Transcriptional Profiling of Rice Treated with MoHrip1 Reveal the Function of Protein Elicitor in Enhancement of Disease Resistance and Plant Growth

Species- and organ-specific contribution of peroxisomal cinnamate:CoA ligases to benzoic and salicylic acid biosynthesis

Salicylic acid (SA) is a prominent defense hormone whose basal level, organ-specific accumulation, and physiological role vary widely among plant species. Of the 2 known pathways of plant SA biosynthesis, the phenylalanine ammonia lyase (PAL) pathway is more ancient and universal but its biosynthetic and physiological roles in diverse plant species remain unclear. Studies in which the PAL pathway is specifically or completely inhibited, as well as a direct comparison of diverse species and different organs within the same species, are needed. To this end, we analyzed the PAL pathway in rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana), 2 distantly related model plants whose basal SA levels and distributions differ tremendously at the organism and tissue levels. Based on our recent identification of the rice peroxisomal cinnamate:CoA ligases (CNLs), we identified 2 peroxisomal CNLs from Arabidopsis and showed CNL as the most functionally specific enzyme among the known enzymes of the PAL pathway. We then revealed the species- and organ-specific contribution of the PAL pathway to benzoic and salicylic acid biosynthesis and clarified its physiological importance in rice and Arabidopsis. Our findings highlight the necessity to consider species and organ types in future SA-related studies and may help to breed new disease-resistant crops.

Systemic resistance induced in tomato plants by Beauveria bassiana-derived proteins against tomato yellow leaf curl virus and aphid Myzus persicae

BACKGROUND

Tomato (Solanum lycopersicum L.) is an economically important vegetable crop around the globe. Tomato yellow leaf curling (TYLC) is the most devastating viral disease posing a serious threat to tomato production throughout the tropical and subtropical world. Induction of microbe-mediated systemic resistance in plants has been of great interest in recent years as a novel microbiological tool in disease and insect pest management. This in-vitro study aimed to determine the effectiveness of different strains (BB252, BB72 and ARSEF-2860) of a hypocreal fungus Beauveria bassiana against TYLCV disease and aphid Myzus persicae. Potted tomato plants exogenously treated with conidial and filtrate suspensions of B. bassiana strains and of their partially purified or purified proteins were exposed to TYLCV inoculum and aphid M. persicae.

RESULTS

Results showed a significant suppression of TYLCV disease severity index by the exogenous application of conidial, filtrate and protein treatments of all B. bassiana strains and this response was directly proportional to the treatment concentration. Similarly, mean fecundity rate of M. persicae was also significantly reduced by the highest concentration of ARSEF-2860-derived elicitor protein PeBb1, followed by the highest concentrations of BB252- and BB72-derived partially purified proteins. Moreover, these B. bassiana-derived proteins also caused a significant upregulation of most of the plant immune marker genes associated with plant defense.

CONCLUSION

Overall, the study findings suggest that these B. bassiana strains and their partially purified or purified elicitor proteins could be effective biological tools for the management of TYLCV and aphid infestation on tomato plants. © 2023 Society of Chemical Industry.

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

BACKGROUND

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

AIM OF REVIEW

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

KEY SCIENTIFIC CONCEPTS OF REVIEW

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

Recent Advances in Effector Research of Magnaporthe oryzae

Recalcitrant rice blast disease is caused by Magnaporthe oryzae, which has a significant negative economic reverberation on crop productivity. In order to induce the disease onto the host, M. oryzae positively generates many types of small secreted proteins, here named as effectors, to manipulate the host cell for the purpose of stimulating pathogenic infection. In M. oryzae, by engaging with specific receptors on the cell surface, effectors activate signaling channels which control an array of cellular activities, such as proliferation, differentiation and apoptosis. The most recent research on effector identification, classification, function, secretion, and control mechanism has been compiled in this review. In addition, the article also discusses directions and challenges for future research into an effector in M. oryzae.

Stress responses of plants through transcriptome plasticity by mRNA alternative polyadenylation

The sessile nature of plants confines their responsiveness to changing environmental conditions. Gene expression regulation becomes a paramount mechanism for plants to adjust their physiological and morphological behaviors. Alternative polyadenylation (APA) is known for its capacity to augment transcriptome diversity and plasticity, thereby furnishing an additional set of tools for modulating gene expression. APA has also been demonstrated to exhibit intimate associations with plant stress responses. In this study, we review APA dynamic features and consequences in plants subjected to both biotic and abiotic stresses. These stresses include adverse environmental stresses, and pathogenic attacks, such as cadmium toxicity, high salt, hypoxia, oxidative stress, cold, heat shock, along with bacterial, fungal, and viral infections. We analyzed the overarching research framework employed to elucidate plant APA response and the alignment of polyadenylation site transitions with the modulation of gene expression levels within the ambit of each stress condition. We also proposed a general APA model where transacting factors, including poly(A) factors, epigenetic regulators, RNA m6A modification factors, and phase separation proteins, assume pivotal roles in APA related transcriptome plasticity during stress response in plants.

