Reactive oxygen species, essential molecules, during plant-pathogen interactions

Defence Warriors: Exploring the crosstalk between polyamines and oxidative stress during microbial pathogenesis

Microbial infections have been a widely studied area of disease research since historical times, yet they are a cause of severe illness and deaths worldwide. Furthermore, infections by pathogens are not just restricted to humans; instead, a diverse range of hosts, including plants, livestock, marine organisms and fish, cause significant economic losses and pose threats to humans through their transmission in the food chain. It is now believed that both the pathogen and the host contribute to the outcomes of a disease pathology. Researchers have unravelled numerous aspects of host-pathogen interactions, offering valuable insights into the physiological, cellular and molecular processes and factors that contribute to the development of infectious diseases. Polyamines are key factors regulating cellular processes and human ageing and health. However, they are often overlooked in the context of host-pathogen interactions despite playing a dynamic role as a defence molecule from the perspective of the host as well as the pathogen. They form a complex network interacting with several molecules within the cell, with reactive oxygen species being a key component. This review presents a thorough overview of the current knowledge of polyamines and their intricate interactions with reactive oxygen species in the infection of multiple pathogens in diverse hosts. Interestingly, the review covers the interplay of the commensals and pathogen infection involving polyamines and reactive oxygen species, highlighting an unexplored area within this field. From a future perspective, the dynamic interplay of polyamines and oxidative stress in microbial pathogenesis is a fascinating area that widens the scope of developing therapeutic strategies to combat deadly infections.

Selenium: The Toxicant for Pathogen and Pest but the Guardian of Soil and Crop

Selenium (Se) is an essential micronutrient for higher organisms and plays a beneficial role in plant growth and development. In recent years, there has been growing interest in the using of Se to enhance plant resilience, particularly in mitigating the effects of diseases and pests in agricultural systems. This review offers a comprehensive analysis of the sources and chemical forms of Se in soil, investigates the mechanisms of plant uptake and metabolism of different Se forms, and evaluates the physical and chemical inhibition of pathogens by various Se forms, as well as the role of Se in enhancing plant systemic resistance for crop protection. Additionally, we summarize current research on the role of Se in pest and disease control and explore potential future research directions, with a focus on integrating Se into sustainable agricultural practices. The insights presented in this review seek to establish a solid scientific foundation for Se-based approaches to pest control and emphasize its potential application in sustainable agriculture.

CarboTag: a modular approach for live and functional imaging of plant cell walls

Plant cells are contained within a rigid network of cell walls. Cell walls serve as a structural material and a crucial signaling hub vital to all aspects of the plant life cycle. However, many features of the cell wall remain enigmatic, as it has been challenging to map its functional properties in live plants at subcellular resolution. Here, we introduce CarboTag, a modular toolbox for live functional imaging of plant walls. CarboTag uses a small molecular motif, a pyridine boronic acid, that directs its cargo to the cell wall. We designed a suite of cell wall imaging probes based on CarboTag in various colors for multiplexing. Additionally, we developed new functional reporters for live quantitative imaging of key cell wall characteristics: network porosity, cell wall pH and the presence of reactive oxygen species. CarboTag paves the way for dynamic and quantitative mapping of cell wall responses at subcellular resolution.

Interplay Between ROS and Hormones in Plant Defense Against Pathogens

Reactive oxygen species (ROS) are toxic by-products of aerobic cellular metabolism. However, ROS conduct multiple functions, and specific ROS sources can have beneficial or detrimental effects on plant health. This review explores the complex dynamics of ROS in plant defense mechanisms, focusing on their involvement in basal resistance, hypersensitive response (HR), and systemic acquired resistance (SAR). ROS, including superoxide anion (O2-), singlet oxygen (1O2), hydroxyl radicals (OH), and hydrogen peroxide (H2O2), are generated through various enzymatic pathways. They may serve to inhibit pathogen growth while also activating defense-related gene expression as signaling molecules. Oxidative damage in cells is mainly attributed to excess ROS production. ROS produce metabolic intermediates that are involved in various signaling pathways. The oxidative burst triggered by pathogen recognition initiates hyper-resistance (HR), a localized programmed cell death restricting pathogen spread. Additionally, ROS facilitate the establishment of SAR by inducing systemic signaling networks that enhance resistance across the plant. The interplay between ROS and phytohormones such as jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) further complicates this regulatory framework, underscoring the importance of ROS in orchestrating both local and systemic defense responses. Grasping these mechanisms is essential for creating strategies that enhance plant resilience to biotic stresses.

Endophytic and Rhizospheric Microorganisms: An Alternative for Sustainable, Organic, and Regenerative Bioinput Formulations for Modern Agriculture

Large amounts of chemical fertilizers are still used to suppress pathogens and boost agricultural productivity and food generation. However, their use can cause harmful environmental imbalance. Furthermore, plants typically absorb limited amounts of the nutrients provided by chemical fertilizers. Recent studies are recommending the use of microbiota present in the soil in different formulations, considering that several microorganisms are found in nature in association with plants in a symbiotic, antagonistic, or synergistic way. This ecological alternative is positive because no undesirable significant alterations occur in the environment while stimulating plant nutrition development and protection against damage caused by control pathogens. Therefore, this review presents a comprehensive discussion regarding endophytic and rhizospheric microorganisms and their interaction with plants, including signaling and bio-control processes concerning the plant's defense against pathogenic spread. A discussion is provided about the importance of these bioinputs as a microbial resource that promotes plant development and their sustainable protection methods aiming to increase resilience in the agricultural system. In modern agriculture, the manipulation of bioinputs through Rhizobium contributes to reducing the effects of greenhouse gases by managing nitrogen runoff and decreasing nitrous oxide. Additionally, mycorrhizal fungi extend their root systems, providing plants with greater access to water and nutrients.

Advances and challenges in green extraction of chitin for food and agriculture applications: A review

Chitin, the second most abundant polysaccharide in nature, offers numerous practical applications due to its versatile functional properties. However, its utilization is constrained by significant challenges in extraction, as well as low solubility and high crystallinity. While traditional chemical and biological fermentation methods can achieve high-purity chitin, these processes are often environmentally harmful or time/energy-consuming. Ionic liquids and deep eutectic solvents have emerged as more sustainable alternatives for chitin extraction, though both methods still face certain limitations, which are comprehensively discussed in this review. Besides extraction, chitin or modified chitin is increasingly being used to create a variety of biomaterials, which have shown considerable potential in food applications, including food packaging, preservation, stabilization, and nutrient encapsulation and delivery. Furthermore, the applications of chitin-based biomaterials are also reviewed in agriculture, where they are utilized as fertilizers, biocides, the elicitation of plants, or to treat seeds. This review not only provides a deeper understanding of the advancements and limitations in green chitin extraction methods but also highlights the broad potential of chitin-based biomaterials in both food and agriculture.

The family of glutathione peroxidase proteins and their role against biotic stress in plants: a systematic review

Introduction

Glutathione peroxidases (GPXs) are extensively studied for their indispensable roles in eliminating reactive oxygen species by catalyzing the reduction of hydrogen peroxide or lipid peroxides to prevent cell damage. However, knowledge of GPXs in plants still has many gaps to be filled. Thus, we present the first systematic review (SR) aimed at examining the function of GPXs and their protective role against cell death in plants subjected to biotic stress.

Methods

To guide the SR and avoid bias, a protocol was developed that contained inclusion and exclusion criteria based on PRISMA guidelines. Three databases (PubMed, Science Direct, and Springer) were used to identify relevant studies for this research were selected.

Results

A total of 28 articles related to the proposed objective. The results highlight the importance of GPXs in plant defense against biotic stress, including their role in protecting against cell death, similar to the anti-apoptotic GPXs in animals. Data from gene expression and protein accumulation studies in plants under various biotic stresses reveal that GPXs can both increase resistance and susceptibility to pathogens. In addition to their antioxidant functions, GPXs act as sensors and transmitters of H2O2 signals, integrating with the ABA signaling pathway during stress.

Discussion

These findings show that GPXs delay senescence or reinforce physical barriers, thereby modulating resistance or susceptibility to pathogens. Additionally, their functions are linked to their cellular localization, which demonstrates an evolutionary relationship between the studied isoforms and their role in plant defense. This information broadens the understanding of molecular strategies involving GPX isoforms and provides a foundation for discussions and actions aimed at controlling necrotrophic and/or hemibiotrophic pathogens.

Proteomic Landscape of Pattern Triggered Immunity in the Arabidopsis Leaf Apoplast

The apoplast is a critical interface in plant-pathogen interactions particularly in the context of pattern-triggered immunity (PTI), which is initiated by recognition of microbe-associated molecular patterns (PAMPs). Our study characterizes the proteomic profile of the Arabidopsis apoplast during PTI induced by flg22, a 22 amino acid bacterial flagellin epitope, to elucidate the output of PTI. Apoplastic washing fluid (AWF) was extracted with minimal cytoplasmic contamination for LC-MS/MS analysis. We observed consistent identification of PTI enriched and depleted peptides across replicates with limited correlation between total protein abundance and transcript abundance. We observed topological bias in peptide recovery of receptor-like kinases with peptides predominantly recovered from their ectodomains. Notably, tetraspanin 8, an exosome marker, was enriched in PTI samples. We additionally confirmed increased concentrations of exosomes during PTI. This study enhances our understanding of the proteomic changes in the apoplast during plant immune responses and lays the groundwork for future investigations into the molecular mechanisms of plant defense under recognition of pathogen molecular patterns.

