (tef1, translation elongation factor 1; rpb2, RNA polymerase B) identified three T. afroharzianum, one T. lixii, one T. atrobrunneum and one T. lentinulae species. These six new strains were selected to determine their suitability as plant growth promoters (PGP) and biocontrol agents (BCA) against Fusarium seedling blight disease (FSB) in wheat caused by Fusarium culmorum. All of the strains exhibited PGP abilities correlated to ammonia and indole-like compound production. In terms of biocontrol activity, all of the strains inhibited the development of F. culmorum in vitro, which is linked to the production of lytic enzymes, as well as diffusible and volatile organic compounds. An in planta assay was carried out on the seeds of a Tunisian modern wheat variety (Khiar) by coating them with Trichoderma. A significant increase in biomass was observed, which is associated with increased chlorophyll and nitrogen. An FSB bioprotective effect was confirmed for all strains (with Th01 being the most effective) by suppressing morbid symptoms in germinated seeds and seedlings, as well as by limiting F. culmorum aggressiveness on overall plant growth. Plant transcriptome analysis revealed that the isolates triggered several SA- and JA-dependent defense-encoding genes involved in F. culmorum resistance in the roots and leaves of three-week-old seedlings. This finding makes these strains very promising in promoting growth and controlling FSB disease in modern wheat varieties.

A small cysteine-rich fungal effector, BsCE66 is essential for the virulence of Bipolaris sorokiniana on wheat plants

The Spot Blotch (SB) caused by hemibiotrophic fungal pathogen Bipolaris sorokiniana is one of the most devastating wheat diseases leading to 15-100% crop loss. However, the biology of Triticum-Bipolaris interactions and host immunity modulation by secreted effector proteins remain underexplored. Here, we identified a total of 692 secretory proteins including 186 predicted effectors encoded by B. sorokiniana genome. Gene Ontology categorization showed that these proteins belong to cellular, metabolic and signaling processes, and exhibit catalytic and binding activities. Further, we functionally characterized a cysteine-rich, B. sorokiniana Candidate Effector 66 (BsCE66) that was induced at 24-96 hpi during host colonization. The Δbsce66 mutant did not show vegetative growth defects or stress sensitivity compared to wild-type, but developed drastically reduced necrotic lesions upon infection in wheat plants. The loss-of-virulence phenotype was rescued upon complementing the Δbsce66 mutant with BsCE66 gene. Moreover, BsCE66 does not form homodimer and conserved cysteine residues form intra-molecular disulphide bonds. BsCE66 localizes to the host nucleus and cytosol, and triggers a strong oxidative burst and cell death in Nicotiana benthamiana. Overall, our findings demonstrate that BsCE66 is a key virulence factor that is necessary for host immunity modulation and SB disease progression. These findings would significantly improve our understanding of Triticum-Bipolaris interactions and assist in the development of SB resistant wheat varieties.

Heritable priming by Trichoderma: A sustainable approach for wheat protection against Bipolaris sorokiniana