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.

Characteristics, Roles and Applications of Proteinaceous Elicitors from Pathogens in Plant Immunity

In interactions between pathogens and plants, pathogens secrete many molecules that facilitate plant infection, and some of these compounds are recognized by plant pattern recognition receptors (PRRs), which induce immune responses. Molecules in both pathogens and plants that trigger immune responses in plants are termed elicitors. On the basis of their chemical content, elicitors can be classified into carbohydrates, lipopeptides, proteinaceous compounds and other types. Although many studies have focused on the involvement of elicitors in plants, especially on pathophysiological changes induced by elicitors in plants and the mechanisms mediating these changes, there is a lack of up-to-date reviews on the characteristics and functions of proteinaceous elicitors. In this mini-review, we provide an overview of the up-to-date knowledge on several important families of pathogenic proteinaceous elicitors (i.e., harpins, necrosis- and ethylene-inducing peptide 1 (nep1)-like proteins (NLPs) and elicitins), focusing mainly on their structures, characteristics and effects on plants, specifically on their roles in plant immune responses. A solid understanding of elicitors may be helpful to decrease the use of agrochemicals in agriculture and gardening, generate more resistant germplasms and increase crop yields.

Rice Phytoalexins: Half a Century of Amazing Discoveries; Part I: Distribution, Biosynthesis, Chemical Synthesis, and Biological Activities

Cultivated rice is a staple food for more than half of the world's population, providing approximately 20% of the world's food energy needs. A broad spectrum of pathogenic microorganisms causes rice diseases leading to huge yield losses worldwide. Wild and cultivated rice species are known to possess a wide variety of antimicrobial secondary metabolites, known as phytoalexins, which are part of their active defense mechanisms. These compounds are biosynthesized transiently by rice in response to pathogens and certain abiotic stresses. Rice phytoalexins have been intensively studied for over half a century, both for their biological role and their potential application in agronomic and pharmaceutical fields. In recent decades, the growing interest of the research community, combined with advances in chemical, biological, and biomolecular investigation methods, has led to a notable acceleration in the growth of knowledge on rice phytoalexins. This review provides an overview of the knowledge gained in recent decades on the diversity, distribution, biosynthesis, chemical synthesis, and bioactivity of rice phytoalexins, with particular attention to the most recent advances in this research field.

Hrip1 mediates rice cell wall fortification and phytoalexins elicitation to confer immunity against Magnaporthe oryzae

Magnaporthe oryzae is a potent fungus that adversely affects rice yield. Combinatorial techniques of prevention, toxic chemicals, and fungicide are used to remedy rice blast infection. We reported the role of Hrip1 in cell death elicitation and expression of systematic acquired resistance that could potentially stifle M. oryzae infection. In this study, transcriptome and metabolomic techniques were used to investigate the mechanism by which Hrip1 reprogramed the transcriptome of rice seedlings to confer immunity against M. oryzae. Our results showed that Hrip1 induces cell wall thickening and phytoalexin elicitation to confer immunity against M. oryzae infection. Hrip1 activates key lignin biosynthetic genes and myeloblastosis transcription factors that act as molecular switches for lignin production. Lignin content was increased by 68.46% and more after 48 h onwards in Hrip1-treated seedlings compared to the control treatment. Further analysis of cell wall morphology using the transmission electron microscopy technique revealed over 100% cell wall robustness. Hrip1 also induced the expression of 24 diterpene synthases. These include class I and II terpene synthases, cytochrome P450 subfamilies (OsCYP76M and OsCYP71Z), and momilactones synthases. The relationship between the expression of these genes and metabolic elicitation was analyzed using ultra-performance liquid chromatography-tandem mass spectrometry. Enhanced amounts of momilactones A and B, oryzalactone, and phytocassane A and G were detected in the Hrip1-treated leaves. We also identified seven benzoxazinoid genes (BX1-BX7) that could improve rice immunity. Our findings show that Hrip1 confers dual immunity by leveraging lignin and phytoalexins for physical and chemical resistance. This study provides novel insights into the mechanisms underlying Hrip1-treated plant immunity.