Molecular Traits of Rapid Alkalinization Factor Family and Functional Analysis of SlRALF2 in Tomato Resistance to Phytophthora infestans

Late blight, caused by Phytophthora infestans (P. infestans), poses a significant threat to tomato yield and quality. Traditional disease control strategies rely heavily on frequent applications of chemical pesticides, leading to environmental pollution and the emergence of pesticide-resistant pathogens. This highlights the urgent need for environmentally friendly plant disease control technologies. Rapid alkalinization factors (RALFs) are secreted peptides that play crucial roles in plant defense. Here, 11 SlRALF genes were identified in tomato. Bioinformatics analyses were conducted to characterize them. SlRALF2, which responded significantly to P. infestans infection, was chosen for investigation. Functional analyses demonstrated that SlRALF2 enhances tomato resistance by promoting the expression level of SlPRs and modulating key enzyme activities. GO and KEGG analyses of key genes influenced by SlRALF2 revealed its involvement in several critical pathways. Altogether, our findings establish SlRALF2 as a pivotal component of tomato defense signaling, offering valuable insights for crop breeding.

MdVQ37 Negatively Regulates Apple Resistance to Valsa Canker via SA-Dependent and SA-Independent Pathways

Apple Valsa canker is one of the major fungal diseases adversely affecting the apple industry. Valine-glutamine motif-containing proteins (VQs) are a kind of plant transcription regulation cofactor, which are involved in regulating the growth and development of plants and their defence responses. Yet little is known about the role of VQs in the biotic stress response of woody plants, especially in apple trees. Recently, we identified MdVQ37 as a negative regulator of apple resistance to Glomerella leaf spot by inhibiting MdWRKY100-mediated salicylic acid (SA) accumulation via protein interaction. Here we found that MdVQ37 expression was induced significantly by Valsa mali infection. Overexpressing MdVQ37 in apple increased its susceptibility to V. mali, accompanied by a reduction in H2O2 accumulation along with the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), chitinase and β-1,3-glucanase. Meanwhile, MdVQ37 overexpression increased the expression of two SA catabolic genes, MdS5H1 and MdS5H2, resulting in a greater accumulation of the SA metabolite 2,5-dihydroxybenzoic acid (2,5-DHBA), but a decreased SA content and less signalling in transgenic plants. MdPER3, a peroxidase-encoding gene, was identified as a direct target of MdWRKY100. Analysis of transcriptional regulation activity showed that MdVQ37 inhibited the binding and transcriptional ability of MdWRKY100 on the MdPER3 promoter, thereby reducing antioxidant enzyme activity and weakening the Valsa canker resistance. Overall, our results show that MdVQ37 negatively regulates apple defence against V. mali through both SA-dependent and SA-independent pathways. Our findings provide novel insight into the mechanisms by which the VQ-WRKY complex modulates plant defence responses against pathogens.

Do different wheat ploidy levels respond differently against stripe rust infection: Interplay between reactive oxygen species (ROS) and the antioxidant defense system?

Wheat stripe rust (Puccinia striiformis f. sp. tritici, Pst) is the most damaging wheat disease, causing substantial losses in global wheat production and productivity. Our study aimed to unravel the complex reciprocity between reactive oxygen species and the antioxidant defense system as a source of resistance against stripe rust in diploid, tetraploid and hexaploid wheat genotypes. The significant genetic variability for stripe rust in the materials under study was evident as the genotypes showed contrasting responses during both the adult and seedling stages. Our thorough perspective on the biochemical responses of wheat genotypes to stripe rust infection revealed distinct patterns in oxidative damage, antioxidant enzymes and photosynthetic pigments. Principal component analysis revealed inverse correlations between antioxidants and ROS, underscoring their key function in maintaining the cellular redox balance and protecting plants against oxidative damage. Diploid (Ae. tauschii) wild wheat exhibited a better biochemical defense system and greater resistance to stripe rust than the tetraploid (T. durum) and hexaploid (Triticum aestivum) wheat genotypes. The antioxidant enzyme activity of durum wheat was moderate compared to diploid and hexaploid wheat genotypes. The hexaploid wheat genotypes exhibited increased ROS production, reduced antioxidant enzyme activity and decreased photosynthetic pigment levels. This study enhances understanding of the antioxidant defense system across different wheat ploidies facing stripe rust, serving as a valuable strategy for improving crop disease resistance. This study validated the biochemical response of stripe rust-resistant and susceptible candidate genotypes, which will be used to develop genetic resources for discovering stripe rust resistance genes in wheat.

Coenzyme M: An Archaeal Antioxidant as an Agricultural Biostimulant

Rising global food demand necessitates improved crop yields. Biostimulants offer a potential solution to meet these demands. Among them, antioxidants have shown potential to improve yield, nutritional quality, and resilience to climate change. However, large-scale production of many antioxidants is challenging. Here, we investigate Coenzyme M (CoM), a small, achiral antioxidant from archaea, as a potential biostimulant, investigating its effects on growth and physiology. CoM significantly increased shoot mass and root length of the model plant, Arabidopsis thaliana, in a concentration-dependent manner. Sulfur-containing CoM supplementation restored growth under sulfur-limited conditions in Arabidopsis, whereas similar recovery was not observed for other macronutrient deficiencies, consistent with it being metabolized. In tobacco, CoM increased photosynthetic light capture capacity, consistent with observed growth improvements. Interestingly, this effect was independent of carbon capture rates. Furthermore, CoM promoted early-stage shoot growth in various crops species, including tobacco, basil, cannabis, and soybean. Our results suggest CoM is a promising, scalable biostimulant with potential to modify photosynthesis and enhance crop productivity.

Effect of elevated ammonium on biotic and abiotic stress defense responses and expression of related genes in cucumber (Cucumis sativus L.) plants

Ammonium (NH4+) enhances plant defense mechanisms but can be phytotoxic as the sole nitrogen source. To investigate the impact of a balanced NH4+ and NO3- ratio on plant defense parameters without adverse effects, cucumber plants (Cucumis sativus L.) were grown under control (14 mM NO3- + 2 mM NH4+) and elevated level of NH4+ (eNH4+, 8 mM NO3-+ 8 mM NH4+). Plants subjected to eNH4+ showed significantly increased shoot and root biomass by about 41% and 47%, respectively. Among the antioxidant enzymes studied, ascorbate peroxidase (EC 1.11.1.11) activity was increased up to 3.3 fold in eNH4+ compared with control plants, which was associated with enhanced resistance to paraquat. Upregulation of PATHOGENESIS RELATED PROTEIN 4 (PR4) and LIPOXYGENASE 1 (LOX1), accompanied by increased concentrations of salicylic acid and nitric oxide, conferred more excellent resistance of eNH4+ plants to powdery mildew infection. However, the expression levels of ACC OXIDASE 1 (ACO1) and RESPIRATORY BURST OXIDASE HOMOLOGS B (RBOHB) were lower in eNH4+ plants, which was consistent with decreased NADPH oxidase activity and lower leaf H2O2 levels. The biosynthesis of phenolics was enhanced, whereas the activities of polymerizing enzymes and lignin deposition were reduced by half in eNH4+ plants. Besides, a significant effect on plant biomass under salt or drought stress has not been observed between control and eNH4+ plants. These results showed that different defense pathways are distinctively affected by eNH4+ treatment, and the NH4+ to NO3- ratio may play a role in fine-tuning the plant defense response.

Antioxidant Responses and Redox Regulation Within Plant-Beneficial Microbe Interaction

The increase in extreme climate events associated with global warming is a great menace to crop productivity nowadays. In addition to abiotic stresses, warmer conditions favor the spread of infectious diseases affecting plant performance. Within this context, beneficial microbes constitute a sustainable alternative for the mitigation of the effects of climate change on plant growth and productivity. Used as biostimulants to improve plant growth, they also increase plant resistance to abiotic and biotic stresses through the generation of a primed status in the plant, leading to a better and faster response to stress. In this review, we have focused on the importance of a balanced redox status for the adequate performance of the plant and revisited the different antioxidant mechanisms supporting the biocontrol effect of beneficial microbes through the adjustment of the levels of reactive oxygen species (ROS). In addition, the different tools for the analysis of antioxidant responses and redox regulation have been evaluated. The importance of redox regulation in the activation of the immune responses through different mechanisms, such as transcriptional regulation, retrograde signaling, and post-translational modification of proteins, emerges as an important research goal for understanding the biocontrol activity of the beneficial microbes.

