Ethylene modulates the role of NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 in cross talk between salicylate and jasmonate signaling

SA and NHP glucosyltransferase UGT76B1 affects plant defense in both SID2- and NPR1-dependent and independent manner

KEY MESSAGE

The small-molecule glucosyltransferase loss-of-function mutant ugt76b1 exhibits both SID2- or NPR1-dependent and independent facets of enhanced plant immunity, whereupon FMO1 is required for the SID2 and NPR1 independence. The small-molecule glucosyltransferase UGT76B1 inactivates salicylic acid (SA), isoleucic acid (ILA), and N-hydroxypipecolic acid (NHP). ugt76b1 loss-of-function plants manifest an enhanced defense status. Thus, we were interested how UGT76B1 genetically integrates in defense pathways and whether all impacts depend on SA and NHP. We study the integration of UGT76B1 by transcriptome analyses of ugt76b1. The comparison of transcripts altered by the loss of UGT76B1 with public transcriptome data reveals both SA-responsive, ISOCHORISMATE SYNTHASE 1/SALICYLIC ACID INDUCTION DEFICIENT 2 (ICS1/SID2)- and NON EXPRESSOR OF PR GENES 1 (NPR1)-dependent, consistent with the role of UGT76B1 in glucosylating SA, and SA-non-responsive, SID2/NPR1-independent genes. We also discovered that UGT76B1 impacts on a group of genes showing non-SA-responsiveness and regulation by infections independent from SID2/NPR1. Enhanced resistance of ugt76b1 against Pseudomonas syringae is partially independent from SID2 and NPR1. In contrast, the ugt76b1-activated resistance is completely dependent on FMO1 encoding the NHP-synthesizing FLAVIN-DEPENDENT MONOOXYGENASE 1). Moreover, FMO1 ranks top among the ugt76b1-induced SID2- and NPR1-independent pathogen responsive genes, suggesting that FMO1 determines the SID2- and NPR1-independent effect of ugt76b1. Furthermore, the genetic study revealed that FMO1, ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), SID2, and NPR1 are required for the SA-JA crosstalk and senescence development of ugt76b1, indicating that EDS1 and FMO1 have a similar effect like stress-induced SA biosynthesis (SID2) or the key SA signaling regulator NPR1. Thus, UGT76B1 influences both SID2/NPR1-dependent and independent plant immunity, and the SID2/NPR1 independence is relying on FMO1 and its product NHP, another substrate of UGT76B1.

Salicylic acid in plant immunity and beyond

As the most widely used herbal medicine in human history and a major defence hormone in plants against a broad spectrum of pathogens and abiotic stresses, salicylic acid (SA) has attracted major research interest. With applications of modern technologies over the past 30 years, studies of the effects of SA on plant growth, development, and defence have revealed many new research frontiers and continue to deliver surprises. In this review, we provide an update on recent advances in our understanding of SA metabolism, perception, and signal transduction mechanisms in plant immunity. An overarching theme emerges that SA executes its many functions through intricate regulation at multiple steps: SA biosynthesis is regulated both locally and systemically, while its perception occurs through multiple cellular targets, including metabolic enzymes, redox regulators, transcription cofactors, and, most recently, an RNA-binding protein. Moreover, SA orchestrates a complex series of post-translational modifications of downstream signaling components and promotes the formation of biomolecular condensates that function as cellular signalling hubs. SA also impacts wider cellular functions through crosstalk with other plant hormones. Looking into the future, we propose new areas for exploration of SA functions, which will undoubtedly uncover more surprises for many years to come.

Antagonistic control of rice immunity against distinct pathogens by the two transcription modules via salicylic acid and jasmonic acid pathways

Although the antagonistic effects of host resistance against biotrophic and necrotrophic pathogens have been documented in various plants, the underlying mechanisms are unknown. Here, we investigated the antagonistic resistance mediated by the transcription factor ETHYLENE-INSENSITIVE3-LIKE 3 (OsEIL3) in rice. The Oseil3 mutant confers enhanced resistance to the necrotroph Rhizoctonia solani but greater susceptibility to the hemibiotroph Magnaporthe oryzae and biotroph Xanthomonas oryzae pv. oryzae. OsEIL3 directly activates OsERF040 transcription while repressing OsWRKY28 transcription. The infection of R. solani and M. oryzae or Xoo influences the extent of binding of OsEIL3 to OsWRKY28 and OsERF040 promoters, resulting in the repression or activation of both salicylic acid (SA)- and jasmonic acid (JA)-dependent pathways and enhanced susceptibility or resistance, respectively. These results demonstrate that the distinct effects of plant immunity to different pathogen types are determined by two transcription factor modules that control transcriptional reprogramming and the SA and JA pathways.

Defense signaling pathways in resistance to plant viruses: Crosstalk and finger pointing

Resistance to infection by plant viruses involves proteins encoded by plant resistance (R) genes, viz., nucleotide-binding leucine-rich repeats (NLRs), immune receptors. These sensor NLRs are activated either directly or indirectly by viral protein effectors, in effector-triggered immunity, leading to induction of defense signaling pathways, resulting in the synthesis of numerous downstream plant effector molecules that inhibit different stages of the infection cycle, as well as the induction of cell death responses mediated by helper NLRs. Early events in this process involve recognition of the activation of the R gene response by various chaperones and the transport of these complexes to the sites of subsequent events. These events include activation of several kinase cascade pathways, and the syntheses of two master transcriptional regulators, EDS1 and NPR1, as well as the phytohormones salicylic acid, jasmonic acid, and ethylene. The phytohormones, which transit from a primed, resting states to active states, regulate the remainder of the defense signaling pathways, both directly and by crosstalk with each other. This regulation results in the turnover of various suppressors of downstream events and the synthesis of various transcription factors that cooperate and/or compete to induce or suppress transcription of either other regulatory proteins, or plant effector molecules. This network of interactions results in the production of defense effectors acting alone or together with cell death in the infected region, with or without the further activation of non-specific, long-distance resistance. Here, we review the current state of knowledge regarding these processes and the components of the local responses, their interactions, regulation, and crosstalk.

Eco-friendly managements and molecular mechanisms for improving postharvest quality and extending shelf life of kiwifruit: A review

Kiwifruit (Actinidia spp.) is a commercially important horticultural fruit crop worldwide. Kiwifruit contains numerous minerals, vitamins, and dietary phytochemicals, that not only responsible for the flavor but can also serve as adjuncts in the treatment of diabetes, digestive disorders, cardiovascular system, cancer and heart disease. However, fruit quality and shelf life affect consumer's acceptance and production chain. Understanding the methods of fruit storage preservation, as well as their biochemical, physiological, and molecular basis is essential. In recent years, eco-friendly (comprehensive and environmentally friendly) treatments such as hot water, ozone, chitosan, quercetin, and antifungal additive from biocontrol bacteria or yeast have been applied to improve postharvest fruit quality with longer shelf life. This review provides a comprehensive overview of the latest advancements in control measures, applications, and mechanisms related to water loss, chilling injury, and pathogen diseases in postharvest kiwifruit. Further studies should utilize genome editing techniques to enhance postharvest fruit quality and disease resistance through site-directed bio-manipulation of the kiwifruit genome.

Lipoxygenases regulate digestive enzyme inhibitor activities in developing seeds of field-grown soybean against the southern green stink bug (Nezara viridula)

Soybean (Glycine max ) is the world's most widely grown seed legume. One of the most important pests that decrease seed quality and reduce yield of soybean crops is the southern green stink bug (Nezara viridula ). Insect damage triggers accumulation of defensive compounds such as protease inhibitors (PIs), isoflavonoids and reactive oxygen species, which are regulated by the lipoxygenase (LOX)-regulated jasmonic acid (JA) to stop insect feeding. This study identified and characterised the role of LOX isoforms in the modulation of chemical defences in seeds of field-grown soybean that decreased digestive enzyme activities of N. viridula after insect attack. Stink bugs attack increased LOX 1 and LOX 2 expression, and activities of LOX 1 and LOX 3 isoenzymes in developing soybean seeds. In addition, stink bug damage and methyl jasmonate application induced expression and activity of both cysteine PIs and trypsin PIs in developing soybean seeds, suggesting that herbivory induced JA in soybean seeds. High PI activity levels in attacked seeds decreased cysteine proteases and α-amylases activities in the gut of stink bugs that fed on field-grown soybean. We demonstrated that LOX isoforms of seeds are concomitantly induced with JA-regulated PIs by stink bugs attack, and these PIs inhibit the activity of insect digestive enzymes. To our knowledge, this is the first study to investigate the participation of LOX in modulating JA-regulated defences against stink bugs in seeds of field-grown soybean, and our results suggest that soybean PIs may inhibit α-amylase activity in the gut of N. viridula .