Crop plants encounter a variety of biotic challenges in the field and faces significant reduction in crop yield. In the current scenario of an ever increasing global population, there is an urgent need to protect plant health by using sustainable approach to maximize the crop productivity and to mitigate the food demands. Nowadays, we mostly rely on chemical crop protection techniques, which are causing a number of environmental and health difficulties. Defence priming is a chemical-free, eco-friendly, and sustainable strategy of crop protection, which is also called "green vaccination. In the present study, for the first time, we used Trichoderma as a priming agent to protect wheat crop from spot blotch disease. We have established Trichoderma-mediated defence priming in wheat against Bipolaris sorokiniana for sustainable crop improvement. We have characterised the morphological, disease phenotype, biochemical and yield parameters of Trichoderma-primed and non-primed wheat under disease pressure. Trichoderma-primed plants were found to be more protected against B. sorokiniana as compared to non-primed plants. Biochemical studies indicated that there is no direct defence response after priming stimulus but the defence response was activated only after triggering stimulus in terms of enhanced defence metabolites in primed plants as compared to non-primed plants. In the present study, since defence was activated only when required, that is under disease pressure, there was no unnecessary allocation of resources towards defence. Hence, no yield penalty was shown in primed plants as compared to control. We further evaluated the inheritance of primed state to the next generation and found that progeny of primed parents also performed better than progeny of non-primed parents under disease pressure in terms of protection from B. sorokiniana as well as yield performance. This strategy has the potential to protect crop without any yield penalty and causing environmental degradation. Our research findings indicate that Trichoderma-mediated defence priming could be an alternative approach for improving wheat productivity under biotic stress. To be our best knowledge, this is the first documented report for the Trichoderma-mediated defence priming and induced inheritance in wheat plant. This study will open new arenas in sustainable crop protection strategies for the exploitation of defence priming in crop plants.

Transcriptomic insights into the molecular mechanism of wheat response to stripe rust fungus

The wheat crop (Triticum aestivum L.) is the widely cultivated and most important staple foods of worlds. Stripe (yellow) rust is prompted by Puccinia striiformis f. sp. tritici (Pst) to reduces the yield and grain quality of the wheat significantly. Although many resistant cultivars have been successfully used in wheat breeding, the size of the regulating network and the underlying molecular mechanisms of wheat to response Pst still unknown. Therefore, in order to identify differentially expression genes (DEGs) and the regulate network related to Pst resistance, 15 cDNA libraries were constructed from wheat with CYR34 infection. In this study, a highly susceptible cv. Chuanyu12 (CY12) was used to study the transcriptome profiles after being inoculated with Pst physiological race CYR34. The DEGs were investigated at 24h, 48h, 72h, and 7 days post-inoculation. Certain key genes and pathways of response for Pst-CYR34 in CY12 were identified. The results revealed that Pst-CYR34 inhibited the DEGs related to energy metabolism, biosynthesis, carbon fixation, phenylalanine metabolism, and plant hormone signaling pathways after post-inoculation at 24h, 48h, 72h, and 7d. Light-harvesting chlorophyll protein complex in photosystem I and photosystem II; F-type ATPase, cytochrome b6/f/complex, and photosynthetic electron transport; ethylene, salicylic acid (SA), and jasmonic acid (JA); and lignin and flavonoids biosynthesis in CY12 are among the down-regulated DEGs. The expression patterns of these DEGs were verified via Quantitative Real-time PCR analysis. Our results give insights into the foundation for further exploring the molecular mechanisms regulating networks of Pst response and opens the door for bread wheat Pst resistance breeding.

Novel Insights into Understanding the Molecular Dialogues between Bipolaroxin and the Gα and Gβ Subunits of the Wheat Heterotrimeric G-Protein during Host–Pathogen Interaction

Spot blotch disease of wheat, caused by the fungus Bipolaris sorokiniana (Sacc.) Shoem., produces several toxins which interact with the plants and thereby increase the blightening of the wheat leaves, and Bipolaroxin is one of them. There is an urgent need to decipher the molecular interaction between wheat and the toxin Bipolaroxin for in-depth understanding of host–pathogen interactions. In the present study, we have developed the three-dimensional structure of G-protein alpha subunit from Triticum aestivum. Molecular docking studies were performed using the active site of the modeled G-protein alpha and cryo-EM structure of beta subunit from T. aestivum and ‘Bipolaroxin’. The study of protein–ligand interactions revealed that six H-bonds are mainly formed by Glu29, Ser30, Lys32, and Ala177 of G-alpha with Bipolaroxin. In the beta subunit, the residues of the core beta strand domain participate in the ligand interaction where Lys256, Phe306, and Leu352 formed seven H-bonds with the ligand Bipolaroxin. All-atoms molecular dynamics (MD) simulation studies were conducted for G-alpha and -beta subunit and Bipolaroxin complexes to explore the stability, conformational flexibility, and dynamic behavior of the complex system. In planta studies clearly indicated that application of Bipolaroxin significantly impacted the physio-biochemical pathways in wheat and led to the blightening of leaves in susceptible cultivars as compared to resistant ones. Further, it interacted with the Gα and Gβ subunits of G-protein, phenylpropanoid, and MAPK pathways, which is clearly supported by the qPCR results. This study gives deeper insights into understanding the molecular dialogues between Bipolaroxin and the Gα and Gβ subunits of the wheat heterotrimeric G-protein during host–pathogen interaction.

