Stories of Salicylic Acid: A Plant Defense Hormone

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

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

Feruloyl Glyceride Mitigates Tomato Postharvest Rot by Inhibiting Penicillium expansum Spore Germination and Enhancing Suberin Accumulation

Postharvest rot, caused by Penicillium expansum, in tomatoes poses significant economic and health risks. Traditional control methods, such as the use of fungicides, raise concerns about pathogen resistance, food safety, and environmental impact. In search of sustainable alternatives, plant secondary metabolites, particularly phenolic compounds and their derivatives, have emerged as promising natural antimicrobials. Among these, feruloyl glyceride (FG), a water-soluble derivative of ferulic acid, stands out due to its antioxidant properties, antibacterial properties, and improved solubility. In this study, we provide evidence demonstrating FG is capable of inhibiting the spore germination of P. expansum and effectively reducing the incidence rate of Penicillium rot of tomatoes, without compromising quality. Electron microscopy observations combined with metabolite and transcriptomic analyses revealed that FG treatments resulted in enhanced suberin accumulation through promoting the expression of suberin synthesis related genes and, consequently, inhibited the growth and expansion of P. expansum on the fruits. This work sheds light on the mechanisms underlying FG's inhibitory effects, allowing its potential application as a natural and safe alternative to replace chemical fungicides for postharvest preservation.

Decoding early stress signaling waves in living plants using nanosensor multiplexing

Increased exposure to environmental stresses due to climate change have adversely affected plant growth and productivity. Upon stress, plants activate a signaling cascade, involving multiple molecules like H2O2, and plant hormones such as salicylic acid (SA) leading to resistance or stress adaptation. However, the temporal ordering and composition of the resulting cascade remains largely unknown. In this study we developed a nanosensor for SA and multiplexed it with H2O2 nanosensor for simultaneous monitoring of stress-induced H2O2 and SA signals when Brassica rapa subsp. Chinensis (Pak choi) plants were subjected to distinct stress treatments, namely light, heat, pathogen stress and mechanical wounding. Nanosensors reported distinct dynamics and temporal wave characteristics of H2O2 and SA generation for each stress. Based on these temporal insights, we have formulated a biochemical kinetic model that suggests the early H2O2 waveform encodes information specific to each stress type. These results demonstrate that sensor multiplexing can reveal stress signaling mechanisms in plants, aiding in developing climate-resilient crops and pre-symptomatic stress diagnoses.

Biological Control of a Root-Knot Nematode Meloidogyne incognita Infection of Tomato (Solanum lycopersicum L.) by the Oomycete Biocontrol Agent Pythium oligandrum

The biocontrol agent Pythium oligandrum, which is a member of the phylum Oomycota, can control diseases caused by a taxonomically wide range of plant pathogens, including fungi, bacteria, and oomycetes. However, whether P. oligandrum could control diseases caused by plant root-knot nematodes (RKNs) was unknown. We investigated a recently isolated P. oligandrum strain GAQ1, and the P. oligandrum strain CBS530.74, for the control of an RKN Meloidogyne incognita infection of tomato (Solanum lycopersicum L.). Initially, P. oligandrum culture filtrates were found to be lethal to M. incognita second-stage juveniles (J2s) with up to 84% mortality 24 h after treatment compared to 14% in the control group. Consistent with the lethality to M. incognita J2s, tomato roots treated with P. oligandrum culture filtrates reduced their attraction of nematodes, and the number of nematodes penetrating the roots was reduced by up to 78%. In a greenhouse pot trial, the P. oligandrum GAQ1 inoculation of tomato plants significantly reduced the gall number by 58% in plants infected with M. incognita. Notably, the P. oligandrum GAQ1 mycelial treatment significantly increased tomato plant height (by 36%), weight (by 27%), and root weight (by 48%). A transcriptome analysis of tomato seedling roots inoculated with the P. oligandrum GAQ1 strain identified ~2500 differentially expressed genes. The enriched GO terms and annotations in the up-regulated genes suggested a modulation of the plant hormone-signaling and defense-related pathways in response to P. oligandrum. In conclusion, our results support that P. oligandrum GAQ1 can serve as a potential biocontrol agent for M. incognita control in tomato. Multiple mechanisms appear to contribute to the biocontrol effect, including the direct inhibition of M. incognita, the potential priming of tomato plant defenses, and plant growth promotion.

The Mh-miR393a-TIR1 module regulates Alternaria alternata resistance of Malus hupehensis mainly by modulating the auxin signaling

miRNAs govern gene expression and regulate plant defense. Alternaria alternata is a destructive fungal pathogen that damages apple. The wild apple germplasm Malus hupehensis is highly resistant to leaf spot disease caused by this fungus. Herein, we elucidated the regulatory and functional role of miR393a in apple resistance against A. alternata by targeting Transport Inhibitor Response 1. Mature miR393 accumulation in infected M. hupehensis increased owing to the transcriptional activation of MIR393a, determined to be a positive regulator of A. alternata resistance to either 'Orin' calli or 'Gala' leaves. 5' RLM-RACE and co-transformation assays showed that the target of miR393a was MhTIR1, a gene encoding a putative F-box auxin receptor that compromised apple immunity. RNA-seq analysis of transgenic calli revealed that MhTIR1 upregulated auxin signaling gene transcript levels and influenced phytohormone pathways and plant-pathogen interactions. miR393a compromised the sensitivity of several auxin-signaling genes to A. alternata infection, whereas MhTIR1 had the opposite effect. Using exogenous indole-3-acetic acid or the auxin synthesis inhibitor L-AOPP, we clarified that auxin enhances apple susceptibility to this pathogen. miR393a promotes SA biosynthesis and impedes pathogen-triggered ROS bursts by repressing TIR1-mediated auxin signaling. We uncovered the mechanism underlying the miR393a-TIR1 module, which interferes with apple defense against A. alternata by modulating the auxin signaling pathway.

Role of methylglyoxal and glyoxalase in the regulation of plant response to heavy metal stress

KEY MESSAGE

Methylglyoxal and glyoxalase function a significant role in plant response to heavy metal stress. We update and discuss the most recent developments of methylglyoxal and glyoxalase in regulating plant response to heavy metal stress. Methylglyoxal (MG), a by-product of several metabolic processes, is created by both enzymatic and non-enzymatic mechanisms. It plays an important role in plant growth and development, signal transduction, and response to heavy metal stress (HMS). Changes in MG content and glyoxalase (GLY) activity under HMS imply that they may be potential biomarkers of plant stress resistance. In this review, we summarize recent advances in research on the mechanisms of MG and GLY in the regulation of plant responses to HMS. It has been discovered that appropriate concentrations of MG assist plants in maintaining a balance between growth and development and survival defense, therefore shielding them from heavy metal harm. MG and GLY regulate plant physiological processes by remodeling cellular redox homeostasis, regulating stomatal movement, and crosstalking with other signaling molecules (including abscisic acid, gibberellic acid, jasmonic acid, cytokinin, salicylic acid, melatonin, ethylene, hydrogen sulfide, and nitric oxide). We also discuss the involvement of MG and GLY in the regulation of plant responses to HMS at the transcriptional, translational, and metabolic levels. Lastly, considering the current state of research, we present a perspective on the future direction of MG research to elucidate the MG anti-stress mechanism and offer a theoretical foundation and useful advice for the remediation of heavy metal-contaminated environments in the future.