GhCNGC31 is critical for conferring resistance to Verticillium wilt in cotton

In the past decades, cyclic nucleotide-gated ion channels (CNGCs) have been extensively studied in diploid species Arabidopsis thaliana. However, the functional diversification of CNGCs in crop plants, mostly polyploid, remains poorly understood. In allotetraploid Upland cotton (Gossypium hirsutum), GhCNGC31 is one of the multiple orthologs of AtCNGC2, being present in the plasma membrane, capable of interacting with itself and binding to calmodulins and cyclic nucleotides. GhCNGC31 knockdown plants exhibited slight growth inhibition, and became more susceptible to Verticillium dahliae infection, which was associated with the reduced lignin and flavonoid accumulation, impaired ROS (reactive oxygen species) burst, and down-regulation of defense-related genes PR1, JAZ2, LOX2, and RBOH10. RNA-Seq analysis identified 1817 differentially expressed genes from GhCNGC31 knockdown, of which 1184 (65%) were responsive to V. dahliae infection and accounted for 57% among a total of 2065 V. dahliae-responsive genes identified in this study. These GhCNGC31-regulated genes mainly function with cell wall organization and biogenesis, cellular carbohydrate metabolic or biosynthetic process, cellular component macromolecule biosynthetic process, and rhythmic process. They are significantly enriched in the pathways of plant MAPK signaling, plant-pathogen interaction, phenylpropanoid biosynthesis, and plant hormone signal transduction. A set of transcription factors (TFs) and resistance (R) genes are among the GhCNGC31-regulated genes, which are significantly over-represented with the TCP and WRKY TFs families, as well as with the R genes of T (TIR) and TNL (TIR-NB-LRR) classes. Together, our results unraveled a critical role of GhCNGC31 for conferring resistance to Verticillium wilt in cotton.

A Colletotrichum fructicola dual specificity phosphatase CfMsg5 is regulated by the CfAp1 transcription factor during oxidative stress and promotes virulence on Camellia oleifera

Anthracnose, caused by Colletotrichum species, induces significant economic damages to crop plants annually, especially for Camellia oleifera. During infection, the counter-defence mechanisms of plant pathogens against ROS-mediated resistance, however, remain poorly understood. By employing Weighted Gene Co-expression Network Analysis (WGCNA), we identified ACTIVATOR PROTEIN-1 (AP-1), a bZIP transcription factor, as significant to infection. And deletion of CfAP1 inhibited aerial hyphae formation and growth under oxidative stress. Furthermore, RNA-seq analysis post H2O2 treatment revealed 33 significantly down-regulated genes in the AP-1 deficient strain, including A12032, a dual specificity phosphatase (DSP) homologous to MSG5 from Saccharomyces cerevisiae. This ΔCfmsg5 strain showed enhanced oxidative tolerance, reduced ROS scavenging, and negative regulation of the CWI MAPK cascade under oxygen stress, suggesting its involvement in oxidative signal transduction. Importantly, we provide evidence that CfMsg5 regulates growth, endoplasmic reticulum stress, and several unfolded protein response genes upregulated in ΔCfmsg5. Collectively, this study identified core components during C. fructicola infection and highlights a potential regulatory module involving CfAp1 and CfMsg5 in response to host ROS bursts. It provides new insights into fungal infection mechanisms and potential targets like CfAP1 and CfMSG5 for managing anthracnose diseases.

Characterization of the chitinase gene family in Saccharum reveals the disease resistance mechanism of ScChiVII1

KEY MESSAGE

A chitinase gene ScChiVII1 which is involved in defense against pathogen stress was characterized in sugarcane. Chitinases, a subclass of pathogenesis-related proteins, catalyze chitin hydrolysis and play a key role in plant defense against chitin-containing pathogens. However, there is little research on disease resistance analysis of chitinase genes in sugarcane, and the systematic identification of their gene families has not been reported. In this study, 85 SsChi and 23 ShChi genes, which were divided into 6 groups, were identified from the wild sugarcane species Saccharum spontaneum and Saccharum hybrid cultivar R570, respectively. Transcriptome analysis and real-time quantitative PCR revealed that SsChi genes responded to smut pathogen stress. The chitinase crude extracted from the leaves of transgenic Nicotiana benthamiana plants overexpressing ScChiVII1 (a homologous gene of SsChi22a) inhibited the hyphal growth of Fusarium solani var. coeruleum and Sporisorium scitamineum. Notably, the chitinase and catalase activities and the jasmonic acid content in the leaves of ScChiVII1 transgenic N. benthamiana increased after inoculation with F solani var. coeruleum, but the salicylic acid, hydrogen peroxide, and malondialdehyde contents decreased. Comprehensive RNA sequencing of leaves before (0 day) and after inoculation (2 days) revealed that ScChiVII1 transgenic tobacco enhanced plant disease resistance by activating transcription factors and disease resistance-related signaling pathways, and modulating the expression of genes involved in the hypersensitive response and ethylene synthesis pathways. Taken together, this study provides comprehensive information on the chitinase gene family and offers potential genetic resources for disease resistance breeding in sugarcane.

Effects of water stress on secondary metabolism of Panax ginseng fresh roots

The roots and rhizomes of Panax ginseng C.A. Mey are commonly used herbal medicine in Asian countries. These components contain a large number of secondary metabolites known as ginsenosides, which serve as primary active ingredient. Environmental factors significantly influence the production of secondary metabolites, which are crucial for enhancing plant adaptability to ecological stress. P. ginseng is a shady plant that thrives in a constantly humid and temperate environment. However, it cannot withstand excessive moisture, making soil moisture a significant ecological stress affecting P. ginseng survival. In this study, we applied a water spray to maintain a water-saturated surface on 5-year-old fresh P. ginseng roots for a duration of 5 days, to establish a short-term water stress condition. The results revealed a notable increase in superoxide anion (O2·-), hydrogen peroxide (H2O2), and NADPH oxidase (NOX) activity (p < 0.01), as well as malondialdehyde (MDA) contents (p < 0.01) in both the main root and fibrous root of P. ginseng. Additionally, superoxide dismutase (SOD), catalase (CAT), peroxides (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities also elevated significantly under water stress (p < 0.01). Ascorbic acid (AsA), glutathione (GSH) and oxidized glutathione (GSSG) contents also showed a marked increase (p < 0.01). The main root treated with water showed the most positive impact on the 5th day. Water stress boosted the activities of key enzymes including 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), farnesyl pyrophosphate synthase (FPS), squalene synthase (SS), squalene epoxidase (SE), and dammarenediol-II synthase (DS) involved in the ginsenoside biosynthesis pathway (p <0.01). This resulted in a significant an increase in the level of ginsenosides Rg1, Rb1, Rf, Rg2+Rh1, Rc, and Rb3, by 42.4%, 21.0%, 15.7%, 157.9%, 18.3%, and 10.6% respectively, and an increase of 40.1% in total saponins content. Similarly, the fibrous root changes in the treated sample showed the most positive impact on the 4th day. Specifically, Rg1, Re, Rb1, Rf, Rg2+Rh1, Rc, Ro, and Rb2 increased by 41.8%, 20.5%, 17.3%, 84.3%, 30.7%, 35.6%, 8.6%, and 7.6%, respectively, and an increase of 4.2% in total saponins content. Furthermore, 1,3-disphosphoglycerate (1,3-DPG) contents and phosphoenolpyruvate carboxylase (PEPC) activities, which are key intermediate of primary metabolism, were significantly elevated under water stress (p < 0.01). This indicates that the primary source of the raw materials used in the biosynthesis of secondary metabolites is sugars. Pharmacodynamic analysis demonstrated that water stress could increase the contents of ginsenosides, improve the quality of ginseng, and enhance the efficacy of ginseng root to a certain extent.

A Golgi vesicle-membrane-localized cytochrome B561 regulates ascorbic acid regeneration and confers Verticillium wilt resistance in cotton

Ascorbic acid (AsA) serves as a key antioxidant involved in the various physiological processes and against diverse stresses in plants. Due to the insufficiency of AsA de novo biosynthesis, the AsA regeneration is essential to supplement low AsA synthesis rates. Redox reactions play a crucial role in response to biotic stress in plants; however, how AsA regeneration participates in hydrogen peroxide (H2O2) homeostasis and plant defense remains largely unknown. Here, we identified a Golgi vesicle-membrane-localized cytochrome B561 (CytB561) encoding gene, GhB561-11, involved in AsA regeneration and plant resistance to Verticillium dahliae in cotton. GhB561-11 was significantly downregulated upon V. dahliae attack. Knocking down GhB561-11 greatly enhanced cotton resistance to V. dahliae. We found that suppressing GhB561-11 inhibited the AsA regeneration, elevated the basal level of H2O2, and enhanced the plant defense against V. dahliae. Further investigation revealed that GhB561-11 interacted with the lipid droplet-associated protein GhLDAP3 to collectively regulate the AsA regeneration. Simultaneously silencing GhB561-11 and GhLDAP3 significantly elevated the H2O2 contents and dramatically improved the Verticillium wilt resistance in cotton. The study broadens our insights into the functional roles of CytB561 in regulating AsA regeneration and H2O2 homeostasis. It also provides a strategy by downregulating GhB561-11 to enhance Verticillium wilt resistance in cotton breeding programs.