Enzyme activity and population genetic structure analysis in wheat associated with resistance to Bipolaris sorokiniana-common root rot diseases

Common root rot disease (CRR) caused by Bipolaris sorokiniana (Sacc.) (Pleosporaceae), is an important fungal disease of wheat, Triticum aestivum (Poaceae), causing considerable yield losses globally. Incorporating genetic resistance in cultivated crops is considered the most efficient and sustainable solution to counter root rot diseases. Moreover, resistance to CCR is quantitative in nature, and thus the mechanism is poorly understood. To this aim, we analyzed the activities of defense-related enzymes; peroxidase (POX), superoxide dismutase (SOD), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL), β-1,3-glucanase (GLU) and chitinase (CHI), as well as total phenol content (TPC) to CRR on the three known resistant wheat 'Alvand' and 'Bam', 'Mehregan' at different time points (wpi) following CRR pathogen, B. sorokiniana inoculation. Of which, were selected out of 33 wheat cultivars previously screened for resistance to CRR. We also analyzed the genetic variability of the entire germplasm, 33 wheat cultivars using seven simple sequence repeat (SSR) primer pairs. The activity of antioxidant enzymes was increased in the related resistant genotypes. Of which, 'Bam' had the highest increase in PPO, and GLU activities, followed by 'Alvand' in SOD, PAL, and CHI significantly. Whereas, 'Mehregan' showed the highest level of TPC, POX, and CAT activities. In addition, five out of seven used SSR primers produced a total of 20 polymorphic bands, of which the number of alleles in each gene locus varied within 3-7 bands. The polymorphism information content (PIC) value also ranged from 0.44 to 0.81, with the mean of 0.65, Shannon Information Index (I) between 0.29 and 0.63 with an average of 0.47 per locus, and Nei's gene diversity (h) value varied from 0.16 to 0.44 with an average of 0.32. The average number of effective alleles was 1.52, ranging between 1.21 and 1.8. The gene locus Xgwm 140 showed the highest diversity in the population genetic structure, which explains the ability of the primers to resolve the assayed germplasm. Thus, resistance to CRR in wheat was mainly related to the enhancement of antioxidant enzymes, although the specific metabolic pathways require further study. This study presents new insights for understanding resistance mechanisms of the selected wheat cultivars to CRR, thus improving wheat yield in the future.

A novel effector, CsSp1, from Bipolaris sorokiniana, is essential for colonization in wheat and is also involved in triggering host immunity

The hemibiotrophic pathogen Bipolaris sorokiniana causes root rot, leaf blotching, and black embryos in wheat and barley worldwide, resulting in significant yield and quality reductions. However, the mechanism underlying the host-pathogen interactions between B. sorokiniana and wheat or barley remains unknown. The B. sorokiniana genome encodes a large number of uncharacterized putative effector proteins. In this study, we identified a putative secreted protein, CsSp1, with a classic N-terminal signal peptide, that is induced during early infection. A split-marker approach was used to knock out CsSP1 in the Lankao 9-3 strain. Compared with the wild type, the deletion mutant ∆Cssp1 displayed less radial growth on potato dextrose agar plates and produced fewer spores, and complementary transformation completely restored the phenotype of the deletion mutant to that of the wild type. The pathogenicity of the deletion mutant in wheat was attenuated even though appressoria still penetrated the host. Additionally, the infectious hyphae in the deletion mutant became swollen and exhibited reduced growth in plant cells. The signal peptide of CsSp1 was functionally verified through a yeast YTK12 secretion system. Transient expression of CsSp1 in Nicotiana benthamiana inhibited lesion formation caused by Phytophthora capsici. Moreover, CsSp1 localized in the nucleus and cytoplasm of plant cells. In B. sorokiniana-infected wheat leaves, the salicylic acid-regulated genes TaPAL, TaPR1, and TaPR2 were down-regulated in the ∆Cssp1 strain compared with the wild-type strain under the same conditions. Therefore, CsSp1 is a virulence effector and is involved in triggering host immunity.