Glutathione-the "master" antioxidant in the regulation of resistant and susceptible host-plant virus-interaction

The interaction between plant hosts and plant viruses is a very unique and complex process, relying on dynamically modulated intercellular redox states and the generation of reactive oxygen species (ROS). Plants strive to precisely control this state during biotic stress, as optimal redox levels enable proper induction of defense mechanisms against plant viruses. One of the crucial elements of ROS regulation and redox state is the production of metabolites, such as glutathione, or the activation of glutathione-associated enzymes. Both of these elements play a role in limiting the degree of potential oxidative damage in plant cells. While the role of glutathione and specific enzymes is well understood in other types of abiotic and biotic stresses, particularly those associated with bacteria or fungi, recent advances in research have highlighted the significance of glutathione modulation and mutations in genes encoding glutathione-associated enzymes in triggering immunity or susceptibility against plant viruses. Apparently, glutathione-associated genes are involved in precisely controlling and protecting host cells from damage caused by ROS during viral infections, playing a crucial role in the host's response. In this review, we aim to outline the significant improvements made in research on plant viruses and glutathione, specifically in the context of their involvement in susceptible and resistant responses, as well as changes in the localization of glutathione. Analyses of essential glutathione-associated enzymes in susceptible and resistant responses have demonstrated that the levels of enzymatic activity or the absence of specific enzymes can impact the spread of the virus and activate host-induced defense mechanisms. This contributes to the complex network of the plant immune system. Although investigations of glutathione during the plant-virus interplay remain a challenge, the use of novel tools and approaches to explore its role will significantly contribute to our knowledge in the field.

Papiliotrema flavescens, a plant growth-promoting fungus, alters root system architecture and induces systemic resistance through its volatile organic compounds in Arabidopsis

The current trend in agricultural development is the establishment of sustainable agricultural systems. This involves utilizing and implementing eco-friendly biofertilizers and biocontrol agents as alternatives to conventional fertilizers and pesticides. A plant growth-promoting fungal strain, that could alter root system architecture and promote the growth of Arabidopsis seedlings in a non-contact manner by releasing volatile organic compounds (VOCs) was isolated in this study. 26S rDNA sequencing revealed that the strain was a yeast-like fungus, Papiliotrema flavescens. Analysis of plant growth-promoting traits revealed that the fungus could produce indole-3-acetic acid and ammonia and fix nitrogen. Transcriptome analysis in combination with inhibitor experiments revealed that P. flavescens VOCs triggered metabolic alterations, promoted auxin accumulation and distribution in the roots, and coordinated ethylene signaling, thus inhibiting primary root elongation and inducing lateral root formation in Arabidopsis. Additionally, transcriptome analysis and fungal infection experiments confirmed that pretreatment with P. flavescens stimulated the defense response of Arabidopsis to boost its resistance to the pathogenic fungus Botrytis cinerea. Solid-phase microextraction, which was followed by gas chromatography-mass spectrometry analysis, identified three VOCs (acetoin, naphthalene and indole) with significant plant growth-promoting attributes. Their roles were confirmed using further pharmacological experiments and upregulated expression of auxin- and ethylene-related genes. Our study serves as an essential reference for utilizing P. flavescens as a potential biological fertilizer and biocontrol agent.

Plant airborne defense against insects, viruses, and beyond

Plants emit volatiles as signals to trigger broad physiological responses, including airborne defense (AD). Gong et al. (Nature 2023; 622: 139-145) recently reported the genetic framework of how plants use AD to combat aphids and viruses. The study elucidates the mutualistic relationships between aphids and the viruses they transmit, revealing the broad biological and ecological significance of AD.

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

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

Volatile Compounds Emitted by Plant Growth-Promoting Fungus Tolypocladium inflatum GT22 Alleviate Copper and Pathogen Stress

Previous studies on the intricate interactions between plants and microorganisms have revealed that fungal volatile compounds (VCs) can affect plant growth and development. However, the precise mechanisms underlying these actions remain to be delineated. In this study, we discovered that VCs from the soilborne fungus Tolypocladium inflatum GT22 enhance the growth of Arabidopsis. Remarkably, priming Arabidopsis with GT22 VCs caused the plant to display an enhanced immune response and mitigated the detrimental effects of both pathogenic infections and copper stress. Transcriptomic analyses of Arabidopsis seedlings treated with GT22 VCs for 3, 24 and 48 h revealed that 90, 83 and 137 genes were differentially expressed, respectively. The responsive genes are known to be involved in growth, hormone regulation, defense mechanisms and signaling pathways. Furthermore, we observed the induction of genes related to innate immunity, hypoxia, salicylic acid biosynthesis and camalexin biosynthesis by GT22 VCs. Among the VCs emitted by GT22, exposure of Arabidopsis seedlings to limonene promoted plant growth and attenuated copper stress. Thus, limonene appears to be a key mediator of the interaction between GT22 and plants. Overall, our findings provide evidence that fungal VCs can promote plant growth and enhance both biotic and abiotic tolerance. As such, our study suggests that exposure of seedlings to T. inflatum GT22 VCs may be a means of improving crop productivity. This study describes a beneficial interaction between T. inflatun GT22 and Arabidopsis. Our investigation of microorganism function in terms of VC activities allowed us to overcome the limitations of traditional microbial application methods. The importance of this study lies in the discovery of T. inflatun GT22 as a beneficial microorganism. This soilborne fungus emits VCs with plant growth-promoting effects and the ability to alleviate both copper and pathogenic stress. Furthermore, our study offers a valuable approach to tracking the activities of fungal VC components via transcriptomic analysis and sheds light on the mechanisms through which VCs promote plant growth and induce resistance. This research significantly advances our knowledge of VC applications and provides an example for further investigations within this field.

Plasmopara viticola effector PvCRN11 induces disease resistance to downy mildew in grapevine

The downy mildew of grapevine (Vitis vinifera L.) is caused by Plasmopara viticola and is a major production problem in most grape-growing regions. The vast majority of effectors act as virulence factors and sabotage plant immunity. Here, we describe in detail one of the putative P. viticola Crinkler (CRN) effector genes, PvCRN11, which is highly transcribed during the infection stages in the downy mildew-susceptible grapevine V. vinifera cv. 'Pinot Noir' and V. vinifera cv. 'Thompson Seedless'. Cell death-inducing activity analyses reveal that PvCRN11 was able to induce spot cell death in the leaves of Nicotiana benthamiana but did not induce cell death in the leaves of the downy mildew-resistant V. riparia accession 'Beaumont' or of the downy mildew-susceptible 'Thompson Seedless'. Unexpectedly, stable expression of PvCRN11 inhibited the colonization of P. viticola in grapevine and Phytophthora capsici in Arabidopsis. Both transgenic grapevine and Arabidopsis constitutively expressing PvCRN11 promoted plant immunity. PvCRN11 is localized in the nucleus and cytoplasm, whereas PvCRN11-induced plant immunity is nucleus-independent. The purified protein PvCRN11Opt initiated significant plant immunity extracellularly, leading to enhanced accumulations of reactive oxygen species, activation of MAPK and up-regulation of the defense-related genes PR1 and PR2. Furthermore, PvCRN11Opt induces BAK1-dependent immunity in the apoplast, whereas PvCRN11 overexpression in intracellular induces BAK1-independent immunity. In conclusion, the PvCRN11 protein triggers resistance against P. viticola in grapevine, suggesting a potential for the use of PvCRN11 in grape production as a protectant against downy mildew.

Methyl-salicylate: A surveillance system for triggering immunity in neighboring plants

After being infested by aphids, plants trigger a signaling pathway that involves methyl salicylate as an airborne signaling molecule. Thus, the regulation of communication for systemically acquired resistance produced via methyl salicylate is helpful in generating stress resistance among plants against aphid infestation.

Comprehensive analysis of annexin gene family and its expression in response to branching architecture and salt stress in crape myrtle

BACKGROUND

Annexin (ANN) is calcium (Ca2+)-dependent and phospholipid binding protein family, which is involved in plant growth and development and response to various stresses. However, little known about ANN genes were identified from crape myrtle, an ornamental horticultural plant widely cultivated in the world.