Deciphering the mechanisms, hormonal signaling, and potential applications of endophytic microbes to mediate stress tolerance in medicinal plants

The global healthcare market in the post-pandemic era emphasizes a constant pursuit of therapeutic, adaptogenic, and immune booster drugs. Medicinal plants are the only natural resource to meet this by supplying an array of bioactive secondary metabolites in an economic, greener and sustainable manner. Driven by the thrust in demand for natural immunity imparting nutraceutical and life-saving plant-derived drugs, the acreage for commercial cultivation of medicinal plants has dramatically increased in recent years. Limited resources of land and water, low productivity, poor soil fertility coupled with climate change, and biotic (bacteria, fungi, insects, viruses, nematodes) and abiotic (temperature, drought, salinity, waterlogging, and metal toxicity) stress necessitate medicinal plant productivity enhancement through sustainable strategies. Plants evolved intricate physiological (membrane integrity, organelle structural changes, osmotic adjustments, cell and tissue survival, reclamation, increased root-shoot ratio, antibiosis, hypersensitivity, etc.), biochemical (phytohormones synthesis, proline, protein levels, antioxidant enzymes accumulation, ion exclusion, generation of heat-shock proteins, synthesis of allelochemicals. etc.), and cellular (sensing of stress signals, signaling pathways, modulating expression of stress-responsive genes and proteins, etc.) mechanisms to combat stresses. Endophytes, colonizing in different plant tissues, synthesize novel bioactive compounds that medicinal plants can harness to mitigate environmental cues, thus making the agroecosystems self-sufficient toward green and sustainable approaches. Medicinal plants with a host set of metabolites and endophytes with another set of secondary metabolites interact in a highly complex manner involving adaptive mechanisms, including appropriate cellular responses triggered by stimuli received from the sensors situated on the cytoplasm and transmitting signals to the transcriptional machinery in the nucleus to withstand a stressful environment effectively. Signaling pathways serve as a crucial nexus for sensing stress and establishing plants' proper molecular and cellular responses. However, the underlying mechanisms and critical signaling pathways triggered by endophytic microbes are meager. This review comprehends the diversity of endophytes in medicinal plants and endophyte-mediated plant-microbe interactions for biotic and abiotic stress tolerance in medicinal plants by understanding complex adaptive physiological mechanisms and signaling cascades involving defined molecular and cellular responses. Leveraging this knowledge, researchers can design specific microbial formulations that optimize plant health, increase nutrient uptake, boost crop yields, and support a resilient, sustainable agricultural system.

Global transcriptome analysis reveals fungal disease responsive core gene regulatory landscape in tea

Fungal infections are the inevitable limiting factor for productivity of tea. Transcriptome reprogramming recruits multiple regulatory pathways during pathogen infection. A comprehensive meta-analysis was performed utilizing previously reported, well-replicated transcriptomic datasets from seven fungal diseases of tea. The study identified a cumulative set of 18,517 differentially expressed genes (DEGs) in tea, implicated in several functional clusters, including the MAPK signaling pathway, transcriptional regulation, and the biosynthesis of phenylpropanoids. Gene set enrichment analyses under each pathogen stress elucidated that DEGs were involved in ethylene metabolism, secondary metabolism, receptor kinase activity, and various reactive oxygen species detoxification enzyme activities. Expressional fold change of combined datasets highlighting 2258 meta-DEGs shared a common transcriptomic response upon fungal stress in tea. Pervasive duplication events caused biotic stress-responsive core DEGs to appear in multiple copies throughout the tea genome. The co-expression network of meta-DEGs in multiple modules demonstrated the coordination of appropriate pathways, most of which involved cell wall organization. The functional coordination was controlled by a number of hub genes and miRNAs, leading to pathogenic resistance or susceptibility. This first-of-its-kind meta-analysis of host-pathogen interaction generated consensus candidate loci as molecular signatures, which can be associated with future resistance breeding programs in tea.

Arbuscular mycorrhizal fungi-mediated activation of plant defense responses in direct seeded rice (Oryza sativa L.) against root-knot nematode Meloidogyne graminicola

Rhizosphere is the battlefield of beneficial and harmful (so called phytopathogens) microorganisms. Moreover, these microbial communities are struggling for their existence in the soil and playing key roles in plant growth, mineralization, nutrient cycling and ecosystem functioning. In the last few decades, some consistent pattern have been detected so far that link soil community composition and functions with plant growth and development; however, it has not been studied in detail. AM fungi are model organisms, besides potential role in nutrient cycling; they modulate biochemical pathways directly or indirectly which lead to better plant growth under biotic and abiotic stress conditions. In the present investigations, we have elucidated the AM fungi-mediated activation of plant defense responses against Meloidogyne graminicola causing root-knot disease in direct seeded rice (Oryza sativa L.). The study describes the multifarious effects of Funneliformis mosseae, Rhizophagus fasciculatus, and Rhizophagus intraradices inoculated individually or in combination under glasshouse conditions in rice plants. It was found that F. mosseae, R. fasciculatus and R. intraradices when applied individually or in combination modulated the biochemical and molecular mechanisms in the susceptible and resistant inbred lines of rice. AM inoculation significantly increased various plant growth attributes in plants with simultaneous decrease in the root-knot intensity. Among these, the combined application of F. mosseae, R. fasciculatus, and R. intraradices was found to enhance the accumulation and activities of biomolecules and enzymes related to defense priming as well as antioxidation in the susceptible and resistant inbred lines of rice pre-challenged with M. graminicola. The application of F. mosseae, R. fasciculatus and R. intraradices, induced the key genes involved in plant defense and signaling and it has been demonstrated for the first time. Results of the present investigation advocated that the application of F. mosseae, R. fasciculatus and R. intraradices, particularly a combination of all three, not only helped in the control of root-knot nematodes but also increased plant growth as well as enhances the gene expression in rice. Thus, it proved to be an excellent biocontrol as well as plant growth-promoting agent in rice even when the crop is under biotic stress of the root-knot nematode, M. graminicola.

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.

Ethylene: A Master Regulator of Plant-Microbe Interactions under Abiotic Stresses

The plant phytohormone ethylene regulates numerous physiological processes and contributes to plant-microbe interactions. Plants induce ethylene production to ward off pathogens after recognition of conserved microbe-associated molecular patterns (MAMPs). However, plant immune responses against pathogens are essentially not different from those triggered by neutral and beneficial microbes. Recent studies indicate that ethylene is an important factor for beneficial plant-microbial association under abiotic stress such as salt and heat stress. The association of beneficial microbes with plants under abiotic stresses modulates ethylene levels which control the expression of ethylene-responsive genes (ERF), and ERFs further regulate the plant transcriptome, epi-transcriptome, Na⁺/K⁺ homeostasis and antioxidant defense mechanisms against reactive oxygen species (ROS). Understanding ethylene-dependent plant-microbe interactions is crucial for the development of new strategies aimed at enhancing plant tolerance to harsh environmental conditions. In this review, we underline the importance of ethylene in beneficial plant-microbe interaction under abiotic stresses.

Ambivalent response in pathogen defense: A double-edged sword?

Plants possess effective immune systems that defend against most microbial attackers. Recent plant immunity research has focused on the classic binary defense model involving the pivotal role of small-molecule hormones in regulating the plant defense signaling network. Although most of our current understanding comes from studies that relied on information derived from a limited number of pathosystems, newer studies concerning the incredibly diverse interactions between plants and microbes are providing additional insights into other novel mechanisms. Here, we review the roles of both classical and more recently identified components of defense signaling pathways and stress hormones in regulating the ambivalence effect during responses to diverse pathogens. Because of their different lifestyles, effective defense against biotrophic pathogens normally leads to increased susceptibility to necrotrophs, and vice versa. Given these opposing forces, the plant potentially faces a trade-off when it mounts resistance to a specific pathogen, a phenomenon referred to here as the ambivalence effect. We also highlight a novel mechanism by which translational control of the proteins involved in the ambivalence effect can be used to engineer durable and broad-spectrum disease resistance, regardless of the lifestyle of the invading pathogen.