Wheat Apoplast-Localized Lipid Transfer Protein TaLTP3 Enhances Defense Responses Against Puccinia triticina

Plant apoplast serves as the frontier battlefield of plant defense in response to different types of pathogens. Many pathogenesis-related (PR) proteins are accumulated in apoplastic space during the onset of plant-pathogen interaction, where they act to suppress pathogen infection. In this study, we found the expression of Triticum aestivum lipid transfer protein 3 (TaLTP3) gene was unregulated during incompatible interaction mediated by leaf rust resistance genes Lr39/41 at the early infection stage. Stable transgenic wheat lines overexpressing TaLTP3 exhibited enhanced resistance to leaf rust pathogen Puccinia triticina. Transcriptome analysis revealed that overexpression of TaLTP3 specifically activated the transcription of pathogenesis-related protein 1a (TaPR1a) and multiple plant hormone pathways, including salicylic acid (SA), jasmonic acid (JA), and auxin, in response to the infection of the model bacterial pathogen Pseudomonas syringae pv. tomato DC3000. Further investigation indicated that TaLTP3 physically associated with wheat TaPR1a protein in the apoplast. Transgenic wheat lines overexpressing TaLTP3 and TaPR1a showed higher accumulations of reactive oxygen species (ROS) during plant defense responses. All these findings suggested that TaLTP3 is involved in wheat resistance against leaf rust pathogen infection and forming a TaLTP3-TaPR1a complex in apoplast against this pathogen, which provides new insights into the functional roles of PR proteins.

GIGANTEA confers susceptibility to plants during spot blotch attack by regulating salicylic acid signalling pathway

Plants throughout their development are challenged by different abiotic and biotic stresses. Growth and developmental plasticity of a plant is under the strict surveillance of the diurnal and circadian control mechanism, fine-tuned by the biological clock. Success of plant life-cycle resides on the continual battle against pathogen that they encounter at different developmental stages. GIGANTEA (GI), a higher plant specific nuclear protein, has been shown to play a major role in shaping plant development by coupling clock function to the circadian phasing of gene expression in Arabidopsis. Despite the central role of GI in regulating light signalling, clock function, flowering time control and in abiotic stress tolerance, its possible function in pathogen defence is not well known. Here we show that, GI expression positively correlates with susceptibility of plants to the spot blotch pathogen infection in both Arabidopsis and bread wheat. Furthermore, we also show that GI expression promotes disease severity by down regulating the salicylic acid (SA) accumulation and alters the phenylpropanoid pathway, thereby suppressing PR gene expression. It is possible that GI-mediated regulation of SA signalling may be one of the possible ways of coupling the light-temperature input pathway to pathogen defence through circadian clock. Our results indicate that the down-regulation of GI could be beneficial in generating disease tolerant crop plants for sustainable agriculture.

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.