Biochemistry of Terpenes and Recent Advances in Plant Protection

Biodiversity is adversely affected by the growing levels of synthetic chemicals released into the environment due to agricultural activities. This has been the driving force for embracing sustainable agriculture. Plant secondary metabolites offer promising alternatives for protecting plants against microbes, feeding herbivores, and weeds. Terpenes are the largest among PSMs and have been extensively studied for their potential as antimicrobial, insecticidal, and weed control agents. They also attract natural enemies of pests and beneficial insects, such as pollinators and dispersers. However, most of these research findings are shelved and fail to pass beyond the laboratory and greenhouse stages. This review provides an overview of terpenes, types, biosynthesis, and their roles in protecting plants against microbial pathogens, insect pests, and weeds to rekindle the debate on using terpenes for the development of environmentally friendly biopesticides and herbicides.

Genome-wide alternative polyadenylation dynamics in response to biotic and abiotic stresses in rice

Alternative polyadenylation (APA) is an important way to regulate gene expression at the post-transcriptional level, and is extensively involved in plant stress responses. However, the systematic roles of APA regulation in response to abiotic and biotic stresses in rice at the genome scale remain unknown. To take advantage of available RNA-seq datasets, using a novel tool APAtrap, we identified thousands of genes with significantly differential usage of polyadenylation [poly(A)] sites in response to the abiotic stress (drought, heat shock, and cadmium) and biotic stress [bacterial blight (BB), rice blast, and rice stripe virus (RSV)]. Genes with stress-responsive APA dynamics commonly exhibited higher expression levels when their isoforms with short 3' untranslated region (3' UTR) were more abundant. The stress-responsive APA events were widely involved in crucial stress-responsive genes and pathways: e.g. APA acted as a negative regulator in heat stress tolerance; APA events were involved in DNA repair and cell wall formation under Cd stress; APA regulated chlorophyll metabolism, being associated with the pathogenesis of leaf diseases under RSV and BB challenges. Furthermore, APA events were found to be involved in glutathione metabolism and MAPK signaling pathways, mediating a crosstalk among the abiotic and biotic stress-responsive regulatory networks in rice. Analysis of large-scale datasets revealed that APA may regulate abiotic and biotic stress-responsive processes in rice. Such post-transcriptome diversities contribute to rice adaption to various environmental challenges. Our study would supply useful resource for further molecular assisted breeding of multiple stress-tolerant cultivars for rice.

The Novel Cerato-Platanin-Like Protein FocCP1 from Fusarium oxysporum Triggers an Immune Response in Plants

Panama disease, or Fusarium wilt, the most serious disease in banana cultivation, is caused by Fusarium oxysporum f. sp. cubense (FOC) and has led to great economic losses worldwide. One effective way to combat this disease is by enhancing host plant resistance. The cerato-platanin protein (CPP) family is a group of small secreted cysteine-rich proteins in filamentous fungi. CPPs as elicitors can trigger the immune system resulting in defense responses in plants. In this study, we characterized a novel cerato-platanin-like protein in the secretome of Fusarium oxysporum f. sp. cubense race 4 (FOC4), named FocCP1. In tobacco, the purified recombinant FocCP1 protein caused accumulation of reactive oxygen species (ROS), formation of necrotic reaction, deposition of callose, expression of defense-related genes, and accumulation of salicylic acid (SA) and jasmonic acid (JA) in tobacco. These results indicated that FocCP1 triggered a hypersensitive response (HR) and systemic acquired resistance (SAR) in tobacco. Furthermore, FocCP1 enhanced resistance tobacco mosaic virus (TMV) disease and Pseudomonas syringae pv. tabaci 6605 (Pst. 6605) infection in tobacco and improved banana seedling resistance to FOC4. All results provide the possibility of further research on immune mechanisms of plant and pathogen interactions, and lay a foundation for a new biological strategy of banana wilt control in the future.

The Secreted Protein MoHrip1 Is Necessary for the Virulence of Magnaporthe oryzae

Secreted effectors from Magnaporthe oryzae play critical roles in the interaction with rice to facilitate fungal infection and disease development. M. oryzae-secreted protein MoHrip1 can improve plant defense as an elicitor in vitro, however, its biological function in fungal infection is not clear. In this study, we found that the expression of mohrip1 was significantly induced in the stages of fungal penetration and colonization. Although dispensable for the growth and conidiation, MoHrip1 was necessary for the full virulence of M. oryzae. Deletion of mohrip1 remarkably compromised fungal virulence on rice seedlings and even on rice leaves with wounds. Rice sheath inoculation assay further demonstrated the defects of mohrip1-deleted mutants on penetration and proliferation in rice cells. Additionally, compared with WT and complementation strain, the inoculation of mohrip1-deleted mutants induced a higher expression of specific defense related genes and a higher production of specific defensive compounds in rice leaves. These data collectively indicated that MoHrip1 is necessary for fungal penetration and invasive expansion, and further full virulence of rice blast fungus.