Endophytes and their potential in biotic stress management and crop production

Biotic stress is caused by harmful microbes that prevent plants from growing normally and also having numerous negative effects on agriculture crops globally. Many biotic factors such as bacteria, fungi, virus, weeds, insects, and nematodes are the major constrains of stress that tends to increase the reactive oxygen species that affect the physiological and molecular functioning of plants and also led to the decrease in crop productivity. Bacterial and fungal endophytes are the solution to overcome the tasks faced with conventional farming, and these are environment friendly microbial commodities that colonize in plant tissues without causing any damage. Endophytes play an important role in host fitness, uptake of nutrients, synthesis of phytohormone and diminish the injury triggered by pathogens via antibiosis, production of lytic enzymes, secondary metabolites, and hormone activation. They are also reported to help plants in coping with biotic stress, improving crops and soil health, respectively. Therefore, usage of endophytes as biofertilizers and biocontrol agent have developed an eco-friendly substitute to destructive chemicals for plant development and also in mitigation of biotic stress. Thus, this review highlighted the potential role of endophytes as biofertilizers, biocontrol agent, and in mitigation of biotic stress for maintenance of plant development and soil health for sustainable agriculture.

Brassinosteroids enhance salicylic acid-mediated immune responses by inhibiting BIN2 phosphorylation of clade I TGA transcription factors in Arabidopsis

Salicylic acid (SA) plays an important role in plant immune response, including resistance to pathogens and systemic acquired resistance. Two major components, NONEXPRESSOR OF PATHOGENESIS-RELATED GENES (NPRs) and TGACG motif-binding transcription factors (TGAs), are known to mediate SA signaling, which might also be orchestrated by other hormonal and environmental changes. Nevertheless, the molecular and functional interactions between SA signaling components and other cellular signaling pathways remain poorly understood. Here we showed that the steroid plant hormone brassinosteroid (BR) promotes SA responses by inactivating BR-INSENSITIVE 2 (BIN2), which inhibits the redox-sensitive clade I TGAs in Arabidopsis. We found that both BR and the BIN2 inhibitor bikinin synergistically increase SA-mediated physiological responses, such as resistance to Pst DC3000. Our genetic and biochemical analyses indicated that BIN2 functionally interacts with TGA1 and TGA4, but not with other TGAs. We further demonstrated that BIN2 phosphorylates Ser-202 of TGA4, resulting in the suppression of the redox-dependent interaction between TGA4 and NPR1 as well as destabilization of TGA4. Consistently, transgenic Arabidopsis overexpressing TGA4-YFP with a S202A mutation displayed enhanced SA responses compared to the wild-type TGA4-YFP plants. Taken together, these results suggest a novel crosstalk mechanism by which BR signaling coordinates the SA responses mediated by redox-sensitive clade I TGAs.

AUXIN RESPONSE FACTOR 16 (StARF16) regulates defense gene StNPR1 upon infection with necrotrophic pathogen in potato

We demonstrate a new regulatory mechanism in the jasmonic acid (JA) and salicylic acid (SA) mediated crosstalk in potato defense response, wherein, miR160 target StARF16 (a gene involved in growth and development) binds to the promoter of StNPR1 (a defense gene) and negatively regulates its expression to suppress the SA pathway. Overall, our study establishes the importance of StARF16 in regulation of StNPR1 during JA mediated defense response upon necrotrophic pathogen interaction. Plants employ antagonistic crosstalk between salicylic acid (SA) and jasmonic acid (JA) to effectively defend them from pathogens. During biotrophic pathogen attack, SA pathway activates and suppresses the JA pathway via NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1). However, upon necrotrophic pathogen attack, how JA-mediated defense response suppresses the SA pathway, is still not well-understood. Recently StARF10 (AUXIN RESPONSE FACTOR), a miR160 target, has been shown to regulate SA and binds to the promoter of StGH3.6 (GRETCHEN HAGEN3), a gene proposed to maintain the balance between the free SA and auxin in plants. In the current study, we investigated the role of StARF16 (a miR160 target) in the regulation of the defense gene StNPR1 in potato upon activation of the JA pathway. We observed that a negative correlation exists between StNPR1 and StARF16 upon infection with the pathogen. The results were further confirmed through the exogenous application of SA and JA. Using yeast one-hybrid assay, we demonstrated that StARF16 binds to the StNPR1 promoter through putative ARF binding sites. Additionally, through protoplast transfection and chromatin immunoprecipitation experiments, we showed that StARF16 could bind to the StNPR1 promoter and regulate its expression. Co-transfection assays using promoter deletion constructs established that ARF binding sites are present in the 2.6 kb sequence upstream to the StNPR1 gene and play a key role in its regulation during infection. In summary, we demonstrate the importance of StARF16 in the regulation of StNPR1, and thus SA pathway, during JA-mediated defense response upon necrotrophic pathogen interaction.

Signal Transduction in Cereal Plants Struggling with Environmental Stresses: From Perception to Response

Cereal plants under abiotic or biotic stressors to survive unfavourable conditions and continue growth and development, rapidly and precisely identify external stimuli and activate complex molecular, biochemical, and physiological responses. To elicit a response to the stress factors, interactions between reactive oxygen and nitrogen species, calcium ions, mitogen-activated protein kinases, calcium-dependent protein kinases, calcineurin B-like interacting protein kinase, phytohormones and transcription factors occur. The integration of all these elements enables the change of gene expression, and the release of the antioxidant defence and protein repair systems. There are still numerous gaps in knowledge on these subjects in the literature caused by the multitude of signalling cascade components, simultaneous activation of multiple pathways and the intersection of their individual elements in response to both single and multiple stresses. Here, signal transduction pathways in cereal plants under drought, salinity, heavy metal stress, pathogen, and pest attack, as well as the crosstalk between the reactions during double stress responses are discussed. This article is a summary of the latest discoveries on signal transduction pathways and it integrates the available information to better outline the whole research problem for future research challenges as well as for the creative breeding of stress-tolerant cultivars of cereals.

The Crosstalk of the Salicylic Acid and Jasmonic Acid Signaling Pathways Contributed to Different Resistance to Phytoplasma Infection Between the Two Genotypes in Chinese Jujube

Jujube witches’ broom disease (JWB), one of the most serious phytoplasma diseases, usually results in the destruction of Chinese jujube (Ziziphus jujuba Mill.). Although most jujube cultivars are sensitive to JWB, we found a few genotypes that are highly resistant to JWB. However, the molecular mechanism of phytoplasma resistance has seldom been studied. Here, we used Chinese jujube “T13,” which has strong resistance to JWB, and a typical susceptible cultivar, “Pozao” (“PZ”), as materials to perform comparative transcriptome, hormone, and regulation analyses. After phytoplasma infection, the differential expression genes (DEGs) were detected at all three growth phases (S1, S2, and S3) in “PZ,” but DEGs were detected only at the first growth phase in “T13.” Meanwhile, no phytoplasma was detected, and the symptoms especially witches’ broom caused by JWB were not observed at the last two growth phases (S2 and S3) in “T13.” Protein–protein interaction analysis also showed that the key genes were mainly involved in hormone and reactive oxygen species (ROS) signaling. In addition, during the recovered growth phase in “T13” from S1 to S2, the level of hydrogen peroxide (H₂O₂) was significantly increased and then decreased from S2 to S3. Moreover, jasmonic acid (JA) was significantly accumulated in “PZ” diseased plants, especially at the S2 phase and at the S2 phase in “T13,” while the content of salicylic acid (SA) decreased significantly at the S2 phase of “T13” compared to that in “PZ.” The changes in H₂O₂ and JA or SA were consistent with the changes in their key synthesis genes in the transcriptome data. Finally, exogenous application of an SA inhibitor [1-aminobenzotriazole (ABT)] rescued witches’ broom symptoms, while the contents of both JA and MeJA increased after ABT treatment compared to the control, demonstrating that exogenous application of an SA inhibitor rescued the symptoms of jujube after phytoplasma infection by decreasing the contents of SA and increasing the contents of JA and MeJA. Collectively, our study provides a new perspective on the transcriptional changes of Chinese jujube in response to JWB and novel insights that the crosstalk of JA and SA signaling communicated together to contribute to “T13” JWB resistance.

(+)-Catechin, epicatechin and epigallocatechin gallate are important inducible defensive compounds against Ectropis grisescens in tea plants

The tea plant, Camellia sinensis (L.) O. Kuntze, is an economically important, perennial woody plant rich in catechins. Although catechins have been reported to play an important role in plant defences against microbes, their roles in the defence of tea plants against herbivores remain unknown. In this study, we allowed the larvae of Ectropis grisescens, a leaf-feeding pest, to feed on the plants, and alternatively, we wounded the plants and then treated them with E. grisescens oral secretions (WOS). Both approaches triggered jasmonic acid-, ethylene- and auxin-mediated signalling pathways; as a result, plants accumulated three catechin compounds: (+)-catechin, epicatechin and epigallocatechin. Not only was the mass of E. grisescens larvae fed on plants previously infested with E. grisescens or treated with WOS significantly lower than that of larvae fed on controls, but also artificial diet supplemented with epicatechin, (+)-catechin or epigallocatechin gallate reduced larval growth rates. In addition, the exogenous application of jasmonic acid, ethylene or auxin induced the biosynthesis of the three catechins, which, in turn, enhanced the resistance of tea plants to E. grisescens, leading to the coordination of the three signalling pathways. Our results suggest that the three catechins play an important role in the defences of tea plants against E. grisescens.