Bipolaris sorokiniana-Induced Black Point, Common Root Rot, and Spot Blotch Diseases of Wheat: A Review

Wheat is among the ten top and most widely grown crops in the world. Several diseases cause losses in wheat production in different parts of the world. Bipolaris sorokiniana (teleomorph, Cochliobolus sativus) is one of the wheat pathogens that can attack all wheat parts, including seeds, roots, shoots, and leaves. Black point, root rot, crown rot and spot blotch are the main diseases caused by B. sorokiniana in wheat. Seed infection by B. sorokiniana can result in black point disease, reducing seed quality and seed germination and is considered a main source of inoculum for diseases such as common root rot and spot blotch. Root rot and crown rot diseases, which result from soil-borne or seed-borne inoculum, can result in yield losses in wheat. Spot blotch disease affects wheat in different parts of the world and cause significant losses in grain yield. This review paper summarizes the latest findings on B. sorokiniana, with a specific emphasis on management using genetic, chemical, cultural, and biological control measures.

Trichoderma harzianum- and Methyl Jasmonate-Induced Resistance to Bipolaris sorokiniana Through Enhanced Phenylpropanoid Activities in Bread Wheat (Triticum aestivum L.)

The aim of the present study was to evaluate the impact of Trichoderma harzianum UBSTH-501- and methyl jasmonate-induced systemic resistance and their integration on the spot blotch pathogen, Bipolaris sorokiniana through enhanced phenylpropanoid activities in bread wheat (Triticum aestivum L.). It was found that the application of MeJA (>100 mg L^-1) inhibits the germination of B. sorokiniana spores under controlled laboratory conditions. To assess the effect of MeJA (150 mg L^-1) in combination with the biocontrol agent T. harzianum UBSTH-501 in vivo, a green house experiment was conducted. For this, biocontrol agent T. harzianum UBSTH-501 was applied as seed treatment, whereas MeJA (150 mg L^-1) was applied 5 days prior to pathogen inoculation. Results indicated that application of MeJA (150 mg L^-1) did not affect the root colonization of wheat by T. harzianum UBSTH-501 in the rhizosphere. The combined application of T. harzianum UBSTH-501 and MeJA also enhanced indole acetic acid production in the rhizosphere (4.92 μg g^-1 of soil) which in turn helps in plant growth and development. Further, the combined application found to enhance the activities of defense related enzymes viz. catalase (5.92 EU min^-1 g^-1 fresh wt.), ascorbate peroxidase [μmol ascorbate oxidized (mg prot)^-1 min^-1], phenylalanine ammonia lyase (102.25 μmol cinnamic acid h^-1 mg^-1 fresh wt.) and peroxidase (6.95 Unit mg^-1 min^-1 fresh wt.) significantly in the plants under treatment which was further confirmed by assessing the transcript level of PAL and peroxidase genes using semi-quantitative PCR approach. The results showed manifold increase in salicylic acid (SA) along with enhanced accumulation of total free phenolics, ferulic acid, caffeic acid, coumaric acid, and chlorogenic acid in the leaves of the plants treated with the biocontrol agent alone or in combination with MeJA. A significant decrease in the disease severity (17.46%) and area under disease progress curve (630.32) were also observed in the treatments with biocontrol agent and MeJA in combination as compared to B. sorokiniana alone treated plant (56.95% and 945.50, respectively). Up-regulation of phenylpropanoid cascades in response to exogenous application of MeJA and the biocontrol agent was observed. It was depicted from the results that PAL is the primary route for lignin production in wheat which reduces cell wall disruption and tissue disintegration and increases suberization and lignification of the plant cell as seen by Scanning Electron microphotographs. These results clearly indicated that exogenous application of MeJA with T. harzianum inducing JA- and/or SA-dependent defense signaling after pathogen challenge may increase the resistance to spot blotch by stimulating enzymatic activities and the accumulation of phenolic compounds in a cooperative manner. This study apparently provides the evidence of biochemical cross-talk and physiological responses in wheat following MeJA and biocontrol agent treatment during the bio-trophic infection.