Transcriptomic analysis reveals differential transcriptional regulation underlying Citrus Bacterial Canker (CBC) tolerance in Citrus sinensis

The sustainable development of the citrus industry is greatly affected by citrus canker, an important bacterial disease. To explore the transcriptional regulatory mechanism of citrus resistance to canker disease, this study used the susceptible Citrus sinensis cv. 'Newhall' and its citrus canker-resistant bud mutation variety 'Longhuitian' (LHT) as materials. Through analysing the variances in leaf phenotypes between Newhall and LHT, as well as the variations in their transcriptional expression under Xanthomonas citri subsp. citri (Xcc) inoculation, our study concluded that LHT displays markedly greater resistance to Xcc compared to Newhall. Additionally, the spongy parenchyma of LHT leaves is significantly thicker than that of Newhall, and the stomatal number is significantly higher in LHT leaves, while the length and width of individual stomata in LHT leaves are significantly smaller than those in Newhall. RNA-seq analysis indicates that the differentially expressed genes between LHT and Newhall are involved in biotic stress-related biological processes, secondary metabolite biosynthesis, as well as phytohormone signalling pathways. Furthermore, significant differences were observed in reactive oxygen metabolism and phenylalanine metabolism pathways. The findings of our study provide data support for a deeper understanding of the citrus-Xcc interactions and offer valuable clues for unravelling citrus resistance to citrus canker.

Colletotrichum gloeosporioides Swiftly Manipulates the Transcriptional Regulation in Citrus sinensis During the Early Infection Stage

Citrus spp. represent an economically important fruit tree crop worldwide. However, molecular mechanisms underlying the interaction between citrus and the Colletotrichum gloeosporioides remain largely unexplored. In this study, we analyzed the physiological and transcriptomic changes in Citrus sinensis at different stages of incubation with C. gloeosporioides. The results indicated that C. gloeosporioides infection rapidly triggered necrosis in the epicarp of C. sinensis fruits, decreased the total flavonoid contents, and suppressed the activity of catalase, peroxidase, and superoxide dismutase enzymes. Upon inoculation with C. gloeosporioides, there were 4600 differentially expressed genes (DEGs) with 1754 down-regulated and 2846 up-regulated after six hours, while there were only 580 DEGs with 185 down-regulated and 395 up-regulated between six and twelve-hours post-inoculation. Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes enrichment analysis indicated that the DEGs, which exhibited consistent up-regulation, were associated with metabolic processes and stress responses. Through Weighted Gene Co-Expression Network Analysis, 11 key genes have been identified that could potentially play a role in the transcriptional regulation of this process, including the transcription factor bHLH189. Furthermore, the infection of C. gloeosporioides had a notable effect on both the flavonoid metabolism and the metabolic pathways related to reactive oxygen species. Our findings help to understand the interaction between citrus and C. gloeosporioides and unveil how new insights into how C. gloeosporioides circumvents citrus defense mechanisms.

Antifungal mechanisms and characteristics of Pseudomonas fluorescens: Promoting peanut growth and combating Fusarium oxysporum-induced root rot

Continuous cropping of peanuts presents significant challenges to sustainable production due to soil-borne diseases like root rot caused by Fusarium species. In this study, field inoculation experiments treatments and in vitro agar plate confrontation tests were conducted, including non-inoculated controls (CK), inoculation with Pseudomonas fluorescens (PF), Fusarium oxysporum (FO), and co-inoculation with both (PF + FO). The aim was to explore the antifungal mechanisms of Pseudomonas fluorescens in mitigating root rot and enhancing peanut yield. The results indicated that PF and PF + FO significantly enhanced peanut root activity, as well as superoxide dismutase, catalase, and glutathione S-transferase activities, while simultaneously decreasing the accumulation of reactive oxygen species and malondialdehyde contents, compared to FO treatment. Additionally, PF treatment notably increased lignin content through enhanced phenylalanine ammonia lyase, cinnamate 3-hydroxylase, and peroxidase activity compared to CK and FO treatment. Moreover, PF treatment resulted in longer roots and a higher average diameter and surface area, potentially due to increased endogenous levels of auxin and zeatin riboside, coupled with decreased abscisic acid content. PF treatment significantly elevated chlorophyll content and the maximum photochemical efficiency of PSII in the light-adapted state, the actual photochemical efficiency and the proportion of PSII reaction centers open, leading to improved photosynthetic performance. Confrontation culture assays revealed PF's notable inhibitory effects on Fusarium oxysporum growth, subsequently reducing rot disease incidence in the field. Ultimately, PF treatment led to increased peanut yield by enhancing plant numbers and pod weight compared to FO treatment, indicating its potential in mitigating Fusarium oxysporum-induced root rot disease under continuous cropping systems.

PbrATG6 modulates reactive oxygen species metabolism and interacts with PbrTLP15 synergistic enhancement of pear resistance to Botryosphaeria dothidea

Autophagy is vital for plant defense against pathogens, with ATG6 being a key gene in this process. At present, little has been reported on the potential function and molecular mechanisms of ATG6 mediated pathogen resistance in pear. This study investigates the function of the pear homolog of ATG6 (PbrATG6) in resistance to Botryosphaeria dothidea. PbrATG6 is expressed differentially in pear tissues and its expression increases upon infection. Overexpression of PbrATG6 enhances resistance in Arabidopsis and pear calli, while silencing it increases susceptibility. PbrTLP15, a pathogenesis-related protein belonging to the PR5 family, was found that interacts with PbrATG6 by a yeast two-hybrid screening. Yeast two-hybrid, luciferase complementation imaging, bimolecular fluorescence complementation assays and pull-down assays showed that PbrATG6 interacts with PbrTLP15. The transient silencing transgenic assays of PbrATG6 and PbrTLP15 revealed that PbrATG6 could cooperate with PbrTLP15 to regulate pear B. dothidea resistance. In addition, transcriptional analyses of autophagy key genes in pTRV-PbrTLP15 and transmission electron microscopy (TEM) assays also implied that PbrTLP15 does affect autophagy. Hence, PbrATG6 and PbrTLP15 may synergistically enhance pear B. dothidea disease resistance. It provides a new strategy for the study of autophagy in pear disease resistance and enriches the research on pear disease resistance mechanism.

BW312 Hordeum vulgare semi-dwarf mutant exhibits a shifted metabolic profile towards pathogen resistance

INTRODUCTION

Plant hormonal mutants, which do not produce or are insensitive to hormones, are often affected in their growth and development, but other metabolic rearrangements might be involved. A trade-off between growth and stress response is necessary for the plant survival.

OBJECTIVES

Here, we explore the metabolic profile and the pathogen resistance of a brassinosteroid-insensitive Hordeum vulgare L. semi-dwarf mutant, BW312.

METHODS

We investigate BW312 metabolism through a chemical enrichment analysis, confirming a shifted metabolic profile towards pathogen resistance. The effective pathogen resistance of the mutant was tested in presence of Pyrenophora teres and Fusarium graminearum.

RESULTS

Four compound families were increased in the mutant (pyrrolidines, basic amino acids, alkaloids, monounsaturated fatty acids), while two compound families were decreased (pyrrolidinones, anthocyanins). Dipeptides were also altered (increased and decreased). BW312 displayed a better resistance to Pyrenophora teres in the earliest stage of infection with a 21.5% decrease of the lesion length 10 days after infection. BW312 also exhibited a reduced lesion length (43.3%) and a reduced browning of the lesions (55.5%) when exposed to Fusarium graminearum at the seedling stage.

CONCLUSION

The observed metabolomic shift strongly suggests that the BW312 semi-dwarf mutant is in a primed state, resulting in a standby state of alertness to pathogens.

Molecular insights into OPR gene family in Saccharum identified a ScOPR2 gene could enhance plant disease resistance

12-Oxo-phytodienoic acid reductases (OPRs) perform vital functions in plants. However, few studies have been reported in sugarcane (Saccharum spp.), and it is of great significance to systematically investigates it in sugarcane. Here, 61 ShOPRs, 32 SsOPRs, and 36 SoOPRs were identified from R570 (Saccharum spp. hybrid cultivar R570), AP85-441 (Saccharum spontaneum), and LA-purple (Saccharum officinarum), respectively. These OPRs were phylogenetically classified into four groups, with close genes similar structures. During evolution, OPR gene family was mainly expanded via whole-genome duplications/segmental events and predominantly underwent purifying selection, while sugarcane OPR genes may function differently in response to various stresses. Further, ScOPR2, a tissue-specific OPR, which was localized in cytoplasm and cell membrane and actively response to salicylic acid (SA), methyl jasmonate, and smut pathogen (Sporisorium scitamineum) stresses, was cloned from sugarcane. In addition, both its transient overexpression and stable overexpression enhanced the resistance of transgenic plants to pathogen infection, most probably through activating pathogen-associated molecular pattern/pattern-recognition receptor-triggered immunity, producing reactive oxygen species, and initiating mitogen-activated protein kinase cascade. Subsequently, the transmission of SA and hypersensitive reaction were triggered, which stimulated the transcription of defense-related genes. These findings provide insights into the function of ScOPR2 gene for disease resistance.