Tomato Prosystemin Is Much More than a Simple Systemin Precursor

Simple Summary

Prosystemin is a 200 amino acid precursor that releases, upon wounding and biotic attacks, an 18 amino acid peptide called Systemin. This peptide was traditionally considered as the principal actor of the resistance of tomato plants induced by triggering multiple defense pathways in response to a wide range of biotic/abiotic stress agents. Recent findings from our group discovered the disordered structure of Prosystemin that promotes the binding of different molecular partners and the possible activation of multiple stress-related pathways. All of our recent findings suggest that Prosystemin could be more than a simple precursor of Systemin peptide. Indeed, we hypothesized that it contains other sequences able to activate multiple stress-related responses. To verify this hypothesis, we produced a truncated Prosystemin protein deprived of the Systemin peptide and the relative deleted gene. Experiments with transgenic tomato plants overexpressing the truncated Prosystemin and with plants exogenously treated with the recombinant truncated protein demonstrated that both transgenic and treated plants modulated the expression of defense-related genes and were protected against a noctuid moth and a fungal pathogen. Taken together, our results demonstrated that Prosystemin is not a mere scaffold of Systemin, but itself contains other biologically active regions.

Abstract

Systemin (Sys) is an octadecapeptide, which upon wounding, is released from the carboxy terminus of its precursor, Prosystemin (ProSys), to promote plant defenses. Recent findings on the disordered structure of ProSys prompted us to investigate a putative biological role of the whole precursor deprived of the Sys peptide. We produced transgenic tomato plants expressing a truncated ProSys gene in which the exon coding for Sys was removed and compared their defense response with that induced by the exogenous application of the recombinant truncated ProSys (ProSys_(1-178), the Prosystemin sequence devoid of Sys region). By combining protein structure analyses, transcriptomic analysis, gene expression profiling and bioassays with different pests, we demonstrate that truncated ProSys promotes defense barriers in tomato plants through a hormone-independent defense pathway, likely associated with the production of oligogalacturonides (OGs). Both transgenic and plants treated with the recombinant protein showed the modulation of the expression of genes linked with defense responses and resulted in protection against the lepidopteran pest Spodoptera littoralis and the fungus Botrytis cinerea. Our results suggest that the overall function of the wild-type ProSys is more complex than previously shown, as it might activate at least two tomato defense pathways: the well-known Sys-dependent pathway connected with the induction of jasmonic acid biosynthesis and the successive activation of a set of defense-related genes, and the ProSys_(1-178)-dependent pathway associated with OGs production leading to the OGs mediate plant immunity.

MYC2 influences salicylic acid biosynthesis and defense against bacterial pathogens in Arabidopsis thaliana

Arabidopsis MYC2 is a basic helix-loop-helix transcription factor that works both as a negative and positive regulator of light and multiple hormonal signaling pathways, including jasmonic acid and abscisic acid. Recent studies have suggested the role of MYC2 as a negative regulator of salicylic acid (SA)-mediated defense against bacterial pathogens. By using myc2 mutant and constitutively MYC2-expressing plants, we further show that MYC2 also positively influences SA-mediated defense; whereas, myc2 mutant plants are resistant to virulent pathogens only, MYC2 over-expressing plants are hyper-resistant to multiple virulent and avirulent strains of bacterial pathogens. MYC2 promotes pathogen-induced callose deposition, SA biosynthesis, expression of PR1 gene, and SA-responsiveness. Using bacterially produced MYC2 protein in electrophoretic mobility shift assay (EMSA), we have shown that MYC2 binds to the promoter of several important defense regulators, including PEPR1, MKK4, RIN4, and the second intron of ICS1. MYC2 positively regulates the expression of RIN4, MKK4, and ICS1; however, it negatively regulates the expression of PEPR1. Pathogen inoculation enhances MYC2 association at ICS1 intron and RIN4 promoter. Mutations of MYC2 binding site at ICS1 intron or RIN4 promoter abolish the associated GUS reporter expression. Hyper-resistance of MYC2 over-expressing plants is largely light-dependent, which is in agreement with the role of MYC2 in SA biosynthesis. The results altogether demonstrate that MYC2 possesses dual regulatory roles in SA biosynthesis, SA signaling, pattern-triggered immunity (PTI), and effector-triggered immunity (ETI) in Arabidopsis.

Methyl jasmonate-induced resistance to Delia platura (Diptera: Anthomyiidae) in Lupinus mutabilis

BACKGROUND

Andean lupin (Lupinus mutabilis Sweet) is an important leguminous crop from South America with a high protein content. In Ecuador, lupin yields are severely affected by the infestation of Delia platura larvae on germinating seeds. The application of elicitor molecules with activity against herbivorous insects to control D. platura infestation constitutes an unexplored and promising alternative for chemical insecticides. In this study, methyl jasmonate (MeJA), hexanoic acid, menadione sodium bisulfite, and DL-β-aminobutyric acid were evaluated for their ability to induce resistance against D. platura in three commercial lupin cultivars.

RESULTS

Only seeds pretreated with MeJA significantly impaired insect performance during choice and no-choice assays. Additionally, fitness indicators such as seed germination and growth were not affected by MeJA treatment. To investigate the molecular mechanisms behind the MeJA-mediated resistance, RT-qPCR assays were performed. First, RT-qPCR reference genes were validated, showing that LmUBC was the most stable reference gene. Next, expression analysis over time revealed that MeJA application up-regulated the activity of the jasmonic acid biosynthetic genes LmLOX2 and LmAOS, together with other jasmonate-related defense genes, such as LmTPS1, LmTPS4, LmPI2, LmMBL, LmL/ODC, LmCSD1, and LmPOD.

CONCLUSION

This study indicates that MeJA can be used as an environmentally friendly elicitor molecule to protect Andean lupin from D. platura attack without fitness cost. MeJA application induces plant defense responses to insects in Andean lupin that may be modulated by the onset of terpenoid biosynthesis, proteinase inhibitors, lectins, polyamines, and antioxidative enzymes. © 2021 Society of Chemical Industry.

A Critical Review on Communication Mechanism within Plant-Endophytic Fungi Interactions to Cope with Biotic and Abiotic Stresses

Endophytic fungi infect plant tissues by evading the immune response, potentially stimulating stress-tolerant plant growth. The plant selectively allows microbial colonization to carve endophyte structures through phenotypic genes and metabolic signals. Correspondingly, fungi develop various adaptations through symbiotic signal transduction to thrive in mycorrhiza. Over the past decade, the regulatory mechanism of plant-endophyte interaction has been uncovered. Currently, great progress has been made on plant endosphere, especially in endophytic fungi. Here, we systematically summarize the current understanding of endophytic fungi colonization, molecular recognition signal pathways, and immune evasion mechanisms to clarify the transboundary communication that allows endophytic fungi colonization and homeostatic phytobiome. In this work, we focus on immune signaling and recognition mechanisms, summarizing current research progress in plant-endophyte communication that converge to improve our understanding of endophytic fungi.

Transcriptomic changes in green bean pods against grey mould and white rot diseases via field application of chemical elicitor nanoparticles

The authors tested the efficacy of two salt nanoparticles (NPs), namely, copper dioxide (CuO) and tri-calcium phosphate [Ca₃(PO₄)₂] to induce resistance in green bean pods against grey mould and white rot diseases caused by Botrytis cinerea and Sclerotinia sclerotiorum, respectively. High amounts of phytoalexins, kievitone, coumestrol, phaseollidin, 6-ά-hydroxyphaseollin, and phaseollin, were detected in naturally infected and artificially inoculated green bean pods in response to the tested NPs. Green bean plants treated in the field with CuO and Ca₃(PO₄)₂ NPs had the highest mRNA quantity of all the studied defence genes, receptor-like kinase (PvRK20), pathogenesis-related protein (PR1), 1,3-β-D-glucanase (pvgluc), polygalacturonase inhibitor protein (PvGIP), and alpha-dioxygenase (a-DOX) than that of the control group. CuO NPs followed by Ca₃(PO₄)₂ NPs at 0.15 mg ml^-1 were the most potent in increasing the transcriptomic levels of pk20, DOX, PR1, PvGIP, and pvgluc. Field applications of both chemical elicitor NPs exhibited a non-genotoxic effect on the Paulista green bean DNA using eight ISSR primers. The field application of the studied NPs could effectively extend the shelf life of green bean pods by up to 21 days at 7 ± 1°C during marketing and export due to its potent effect against grey mould and white rot diseases.