RESULTS

Here, 9 LiANN genes were identified from Lagerstroemia indica, and their characterizations and functions were investigated in L. indica for the first time. The LiANN genes were divided into 2 subfamilies. The gene structure, chromosomal location, and collinearity relationship were also explored. In addition, the GO annotation analysis of these LiANNs indicated that they are enriched in molecular functions, cellular components, and biological processes. Moreover, transcription factors (TFs) prediction analysis revealed that bHLH, MYB, NAC, and other TFs can interact with the LiANN promoters. Interestingly, the LiANN2/4/6-9 were demonstrated to play critical roles in the branching architecture of crape myrtle. Furthermore, the LiANN2/6/8/9 were differentially expressed under salt treatment, and a series of TFs regulating LiANN2/6/8/9 expression were predicted to play essential roles in salt resistance.

CONCLUSIONS

These results shed light on profile and function of the LiANN gene family, and lay a foundation for further studies of the LiANN genes.

Photodegradation of typical pharmaceuticals changes toxicity to algae in estuarine water: A metabolomic insight

The ubiquitous existence of various pharmaceuticals in the marine environment has received global attention for their risk assessment. However, rather little is known thus far regarding the natural attenuation (e.g., photolysis)-induced product/mixture toxicity of these pharmaceuticals on marine organisms. In this study, the photodegradation behavior, product formation, and risks of two representative pharmaceuticals (i.e., ciprofloxacin, CIP; diclofenac, DCF) were explored in the simulated estuary water. It was noted that both pharmaceuticals can be completely photolyzed within 1 h, and five products of CIP and three products of DCF were identified by a high-resolution liquid chromatography-mass spectrometer. Accordingly, their photodecomposition pathways were tentatively proposed. The in silico prediction suggested that the formed transformation products maintained the persistence, bioaccumulation potential, and multi-endpoint toxic effects such as genotoxicity, developmental toxicity, and acute/chronic toxicity on different aquatic species. Particularly, the non-targeted metabolomics first elucidated that DCF and its photolytic mixtures can significantly affect the antioxidant status of marine algae (Heterosigma akashiwo), triggering oxidative stress and damage to cellular components. It is very alarming that the complete photolyzed DCF sample induced more serious oxidative stress than DCF itself, which called for more concern about the photolysis-driven ecological risks. Overall, this investigation first uncovered the overlooked but serious toxicity of the transformation products of prevalent pharmaceuticals during natural attenuation on marine species.

Salicylic acid alleviates the effects of cadmium and drought stress by regulating water status, ions, and antioxidant defense in Pterocarya fraxinifolia

Introduction

Pterocarya fraxinifolia (Poiret) Spach (Caucasian wingnut, Juglandaceae) is a relict tree species, and little is known about its tolerance to abiotic stress factors, including drought stress and heavy metal toxicity. In addition, salicylic acid (SA) has been shown to have a pivotal role in plant responses to biotic and abiotic stresses.

Methods

The current study is focused on evaluating the impact of foliar application of SA in mediating Caucasian wingnut physiological and biochemical responses, including growth, relative water content (RWC), osmotic potential (Ψs), quantum yield (Fv/Fm), electrolyte leakage, lipid peroxidation, hydrogen peroxide, and antioxidant enzymes, to cadmium (Cd; 100 µM) and drought stress, as well as their interaction. Moreover, the antioxidant activity (e.g., ascorbate peroxidase, catalase, glutathione reductase, peroxidase, and superoxide dismutase activities) of the stressed trees was investigated. The study was conducted on 6-month-old seedlings under controlled environmental conditions in a greenhouse for 3 weeks.

Results and discussion

Leaf length, RWC, Ψs, and Fv/Fm were decreased under all treatments, although the effect of drought stress was the most pronounced. An efficient antioxidant defense mechanism was detected in Caucasian wingnut. Moreover, SA-treated Caucasian wingnut plants had lower lipid peroxidation, as one of the indicators of oxidative stress, when compared to non-SA-treated groups, suggesting the tolerance of this plant to Cd stress, drought stress, and their combination. Cadmium and drought stress also changed the ion concentrations in Caucasian wingnut, causing excessive accumulation of Cd in leaves. These results highlight the beneficial function of SA in reducing the negative effects of Cd and drought stress on Caucasian wingnut plants.

Genome-wide identification of the GRF family in sweet orange (Citrus sinensis) and functional analysis of the CsGRF04 in response to multiple abiotic stresses

BACKGROUND

Citrus is one of the most valuable fruits worldwide and an economic pillar industry in southern China. Nevertheless, it frequently suffers from undesirable environmental stresses during the growth cycle, which severely restricts the growth, development and yield of citrus. In plants, the growth-regulating factor (GRF) family of transcription factors (TF) is extensively distributed and plays an vital part in plant growth and development, hormone response, as well as stress adaptation. However, the systematic identification and functional analysis of GRF TFs in citrus have not been reported.

RESULTS

Here, a genome-wide identification of GRF TFs was performed in Citrus sinensis, 9 members of CsGRFs were systematically identified and discovered to be scattered throughout 5 chromosomes. Subsequently, physical and chemical properties, phylogenetic relationships, structural characteristics, gene duplication events, collinearity and cis-elements of promoter were elaborately analyzed. In particular, the expression patterns of the CsGRF genes in response to multiple phytohormone and abiotic stress treatments were investigated. Predicated on this result, CsGRF04, which exhibited the most differential expression pattern under multiple phytohormone and abiotic stress treatments was screened out. Virus-induced gene silencing (VIGS) technology was utilized to obtain gene silenced plants for CsGRF04 successfully. After the three stress treatments of high salinity, low temperature and drought, the CsGRF04-VIGS lines showed significantly reduced resistance to high salinity and low temperature stresses, but extremely increased resistance to drought stress.

CONCLUSIONS

Taken together, our findings systematically analyzed the genomic characterization of GRF family in Citrus sinensis, and excavated a CsGRF04 with potential functions under multiple abiotic stresses. Our study lay a foundation for further study on the function of CsGRFs in abiotic stress and hormone signaling response.

PatWRKY71 transcription factor regulates patchoulol biosynthesis and plant defense response

Patchoulol, a valuable compound belonging to the sesquiterpenoid family, is the primary component of patchouli oil produced by Pogostemon cablin (P. cablin). It has a variety of pharmacological and biological activities and is widely used in the medical and cosmetic industries. However, despite its significance, there is a lack of research on the transcriptional modulation of patchoulol biosynthesis.Salicylic acid (SA), is a vital plant hormone that serves as a critical signal molecule and plays an essential role in plant growth and defense. However, to date, no studies have explored the modulation of patchoulol biosynthesis by SA. In our study, we discovered that the application of SA can enhance the production of patchoulol. Utilizing transcriptome analysis of SA-treated P. cablin, we identified a crucial downstream transcription factor, PatWRKY71. The transcription level of PatWRKY71 was significantly increased with the use of SA. Furthermore, our research has revealed that PatWRKY71 was capable of binding to the promoter of PatPTS, ultimately leading to an increase in its expression. When PatWRKY71 was silenced by a virus, the expression of both PatWRKY71 and PatPTS was reduced, resulting in the down-regulation of patchoulol production. Through our studies, we discovered that heterologous expression of PatWRKY71 leads to an increase in the sensitivity of Arabidopsis to salt and Cd, as well as an outbreak of reactive oxygen species (ROS). Additionally, we uncovered the regulatory role of PatWRKY71 in both patchoulol biosynthesis and plant defense response. This discovery provided a theoretical basis for the improvement of the content of patchoulol and the resistance of P. cablin through genetic engineering.