Biosynthesis and Signaling of Strigolactones Act Synergistically With That of ABA and JA to Enhance Verticillium dahliae Resistance in Cotton (Gossypium hirsutum L.)

Verticillium wilt (VW) caused by the soil-borne fungal pathogen Verticillium dahliae reduces cotton productivity and quality. Numerous studies have explored the genetic and molecular mechanisms regulating VW resistance in cotton, but the role and mechanism of strigolactone (SL) is still elusive. We investigated the function of SL in cotton's immune response to V. dahliae infection by exogenously applying SL analog, blocking or enhancing biosynthesis of endogenous SLs in combination with comparative transcriptome analysis and by exploring cross-talk between SL and other phytohormones. Silencing GhDWARF27 and applying the SL analog GR24 or overexpressing GhDWARF27 decreased and enhanced V. dahliae resistance, respectively. Transcriptome analysis revealed SL-mediated activation of abscisic acid (ABA) and jasmonic acid (JA) biosynthesis and signaling pathways. Enhanced ABA biosynthesis and signaling led to increased activity of antioxidant enzymes and reduced buildup of excess reactive oxygen species. Enhanced JA biosynthesis and signaling facilitated transcription of JA-dependent disease resistance genes. One of the components of the SL signal transduction pathway, GhD53, was found to interact with GhNCED5 and GhLOX2, the key enzymes of ABA and JA biosynthesis, respectively. We revealed the molecular mechanism underlying SL-enabled V. dahliae resistance and provided potential solutions for improving VW resistance in cotton.

Multi-omics analyses reveal the mechanisms underlying the responses of Casuarina equisetifolia ssp. incana to seawater atomization and encroachment stress

Casuarina equisetifolia trees are used as windbreaks in subtropical and tropical coastal zones, while C. equisetifolia windbreak forests can be degraded by seawater atomization (SA) and seawater encroachment (SE). To investigate the mechanisms underlying the response of C. equisetifolia to SA and SE stress, the transcriptome and metabolome of C. equisetifolia seedlings treated with control, SA, and SE treatments were analyzed. We identified 737, 3232, 3138, and 3899 differentially expressed genes (SA and SE for 2 and 24 h), and 46, 66, 62, and 65 differentially accumulated metabolites (SA and SE for 12 and 24 h). The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that SA and SE stress significantly altered the expression of genes related to plant hormone signal transduction, plant-pathogen interaction, and starch and sucrose metabolism pathways. The accumulation of metabolites associated with the biosynthetic pathways of phenylpropanoid and amino acids, as well as starch and sucrose metabolism, and glycolysis/gluconeogenesis were significantly altered in C. equisetifolia subjected to SA and SE stress. In conclusion, C. equisetifolia responds to SA and SE stress by regulating plant hormone signal transduction, plant-pathogen interaction, biosynthesis of phenylpropanoid and amino acids, starch and sucrose metabolism, and glycolysis/gluconeogenesis pathways. Compared with SA stress, C. equisetifolia had a stronger perception and response to SE stress, which required more genes and metabolites to be regulated. This study enhances our understandings of how C. equisetifolia responds to two types of seawater stresses at transcriptional and metabolic levels. It also offers a theoretical framework for effective coastal vegetation management in tropical and subtropical regions.

Effector CLas0185 targets methionine sulphoxide reductase B1 of Citrus sinensis to promote multiplication of 'Candidatus Liberibacter asiaticus' via enhancing enzymatic activity of ascorbate peroxidase 1

Citrus huanglongbing (HLB) has been causing enormous damage to the global citrus industry. As the main causal agent, 'Candidatus Liberibacter asiaticus' (CLas) delivers a set of effectors to modulate host responses, while the modes of action adopted remain largely unclear. Here, we demonstrated that CLIBASIA_00185 (CLas0185) could attenuate reactive oxygen species (ROS)-mediated cell death in Nicotiana benthamiana. Transgenic expression of CLas0185 in Citrus sinensis 'Wanjincheng' enhanced plant susceptibility to CLas. We found that methionine sulphoxide reductase B1 (CsMsrB1) was targeted by the effector, and its abundance was elevated in CLas0185-transgenic citrus plants. Their interaction promoted CLas proliferation. We then determined that CsMsrB1 sustained redox state and enzymatic activity of ascorbate peroxidase 1 (CsAPX1) under oxidative stress. The latter reduced H2O2 accumulation and was associated with host susceptibility to CLas infection. Consistently, citrus plants expressing CLas0185 and CsMsrB1 conferred enhanced APX activity and decreased H2O2 content. Taken together, these findings revealed how CLas0185 benefits CLas colonization by targeting CsMsrB1, which facilitated the antioxidant activity and depressed ROS during pathogen infection.

Ripening and rot: How ripening processes influence disease susceptibility in fleshy fruits

Fleshy fruits become more susceptible to pathogen infection when they ripen; for example, changes in cell wall properties related to softening make it easier for pathogens to infect fruits. The need for high-quality fruit has driven extensive research on improving pathogen resistance in important fruit crops such as tomato (Solanum lycopersicum). In this review, we summarize current progress in understanding how changes in fruit properties during ripening affect infection by pathogens. These changes affect physical barriers that limit pathogen entry, such as the fruit epidermis and its cuticle, along with other defenses that limit pathogen growth, such as preformed and induced defense compounds. The plant immune system also protects ripening fruit by recognizing pathogens and initiating defense responses involving reactive oxygen species production, mitogen-activated protein kinase signaling cascades, and jasmonic acid, salicylic acid, ethylene, and abscisic acid signaling. These phytohormones regulate an intricate web of transcription factors (TFs) that activate resistance mechanisms, including the expression of pathogenesis-related genes. In tomato, ripening regulators, such as RIPENING INHIBITOR and NON_RIPENING, not only regulate ripening but also influence fruit defenses against pathogens. Moreover, members of the ETHYLENE RESPONSE FACTOR (ERF) family play pivotal and distinct roles in ripening and defense, with different members being regulated by different phytohormones. We also discuss the interaction of ripening-related and defense-related TFs with the Mediator transcription complex. As the ripening processes in climacteric and non-climacteric fruits share many similarities, these processes have broad applications across fruiting crops. Further research on the individual contributions of ERFs and other TFs will inform efforts to diminish disease susceptibility in ripe fruit, satisfy the growing demand for high-quality fruit and decrease food waste and related economic losses.

Elucidation of mechanisms underlying active oxygen burst in Citrus sinensis after Diaporthe citri infection using transcriptome analysis

Introduction

Reactive oxygen species (ROS) generation is a common disease defense mechanism in plants. However, it is unclear whether Citrus host activates defense response against Diaporthe citri causing citrus melanose disease by producing ROS, and the underlying molecular mechanisms are unknown.

Methods

DAB staining and RNA-Seq technology were used to compare the active oxygen burst and differential gene expression, respectively, in uninfected and infected Citrus sinensis leaves at different time points during D. citri infection in vivo. The functions of CsRBOH (a significant DEG) were confirmed in N. benthamiana through the Agrobacterium-mediated transient expression system.

Results

DAB staining indicated that C. sinensis initiated defense against D. citri infection within 24 h by generating ROS. Illumina sequencing revealed 25,557 expressed genes of C. sinensis. The most upregulated DEGs (n = 1,570) were identified 72 h after fungal inoculation (sample denoted as CD72). In the CD72 vs. Cs (samples at 0 h after fungal inoculation) comparison, the KEGG pathway category with the highest number of genes (n = 62) and most significant enrichment was Protein processing in endoplasmic reticulum, followed by Glutathione metabolism and MAPK signaling pathway-plant. GO analysis revealed that the DEGs of CD72 vs. Cs related to active oxygen burst and chitin recognition were significantly grouped into the regulation of biological processes and molecular functions, with GO terms including response to ROS, response to fungus, and oxidoreductase activity. Remarkably, CsRBOH was significantly enriched in the GO and KEGG analyses, and its expression pattern in qRT-PCR and DAB staining results were consistent. Among the 63 ROS-related DEGs, HSP genes and genes associated with the peroxidase family were highly significant as revealed by protein-protein interaction networks. Furthermore, ROS accumulation, cell death, and upregulation of defense-related genes were observed in N. benthamiana leaves with CsRBOH expressed through the Agrobacterium-mediated transient expression system.

Conclusion

Our findings suggested that C. sinensis activates CsRBOH and ROS-related genes, leading to ROS accumulation to resist the invasion by D. citri. This study laid the foundation for future research on molecular mechanisms and breeding of C. sinensis cultivars resistant to citrus melanose.