Sulfur Deprivation Modulates Salicylic Acid Responses via Nonexpressor of Pathogenesis-Related Gene 1 in Arabidopsis thaliana

Mineral nutrients are essential for plant growth and reproduction, yet only a few studies connect the nutritional status to plant innate immunity. The backbone of plant defense response is mainly controlled by two major hormones: salicylic acid (SA) and jasmonic acid (JA). This study investigated changes in the macronutrient concentration (deficiency/excess of nitrogen, phosphorus, potassium, magnesium, and sulfur) on the expression of PR1, a well-characterized marker in the SA-pathway, and PDF1.2 and LOX2 for the JA-pathway, analyzing plants carrying the promoter of each gene fused to GUS as a reporter. After histochemical GUS assays, we determined that PR1 gene was strongly activated in response to sulfur (S) deficiency. Using RT-PCR, we observed that the induction of PR1 depended on the function of Non-expressor of Pathogenesis-Related gene 1 (NPR1) and SA accumulation, as PR1 was not expressed in npr1-1 mutant and NahG plants under S-deprived conditions. Plants treated with different S-concentrations showed that total S-deprivation was required to induce SA-mediated defense responses. Additionally, bioassays revealed that S-deprived plants, induced resistance to the hemibiotrophic pathogen Pseudomonas syringae pv. DC3000 and increase susceptibility to the necrotrophic Botrytis cinerea. In conclusion, we observed a relationship between S and SA/JA-dependent defense mechanisms in Arabidopsis.

A basic helix-loop-helix transcription factor CabHLH113 positively regulate pepper immunity against Ralstonia solanacearum

Pepper's (Capsicum annum) response to bacterial pathogen Ralstonia solanacearm inoculation (RSI) and abiotic stresses is known to be synchronized by transcriptional network; however, related molecular mechanisms need extensive experimentation. We identified and characterized functions of CabHLH113 -a basic helix-loop-helix transcription factor-in pepper immunity to R. solanacearum infection. The RSI and foliar spray of phytohormones, including salicylic acid (SA), methyl jasmonate (MeJA), ethylene (ETH), and absicic acid (ABA) induced transcription of CabHLH113 in pepper. Loss of function of CabHLH113 by virus-induced-gene-silencing (VIGS) compromised defense of pepper plants against RSI and suppressed relative expression levels of immunity-associated marker genes, i.e., CaPR1, CaNPR1, CaDEF1, CaHIR1 and CaABR1. Pathogen growth was significantly increased after loss of function of CabHLH113 compared with un-silenced plants with remarkable increase in pepper susceptibility. Besides, transiently over-expression of CabHLH113 induced HR-like cell death, H₂O₂ accumulation and up-regulation of defense-associated marker genes, e.g. CaPR1, CaNPR1, CaDEF1, CaHIR1 and CaABR1. Additionally, transient over-expression of CabHLH113 enhanced the transcriptional levels of CaWRKY6, CaWRKY27 and CaWRKY40. Conversely, transient over-expression of CaWRKY6, CaWRKY27 and CaWRKY40 enhanced the transcriptional levels of CabHLH113. Collectively, our results indicate that newly characterized CabHLH113 has novel defense functions in pepper immunity against RSI via triggering HR-like cell death and cellular levels of defense linked genes.

Virus-induced phytohormone dynamics and their effects on plant-insect interactions

Attacks on plants by both viruses and their vectors is common in nature. Yet the dynamics of the plant-virus-vector tripartite system, in particular the effects of viral infection on plant-insect interactions, have only begun to emerge in the last decade. Viruses can modulate the interactions between insect vectors and plants via the jasmonate, salicylic acid and ethylene phytohormone pathways, resulting in changes in fitness and viral transmission capacity of their insect vectors. Virus infection of plants may also modulate other phytohormones, such as auxin, gibberellins, cytokinins, brassinosteroids and abscisic acid, with yet undefined consequences on plant-insect interactions. Moreover, virus infection in plants may incur changes to other plant traits, such as nutrition and secondary metabolites, that potentially contribute to virus-associated, phytohormone-mediated manipulation of plant-insect interactions. In this article, we review the research progress, discuss issues related to the complexity and variability of the viral modulation of plant interactions with insect vectors, and suggest future directions of research in this field.

Transcriptome profiling analysis reveals distinct resistance response of cucumber leaves infected with powdery mildew

Powdery mildew is the main disease affecting cucumber cultivation and causes severe economic loss. So far, research on cucumber resistance to powdery mildew has not yielded feasible solutions. This study selected two inbred cucumber lines, XY09-118 (resistant) and Q10 (susceptible) and investigated their responses to powdery mildew infection (harvested 24 and 48 h after inoculation) using RNA sequencing. More than 20,000 genes were detected in cucumber leaves both with and without powdery mildew infection at the above two time points. Among these, 5478 genes were identified as differently expressed genes (DEGs) between XY09-118 and Q10. Based on the databases GO and KEGG, the functions of DEGs were analysed. Moreover, the complex regulatory network for powdery mildew resistance was assessed, which involves plant hormone signal transduction, phenylpropanoid biosynthesis, plant-pathogen interaction and the MAPK signalling pathway. In particular, genes encoding WRKY, NAC and TCP were highlighted. In addition, genes involved in plant hormone biosynthesis, metabolism and signal transduction, pathogen resistance and abiotic stress response were analysed. Co-expression analysis indicated that the transcription factors correlated with plant hormone signal pathway and metabolism, defence and abiotic response. The expression of several genes was validated by qRT-PCR. The pathogen resistance regulatory network was identified by comparing resistant and susceptible inbred lines infected with powdery mildew. The transcriptome data provide novel insights into cucumber response to powdery mildew infection and the identified pathogen resistance genes will be highly useful for breeding efforts to enhance the resistance of cucumber to powdery mildew.

Regulation of Postharvest Tomato Fruit Ripening by Endogenous Salicylic Acid

Exogenous application of salicylic acid (SA) has been known for delaying ripening in many fruit and vegetables. But the function of endogenous SA in relation to postharvest fruit performance is still unexplored. To understand the role of endogenous SA in postharvest fruit ripening of tomato, 33 tomato lines were examined for their endogenous SA content, membrane stability index (MSI), and shelf life (SL) at turning and red stages of tomato fruit ripening. Six tomato lines having contrasting shelf lives from these categories were subjected further for ethylene (ET) evolution, 1-aminocyclopropane-1-carboxylic acid synthase (ACS), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), polygalacturonase (PG), pectin methyl esterase (PME), antioxidant assays and lipid peroxidation. It was found that high endogenous SA has a direct association with low ET evolution, which leads to the high SL of fruit. High lycopene content was also found to be correlated with high SA. Total antioxidants, PG, and PME decreased and lipid peroxidation increased from turning to red stage of tomato fruit development. Furthermore, these lines were subjected to expression analysis for SA biosynthesis enzymes viz. Solanum lycopersicum Isochorismate Synthase (SlICS) and SlPAL. Real-time PCR data revealed that high SL lines have high SlPAL4 expression and low SL lines have high SlPAL6 expression. Based on the results obtained in this study, it was concluded that endogenous SA regulates ET evolution and SL with the aid of the antioxidative defense system, and SlPAL4 and SlPAL6 genes play significant but opposite roles during fruit ripening.

Multiple levels of crosstalk in hormone networks regulating plant defense

Plant hormones are essential for regulating the interactions between plants and their complex biotic and abiotic environments. Each hormone initiates a specific molecular pathway and these different hormone pathways are integrated in a complex network of synergistic, antagonistic and additive interactions. This inter-pathway communication is called hormone crosstalk. By influencing the immune network topology, hormone crosstalk is essential for tailoring plant responses to diverse microbes and insects in diverse environmental and internal contexts. Crosstalk provides robustness to the immune system but also drives specificity of induced defense responses against the plethora of biotic interactors. Recent advances in dry-lab and wet-lab techniques have greatly enhanced our understanding of the broad-scale effects of hormone crosstalk on immune network functioning and have revealed underlying principles of crosstalk mechanisms. Molecular studies have demonstrated that hormone crosstalk is modulated at multiple levels of regulation, such as by affecting protein stability, gene transcription and hormone homeostasis. These new insights into hormone crosstalk regulation of plant defense are reviewed here, with a focus on crosstalk acting on the jasmonic acid pathway in Arabidopsis thaliana, highlighting the transcription factors MYC2 and ORA59 as major targets for modulation by other hormones.