The mixed blessings of rare earth element supplements for tomatoes and ferns

Rare earth elements (REEs) constitute a key group of critical minerals that are strategic for the global low-carbon economy and several United Nations Sustainable Development Goals. Their expected escalating emissions into the environment from emerging anthropogenic sources can negatively affect natural ecosystems. However, their hormetic effects make these elements effective fertilizers to promote crop production. Here, we investigate the response of tomatoes and ferns to REE exposure (La, Gd, Yb). While ferns were unresponsive to REEs, these elements promote evident benefits in tomatoes, e.g., elevating nutrient uptake, higher photosynthetic capacity and phytohormone enhancement to allocate energy to green tissue and root development. Nevertheless, the non-selective cation uptake incurs risks of accumulating non-essential elements in edible tissues. These evident benefits of REEs on crops support applications in agricultural production systems, create added value to the global distribution and promote better material flow management of REEs as strategic and critical resources.

Enhanced Resistance to Viruses in Nicotiana edwardsonii 'Columbia' Is Dependent on Salicylic Acid, Correlates with High Glutathione Levels, and Extends to Plant-Pathogenic Bacteria and Abiotic Stress

Our earlier research showed that an interspecific tobacco hybrid (Nicotiana edwardsonii 'Columbia' [NEC]) displays elevated levels of salicylic acid (SA) and enhanced resistance to localized necrotic symptoms (hypersensitive response [HR]) caused by tobacco mosaic virus (TMV) and tobacco necrosis virus (TNV), as compared with another interspecific hybrid (Nicotiana edwardsonii [NE]) derived from the same parents. In the present study, we investigated whether symptomatic resistance in NEC is indeed associated with the inhibition of TMV and TNV and whether SA plays a role in this process. We demonstrated that enhanced viral resistance in NEC is manifested as both milder local necrotic (HR) symptoms and reduced levels of TMV and TNV. The presence of an adequate amount of SA contributes to the enhanced defense response of NEC to TMV and TNV, as the absence of SA resulted in seriously impaired viral resistance. Elevated levels of subcellular tripeptide glutathione (GSH) in NEC plants in response to viral infection suggest that in addition to SA, GSH may also contribute to the elevated viral resistance of NEC. Furthermore, we found that NEC displays an enhanced resistance not only to viral pathogens but also to bacterial infections and abiotic oxidative stress induced by paraquat treatments. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Insights into plant salt stress signaling and tolerance

Soil salinization is an essential environmental stressor, threatening agricultural yield and ecological security worldwide. Saline soils accumulate excessive soluble salts which are detrimental to most plants by limiting plant growth and productivity. It is of great necessity for plants to efficiently deal with the adverse effects caused by salt stress for survival and successful reproduction. Multiple determinants of salt tolerance have been identified in plants, and the cellular and physiological mechanisms of plant salt response and adaption have been intensely characterized. Plants respond to salt stress signals and rapidly initiate signaling pathways to re-establish cellular homeostasis with adjusted growth and cellular metabolism. This review summarizes the advances in salt stress perception, signaling, and response in plants. A better understanding of plant salt resistance will contribute to improving crop performance under saline conditions using multiple engineering approaches. The rhizosphere microbiome-mediated plant salt tolerance as well as chemical priming for enhanced plant salt resistance are also discussed in this review.

The rhizobacterial strain, Pseudomonas putida AKMP7, causes conditional pathogenesis in Arabidopsis thaliana via negative regulation of salicylic acid signaling, under water stress

We have previously reported a phenomenon of "conditional pathogenesis", in which, a drought-tolerant rhizobacterium, Pseudomonas putida AKMP7, promotes plant growth under well-watered conditions, while, deteriorating plant health under water-stressed conditions, in Arabidopsis thaliana seedlings. To understand the molecular mechanisms behind this phenomenon, we studied the modulation of salicylic acid (SA) biosynthesis as well as SA-responsive gene expression, involved in systemic acquired resistance (SAR), in A. thaliana, by AKMP7, under well-watered and water-stressed conditions. We found that, the plant SA levels were upregulated by AKMP7, both under, well-watered as well as water-stressed conditions. However, the SA signaling gene, Non-expressor of Pathogenesis Related gene 1 (NPR1) and Pathogenesis Related gene 1 (PR1) were upregulated under well-watered conditions and suppressed under water-stress, in AKMP7 inoculated seedlings. To understand the reason for this, we studied the expression of NPR4, a negative regulator of NPR1, and, NPR3, a negative regulator of PR1. We observed that, AKMP7 suppresses NPR1 and, consequently, PR1 genes, by upregulating NPR4 under water stress. To understand the potential role of NPR4 in conditional-pathogenesis, we performed physiological studies with NPR4 knockout mutants of A. thaliana and found that the NPR4 mutants did not exhibit any signs of the characteristic growth retardation caused by AKMP7 inoculation, under water stress. Preliminary studies with the model pathogen, Pseudomonas syringae, indicate that AKMP7 may lead to enhanced disease suppression under well-watered conditions, but not under water-stress. Taken together, our data suggest that, AKMP7 causes conditional pathogenesis by an overall compromise in plant immune response under water-stress.

Exploring the role of FBXL fbxl gene family in Soybean: Implications for plant height and seed size regulation

F-box proteins constitute a significant family in eukaryotes and, as a component of the Skp1p-cullin-F-box complex, are considered critical for cellular protein degradation and other biological processes in plants. Despite their importance, the functions of F-box proteins, particularly those with C-terminal leucine-rich repeat (LRR) domains, remain largely unknown in plants. Therefore, the present study conducted genome-wide identification and in silico characterization of F-BOX proteins with C-terminal LRR domains in soybean (Glycine max L.) (GmFBXLs). A total of 45 GmFBXLs were identified. The phylogenetic analysis showed that GmFBXLs could be subdivided into ten subgroups and exhibited a close relationship with those from Arabidopsis thaliana, Cicer aretineum, and Medicago trunculata. It was observed that most cis-regulatory elements in the promoter regions of GmFBXLs are involved in hormone signalling, stress responses, and developmental stages. In silico transcriptome data illustrated diverse expression patterns of the identified GmFBXLs across various tissues, such as shoot apical meristem, flower, green pods, leaves, nodules, and roots. Overexpressing (OE) GmFBXL12 in Tianlong No.1 cultivar resulted in a significant difference in seed size, number of pods, and number of seeds per plant, indicated a potential increase in yield compared to wild type. This study offers valuable perspectives into the role of FBXLs in soybean, serving as a foundation for future research. Additionally, the identified OE lines represent valuable genetic resources for enhancing seed-related traits in soybean.

Quercetin induces pathogen resistance through the increase of salicylic acid biosynthesis in Arabidopsis

Quercetin is a flavonol belonging to the flavonoid group of polyphenols. Quercetin is reported to have a variety of biological functions, including antioxidant, pigment, auxin transport inhibitor and root nodulation factor. Additionally, quercetin is known to be involved in bacterial pathogen resistance in Arabidopsis through the transcriptional increase of pathogenesis-related (PR) genes. However, the molecular mechanisms underlying how quercetin promotes pathogen resistance remain elusive. In this study, we showed that the transcriptional increases of PR genes were achieved by the monomerization and nuclear translocation of nonexpressor of pathogenesis-related proteins 1 (NPR1). Interestingly, salicylic acid (SA) was approximately 2-fold accumulated by the treatment with quercetin. Furthermore, we showed that the increase of SA biosynthesis by quercetin was induced by the transcriptional increases of typical SA biosynthesis-related genes. In conclusion, this study strongly suggests that quercetin induces bacterial pathogen resistance through the increase of SA biosynthesis in Arabidopsis.