Fungal Extracellular Vesicle Proteins with Potential in Biological Interaction

Extracellular vesicles (EVs) are vesicle-like structures composed of lipid bilayers, which can be divided into apoptotic bodies, microbubbles and exosomes. They are nanoparticles used for the exchange of information between cells. EVs contains many substances, including protein. With the development of proteomics, we know more about the types and functions of protein in vesicles. The potential functions of proteins in the envelope are mainly discussed, including cell wall construction, fungal virulence transmission, signal transmission and redox reactions, which provides a new perspective for studying the interaction mechanism between fungi and other organisms. The fungal protein markers of EVs are also summarized, which provided an exploration tool for studying the mechanism of vesicles. In addition, the possible role of immune protein in the EVs in the treatment of human diseases is also discussed, which provides new ideas for vaccine development.

Study on the Function of SlWRKY80 in Tomato Defense against Meloidogyne incognita

WRKY transcription factors (TFs) can participate in plant biological stress responses and play important roles. SlWRKY80 was found to be differentially expressed in the Mi-1- and Mi-3-resistant tomato lines by RNA-seq and may serve as a key node for disease resistance regulation. This study used RNAi to determine whether SlWRKY80 silencing could influence the sensitivity of 'M82' (mi-1/mi-1)-susceptible lines to M. incognita. Further overexpression of this gene revealed a significant increase in tomato disease resistance, ranging from highly susceptible to susceptible, combined with the identification of growth (plant height, stem diameter, and leaf area) and physiological (soluble sugars and proteins; root activity) indicators, clarifying the role of SlWRKY80 as a positive regulatory factor in tomato defense against M. incognita. Based on this phenomenon, a preliminary exploration of its metabolic signals revealed that SlWRKY80 stimulates different degrees of signaling, such as salicylic acid (SA), jasmonic acid (JA), and ethylene (ETH), and may synergistically regulate reactive oxygen species (ROS) accumulation and scavenging enzyme activity, hindering the formation of feeding sites and ultimately leading to the reduction of root gall growth. To our knowledge, SlWRKY80 has an extremely high utilization value for improving tomato resistance to root-knot nematodes and breeding.

MoRgs3 functions in intracellular reactive oxygen species perception-integrated cAMP signaling to promote appressorium formation in Magnaporthe oryzae

Regulator of G-protein signaling (RGS) proteins exhibit GTPase-accelerating protein activities to govern G-protein function. In the rice blast fungus Magnaporthe oryzae, there is a family of at least eight RGS and RGS-like proteins (MoRgs1 to MoRgs8), each exhibiting distinct or shared functions in the growth, appressorium formation, and pathogenicity. MoRgs3 recently emerged as one of the crucial regulators that senses intracellular oxidation during appressorium formation. To explore this unique regulatory mechanism of MoRgs3, we identified the nucleoside diphosphate kinase MoNdk1 that interacts with MoRgs3. MoNdk1 phosphorylates MoRgs3 under induced intracellular reactive oxygen species levels, and MoRgs3 phosphorylation is required for appressorium formation and pathogenicity. In addition, we showed that MoRgs3 phosphorylation determines its interaction with MoCrn1, a coronin-like actin-binding protein homolog, which regulates MoRgs3 internalization. Finally, we provided evidence demonstrating that MoRgs3 functions in MoMagA-mediated cAMP signaling to regulate normal appressorium induction. By revealing a novel signal perception mechanism, our studies highlighted the complexity of regulation during the appressorium function and pathogenicity of the blast fungus.

IMPORTANCE

We report that MoRgs3 becomes phosphorylated in an oxidative intracellular environment during the appressorium formation stage. We found that this phosphorylation is carried out by MoNdk1, a nucleoside diphosphate kinase. In addition, this phosphorylation leads to a higher binding affinity between MoRgs3 and MoCrn1, a coronin-like actin-binding protein that was implicated in the endocytic transport of several other RGS proteins of Magnaporthe oryzae. We further found that the internalization of MoRgs3 is indispensable for its GTPase-activating protein function toward the Gα subunit MoMagA. Importantly, we characterized how such cellular regulatory events coincide with cAMP signaling-regulated appressorium formation and pathogenicity in the blast fungus. Our studies uncovered a novel intracellular reactive oxygen species signal-transducing mechanism in a model pathogenic fungus with important basic and applied implications.

ROS and RNS production, subcellular localization, and signaling triggered by immunogenic danger signals

Plants continuously monitor the environment to detect changing conditions and to properly respond, avoiding deleterious effects on their fitness and survival. An enormous number of cell surface and intracellular immune receptors are deployed to perceive danger signals associated with microbial infections. Ligand binding by cognate receptors represents the first essential event in triggering plant immunity and determining the outcome of the tissue invasion attempt. Reactive oxygen and nitrogen species (ROS/RNS) are secondary messengers rapidly produced in different subcellular localizations upon the perception of immunogenic signals. Danger signal transduction inside the plant cells involves cytoskeletal rearrangements as well as several organelles and interactions between them to activate key immune signaling modules. Such immune processes depend on ROS and RNS accumulation, highlighting their role as key regulators in the execution of the immune cellular program. In fact, ROS and RNS are synergic and interdependent intracellular signals required for decoding danger signals and for the modulation of defense-related responses. Here we summarize current knowledge on ROS/RNS production, compartmentalization, and signaling in plant cells that have perceived immunogenic danger signals.

Dynamic interplay of reactive oxygen and nitrogen species (ROS and RNS) in plant resilience: unveiling the signaling pathways and metabolic responses to biotic and abiotic stresses

KEY MESSAGE

Plants respond to environmental challenges by producing reactive species such as ROS and RNS, which play critical roles in signaling pathways that lead to adaptation and survival strategies. Understanding these pathways, as well as their detection methods and effects on plant development and metabolism, provides insight into increasing crop tolerance to combined stresses. Plants encounter various environmental stresses (abiotic and biotic) that affect plant growth and development. Plants sense biotic and abiotic stresses by producing different molecules, including reactive species, that act as signaling molecules and stimulate secondary messengers and subsequent gene transcription. Reactive oxygen and nitrogen species (ROS and RNS) are produced in both physiological and pathological conditions in the plasma membranes, chloroplasts, mitochondria, and endoplasmic reticulum. Various techniques, including spectroscopy, chromatography, and fluorescence methods, are used to detect highly reactive, short-half-life ROS and RNS either directly or indirectly. In this review, we highlight the roles of ROS and RNS in seed germination, root development, senescence, mineral nutrition, and post-harvest control. In addition, we provide information on the specialized metabolism involved in plant growth and development. Secondary metabolites, including alkaloids, flavonoids, and terpenoids, are produced in low concentrations in plants for signaling and metabolism. Strategies for improving crop performance under combined drought and pathogen stress conditions are discussed in this review.

Exploring the effects of red light night break on the defence mechanisms of tomato against fungal pathogen Botrytis cinerea

Plant infections caused by fungi lead to significant crop losses worldwide every year. This study aims to better understand the plant defence mechanisms regulated by red light, in particular, the effects of red light at night when most phytopathogens are highly infectious. Our results showed that superoxide production significantly increased immediately after red light exposure and, together with hydrogen peroxide levels, was highest at dawn after 30 min of nocturnal red-light treatment. In parallel, red-light-induced expression and increased the activities of several antioxidant enzymes. The nocturnal red light did not affect salicylic acid but increased jasmonic acid levels immediately after illumination, whereas abscisic acid levels increased 3 h after nocturnal red-light exposure at dawn. Based on the RNAseq data, red light immediately increased the transcription of several chloroplastic chlorophyll a-b binding protein and circadian rhythm-related genes, such as Constans 1, CONSTANS interacting protein 1 and zinc finger protein CONSTANS-LIKE 10. In addition, the levels of several transcription factors were also increased after red light exposure, such as the DOF zinc finger protein and a MYB transcription factor involved in the regulation of circadian rhythms and defence responses in tomato. In addition to identifying these key transcription factors in tomato, the application of red light at night for one week not only reactivated key antioxidant enzymes at the gene and enzyme activity level at dawn but also contributed to a more efficient and successful defence against Botrytis cinerea infection.

The role of Phanerochaete australis in enhancing defense activity against Magnaporthe oryzae in upland rice

The inclusion of biological control in the integrated management of rice blast (Magnaporthe oryzae [Mo]) reduces pesticide application. Phanerochaete australis (Pha) has been shown to be a potential inducer of resistance to rice blast. Pha was isolated saprophytically from the rice phylloplane and studied for its interaction with Mo in the defense process of upland rice plants against the pathogen attack. Investigating the Pha × Mo interaction in a completely randomized design, the suppression of leaf blast and the epidemiological components of disease development were quantified in vivo, whereas the physiological and biochemical aspects, as defense enzymes and oxidative complex components, were evaluated in vitro during the induction of resistance. In the Pha × Mo interaction, it was found that seed treatment can significantly reduce disease severity by up to 93%, increase the photosynthetic apparatus, mobilize photoassimilates to the defense system, intensify defense enzyme and oxidant complex activities (chitinase [CHI], β-1,3-glucanase [GLU], lipoxygenase [LOX], phenylalanine ammonia-lyase [PAL], poliphenoloxidase [PPO], peroxidase [POX], catalase [CAT], cuperoxide dismutase [SOD]), decrease phenolic compounds (TPCs), and increase photosynthetic pigment levels compared with the negative control (Mo). When treating the seed, we are referring to an induction process where there is no physical contact between the pathogens. The enzymes produced by the interaction between the microorganisms validate this process; thus, Pha acts as an inducer of resistance to upland rice plants challenged with Mo.