Bioeffectors as Biotechnological Tools to Boost Plant Innate Immunity: Signal Transduction Pathways Involved

The use of beneficial rhizobacteria (bioeffectors) and their derived metabolic elicitors are efficient biotechnological alternatives in plant immune system elicitation. This work aimed to check the ability of 25 bacterial strains isolated from the rhizosphere of Nicotiana glauca, and selected for their biochemical traits from a group of 175, to trigger the innate immune system of Arabidopsis thaliana seedlings against the pathogen Pseudomonas syringae pv. tomato DC3000. The five strains more effective in preventing pathogen infection were used to elucidate signal transduction pathways involved in the plant immune response by studying the differential expression of Salicylic acid and Jasmonic acid/Ethylene pathway marker genes. Some strains stimulated both pathways, while others stimulated either one or the other. The metabolic elicitors of two strains, chosen for the differential expression results of the genes studied, were extracted using n-hexane, ethyl acetate, and n-butanol, and their capacity to mimic bacterial effect to trigger the plant immune system was studied. N-hexane and ethyl acetate were the most effective fractions against the pathogen in both strains, achieving similar protection rates although gene expression responses were different from that obtained by the bacteria. These results open an amount of biotechnological possibilities to develop biological products for agriculture.

Knockout of SlNPR1 enhances tomato plants resistance against Botrytis cinerea by modulating ROS homeostasis and JA/ET signaling pathways

Tomato is one of the most popular horticultural crops, and many commercial tomato cultivars are particularly susceptible to Botrytis cinerea. Non-expressor of pathogenesis-related gene 1 (NPR1) is a critical component of the plant defense mechanisms. However, our understanding of how SlNPR1 influences disease resistance in tomato is still limited. In this study, two independent slnpr1 mutants were used to study the role of SlNPR1 in tomato resistance against B. cinerea. Compared to (WT), slnpr1 leaves exhibited enhanced resistance against B. cinerea with smaller lesion sizes, higher activities of chitinase (CHI), β-1, 3-glucanases (GLU) and phenylalanine ammonia-lyase (PAL), and significantly increased expressions of pathogenesis-related genes (PRs). The increased activities of peroxidase (POD), ascorbate peroxidase (APX) and decreased catalase (CAT) activities collectively regulated reactive oxygen species (ROS) homeostasis in slnpr1 mutants. The integrity of the cell wall in slnpr1 mutants was maintained. Moreover, the enhanced resistance was further reflected by induction of defense genes involved in jasmonic acid (JA) and ethylene (ET) signaling pathways. Taken together, these findings revealed that knocking out SlNPR1 resulted in increased activities of defense enzymes, changes in ROS homeostasis and integrity of cell walls, and activation of JA and ET pathways, which confers resistance against B. cinerea in tomato plants.

Quantitative Hormone Signaling Output Analyses of Arabidopsis thaliana Interactions With Virulent and Avirulent Hyaloperonospora arabidopsidis Isolates at Single-Cell Resolution

The phytohormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) are central regulators of biotic and abiotic stress responses in Arabidopsis thaliana. Here, we generated modular fluorescent protein-based reporter lines termed COLORFUL-PR1pro, -VSP2pro, and -PDF1.2apro. These feature hormone-controlled nucleus-targeted transcriptional output sensors and the simultaneous constitutive expression of spectrally separated nuclear reference and plasma membrane-localized reporters. This set-up allowed the study of cell-type specific hormone activities, cellular viability and microbial invasion. Moreover, we developed a software-supported high-throughput confocal microscopy imaging protocol for output quantification to resolve the spatio-temporal dynamics of respective hormonal signaling activities at single-cell resolution. Proof-of-principle analyses in A. thaliana leaves revealed distinguished hormone sensitivities in mesophyll, epidermal pavement and stomatal guard cells, suggesting cell type-specific regulatory protein activities. In plant-microbe interaction studies, we found that virulent and avirulent Hyaloperonospora arabidopsidis (Hpa) isolates exhibit different invasion dynamics and induce spatio-temporally distinct hormonal activity signatures. On the cellular level, these hormone-controlled reporter signatures demarcate the nascent sites of Hpa entry and progression, and highlight initiation, transduction and local containment of immune signals.

Jasmonic Acid at the Crossroads of Plant Immunity and Pseudomonas syringae Virulence

Sensing of pathogen infection by plants elicits early signals that are transduced to affect defense mechanisms, such as effective blockage of pathogen entry by regulation of stomatal closure, cuticle, or callose deposition, change in water potential, and resource acquisition among many others. Pathogens, on the other hand, interfere with plant physiology and protein functioning to counteract plant defense responses. In plants, hormonal homeostasis and signaling are tightly regulated; thus, the phytohormones are qualified as a major group of signaling molecules controlling the most widely tinkered regulatory networks of defense and counter-defense strategies. Notably, the phytohormone jasmonic acid mediates plant defense responses to a wide array of pathogens. In this review, we present the synopsis on the jasmonic acid metabolism and signaling, and the regulatory roles of this hormone in plant defense against the hemibiotrophic bacterial pathogen Pseudomonas syringae. We also elaborate on how this pathogen releases virulence factors and effectors to gain control over plant jasmonic acid signaling to effectively cause disease. The findings discussed in this review may lead to ideas for the development of crop cultivars with enhanced disease resistance by genetic manipulation.

Molecular Cloning and Functional Analysis of the NPR1 Homolog in Kiwifruit (Actinidia eriantha)

Kiwifruit bacterial canker, caused by the bacterial pathogen Pseudomonas syringae pv. actinidiae (Psa), is a destructive disease in the kiwifruit industry globally. Consequently, understanding the mechanism of defense against pathogens in kiwifruit could facilitate the development of effective novel protection strategies. The Non-expressor of Pathogenesis-Related genes 1 (NPR1) is a critical component of the salicylic acid (SA)-dependent signaling pathway. Here, a novel kiwifruit NPR1-like gene, designated AeNPR1a, was isolated by using PCR and rapid amplification of cDNA ends techniques. The full-length cDNA consisted of 1952 base pairs with a 1,746-bp open-reading frame encoding a 582 amino acid protein. Homology analysis showed that the AeNPR1a protein is significantly similar to the VvNPR1 of grape. A 2.0 Kb 5'-flanking region of AeNPR1a was isolated, and sequence identification revealed the presence of several putative cis-regulatory elements, including basic elements, defense and stress response elements, and binding sites for WRKY transcription factors. Real-time quantitative PCR results demonstrated that AeNPR1a had different expression patterns in various tissues, and its transcription could be induced by phytohormone treatment and Psa inoculation. The yeast two-hybrid assay revealed that AeNPR1a interacts with AeTGA2. Constitutive expression of AeNPR1a induced the expression of pathogenesis-related gene in transgenic tobacco plants and enhanced tolerance to bacterial pathogens. In addition, AeNPR1a expression could restore basal resistance to Pseudomonas syringae pv. tomato DC3000 (Pst) in Arabidopsis npr1-1 mutant. Our data suggest that AeNPR1a gene is likely to play a pivotal role in defense responses in kiwifruit.

Computational analysis of microarray data of Arabidopsis thaliana challenged with Alternaria brassicicola for identification of key genes in Brassica

Background

Alternaria blight, a recalcitrant disease caused by Alternaria brassicae and Alternaria brassicicola, has been recognized for significant losses of oilseed crops especially rapeseed-mustard throughout the world. Till date, no resistance source is available against the disease; hence, plant breeding methods cannot be used to develop disease-resistant varieties. Therefore, in the present study, efforts have been made to identify resistance and defense-related genes as well as key components of JA-SA-ET-mediated pathway involved in resistance against Alternaria brasscicola through computational analysis of microarray data and network biology approach. Microarray profiling data from wild type and mutant Arabidopsis plants challenged with Alternaria brassicicola along with control plant were obtained from the Gene Expression Omnibus (GEO) database. The data analysis, including DEGs extraction, functional enrichment, annotation, and network analysis, was used to identify genes associated with disease resistance and defense response.

Results

A total of 2854 genes were differentially expressed in WT9C9; among them, 1327 genes were upregulated and 1527 genes were downregulated. A total of 1159 genes were differentially expressed in JAM9C9; among them, 809 were upregulated and 350 were downregulated. A total of 2516 genes were differentially expressed in SAM9C9; among them, 1355 were upregulated and 1161 were downregulated. A total of 1567 genes were differentially expressed in ETM9C9; among them, 917 were upregulated and 650 were downregulated. Besides, a total of 2965 genes were differentially expressed in contrast WT24C24; among them, 1510 genes were upregulated and 1455 genes were downregulated. A total of 4598 genes were differentially expressed in JAM24C24; among them, 2201 were upregulated and 2397 were downregulated. A total of 3803 genes were differentially expressed in SAM24C24; among them, 1819 were upregulated and 1984 were downregulated. A total of 4164 genes were differentially expressed in ETM24C24; among them, 1895 were upregulated and 2269 were downregulated. The upregulated genes of Arabidopsis thaliana were mapped and annotated with CDS sequences of Brassica rapa obtained from PlantGDB database. Additionally, PPI network of these genes were constructed to investigate the key components of hormone-mediated pathway involved in resistance during pathogenesis.