Verticillium dahliae PevD1, an Alt a 1-like protein, targets cotton PR5-like protein and promotes fungal infection

Alt a 1 family proteins (AA1s) have only been observed in the Dothideomycetes and Sordariomycetes classes of fungi, and their biological functions have remained poorly understood. Verticillium dahliae, a soil-borne pathogen that causes plant wilt disease, secretes hundreds of proteins during the process of pathogenic infection, including the AA1 member PevD1. In this study, we found that the pevd1 transcript was present in all of the hosts studied (cotton, Arabidopsis, tomato, and tobacco) and showed elevated expression throughout the infection process. Furthermore, pevd1 knockout mutants displayed attenuated pathogenicity compared with the wild-type (WT) strain and complemented strains in hosts. A partner protein of PevD1, pathogenesis-related protein 5 (PR5)-like protein GhPR5, was isolated from cotton (Gossypium hirsutum) plants by co-purification assays, and the PevD1-GhPR5 interaction was determined to be localized in the C-terminus (PevD1b, amino acids residues 113-155) by pull-down and yeast two-hybrid techniques. Re-introduction of the pevd1b gene into a pevd1 knockout mutant resulted in restoration of the virulence phenotype to WT levels. In addition, PevD1b, which is similar to PevD1, decreased the antifungal activity of GhPR5 in vitro. Our findings reveal an infection strategy in which V. dahliae secretes PevD1 to inhibit GhPR5 antifungal activity in order to overcome the host defence system.

The Magnaporthe oryzae Alt A 1-like protein MoHrip1 binds to the plant plasma membrane

MoHrip1, a protein isolated from Magnaporthe oryzae, belongs to the Alt A 1 (AA1) family. mohrip1 mRNA levels showed inducible expression throughout the infection process in rice. To determine the location of MoHrip1 in M. oryzae, a mohrip1-gfp mutant was generated. Fluorescence microscopy observations and western blotting analysis showed that MoHrip1 was both present in the secretome and abundant in the fungal cell wall. To obtain MoHrip1 protein, we carried out high-yield expression of MoHrip1 in Pichia pastoris. Treatment of tobacco plants with MoHrip1 induced the formation of necrosis, accumulation of reactive oxygen species and expression of several defense-related genes, as well as conferred disease resistance. By fusion to green fluorescent protein, we showed that MoHrip1 was able to bind to the tobacco and rice plant plasma membrane, causing rapid morphological changes at the cellular level, such as cell shrinkage and chloroplast disorganization. These findings indicate that MoHrip1 is a microbe-associated molecular pattern that is perceived by the plant immune system. This is the first study on an AA1 family protein that can bind to the plant plasma membrane.

The Verticillium dahliae SnodProt1-Like Protein VdCP1 Contributes to Virulence and Triggers the Plant Immune System

During pathogenic infection, hundreds of proteins that play vital roles in the Verticillium dahliae-host interaction are secreted. In this study, an integrated proteomic analysis of secreted V. dahliae proteins was performed, and a conserved secretory protein, designated VdCP1, was identified as a member of the SnodProt1 phytotoxin family. An expression analysis of the vdcp1 gene revealed that the transcript is present in every condition studied and displays elevated expression throughout the infection process. To investigate the natural role of VdCP1 in V. dahliae, two vdcp1 knockout mutants and their complementation strains were generated. Bioassays of these mutants revealed no obvious phenotypic differences from the wild-type (WT) in terms of mycelial growth, conidial production or mycelial/spore morphology. However, compared with the WT, the vdcp1 knockout mutants displayed attenuated pathogenicity in cotton plants. Furthermore, treating plants with purified recombinant VdCP1 protein expressed in Pichia pastoris induced the accumulation of reactive oxygen species (ROS), expression of several defense-related genes, leakage of ion electrolytes, enhancement of defense-related enzyme activity and production of salicylic acid. Moreover, VdCP1 conferred resistance to Botrytis cinerea and Pseudomonas syringae pv. tabaci in tobacco and to V. dahliae in cotton. Further research revealed that VdCP1 possesses chitin-binding properties and that the growth of vdcp1 knockout mutants was more affected by treatments with chitinase, indicating that VdCP1 could protect V. dahliae cell wall from enzymatic degradation, which suggests an effector role of VdCP1 in infecting hosts.