Systemic acquired resistance

The Impact of a Commercial Biostimulant on the Grape Mycobiota of Vitis vinifera cv. Barbera

Reducing the use of fungicides, insecticides, and herbicides in order to limit environmental pollution and health risks for agricultural operators and consumers is one of the goals of European regulations. In fact, the European Commission developed a package of measures (the European Green Deal) to promote the sustainable use of natural resources and strengthen the resilience of European agri-food systems. As a consequence, new plant protection products, such as biostimulants, have been proposed as alternatives to agrochemicals. Their application in agroecosystems could potentially open new scenarios regarding the microbiota. In particular, the vineyard microbiota and the microbiota on the grape surface can be affected by biostimulants and lead to different wine features. The aim of this work was to assess the occurrence of a possible variation in the mycobiota due to the biostimulant application. Therefore, our attention has been focused on the yeast community of grape bunches from vines subjected to the phytostimulant BION®50WG treatment. This work was carried out in the CREA-VE experimental vineyard of Vitis vinifera cv. Barbera in Asti (Piedmont, Italy). The composition of fungal communities on grapes from three experimental conditions such as IPM (integrated pest management), IPM+BION®50WG, and IPM+water foliar nebulization was compared by a metabarcoding approach. Our results revealed the magnitude of alpha and beta diversity, and the microbial biodiversity index and specific fungal signatures were highlighted by comparing the abundance of yeast and filamentous fungi in IPM and BION®50WG treatments. No significant differences in the mycobiota of grapevines subjected to the three treatments were detected.

Overexpression of flowering locus D (FLD) in Indian mustard (Brassica juncea) enhances tolerance to Alternaria brassicae and Sclerotinia sclerotiorum

KEY MESSAGE

Overexpression of BjFLD in Brassica juncea imparts resistance against fungal pathogens and increases the yield. These transgenics could lower the use of fungicides, which have detrimental effects on the environment. Productivity of Indian mustard (Brassica juncea) is adversely affected by fungal phytopathogens, Alternaria brassicae and Sclerotinia sclerotiorum. Arabidopsis flowering locus D (FLD) positively regulates jasmonic acid signaling and defense against necrotrophic pathogens. In this study, the endogenous FLD (B. juncea FLD; BjFLD) in Indian mustard was overexpressed in B. juncea to determine its role in biotic stress tolerance. We report the isolation, characterization, and functional validation of BjFLD. The transgene expression was confirmed by qRT-PCR. The constitutive overexpression of BjFLD enhanced the tolerance of B. juncea to A. brassicae and S. sclerotiorum, which was manifested as delayed appearance of symptom, impeded disease progression, and enhanced percentage of disease protection. The transgenic lines maintained a higher photosynthetic capacity and redox potential under biotic stress and could detoxify reactive oxygen species (ROS) by modulating the antioxidant machinery and physiochemical attributes. The BjFLD-overexpressing lines showed enhanced SA level as well higher NPR1 expression. The overexpression of BjFLD induced early flowering and higher seed yield in the transgenic lines. These findings indicate that overexpression of BjFLD enhances the tolerance of B. juncea to A. brassicae and S. sclerotiorum by induction of systemic acquired resistance and mitigating the damage caused by stress-induced ROS.

Aureobasidium pullulans from the Fire Blight Biocontrol Product, Blossom Protect, Induces Host Resistance in Apple Flowers

Fire blight, caused by Erwinia amylovora, is a devastating disease of apple. Blossom Protect, a product that contains Aureobasidium pullulans as the active ingredient, is one of the most effective biological controls of fire blight. It has been postulated that the mode of action of A. pullulans is to compete against and antagonize epiphytic growth of E. amylovora on flowers, but recent studies have found that flowers treated with Blossom Protect harbored similar to or only slightly reduced E. amylovora populations compared with nontreated flowers. In this study, we tested the hypothesis that A. pullulans-mediated biocontrol of fire blight is the result of induced host resistance. We found that PR genes in the systemic acquired resistance pathway, but not genes in the induced systemic resistance pathway, were induced in hypanthial tissue of apple flowers after the Blossom Protect treatment. Additionally, the induction of PR gene expression was coupled with an increase of plant-derived salicylic acid in this tissue. After inoculation with E. amylovora, PR gene expression was suppressed in nontreated flowers, but in flowers pretreated with Blossom Protect, the heightened PR expression offset the immune repression caused by E. amylovora, and prevented infection. Temporal and spatial analysis of PR gene induction showed that induction of PR genes occurred 2 days after the Blossom Protect treatment, and required direct flower-yeast contact. Finally, we observed deterioration of the epidermal layer of the hypanthium in some of the Blossom Protect-treated flowers, suggesting that PR gene induction in flowers may be a result of pathogenesis by A. pullulans.