Conclusion

The obtained information from present study can be used to engineer resistance to Alternaria blight caused by Alternaria brasscicola through molecular breeding or genetic manipulation-based approaches for improving Brassica oilseed productivity.

Effects of melon yellow spot orthotospovirus infection on the preference and developmental traits of melon thrips, Thrips palmi, in cucumber

Melon yellow spot orthotospovirus (MYSV), a member of the genus Orthotospovirus, is an important virus in cucurbits. Thrips palmi is considered the most serious pest of cucurbits because it directly damages and indirectly transmits MYSV to the plant. The effects of MYSV-infected plants on the development time, fecundity, and preference of the thrips were analyzed in this study. Our results showed that the development time of male and female thrips did not differ significantly between MYSV-infected and non-infected cucumbers. The survival rate of thrips in non-infected and MYSV-infected cucumbers were not significantly different. In a non-choice assay, T. palmi adults were released on non-infected and MYSV-infected cucumbers and allowed to lay eggs. The number of hatched larvae did not significantly differ between non-infected and MYSV-infected cucumbers. In a choice assay, MYSV had no detectable effect on the number of adult thrips and preceding hatched larvae. In a pull assay, the settling rate of thrips on the released plant did not differ significantly when the adult thrips were released to non-infected or MYSV infected cucumbers for any cucumber cultivar. Based on our results, we propose that the effects of MYSV-infected cucumbers on the development time, fecundity, or preference of T. palmi may not be an important factor in MYSV spread between cucumbers.

R gene mediated defense against viruses

The relationship of Resistance (R) gene-mediated defense to other forms of resistance in plants is considered, and the natures of the products of dominant and recessive R genes are reviewed. Various factors involved in expressing R gene-mediated resistance are described. These include phytohormones and plant effector molecules: the former regulating different pathways for disease resistance and the latter having direct effects on viral genomes or encoded proteins. Finally, the status of our knowledge concerning the cell-death hypersensitive response and its relationship to the actual resistance response involved in inhibiting virus infection is examined.

Ethylene mediates salicylic-acid-induced stomatal closure by controlling reactive oxygen species and nitric oxide production in Arabidopsis

Both salicylic acid (SA) and ethylene induce stomatal closure and positively regulate stomatal immunity, but their interactions in guard cell signaling are unclear. Here, we observed that SA induced the expression of ethylene biosynthetic genes; the production of ethylene, reactive oxygen species (ROS) and nitric oxide (NO); and stomatal closure in Arabidopsis thaliana. However, SA-induced stomatal closure was inhibited by an ethylene biosynthetic inhibitor and mutations in ethylene biosynthetic genes, ethylene-signaling genes [RESPONSE TO ANTAGONIST 1 (RAN1), ETHYLENE RESPONSE 1 (ETR1), ETHYLENE INSENSITIVE 2 (EIN2), EIN3 and ARABIDOPSIS RESPONSE REGULATOR 2 (ARR2)], NADPH oxidase genes [ATRBOHD and ATRBOHF], and nitrate reductase genes (NIA1 and NIA2). Furthermore, SA-triggered ROS production in guard cells was impaired in ran1, etr1, AtrbohD and AtrbohF, but not in ein2, ein3 or arr2. SA-triggered NO production was impaired in all ethylene-signaling mutants tested and in nia1 and nia2. The stomata of mutants for CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) showed constitutive ROS and NO production and closure. These results indicate that ethylene mediates SA-induced stomatal closure by activating ATRBOHD/F-mediated ROS synthesis in an RAN1-, ETR1- and CTR1-dependent manner. This in turn induces NIA1/2-mediated NO production and subsequent stomatal closure via the ETR1, EIN2, EIN3 and ARR2-dependent pathway(s).

Differential Quantitative Requirements for NPR1 Between Basal Immunity and Systemic Acquired Resistance in Arabidopsis thaliana

Non-expressor of pathogenesis-related (PR) genes1 (NPR1) is a key transcription coactivator of plant basal immunity and systemic acquired resistance (SAR). Two mutant alleles, npr1-1 and npr1-3, have been extensively used for dissecting the role of NPR1 in various signaling pathways. However, it is unknown whether npr1-1 and npr1-3 are null mutants. Moreover, the NPR1 transcript levels are induced two- to threefold upon pathogen infection or salicylic acid (SA) treatment, but the biological relevance of the induction is unclear. Here, we used molecular and biochemical approaches including quantitative PCR, immunoblot analysis, site-directed mutagenesis, and CRISPR/Cas9-mediated gene editing to address these questions. We show that npr1-3 is a potential null mutant, whereas npr1-1 is not. We also demonstrated that a truncated npr1 protein longer than the hypothesized npr1-3 protein is not active in SA signaling. Furthermore, we revealed that TGACG-binding (TGA) factors are required for NPR1 induction, but the reverse TGA box in the 5'UTR of NPR1 is dispensable for the induction. Finally, we show that full induction of NPR1 is required for basal immunity, but not for SAR, whereas sufficient basal transcription is essential for full-scale establishment of SAR. Our results indicate that induced transcript accumulation may be differentially required for different functions of a specific gene. Moreover, as npr1-1 is not a null mutant, we recommend that future research should use npr1-3 and potential null T-DNA insertion mutants for dissecting NPR1's function in various physiopathological processes.

The role of activation of KАTP channels on hydrogen sulfide induced renoprotective effect on diabetic nephropathy

This work aims to investigate the renal effect of hydrogen sulfide (H₂ S), in the experimentally induced diabetic nephropathy, besides the role of activation of АТP-sensitive potassium (K_АTP ) channel in that effect. Thirty-two adult male albino rats randomly divided into four groups: Control, streptozotocin-induced diabetic (diabetic nephropathy [DN]), DN+NaHS (the H₂ S inducer), and DN+NaHS+Glibenclamide (a selective K_АTP channel blocker) groups. Results showed that kidney functions in the diabetic group improved by NaHS proved by the significant decrease in the measured renal injury markers when compared with the diabetic group with an obvious role of inflammation and oxidative stress. However, the improved kidney functions produced by NaHS was reduced by the combination with Glibenclamide. Glibenclamide combination led also to a significant increase in renal total antioxidant capacity, in addition to a significant decrease in renal total nitric oxide (NO) level. Аccordingly, the results from the present work revealed that the renoprotective effects of H₂ S in the case of DN through its effects on renal tissue antioxidants and NO can be partially dependent on activation of K_АTP channels, while its effect on renal tissue proinflammatory cytokines is independent of it.

Characterization, expression profiling, and functional analysis of a Populus trichocarpa defensin gene and its potential as an anti-Agrobacterium rooting medium additive

The diverse antimicrobial properties of defensins have attracted wide scientific interest in recent years. Also, antimicrobial peptides (AMPs), including cecropins, histatins, defensins, and cathelicidins, have recently become an antimicrobial research hotspot for their broad-spectrum antibacterial and antifungal activities. In addition, defensins play important roles in plant growth, development, and physiological metabolism, and demonstrate tissue specificity and regulation in response to pathogen attack or abiotic stress. In this study, we performed molecular cloning, characterization, expression profiling, and functional analysis of a defensin from Populus trichocarpa. The PtDef protein was highly expressed in the prokaryotic Escherichia coli system as a fusion protein (TrxA–PtDef). The purified protein exhibited strong antibacterial and antifungal functions. We then applied PtDef to rooting culture medium as an alternative exogenous additive to cefotaxime. PtDef expression levels increased significantly following both biotic and abiotic treatment. The degree of leaf damage observed in wild-type (WT) and transgenic poplars indicates that transgenic poplars that overexpress the PtDef gene gain enhanced disease resistance to Septotis populiperda. To further study the salicylic acid (SA) and jasmonic acid (JA) signal transduction pathways, SA- and JA-related and pathogenesis-related genes were analyzed using quantitative reverse-transcription polymerase chain reaction; there were significant differences in these pathways between transgenic and WT poplars. The defensin from Populus trichocarpa showed significant activity of anti-bacteria and anti-fungi. According to the results of qRT-PCR and physiological relevant indicators, the applied PtDef to rooting culture medium was chosen as an alternative exogenous additive to cefotaxime. Overexpressing the PtDef gene in poplar improve the disease resistance to Septotis populiperda.