Tomato SlWRKY3 Negatively Regulates Botrytis cinerea Resistance via TPK1b

Botrytis cinerea is considered the second most important fungal plant pathogen, and can cause serious disease, especially on tomato. The TPK1b gene encodes a receptor-like kinase that can positively regulate plant resistance to B. cinerea. Here, we identified a tomato WRKY transcription factor SlWRKY3 that binds to the W-box on the TPK1b promoter. It can negatively regulate TPK1b transcription, then regulate downstream signaling pathways, and ultimately negatively regulate tomato resistance to B. cinerea. SlWRKY3 interference can enhance resistance to B. cinerea, and SlWRKY3 overexpression leads to susceptibility to B. cinerea. Additionally, we found that B. cinerea can significantly, and rapidly, induce the upregulation of SlWRKY3 expression. In SlWRKY3 transgenic plants, the TPK1b expression level was negatively correlated with SlWRKY3 expression. Compared with the control, the expression of the SA pathway marker gene PR1 was downregulated in W3-OE plants and upregulated in W3-Ri plants when inoculated with B. cinerea for 48 h. Moreover, SlWRKY3 positively regulated ROS production. Overall, SlWRKY3 can inhibit TPK1b transcription in tomato, and negatively regulate resistance to B. cinerea by modulating the downstream SA and ROS pathways.

Oxidative stress responses in biofilms

Oxidizing agents are low-molecular-weight molecules that oxidize other substances by accepting electrons from them. They include reactive oxygen species (ROS), such as superoxide anions (O2-), hydrogen peroxide (H2O2), and hydroxyl radicals (HO-), and reactive chlorine species (RCS) including sodium hypochlorite (NaOCl) and its active ingredient hypochlorous acid (HOCl), and chloramines. Bacteria encounter oxidizing agents in many different environments and from diverse sources. Among them, they can be produced endogenously by aerobic respiration or exogenously by the use of disinfectants and cleaning agents, as well as by the mammalian immune system. Furthermore, human activities like industrial effluent pollution, agricultural runoff, and environmental activities like volcanic eruptions and photosynthesis are also sources of oxidants. Despite their antimicrobial effects, bacteria have developed many mechanisms to resist the damage caused by these toxic molecules. Previous research has demonstrated that growing as a biofilm particularly enhances bacterial survival against oxidizing agents. This review aims to summarize the current knowledge on the resistance mechanisms employed by bacterial biofilms against ROS and RCS, focussing on the most important mechanisms, including the formation of biofilms in response to oxidative stressors, the biofilm matrix as a protective barrier, the importance of detoxifying enzymes, and increased protection within multi-species biofilm communities. Understanding the complexity of bacterial responses against oxidative stress will provide valuable insights for potential therapeutic interventions and biofilm control strategies in diverse bacterial species.

Phenotype, Biomass, Carbon and Nitrogen Assimilation, and Antioxidant Response of Rapeseed under Salt Stress

Salt stress is one of the major adverse factors affecting plant growth and crop production. Rapeseed is an important oil crop, providing high-quality edible oil for human consumption. This experiment was conducted to investigate the effects of salt stress on the phenotypic traits and physiological processes of rapeseed. The soil salinity was manipulated by setting three different levels: 0 g NaCl kg-1 soil (referred to as S0), 1.5 g NaCl kg-1 soil (referred to as S1), and 3.0 g NaCl kg-1 soil (referred to as S2). In general, the results indicated that the plant height, leaf area, and root neck diameter decreased with an increase in soil salinity. In addition, the biomass of various organs at all growth stages decreased as soil salinity increased from S0 to S2. The increasing soil salinity improved the distribution of biomass in the root and leaf at the seedling and flowering stages, indicating that rapeseed plants subjected to salt stress during the vegetative stage are capable of adapting their growth pattern to sustain their capacity for nutrient and water uptake, as well as leaf photosynthesis. However, as the soil salinity increased, there was a decrease in the distribution of biomass in the pod and seed at the maturity stage, while an increase was observed in the root and stem, suggesting that salt stress inhibited carbohydrate transport into reproductive organs. Moreover, the C and N accumulation at the flowering and maturity stages exhibited a reduction in direct correlation with the increase in soil salinity. High soil salinity resulted in a reduction in the C/N, indicating that salt stress exerted a greater adverse effect on C assimilation compared to N assimilation, leading to an increase in seed protein content and a decrease in oil content. Furthermore, as soil salinity increased from S0 to S2, the activity of superoxide dismutase (SOD) and catalase (CAT) and the content of soluble protein and sugar increased by 58.39%, 33.38%, 15.57%, and 13.88% at the seedling stage, and 38.69%, 22.85%, 12.04%, and 8.26% at the flowering stage, respectively. In summary, this study revealed that salt stress inhibited C and N assimilation, leading to a suppressed phenotype and biomass accumulation. The imbalanced C and N assimilation under salt stress contributed to the alterations in the seed oil and protein content. Rapeseed had a certain degree of salt tolerance by improving antioxidants and osmolytes.

Sirt5-mediated lysine desuccinylation regulates oxidative stress adaptation in Magnaporthe oryzae during host intracellular infection

Plant pathogenic fungi elaborate numerous detoxification strategies to suppress host reactive oxygen species (ROS), but their coordination is not well-understood. Here, we show that Sirt5-mediated protein desuccinylation in Magnaporthe oryzae is central to host ROS detoxification. SIRT5 encodes a desuccinylase important for virulence via adaptation to host oxidative stress. Quantitative proteomics analysis identified a large number of succinylated proteins targeted by Sirt5, most of which were mitochondrial proteins involved in oxidative phosphorylation, TCA cycle, and fatty acid oxidation. Deletion of SIRT5 resulted in hypersuccinylation of detoxification-related enzymes, and significant reduction in NADPH : NADP+ and GSH : GSSG ratios, disrupting redox balance and impeding invasive growth. Sirt5 desuccinylated thioredoxin Trx2 and glutathione peroxidase Hyr1 to activate their enzyme activity, likely by affecting proper folding. Altogether, this work demonstrates the importance of Sirt5-mediated desuccinylation in controlling fungal process required for detoxifying host ROS during M. oryzae infection.

Interactive transcriptome analyses of Northern Wild Rice (Zizania palustris L.) and Bipolaris oryzae show convoluted communications during the early stages of fungal brown spot development

Fungal diseases, caused mainly by Bipolaris spp., are past and current threats to Northern Wild Rice (NWR) grain production and germplasm preservation in both natural and cultivated settings. Genetic resistance against the pathogen is scarce. Toward expanding our understanding of the global gene communications of NWR and Bipolaris oryzae interaction, we designed an RNA sequencing study encompassing the first 12 h and 48 h of their encounter. NWR activated numerous plant recognition receptors after pathogen infection, followed by active transcriptional reprogramming of signaling mechanisms driven by Ca2+ and its sensors, mitogen-activated protein kinase cascades, activation of an oxidative burst, and phytohormone signaling-bound mechanisms. Several transcription factors associated with plant defense were found to be expressed. Importantly, evidence of diterpenoid phytoalexins, especially phytocassane biosynthesis, among expression of other defense genes was found. In B. oryzae, predicted genes associated with pathogenicity including secreted effectors that could target plant defense mechanisms were expressed. This study uncovered the early molecular communication between the NWR-B. oryzae pathosystem, which could guide selection for allele-specific genes to boost NWR defenses, and overall aid in the development of more efficient selection methods in NWR breeding through the use of the most virulent fungal isolates.

Maize catalases are recruited by a virus to modulate viral multiplication and infection

Given the detrimental effects of excessive reactive oxygen species (ROS) accumulation in plant cells, various antioxidant mechanisms have evolved to maintain cellular redox homeostasis, encompassing both enzymatic components (e.g., catalase, superoxide dismutase) and non-enzymatic ones. Despite extensive research on the role of antioxidant systems in plant physiology and responses to abiotic stresses, the potential exploitation of antioxidant enzymes by plant viruses to facilitate viral infection remains insufficiently addressed. Herein, we demonstrate that maize catalases (ZmCATs) exhibited up-regulated enzymatic activities upon sugarcane mosaic virus (SCMV) infection. ZmCATs played crucial roles in SCMV multiplication and infection by catalysing the decomposition of excess cellular H2 O2 and promoting the accumulation of viral replication-related cylindrical inclusion (CI) protein through interaction. Peroxisome-localized ZmCATs were found to be distributed around SCMV replication vesicles in Nicotiana benthamiana leaves. Additionally, the helper component-protease (HC-Pro) of SCMV interacted with ZmCATs and enhanced catalase activities to promote viral accumulation. This study unveils a significant involvement of maize catalases in modulating SCMV multiplication and infection through interaction with two viral factors, thereby enhancing our understanding regarding viral strategies for manipulating host antioxidant mechanisms towards robust viral accumulation.