Fusaric acid-evoked oxidative stress affects plant defence system by inducing biochemical changes at subcellular level

Fusaric acid (FA) is one of the most harmful phytotoxins produced in various plant-pathogen interactions. Fusarium species produce FA as a secondary metabolite, which can infect many agronomic crops at all stages of development from seed to fruit, and FA production can further compromise plant survival because of its phytotoxic effects. FA exposure in plant species adversely affects plant growth, development and crop yield. FA exposure in plants leads to the generation of reactive oxygen species (ROS), which cause cellular damage and ultimately cell death. Therefore, FA-induced ROS accumulation in plants has been a topic of interest for many researchers to understand the plant-pathogen interactions and plant defence responses. In this study, we reviewed the FA-mediated oxidative stress and ROS-induced defence responses of antioxidants, as well as hormonal signalling in plants. The effects of FA phytotoxicity on lipid peroxidation, physiological changes and ultrastructural changes at cellular and subcellular levels were reported. Additionally, DNA damage, cell death and adverse effects on photosynthesis have been explained. Some possible approaches to overcome the harmful effects of FA in plants were also discussed. It is concluded that FA-induced ROS affect the enzymatic and non-enzymatic antioxidant system regulated by phytohormones. The effects of FA are also associated with other photosynthetic, ultrastructural and genotoxic modifications in plants.

The advent of plant cells in bioreactors

Ever since agriculture started, plants have been bred to obtain better yields, better fruits, or sustainable products under uncertain biotic and abiotic conditions. However, a new way to obtain products from plant cells emerged with the development of recombinant DNA technologies. This led to the possibility of producing exogenous molecules in plants. Furthermore, plant chemodiversity has been the main source of pharmacological molecules, opening a field of plant biotechnology directed to produce high quality plant metabolites. The need for different products by the pharma, cosmetics agriculture and food industry has pushed again to develop new procedures. These include cell production in bioreactors. While plant tissue and cell culture are an established technology, beginning over a hundred years ago, plant cell cultures have shown little impact in biotechnology projects, compared to bacterial, yeasts or animal cells. In this review we address the different types of bioreactors that are currently used for plant cell production and their usage for quality biomolecule production. We make an overview of Nicotiana tabacum, Nicotiana benthamiana, Oryza sativa, Daucus carota, Vitis vinifera and Physcomitrium patens as well-established models for plant cell culture, and some species used to obtain important metabolites, with an insight into the type of bioreactor and production protocols.

Functional Analysis of a Salicylate Hydroxylase in Sclerotinia sclerotiorum

Salicylic acid plays a crucial role during plant defense to Sclerotinia sclerotiorum. Some bacteria and a few fungi can produce salicylate hydroxylase to degrade SA to suppress plant defense and increase their virulence. But there has been no single salicylate hydroxylase in Sclerotinia sclerotiorum identified until now. In this study, we found that SS1G_02963 (SsShy1), among several predicted salicylate hydroxylases in S. sclerotiorum, was induced approximately 17.6-fold during infection, suggesting its potential role in virulence. SsShy1 could catalyze the conversion of SA to catechol when heterologous expression in E. coli. Moreover, overexpression of SsShy1 in Arabidopsis thaliana decreased the SA concentration and the resistance to S. sclerotiorum, confirming that SsShy1 is a salicylate hydroxylase. Deletion mutants of SsShy1 (∆Ssshy1) showed slower growth, less sclerotia production, more sensitivity to exogenous SA, and lower virulence to Brassica napus. The complemented strain with a functional SsShy1 gene recovered the wild-type phenotype. These results indicate that SsShy1 plays an important role in growth and sclerotia production of S. sclerotiorum, as well as the ability to metabolize SA affects the virulence of S. sclerotiorum.

Inspired by Nature: Isostere Concepts in Plant Hormone Chemistry

Chemical concepts such as isosteres and scaffold hopping have proven to be powerful tools in agrochemical innovation processes. They offer opportunities to modify known molecular lead structures with the aim to improve a range of parameters, including biological efficacy and spectrum, physicochemical properties, stability, and toxicity. While recent biochemical insights into plant-specific receptors and signaling pathways trigger the discovery of the first lead structures, the disclosure of such a new chemical structure sparks a broad range of synthesis activities giving rise to diverse chemical innovation and often a considerable boost in biological activity. Herein, recent examples of isostere concepts in plant-hormone chemistry will be discussed, outlining how synthetic creativity can broaden the scope of natural product chemistry and giving rise to new opportunities in research fields such as abiotic stress tolerance and growth promotion.

Continuous In Vivo Monitoring of Indole-3-Acetic Acid and Salicylic Acid in Tomato Leaf Veins Based on an Electrochemical Microsensor

Indole-3-acetic acid (IAA) and salicylic acid (SA), as critical plant hormones, are involved in multiple physiological regulatory processes of plants. Simultaneous and continuous in vivo detection of IAA and SA will help clarify the mechanisms of their regulation and crosstalk. First, this study reports the development and application of an electrochemical microsensor for simultaneous and continuous in vivo detection of IAA and SA. This electrochemical microsensor system consisted of a tip (length, 2 mm) of platinum wire (diameter, 0.1 mm) modified with carbon cement and multi-walled carbon nanotubes, an untreated tip (length, 2 mm) of platinum wire (diameter, 0.1 mm), as well as a tip (length, 2 mm) of Ag/AgCl wire (diameter, 0.1 mm). It was capable of detecting IAA in the level ranging from 0.1 to 30 µM and SA ranging from 0.1 to 50 µM based on the differential pulse voltammetry or amperometric i-t., respectively. The dynamics of IAA and SA levels in tomato leaf veins under high salinity stress were continuously detected in vivo, and very little damage occurred. Compared to conventional detection methods, the constructed microsensor is not only suitable for continuously detecting IAA and SA in microscopic plant tissue in vivo, it also reduces the damage done to plants during the detection. More importantly, the continuous and dynamic changes in IAA and SA data obtained in stiu through this system not only can help clarify the interaction mechanisms of IAA and SA in plants, it also helps to evaluate the health status of plants, which will promote the development of basic research in botany and precision agriculture.

Highly Selective and Rapid "Turn-On" Fluorogenic Chemosensor for Detection of Salicylic Acid in Plants and Food Samples

Salicylic acid (SA) is one of the chemical molecules, involved in plant growth and immunity, thereby contributing to the control of pests and pathogens, and even applied in fruit and vegetable preservation. However, only a few tools have ever been designed or executed to understand the physiological processes induced by SA or its function in plant immunity and residue detection in food. Hence, three Rh6G-based fluorogenic chemosensors were synthesized to detect phytohormone SA based on the "OFF-ON" mechanism. The probes showed high selectivity, ultrafast response time (<60 s), and nanomolar detection limit for SA. Moreover, the probe possessed outstanding profiling that can be successfully used for SA imaging of callus and plants. Furthermore, the fluorescence pattern indicated that SA could occur in the distal transport in plants. These remarkable results contribute to improving our understanding of the multiple physiological and pathological processes involved in SA for plant disease diagnosis and for the development of immune activators. In addition, SA detection in some agricultural products used probes to extend the practical application because its use is prohibited in some countries and is harmful to SA-sensitized persons. Interestingly, the as-obtained test paper displayed that SA could be imaged by ultraviolet (UV) and was directly visible to the naked eye. Given the above outcomes, these probes could be used to monitor SA in vitro and in vivo, including, but not limited to, plant biology, food residue detection, and sewage detection.

A tug-of-war to control plant emission of an airborne alarm signal

Aphids represent a major threat to crops. Hundreds of different viruses are aphid-borne. Upon aphid attack, plants release volatile organic compounds (VOCs) as airborne alarm signals to turn on the airborne defense (AD) of neighboring plants, thereby repelling aphids as well as reducing aphid fitness and virus transmission. This phenomenon provides a critical community-wide plant protection to fend off aphids, but the underlying molecular basis remains undetermined for a long time. In a recent article, Gong et al. established the NAC2-SAMT1 module as the core component regulating the emission of methyl-salicylate (MeSA), a major component of VOCs in aphid-attacked plants. Furthermore, they showed that SABP2 protein is critical for the perception of volatile MeSA signal by converting MeSA to Salicylic Acid (SA), which is the cue to elicit AD against aphids at the community level. Moreover, they showed that multiple viruses use a conserved glycine residue in the ATP-dependent helicase domain in viral proteins to shuttle NAC2 from the nucleus to the cytoplasm for degradation, leading to the attenuation of MeSA emission and AD. These findings illuminate the functional roles of key regulators in the complex MeSA-mediated airborne defense process and a counter-defense mechanism used by viruses, which has profound significance in advancing the knowledge of plant-pathogen interactions as well as providing potential targets for gene editing-based crop breeding.