A halotolerant growth promoting rhizobacteria triggers induced systemic resistance in plants and defends against fungal infection

A halotolerant rhizobacteria, Klebsiella species (referred to MBE02), was identified that had a growth stimulation effect on peanut. To gain mechanistic insights into how molecular components were reprogrammed during the interaction of MBE02 and peanut roots, we performed deep RNA-sequencing. In total, 1260 genes were differentially expressed: 979 genes were up-regulated, whereas 281 were down-regulated by MBE02 treatment as compared to uninoculated controls. A large component of the differentially regulated genes were related to phytohormone signalling. This included activation of a significant proportion of genes involved in jasmonic acid, ethylene and pathogen-defense signalling, which indicated a role of MBE02 in modulating plant immunity. In vivo and in vitro pathogenesis assays demonstrated that MBE02 treatment indeed provide fitness benefits to peanut against Aspergillus infection under controlled as well as field environment. Further, MBE02 directly reduced the growth of a wide range of fungal pathogens including Aspergillus. We also identified possible molecular components involved in rhizobacteria-mediated plant protection. Our results show the potential of MBE02 as a biocontrol agent in preventing infection against several fungal phytopathogens.

Wheat phenolics suppress doxorubicin-induced cardiotoxicity via inhibition of oxidative stress, MAP kinase activation, NF-κB pathway, PI3K/Akt/mTOR impairment, and cardiac apoptosis

The present investigation has been undertaken to reveal the protective mechanism of polyphenolics extract of whole wheat grains (WWGPE), ferulic acid and apigenin against doxorubicin (Dox)-induced cardio-toxicity. WWGPE, apigenin, and ferulic acid exhibited concentration dependent cyto-protective effect against Dox (1 μM) in rat cardiomyocytes. Dox treatment significantly (p < 0.01) induced oxidative stress in the myocardial cells via excessive ROS production, increase in iNOS expression, NADPH oxidase activation, Nrf-2/HO-1 impairment, and inactivation of cellular redox defense system. In addition, Dox significantly (p < 0.01) activated MAP kinases, NF-κB, and apoptosis in cardiac cells; while, significant (p < 0.01) impairment in PI3K/Akt/mTOR signaling was observed in Dox-treated myocardial cells. On the other hand, WWGPE, apigenin, and ferulic acid significantly (p < 0.05-0.01) attenuated Dox-induced redox stress and oxidative stress-mediated signal transduction in myocardial cells. WWGPE, apigenin, and ferulic acid treatment also could significantly (p < 0.05-0.01) reinstate Dox-mediated changes in blood parameters in rats. Histological assessments were in agreement with the biochemical findings. Results showed that, WWGPE exhibited better cardio-protective effect over ferulic acid and apigenin, which may be due to the synergy between the comprising compounds and better oral bioavailability of dietary antioxidant molecules from whole phenolic extract.

Gracilaria dura extract confers drought tolerance in wheat by modulating abscisic acid homeostasis

Water stress severely reduces the production of wheat. Application of seaweed extracts have started to show promise in protecting plants from environmental stresses as they contain several biostimulants. However, the modes of action of these biostimulants are not clear. Here, we investigated the role of Gracilaria dura (GD), a red alga, in conferring stress tolerance to wheat during drought under glasshouse and agro-ecological conditions by integrating molecular studies with physiological and field investigations. GD-sap application conferred drought tolerance (as the biomass increased by up to 57% and crop yield by 70%), via facilitating physiological changes associated to maintaining higher water content. GD-sap application significantly increased ABA accumulation (2.34 and 1.46 fold at 4 and 6 days of drought, respectively) due to enhanced expression of biosynthesis genes. This followed an activation of ABA response genes and physiological processes including reduced stomatal opening, thus reducing water loss. Moreover, GD-sap application enhanced the expression of stress-protective genes specifically under water stress. Treatment with fluridone, an ABA inhibitor, further support the role of ABA in GD-sap mediated drought tolerance in wheat. The findings of this study provide insights into the functional role of GD-sap in improving drought tolerance and show the potential to commercialize GD-sap as a potent biostimulant for sustainable agriculture in regions prone to drought.