A hybrid multifunctional physicochemical sensor suite for continuous monitoring of crop health

This work reports a first-of-its-kind hybrid wearable physicochemical sensor suite that we call PlantFit for simultaneous measurement of two key phytohormones, salicylic acid, and ethylene, along with vapor pressure deficit and radial growth of stem in live plants. The sensors are developed using a low-cost and roll-to-roll screen printing technology. A single integrated flexible patch that contains temperature, humidity, salicylic acid, and ethylene sensors, is installed on the leaves of live plants. The strain sensor with in-built pressure correction capability is wrapped around the plant stem to provide pressure-compensated stem diameter measurements. The sensors provide real-time information on plant health under different amounts of water stress conditions. The sensor suite is installed on bell pepper plants for 40 days and measurements of salicylic acid, ethylene, temperature, humidity, and stem diameter are recorded daily. In addition, sensors are installed on different parts of the same plant to investigate the spatiotemporal dynamics of water transport and phytohormone responses. Subsequent correlation and principal component analyses demonstrate the strong association between hormone levels, vapor pressure deficit, and water transport in the plant. Our findings suggest that the mass deployment of PlantFit in agricultural settings will aid growers in detecting water stress/deficiency early and in implementing early intervention measures to reduce stress-induced yield decline.

Re-recognition of innate immune memory as an integrated multidimensional concept

In the past decade, the concept of immunological memory, which has long been considered a phenomenon observed in the adaptive immunity of vertebrates, has been extended to the innate immune system of various organisms. This de novo immunological memory is mainly called "innate immune memory", "immune priming", or "trained immunity" and has received increased attention because of its potential for clinical and agricultural applications. However, research on different species, especially invertebrates and vertebrates, has caused controversy regarding this concept. Here we discuss the current studies focusing on this immunological memory and summarize several mechanisms underlying it. We propose "innate immune memory" as a multidimensional concept as an integration between the seemingly different immunological phenomena.

Transcriptomic analysis towards identification of defence-responsive genes and pathways upon application of Sargassum seaweed extract on tomato plants infected with Macrophominaphaseolina

The charcoal-rot caused by Macrophomina phaseolina is one of the major disease in many economically important crop plants including tomato. The molecular responses of the host plant against the M. phaseolina are poorly stated. In the present study, for the first time the molecular insight of tomato-Macrophomina interaction and Sargassum tenerrimum extract (SE) toward managing disease through RNA-seq approach is established. A total of 449 million high-quality reads (HQRs) were obtained and aligned to the tomato genome with an average mapping of 89.12%. The differentially expressed genes (DEGs) regulated across the different treatment pairs were identified. Several DEGs, such as receptor-like kinases (SlRLKs), transcription factors including SlWRKY70, SlGRAS4, SlERF4, SlERF25, pathogenesis related-1 (SlPR1), SlPR2, endochitinase and peroxidase were significantly up-regulated in SE + Macrophomina treated sample as compared to only Macrophomina treated sample. The crosstalk between salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) was a key factor to regulate resistance in tomato during SE + Macrophomina treatment. The KEGG pathway including plant hormone signal transduction, plant-pathogen interaction and mitogen-activated protein kinase (MAPK) signaling pathway were significantly enriched. The RNA-seq data were validated through qPCR using 12 disease-responsive genes and correlated significantly with R2 = 0.73. The present study suggests that SE act as an elicitor molecule and activate the defence-related pathways similar to PAMP-triggered immunity in tomato. The jasmonic acid (JA) mediated signaling pathway was identified as a key factor to induce resistance in tomato against Macrophomina infection. The present study depicts the beneficial effects of SE by regulating molecular mechanism towards defence responses in tomato against Macrophomina infection. The application of SE brings out new prospects to induce disease tolerance in the agricultural crops.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03565-4.