High air humidity dampens salicylic acid pathway and NPR1 function to promote plant disease

The occurrence of plant disease is determined by interactions among host, pathogen, and environment. Air humidity shapes various aspects of plant physiology and high humidity has long been known to promote numerous phyllosphere diseases. However, the molecular basis of how high humidity interferes with plant immunity to favor disease has remained elusive. Here we show that high humidity is associated with an "immuno-compromised" status in Arabidopsis plants. Furthermore, accumulation and signaling of salicylic acid (SA), an important defense hormone, are significantly inhibited under high humidity. NPR1, an SA receptor and central transcriptional co-activator of SA-responsive genes, is less ubiquitinated and displays a lower promoter binding affinity under high humidity. The cellular ubiquitination machinery, particularly the Cullin 3-based E3 ubiquitin ligase mediating NPR1 protein ubiquitination, is downregulated under high humidity. Importantly, under low humidity the Cullin 3a/b mutant plants phenocopy the low SA gene expression and disease susceptibility that is normally observed under high humidity. Our study uncovers a mechanism by which high humidity dampens a major plant defense pathway and provides new insights into the long-observed air humidity influence on diseases.

The Sw-5b NLR Immune Receptor Induces Early Transcriptional Changes in Response to Thrips and Mechanical Modes of Inoculation of Tomato spotted wilt orthotospovirus

The NLR (nucleotide-binding leucine-rich repeat) class immune receptor Sw-5b confers resistance to Tomato spotted wilt orthotospovirus (TSWV). Although Sw-5b is known to activate immunity upon recognition of the TSWV movement protein NSm, we know very little about the downstream events that lead to resistance. Here, we investigated the Sw-5b-mediated early transcriptomic changes that occur in response to mechanical and thrips-mediated inoculation of TSWV, using near-isogenic tomato lines CNPH-LAM 147 (Sw5b+/+) and Santa Clara (Sw-5b-/-). We observed earlier Sw-5b-mediated transcriptional changes in response to thrips-mediated inoculation compared with that in response to mechanical inoculation of TSWV. With thrips-mediated inoculation, differentially expressed genes (DEGs) were observed at 12, 24, and 72 h postinoculation (hpi). Whereas with mechanical inoculation, DEGs were observed only at 72 hpi. Although some DEGs were shared between the two methods of inoculation, many DEGs were specific to either thrips-mediated or mechanical inoculation of TSWV. In response to thrips-mediated inoculation, an NLR immune receptor, cysteine-rich receptor-like kinase, G-type lectin S-receptor-like kinases, the ethylene response factor 1, and the calmodulin-binding protein 60 were induced. Fatty acid desaturase 2-9, cell death genes, DCL2b, RIPK/PBL14-like, ERF017, and WRKY75 were differentially expressed in response to mechanical inoculation. Our findings reveal Sw-5b responses specific to the method of TSWV inoculation. Although TSWV is transmitted in nature primarily by the thrips, Sw-5b responses to thrips inoculation have not been previously studied. Therefore, the DEGs we have identified in response to thrips-mediated inoculation provide a new foundation for understanding the mechanistic roles of these genes in the Sw-5b-mediated resistance. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Transcription factor PbbZIP4 is targeted for proteasome-mediated degradation by the ubiquitin ligase PbATL18 to influence pear's resistance to Colletotrichum fructicola by regulating the expression of PbNPR3

Pear anthracnose caused by Colletotrichum fructicola is one of the main fungal diseases in all pear-producing areas. The degradation of ubiquitinated proteins by the 26S proteasome is a regulatory mechanism of eukaryotes. E3 ubiquitin ligase is substrate specific and is one of the most diversified and abundant enzymes in the regulation mechanism of plant ubiquitination. Although numerous studies in other plants have shown that the degradation of ubiquitinated proteins by the 26S proteasome is closely related to plant immunity, there are limited studies on them in pear trees. Here, we found that an E3 ubiquitin ligase, PbATL18, interacts with and ubiquitinates the transcription factor PbbZIP4, and this process is enhanced by C. fructicola infection. PbATL18 overexpression in pear callus enhanced resistance to C. fructicola infection, whereas PbbZIP4 overexpression increased sensitivity to C. fructicola infection. Silencing PbATL18 and PbbZIP4 in Pyrus betulaefolia seedlings resulted in opposite effects, with PbbZIP4 silencing enhancing resistance to C. fructicola infection and PbATL18 silencing increasing sensitivity to C. fructicola infection. Using yeast one-hybrid screens, an electrophoretic mobility shift assay, and dual-luciferase assays, we demonstrated that the transcription factor PbbZIP4 upregulated the expression of PbNPR3 by directly binding to its promoter. PbNPR3 is one of the key genes in the salicylic acid (SA) signal transduction pathway that can inhibit SA signal transduction. Here, we proposed a PbATL18-PbbZIP4-PbNPR3-SA model for plant response to C. fructicola infection. PbbZIP4 was ubiquitinated by PbATL18 and degraded by the 26S proteasome, which decreased the expression of PbNPR3 and promoted SA signal transduction, thereby enhancing plant C. fructicola resistance. Our study provides new insights into the molecular mechanism of pear response to C. fructicola infection, which can serve as a theoretical basis for breeding superior disease-resistant pear varieties.

Molecular mechanism overview of metabolite biosynthesis in medicinal plants

Medicinal plants are essential and rich resources for plant-based medicines and new drugs. Increasing attentions are paid to the secondary metabolites of medicinal plants due to their unique biological activity, pharmacological action, and high utilization value. However, the development of medicinal plants is constrained by limited natural resources and an unclear understanding of the mechanisms underlying active medicinal ingredients, thereby rendering the utilization and exploration of secondary metabolites more challenging. Besides, with the advancement of research on biosynthesis and molecular metabolism of natural products from medicinal plants, the methods for studying the biological activity and pharmacological effects of these products are constantly evolving. In recent years, significant progress has been made in the biosynthetic pathways and related regulatory genes of secondary metabolites in medicinal plants, which has greatly advanced both basic research and the development of clinical applications for medicinal plants. In this review, we discuss the past two decades of international research on the development of medicinal plant resources, mainly focusing on the biosynthetic pathway of secondary metabolites, intracellular signal transduction processes, multi-omics applications, and the application of gene editing technology in related research progress. We also discuss future development trends to promote the deep mining and development of natural products from medicinal plants, providing a useful reference.

Salicylic acid accelerates carbon starvation-induced leaf senescence in Arabidopsis thaliana by inhibiting autophagy through Nonexpressor of pathogenesis-related genes 1

In plants, leaf senescence is regulated by several factors, including age and carbon starvation. The molecular mechanism of age-regulated developmental leaf senescence differs from that of carbon starvation-induced senescence. Salicylic acid (SA) and Nonexpressor of pathogenesis-related genes 1 (NPR1) play important roles in promoting developmental leaf senescence. However, the relationship between SA signaling and carbon starvation-induced leaf senescence is not currently well understood. Here, we used Arabidopsis thaliana as material and found that carbon starvation-induced leaf senescence was accelerated in the SA dihydroxylase mutants s3hs5h compared to the Columbia ecotype (Col). Exogenous SA treatment significantly promoted carbon starvation-induced leaf senescence, especially in NPR1-GFP. Increasing the endogenous SA and overexpression of NPR1 inhibited carbon starvation-induced autophagy. However, mutation of NPR1 delayed carbon starvation-induced leaf senescence, increased autophagosome production and accelerated autophagic degradation of the Neighbor of BRCA1 gene 1 (NBR1). In conclusion, SA promotes carbon starvation-induced leaf senescence by inhibiting autophagy via NPR1.