Natural Variation in Elicitation of Defense-Signaling Associates to Field Resistance Against the Spot Blotch Disease in Bread Wheat (Triticum aestivum L.)

Spot blotch, caused by the hemibiotropic fungus Bipolaris sorokiniana, is amongst the most damaging diseases of wheat. Still, natural variation in expression of biochemical traits that determine field resistance to spot blotch in wheat remain unaddressed. To understand how genotypic variations relate to metabolite profiles of the components of defense-signaling and the plant performance, as well as to discover novel sources of resistance against spot blotch, we have conducted field studies using 968 wheat genotypes at 5 geographical locations in South-Asia in 2 years. 46 genotypes were identified as resistant. Further, in independent confirmatory trials in subsequent 3 years, over 5 geographical locations, we re-characterized 55 genotypes for their resistance (above 46 along with Yangmai#6, a well characterized resistant genotype, and eight susceptible genotypes). We next determined time-dependent spot blotch-induced metabolite profiles of components of defense-signaling as well as levels of enzymatic components of defense pathway (such as salicylic acid (SA), phenolic acids, and redox components), and derived co-variation patterns with respect to resistance in these 55 genotypes. Spot blotch-induced SA accumulation was negatively correlated to disease progression. Amongst phenolic acids, syringic acid was most strongly inversely correlated to disease progression, indicating a defensive function, which was independently confirmed. Thus, exploring natural variation proved extremely useful in determining traits influencing phenotypic plasticity and adaptation to complex environments. Further, by overcoming environmental heterogeneity, our study identifies germplasm and biochemical traits that are deployable for spot blotch resistance in wheat along South-Asia.

Genome-wide characterization of cellulases from the hemi-biotrophic plant pathogen, Bipolaris sorokiniana, reveals the presence of a highly stable GH7 endoglucanase

BACKGROUND

Bipolaris sorokiniana is a filamentous fungus that causes spot blotch disease in cereals like wheat and has severe economic consequences. However, information on the identities and role of the cell wall-degrading enzymes (CWDE) in B. sorokiniana is very limited. Several fungi produce CWDE like glycosyl hydrolases (GHs) that help in host cell invasion. To understand the role of these CWDE in B. sorokiniana, the first step is to identify and annotate all possible genes of the GH families like GH3, GH6, GH7, GH45 and AA9 and then characterize them biochemically.

RESULTS

We confirmed and annotated the homologs of GH3, GH6, GH7, GH45 and AA9 enzymes in the B. sorokiniana genome using the sequence and domain features of these families. Quantitative real-time PCR analyses of these homologs revealed that the transcripts of the BsGH7-3 (3rd homolog of the GH 7 family in B. sorokiniana) were most abundant. BsGH7-3, the gene of BsGH7-3, was thus cloned into pPICZαC Pichia pastoris vector and expressed in X33 P. pastoris host to be characterized. BsGH7-3 enzyme showed a temperature optimum of 60 °C and a pH_opt of 8.1. BsGH7-3 was identified to be an endoglucanase based on its broad substrate specificity and structural comparisons with other such endoglucanases. BsGH7-3 has a very long half-life and retains 100% activity even in the presence of 4 M NaCl, 4 M KCl and 20% (v/v) ionic liquids. The enzyme activity is stimulated up to fivefold in the presence of Mn⁺² and Fe⁺² without any deleterious effects on enzyme thermostability.

CONCLUSIONS

Here we reanalysed the B. sorokiniana genome and selected one GH7 enzyme for further characterization. The present work demonstrates that BsGH7-3 is an endoglucanase with a long half-life and no loss in activity in the presence of denaturants like salt and ionic liquids, and lays the foundation towards exploring the Bipolaris genome for other cell wall-degrading enzymes.