Gene Expression Profiling Reveals Enhanced Defense Responses in an Invasive Weed Compared to Its Native Congener During Pathogenesis

Invasive plants are a huge burden on the environment, and modify local ecosystems by affecting the indigenous biodiversity. Invasive plants are generally less affected by pathogens, although the underlying molecular mechanisms responsible for their enhanced resistance are unknown. We investigated expression profiles of three defense hormones (salicylic acid, jasmonic acid, and ethylene) and their associated genes in the invasive weed, Alternanthera philoxeroides, and its native congener, A. sessilis, after inoculation with Rhizoctonia solani. Pathogenicity tests showed significantly slower disease progression in A. philoxeroides compared to A. sessilis. Expression analyses revealed jasmonic acid (JA) and ethylene (ET) expressions were differentially regulated between A. philoxeroides and A. sessilis, with the former having prominent antagonistic cross-talk between salicylic acid (SA) and JA, and the latter showing weak or no cross-talk during disease development. We also found that JA levels decreased and SA levels increased during disease development in A. philoxeroides. Variations in hormonal gene expression between the invasive and native species (including interspecific differences in the strength of antagonistic cross-talk) were identified during R. solani pathogenesis. Thus, plant hormones and their cross-talk signaling may improve the resistance of invasive A. philoxeroides to pathogens, which has implications for other invasive species during the invasion process.

Molecular Basis of Soybean Resistance to Soybean Aphids and Soybean Cyst Nematodes

Soybean aphid (SBA; Aphis glycines Matsumura) and soybean cyst nematode (SCN; Heterodera glycines Ichninohe) are major pests of the soybean (Glycine max [L.] Merr.). Substantial progress has been made in identifying the genetic basis of limiting these pests in both model and non-model plant systems. Classical linkage mapping and genome-wide association studies (GWAS) have identified major and minor quantitative trait loci (QTLs) in soybean. Studies on interactions of SBA and SCN effectors with host proteins have identified molecular cues in various signaling pathways, including those involved in plant disease resistance and phytohormone regulations. In this paper, we review the molecular basis of soybean resistance to SBA and SCN, and we provide a synthesis of recent studies of soybean QTLs/genes that could mitigate the effects of virulent SBA and SCN populations. We also review relevant studies of aphid–nematode interactions, particularly in the soybean–SBA–SCN system.

Tobacco transcription repressors NtJAZ: Potential involvement in abiotic stress response and glandular trichome induction

Members of the Jasmonate ZIM domain (JAZ) proteins act as transcriptional repressors in the jasmonate (JA) hormonal response. To characterize the potential roles of JAZ gene family in plant development and abiotic stress response, fifteen JAZs were identified based on the genome of Nicotiana tabacum. Structural analysis confirmed the presence of single Jas and TIFY motif. Tissue expression pattern analysis indicated that NtJAZ-2, -3, -5, and -10 were highly expressed in roots and NtJAZ-11 was expressed only in the cotyledons. The transcript level of NtJAZ-3, -5, -9, and -10 in the stem epidermis was higher than that in the stem without epidermis. Dynamic expression of NtJAZs exposed to abiotic stress and phytohormone indicated that the expression of most NtJAZs was activated by salicylic acid, methyl jasmonate, gibberellic acid, cold, salt, and heat stresses. With abscisic acid treatment, NtJAZ-1, -2, and -3 were not activated; NtJAZ-4, -5, and -6 were up-regulated; and the remaining NtJAZ genes were inhibited. With drought stress, the expression of NtJAZ-1, -2, -3, -4, -5, -6, -7, and -8 was up-regulated, whereas the transcript of the remaining genes was inhibited. Moreover, high concentration MeJA (more than 1 mM MeJA) had an effect on secreting trichome induction, but inhabited the plant growth. Nine NtJAZs may play important role in secreting trichome induction. These results indicate that the JAZ proteins are convergence points for various phytohormone signal networks, which are involved in abiotic stress responses.

Genome-Wide Identification and Characterization of JAZ Protein Family in Two Petunia Progenitors

Jasmonate ZIM-domain (JAZ) family proteins are the key repressors in the jasmonate signaling pathway and play crucial roles in plant development, defenses, and responses to stresses. However, our knowledge about the JAZ protein family in petunia is limited. This research respectively identified 12 and 16 JAZ proteins in two Petunia progenitors, Petunia axillaris and Petunia inflata. Phylogenetic analysis showed that the 28 proteins could be divided into four groups (Groups A–D) and further classified into six subgroups (A1, A2, B1, B3, C, and D1); members in the same subgroup shared some similarities in motif composition and sequence structure. The Ka/Ks ratios of seven paralogous pairs were less than one, suggesting the petunia JAZ family might have principally undergone purifying selection. Quantitative real-time PCR (qRT-PCR) analysis revealed that PaJAZ genes presented differential expression patterns during the development of flower bud and anther in petunia, and the expression of PaJAZ5, 9, 12 genes was generally up-regulated after MeJA treatment. Subcellular localization assays demonstrated that proteins PaJAZ5, 9, 12 were localized in nucleus. Yeast two hybrid (Y2H) elucidated most PaJAZ proteins (PaJAZ1-7, 9, 12) might interact with transcription factor MYC2. This study provides insights for further investigation of functional analysis in petunia JAZ family proteins.

Methyl jasmonate and cyclodextrin-mediated defense mechanism and protective effect in response to paraquat-induced stress in peanut hairy root

Plant cells have a variety of defense mechanisms to alleviate the deleterious effects of oxidative stress. The present work elucidated a schematic diagram of the proposed pathway of peanut hairy root tissue treated with different elicitors; paraquat (PQ), methyl jasmonate (MeJA), and cyclodextrin (CD). The different elicitation approaches could provoke intrinsic stress in plant cells and might activate a distinct response pathway, allowing plants to overcome the deleterious effects of oxidative stress. Among all strategies, hairy root culture pretreated with PQ followed by application of MeJA plus CD showed an extensive induction of antioxidant defense mechanisms. The expression of the antioxidant enzyme genes and stilbene-synthesized enzyme genes were up-regulated in accordance with the dramatic increase in the production of stilbene compounds. The non-enzymatic antioxidant substances exhibited a highly enhanced capability. The pathogenesis-related protein (PR) genes were also highly up-regulated. In summary, we demonstrated that the interplay among MeJA plus CD and PQ may activate a complex signaling network to regulate plant defense mechanisms involving the up-regulation of detoxifying enzymes, induction of free-radical scavengers and overexpression of genes associated with plant defense pathways.

Trichoderma/pathogen/plant interaction in pre-harvest food security

Large losses before crop harvesting are caused by plant pathogens, such as viruses, bacteria, oomycetes, fungi, and nematodes. Among these, fungi are the major cause of losses in agriculture worldwide. Plant pathogens are still controlled through application of agrochemicals, causing human disease and impacting environmental and food security. Biological control provides a safe alternative for the control of fungal plant pathogens, because of the ability of biocontrol agents to establish in the ecosystem. Some Trichoderma spp. are considered potential agents in the control of fungal plant diseases. They can interact directly with roots, increasing plant growth, resistance to diseases, and tolerance to abiotic stress. Furthermore, Trichoderma can directly kill fungal plant pathogens by antibiosis, as well as via mycoparasitism strategies. In this review, we will discuss the interactions between Trichoderma/fungal pathogens/plants during the pre-harvest of crops. In addition, we will highlight how these interactions can influence crop production and food security. Finally, we will describe the future of crop production using antimicrobial peptides, plants carrying pathogen-derived resistance, and plantibodies.

Cotton plant defence against a fungal pathogen is enhanced by expanding BLADE-ON-PETIOLE1 expression beyond lateral-organ boundaries

In the plant response to pathogen infection, many genes' expression is temporally induced, while few spatially induced expression genes have been reported. Here, we show that GhBOP1 can autonomously expand expression from restrained tissue when Gossypium hirsutum plants are attacked by Verticillium dahliae, which is considered to be spatially induced expression. Loss- and gain-of-function analyses show that GhBOP1 is a positive regulator in the modulation of plant resistance to V. dahliae. Yeast two-hybrid assays, luciferase complementation imaging and GUS reporting show that GhBOP1 interaction with GhTGA3 promotes its activation activity, regulating the expression of down-stream defence-related genes. Moreover, the induced spatial expression of GhBOP1 is accompanied by GhBP1 repression. Both antagonistically regulate the lignin biosynthesis, conferring cotton plants enhanced resistance to V. dahliae. Taken together, these results demonstrate that GhBOP1 is an economic positive regulator participating in plant defence through both the GhBOP1-GhTGA3 module and lignin accumulation.