Rice stripe virus nonstructural protein 3 suppresses plant defence responses mediated by the MEL-SHMT1 module

Our previous study identified an evolutionarily conserved C4HC3-type E3 ligase, named microtubule-associated E3 ligase (MEL), that regulates broad-spectrum plant resistance against viral, fungal and bacterial pathogens in multiple plant species by mediating serine hydroxymethyltransferase (SHMT1) degradation via the 26S proteasome pathway. In the present study, we found that NS3 protein encoded by rice stripe virus could competitively bind to the MEL substrate recognition site, thereby inhibiting MEL interacting with and ubiquitinating SHMT1. This, in turn, leads to the accumulation of SHMT1 and the repression of downstream plant defence responses, including reactive oxygen species accumulation, mitogen-activated protein kinase pathway activation, and the up-regulation of disease-related gene expression. Our findings shed light on the ongoing arms race between pathogens and demonstrate how a plant virus can counteract the plant defence response.

Insights into the molecular mechanism of Trichoderma stimulating plant growth and immunity against phytopathogens

Trichoderma species have received significant interest as beneficial fungi for boosting plant growth and immunity against phytopathogens. By establishing a mutualistic relationship with plants, Trichoderma causes a series of intricate signaling events that eventually promote plant growth and improve disease resistance. The mechanisms contain the indirect or direct involvement of Trichoderma in enhancing plant growth by modulating phytohormones signaling pathways, improving uptake and accumulation of nutrients, and increasing soil bioavailability of nutrients. They contribute to plant resistance by stimulating systemic acquired resistance through salicylic acid, jasmonic acid, and ethylene signaling. A cascade of signal transduction processes initiated by the interaction of Trichoderma and plants regulate the expression of defense-related genes, resulting in the synthesis of defense hormones and pathogenesis-related proteins (PRPs), which collectively improve plant resistance. Additionally, advancements in omics technologies has led to the identification of key pathways, their regulating genes, and molecular interactions in the plant defense and growth promotion responses induced by Trichoderma. Deciphering the molecular mechanism behind Trichoderma's induction of plant defense and immunity is essential for harnessing the full plant beneficial potential of Trichoderma. This review article sheds light on the molecular mechanisms that underlie the positive effects of Trichoderma-induced plant immunity and growth and opens new opportunities for developing environmentally friendly and innovative approaches to improve plant immunity and growth.

Can plant hormonomics be built on simple analysis? A review

The field of plant hormonomics focuses on the qualitative and quantitative analysis of the hormone complement in plant samples, akin to other omics sciences. Plant hormones, alongside primary and secondary metabolites, govern vital processes throughout a plant's lifecycle. While active hormones have received significant attention, studying all related compounds provides valuable insights into internal processes. Conventional single-class plant hormone analysis employs thorough sample purification, short analysis and triple quadrupole tandem mass spectrometry. Conversely, comprehensive hormonomics analysis necessitates minimal purification, robust and efficient separation and better-performing mass spectrometry instruments. This review summarizes the current status of plant hormone analysis methods, focusing on sample preparation, advances in chromatographic separation and mass spectrometric detection, including a discussion on internal standard selection and the potential of derivatization. Moreover, current approaches for assessing the spatiotemporal distribution are evaluated. The review touches on the legitimacy of the term plant hormonomics by exploring the current status of methods and outlining possible future trends.

Horizontally Transferred Salivary Protein Promotes Insect Feeding by Suppressing Ferredoxin-Mediated Plant Defenses

Herbivorous insects such as whiteflies, planthoppers, and aphids secrete abundant orphan proteins to facilitate feeding. Yet, how these genes are recruited and evolve to mediate plant-insect interaction remains unknown. In this study, we report a horizontal gene transfer (HGT) event from fungi to an ancestor of Aleyrodidae insects approximately 42 to 190 million years ago. BtFTSP1 is a salivary protein that is secreted into host plants during Bemisia tabaci feeding. It targets a defensive ferredoxin 1 in Nicotiana tabacum (NtFD1) and disrupts the NtFD1-NtFD1 interaction in plant cytosol, leading to the degradation of NtFD1 in a ubiquitin-dependent manner. Silencing BtFTSP1 has negative effects on B. tabaci feeding while overexpressing BtFTSP1 in N. tabacum benefits insects and rescues the adverse effect caused by NtFD1 overexpression. The association between BtFTSP1 and NtFD1 is newly evolved after HGT, with the homologous FTSP in its fungal donor failing to interact and destabilize NtFD1. Our study illustrates the important roles of horizontally transferred genes in plant-insect interactions and suggests the potential origin of orphan salivary genes.

Fuels for ROS signaling in plant immunity

Reactive oxygen species (ROS) signaling has an important role in plant innate immune responses and is primarily mediated by NADPH oxidase, also known as respiratory burst oxidase homologs (RBOHs) in plants. NADPH serves as a fuel for RBOHs and limits the rate or amount of ROS production. Molecular regulation of RBOHs has been extensively studied; however, the source of NADPH for RBOHs has received little attention. Here, we review ROS signaling and the regulation of RBOHs in the plant immune system with a focus on NADPH regulation to achieve ROS homeostasis. We propose an idea to regulate the levels of NADPH as part of a new strategy to control ROS signaling and the corresponding downstream defense responses.

Wall-associated kinase BrWAK1 confers resistance to downy mildew in Brassica rapa

The plant cell wall is the first line of defence against physical damage and pathogen attack. Wall-associated kinase (WAK) has the ability to perceive the changes in the cell wall matrix and transform signals into the cytoplasm, being involved in plant development and the defence response. Downy mildew, caused by Hyaloperonospora brassicae, can result in a massive loss in Chinese cabbage (Brassica rapa L. ssp. pekinensis) production. Herein, we identified a candidate resistant WAK gene, BrWAK1, in a major resistant quantitative trait locus, using a double haploid population derived from resistant inbred line T12-19 and the susceptible line 91-112. The expression of BrWAK1 could be induced by salicylic acid and pathogen inoculation. Expression of BrWAK1 in 91-112 could significantly enhance resistance to the pathogen, while truncating BrWAK1 in T12-19 increased disease susceptibility. Variation in the extracellular galacturonan binding (GUB) domain of BrWAK1 was found to mainly confer resistance to downy mildew in T12-19. Moreover, BrWAK1 was proved to interact with BrBAK1 (brassinosteroid insensitive 1 associated kinase), resulting in the activation of the downstream mitogen-activated protein kinase (MAPK) cascade to trigger the defence response. BrWAK1 is the first identified and thoroughly characterized WAK gene conferring disease resistance in Chinese cabbage, and the plant biomass is not significantly influenced by BrWAK1, which will greatly accelerate Chinese cabbage breeding for downy mildew resistance.

Immune activation during Pseudomonas infection causes local cell wall remodeling and alters AGP accumulation

The plant cell boundary generally comprises constituents of the primary and secondary cell wall (CW) that are deposited sequentially during development. Although it is known that the CW acts as a barrier against phytopathogens and undergoes modifications to limit their invasion, the extent, sequence, and requirements of the pathogen-induced modifications of the CW components are still largely unknown, especially at the level of the polysaccharide fraction. To address this significant knowledge gap, we adopted the compatible Pseudomonas syringae-Arabidopsis thaliana system. We found that, despite systemic signaling actuation, Pseudomonas infection leads only to local CW modifications. Furthermore, by utilizing a combination of CW and immune signaling-deficient mutants infected with virulent or non-virulent bacteria, we demonstrated that the pathogen-induced changes in CW polysaccharides depend on the combination of pathogen virulence and the host's ability to mount an immune response. This results in a pathogen-driven accumulation of CW hexoses, such as galactose, and an immune signaling-dependent increase in CW pentoses, mainly arabinose, and xylose. Our analyses of CW changes during disease progression also revealed a distinct spatiotemporal pattern of arabinogalactan protein (AGP) deposition and significant modifications of rhamnogalacturonan sidechains. Furthermore, genetic analyses demonstrated a critical role of AGPs, specifically of the Arabinoxylan Pectin Arabinogalactan Protein1, in limiting pathogen growth. Collectively, our results provide evidence for the actuation of significant remodeling of CW polysaccharides in a compatible host-pathogen interaction, and, by identifying AGPs as critical elements of the CW in plant defense, they pinpoint opportunities to improve plants against diverse pathogens.