Unravelling the Transcriptional Response of Agaricus bisporus under Lecanicillium fungicola Infection

Mushrooms are a nutritionally rich and sustainably-produced food with a growing global market. Agaricus bisporus accounts for 11% of the total world mushroom production and it is the dominant species cultivated in Europe. It faces threats from pathogens that cause important production losses, including the mycoparasite Lecanicillium fungicola, the causative agent of dry bubble disease. Through quantitative real-time polymerase chain reaction (qRT-PCR), we determine the impact of L. fungicola infection on the transcription patterns of A. bisporus genes involved in key cellular processes. Notably, genes related to cell division, fruiting body development, and apoptosis exhibit dynamic transcriptional changes in response to infection. Furthermore, A. bisporus infected with L. fungicola were found to accumulate increased levels of reactive oxygen species (ROS). Interestingly, the transcription levels of genes involved in the production and scavenging mechanisms of ROS were also increased, suggesting the involvement of changes to ROS homeostasis in response to L. fungicola infection. These findings identify potential links between enhanced cell proliferation, impaired fruiting body development, and ROS-mediated defence strategies during the A. bisporus (host)-L. fungicola (pathogen) interaction, and offer avenues for innovative disease control strategies and improved understanding of fungal pathogenesis.

Screening of rhizosphere nitrogen fixing, phosphorus and potassium solubilizing bacteria of Malus sieversii (Ldb.) Roem. and the effect on apple growth

Nitrogen, phosphorus and potassium inorganic fertilizers are commonly used when growing apples, but their excessive application has resulted in a decline in soil fertility and therefore an inability to maintain sustainable cultivation systems. It is possible to compensate for this with biofertilizers. Nitrogen-fixing, phosphorus solubilizing, and potassium solubilizing bacteria are biofertilizers with a broad range of possible uses. In this study, beneficial microorganisms were screened from the rhizosphere soil of the apple tree, Malus sieversii (Ldb.) Roem., which is rich in microbial diversity in natural environments. It was essential to investigate their effects on the growth of apple seedlings. Eight populations of organic phosphorus solubilizing bacteria (56), inorganic phosphorus solubilizing bacteria (13), nitrogen-fixing bacteria (22), and potassium solubilizing bacteria (24) were isolated from eight populations of Xinjiang wild apple rhizosphere in Ili by medium culture. Their morphological characteristics were recorded and their activity was determined. The most active strains were Pseudomonas migulae, Pseudomonas poae, and Pseudomonas extremaustralis, which was determined by physiological and biochemical properties and 16S rDNA sequence analysis. The L16 (45) orthogonal experiment, which used the three strains as testing materials, was created to assess the effects of the strains on apple physiological indicators, soil nutrients, leaf nutrients, and biomass, as well as to identify the ideal combination, concentration, timing, and application method. The results indicated that the peroxidase (POD) and catalase (CAT) activities of apple seedlings increased significantly under the 10 treatment, and the (SOD) activities of the 0 (control) and 1 (inorganic fertilizer only) treatments were significantly lower than the other treatments; soluble sugar, soluble protein and chlorophyll contents increased in all treatments compared to 0 and 1, while malondialdehyde and proline contents increased or decreased compared to 0 and 1; apple seedlings in treatment 10 had the highest soil N, P, and K content, leaf N, P, and K content and biomass were also all highest in treatment 10. In summary, the strains screened for the test can be used as biofertilizers and the optimum application was determined for treatment 10, meaning that the results also provide a theoretical basis for their application in artificially grown orchards.

Flavonols affect the interrelated glucosinolate and camalexin biosynthetic pathways in Arabidopsis thaliana

Flavonols are structurally and functionally diverse biomolecules involved in plant biotic and abiotic stress tolerance, pollen development, and inhibition of auxin transport. However, their effects on global gene expression and signaling pathways are unclear. To explore the roles of flavonol metabolites in signaling, we performed comparative transcriptome and targeted metabolite profiling of seedlings from the flavonol-deficient Arabidopsis loss-of-function mutant flavonol synthase1 (fls1) with and without exogenous supplementation of flavonol derivatives (kaempferol, quercetin, and rutin). RNA-seq results indicated that flavonols modulate various biological and metabolic pathways, with significant alterations in camalexin and aliphatic glucosinolate synthesis. Flavonols negatively regulated camalexin biosynthesis but appeared to promote the accumulation of aliphatic glucosinolates via transcription factor-mediated up-regulation of biosynthesis genes. Interestingly, upstream amino acid biosynthesis genes involved in methionine and tryptophan synthesis were altered under flavonol deficiency and exogenous supplementation. Quercetin treatment significantly up-regulated aliphatic glucosinolate biosynthesis genes compared with kaempferol and rutin. In addition, expression and metabolite analysis of the transparent testa7 mutant, which lacks hydroxylated flavonol derivatives, clarified the role of quercetin in the glucosinolate biosynthesis pathway. This study elucidates the molecular mechanisms by which flavonols interfere with signaling pathways, their molecular targets, and the multiple biological activities of flavonols in plants.

Transcriptional insights of citrus defense response against Diaporthe citri

Citrus melanose, caused by Diaporthe citri, is one of the most important and widespread fungal diseases of citrus. Previous studies demonstrated that the citrus host was able to trigger the defense response to restrict the spread of D. citri. However, the molecular mechanism underlying this defense response has yet to be elucidated. Here, we used RNA-Seq to explore the gene expression pattern at the early (3 days post infection, dpi) and late (14 dpi) infection stages of citrus leaves in response to D. citri infection, and outlined the differences in transcriptional regulation associated with defense responses. The functional enrichment analysis indicated that the plant cell wall biogenesis was significantly induced at the early infection stage, while the callose deposition response was more active at the late infection stage. CYP83B1 genes of the cytochrome P450 family were extensively induced in the callus deposition-mediated defense response. Remarkably, the gene encoding pectin methylesterase showed the highest upregulation and was only found to be differentially expressed at the late infection stage. Genes involved in the synthesis and regulation of phytoalexin coumarin were effectively activated. F6'H1 and S8H, encoding key enzymes in the biosynthesis of coumarins and their derivatives, were more strongly expressed at the late infection stage than at the early infection stage. Collectively, our study profiled the response pattern of citrus leaves against D. citri infection and provided the transcriptional evidence to support the defense mechanism.

Contemporary understanding of transcription factor regulation of terpenoid biosynthesis in plants

KEY MESSAGE

This review summarized how TFs function independently or in response to environmental factors to regulate terpenoid biosynthesis via fine-tuning the expression of rate-limiting enzymes. Terpenoids are derived from various species and sources. They are essential for interacting with the environment and defense mechanisms, such as antimicrobial, antifungal, antiviral, and antiparasitic properties. Almost all terpenoids have high medicinal value and economic performance. Recently, the control of enzyme genes on terpenoid biosynthesis has received a great deal of attention, but transcriptional factors regulatory network on terpenoid biosynthesis and accumulation has yet to get a thorough review. Transcription factors function as activators or suppressors independently or in response to environmental stimuli, fine-tuning terpenoid accumulation through regulating rate-limiting enzyme expression. This study investigates the advancements in transcription factors related to terpenoid biosynthesis and systematically summarizes previous works on the specific mechanisms of transcription factors that regulate terpenoid biosynthesis via hormone signal-transcription regulatory networks in plants. This will help us to better comprehend the regulatory network of terpenoid biosynthesis and build the groundwork for terpenoid development and effective utilization.

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.

ROS interplay between plant growth and stress biology: Challenges and future perspectives

In plants, reactive oxygen species (ROS) have emerged as a multifunctional signaling molecules that modulate diverse stress and growth responses. Earlier studies on ROS in plants primarily focused on its toxicity and ROS-scavenging processes, but recent findings are offering new insights on its role in signal perception and transduction. Further, the interaction of cell wall receptors, calcium channels, HATPase, protein kinases, and hormones with NADPH oxidases (respiratory burst oxidase homologues (RBOHs), provides concrete evidence that ROS regulates major signaling cascades in different cellular compartments related to stress and growth responses. However, at the molecular level there are many knowledge gaps regarding how these players influence ROS signaling and how ROS regulate them during growth and stress events. Furthermore, little is known about how plant sensors or receptors detect ROS under various environmental stresses and induce subsequent signaling cascades. In light of this, we provided an update on the role of ROS signaling in plant growth and stress biology. First, we focused on ROS signaling, its production and regulation by cell wall receptor like kinases. Next, we discussed the interplay between ROS, calcium and hormones, which forms a major signaling trio regulatory network of signal perception and transduction. We also provided an overview on ROS and nitric oxide (NO) crosstalk. Furthermore, we emphasized the function of ROS signaling in biotic, abiotic and mechanical stresses, as well as in plant growth and development. Finally, we conclude by highlighting challenges and future perspectives of ROS signaling in plants that warrants future investigation.