WRKY transcription factors in plant defense

Environmental stressors caused by climate change are fundamental barriers to agricultural sustainability. Enhancing the stress resilience of crops is a key strategy in achieving global food security. Plants perceive adverse environmental conditions and initiate signaling pathways to activate precise responses that contribute to their survival. WRKY transcription factors (TFs) are essential players in several signaling cascades and regulatory networks that have crucial implications for defense responses in plants. This review summarizes advances in research concerning how WRKY TFs mediate various signaling cascades and metabolic adjustments as well as how epigenetic modifications involved in environmental stress responses in plants can modulate WRKYs and/or their downstream genes. Emerging research shows that clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas)-mediated genome editing of WRKYs could be used to improve crop resilience.

Salicylic acid regulates phenolic acid biosynthesis via SmNPR1-SmTGA2/SmNPR4 modules in Salvia miltiorrhiza

Phenolic acids are the main active ingredients in Salvia miltiorrhiza, which can be used for the treatment of many diseases, particularly cardiovascular diseases. It is known that salicylic acid (SA) can enhance phenolic acid content, but the molecular mechanism of its regulation is still unclear. Nonexpresser of PR genes 1 (NPR1) plays a positive role in the SA signaling pathway. In this study, we identified a SmNPR1 gene that responds to SA induction and systematically investigated its function. We found that SmNPR1 positively affected phenolic acid biosynthesis. Then, we identified a novel TGA transcription factor, SmTGA2, which interacts with SmNPR1. SmTGA2 positively regulates phenolic acid biosynthesis by directly up-regulating SmCYP98A14 expression. After double-gene transgenic analysis and other biochemical assays, it was found that SmNPR1 and SmTGA2 work synergistically to regulate phenolic acid biosynthesis. In addition, SmNPR4 forms a heterodimer with SmNPR1 to inhibit the function of SmNPR1, and SA can alleviate this effect. Collectively, these findings elucidate the molecular mechanism underlying the regulation of phenolic acid biosynthesis by SmNPR1-SmTGA2/SmNPR4 modules and provide novel insights into the SA signaling pathway regulating plant secondary metabolism.

The Hypersensitive Response to Plant Viruses

Plant proteins with domains rich in leucine repeats play important roles in detecting pathogens and triggering defense reactions, both at the cellular surface for pattern-triggered immunity and in the cell to ensure effector-triggered immunity. As intracellular parasites, viruses are mostly detected intracellularly by proteins with a nucleotide binding site and leucine-rich repeats but receptor-like kinases with leucine-rich repeats, known to localize at the cell surface, have also been involved in response to viruses. In the present review we report on the progress that has been achieved in the last decade on the role of these leucine-rich proteins in antiviral immunity, with a special focus on our current understanding of the hypersensitive response.

Identification of ARF transcription factor gene family and its defense responses to bacterial infection and salicylic acid treatment in sugarcane

Auxin response factor (ARF) is a critical regulator in the auxin signaling pathway, involved in a variety of plant biological processes. Here, gene members of 24 SpapARFs and 39 SpnpARFs were identified in two genomes of Saccharum spontaneum clones AP85-441 and Np-X, respectively. Phylogenetic analysis showed that all ARF genes were clustered into four clades, which is identical to those ARF genes in maize (Zea mays) and sorghum (Sorghum bicolor). The gene structure and domain composition of this ARF family are conserved to a large degree across plant species. The SpapARF and SpnpARF genes were unevenly distributed on chromosomes 1-8 and 1-10 in the two genomes of AP85-441 and Np-X, respectively. Segmental duplication events may also contribute to this gene family expansion in S. spontaneum. The post-transcriptional regulation of ARF genes likely involves sugarcane against various stressors through a miRNA-medicated pathway. Expression levels of six representative ShARF genes were analyzed by qRT-PCR assays on two sugarcane cultivars [LCP85-384 (resistant to leaf scald) and ROC20 (susceptible to leaf scald)] triggered by Acidovorax avenae subsp. avenae (Aaa) and Xanthomonas albilineans (Xa) infections and salicylic acid (SA) treatment. ShARF04 functioned as a positive regulator under Xa and Aaa stress, whereas it was a negative regulator under SA treatment. ShARF07/17 genes played positive roles against both pathogenic bacteria and SA stresses. Additionally, ShARF22 was negatively modulated by Xa and Aaa stimuli in both cultivars, particularly LCP85-384. These findings imply that sugarcane ARFs exhibit functional redundancy and divergence against stressful conditions. This work lays the foundation for further research on ARF gene functions in sugarcane against diverse environmental stressors.

Catalases mediate tobacco resistance to virus infection through crosstalk between salicylic acid and auxin signaling pathways

Catalases (CATs) play important roles in plant growth, development and defense responses. Previous studies have shown that CATs exhibit different or even opposite effects on plant immunity in different plant-pathogen interactions, but little is known about the mechanisms. In this study, Nicotiana tabacum plants with overexpression or knockout of CAT genes, tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV) were employed to investigate the role of CAT in compatible plant-virus interactions. The results showed that there were dynamic changes in the effect of CAT on N. tabacum defense responses. Overexpression of catalase 1 (CAT1) and catalase 3 (CAT3) improved N. tabacum resistance in the early stage of virus infection but depressed it during the late stages of pathogenesis, especially in CAT3 overexpressing plants. The lower level of electrolyte leakage, lower contents of malonaldehyde and hydrogen peroxide (H2 O2 ), higher activities of antioxidant enzymes and improved functions of photosystem II corresponded to the milder symptoms and higher resistance of infected tobacco plants. In addition, the infection of TMV and CMV resulted in expression changes of CATs in tobacco plants, and pretreatment with H2 O2 facilitated TMV and CMV infection. Further experiments showed that the content of salicylic acid (SA) and the expression of genes related to SA signaling pathway were positively correlated with plant resistance, whereas auxin and its related signaling pathway were related to the viral susceptibility of plants. Taken together, our results demonstrated that CAT1 and CAT3 mediated tobacco resistance to virus infection through crosstalk between SA and auxin signaling pathways.

Volatilome and proteome responses to Colletotrichum lindemuthianum infection in a moderately resistant and a susceptible bean genotype

We analyzed the changes in the volatilome, proteome, stomatal conductance, salicylic and jasmonic acid contents of a susceptible and a moderately resistant genotype of common bean, Phaseoulus vulgaris L., challenged with Colletotrichum lindemuthianum, the causal agent of fungal anthracnose. Our results indicate differences at both proteome and volatilome levels between the two genotypes, before and after the infection, and different defense strategies. The moderately resistant genotype hindered pathogen infection, invasion, and replication mainly by maintaining epidermal and cell wall structure. The susceptible genotype was not able to limit the early stages of pathogen infection. Rather, stomatal conductance increased in the infected susceptible genotype, and enhanced synthesis of Green Leaf Volatiles and salicylic acid was observed, together with a strong hypersensitive response. Proteomic investigation provided a general framework for physiological changes, whereas observed variations in the volatilome suggested that volatile organic compounds may principally represent stress markers rather than defensive compounds per se.