Nucleoredoxin gene SINRX1 negatively regulates tomato immunity by activating SA signaling pathway

The tomato (Solanum lycopersicum) is widely consumed globally and renowned for its health benefits, including the reduction of cardiovascular disease and prostate cancer risk. However, tomato production faces significant challenges, particularly due to various biotic stresses such as fungi, bacteria, and viruses. To address this challenges, we employed the CRISPR/Cas9 system to modify the tomato NUCLEOREDOXIN (SlNRX) genes (SlNRX1 and SlNRX2) belonging to the nucleocytoplasmic THIOREDOXIN subfamily. CRISPR/Cas9-mediated mutations in SlNRX1 (slnrx1) plants exhibited resistance against bacterial leaf pathogen Pseudomonas syringae pv. maculicola (Psm) ES4326, as well as the fungal pathogen Alternaria brassicicola. However, the slnrx2 plants did not display resistance. Notably, the slnrx1 demonstrated elevated levels of endogenous salicylic acid (SA) and reduced levels of jasmonic acid after Psm infection, in comparison to both wild-type (WT) and slnrx2 plants. Furthermore, transcriptional analysis revealed that genes involved in SA biosynthesis, such as ISOCHORISMATE SYNTHASE 1 (SlICS1) and ENHANCED DISEASE SUSCEPTIBILITY 5 (SlEDS5), were upregulated in slnrx1 compared to WT plants. In addition, a key regulator of systemic acquired resistance, PATHOGENESIS-RELATED 1 (PR1), exhibited increased expression in slnrx1 compared to WT. These findings suggest that SlNRX1 acts as a negative regulator of plant immunity, facilitating infection by the Psm pathogen through interference with the phytohormone SA signaling pathway. Thus, targeted mutagenesis of SlNRX1 is a promising genetic means to enhance biotic stress resistance in crop breeding.

ATM and ATR, two central players of the DNA damage response, are involved in the induction of systemic acquired resistance by extracellular DNA, but not the plant wound response

Background

The plant immune response to DNA is highly self/nonself-specific. Self-DNA triggered stronger responses by early immune signals such as H2O2 formation than nonself-DNA from closely related plant species. Plants lack known DNA receptors. Therefore, we aimed to investigate whether a differential sensing of self-versus nonself DNA fragments as damage- versus pathogen-associated molecular patterns (DAMPs/PAMPs) or an activation of the DNA-damage response (DDR) represents the more promising framework to understand this phenomenon.

Results

We treated Arabidopsis thaliana Col-0 plants with sonicated self-DNA from other individuals of the same ecotype, nonself-DNA from another A. thaliana ecotype, or nonself-DNA from broccoli. We observed a highly self/nonself-DNA-specific induction of H2O2 formation and of jasmonic acid (JA, the hormone controlling the wound response to chewing herbivores) and salicylic acid (SA, the hormone controlling systemic acquired resistance, SAR, to biotrophic pathogens). Mutant lines lacking Ataxia Telangiectasia Mutated (ATM) or ATM AND RAD3-RELATED (ATR) - the two DDR master kinases - retained the differential induction of JA in response to DNA treatments but completely failed to induce H2O2 or SA. Moreover, we observed H2O2 formation in response to in situ-damaged self-DNA from plants that had been treated with bleomycin or SA or infected with virulent bacteria Pseudomonas syringae pv. tomato DC3000 or pv. glycinea carrying effector avrRpt2, but not to DNA from H2O2-treated plants or challenged with non-virulent P. syringae pv. glycinea lacking avrRpt2.

Conclusion

We conclude that both ATM and ATR are required for the complete activation of the plant immune response to extracellular DNA whereas an as-yet unknown mechanism allows for the self/nonself-differential activation of the JA-dependent wound response.

The Role of Plant Transcription Factors in the Fight against Plant Viruses

Plants are vulnerable to the challenges of unstable environments and pathogen infections due to their immobility. Among various stress conditions, viral infection is a major threat that causes significant crop loss. In response to viral infection, plants undergo complex molecular and physiological changes, which trigger defense and morphogenic pathways. Transcription factors (TFs), and their interactions with cofactors and cis-regulatory genomic elements, are essential for plant defense mechanisms. The transcriptional regulation by TFs is crucial in establishing plant defense and associated activities during viral infections. Therefore, identifying and characterizing the critical genes involved in the responses of plants against virus stress is essential for the development of transgenic plants that exhibit enhanced tolerance or resistance. This article reviews the current understanding of the transcriptional control of plant defenses, with a special focus on NAC, MYB, WRKY, bZIP, and AP2/ERF TFs. The review provides an update on the latest advances in understanding how plant TFs regulate defense genes expression during viral infection.

Wheat yellow mosaic virus NIb targets TaVTC2 to elicit broad-spectrum pathogen resistance in wheat

GDP-L-galactose phosphorylase (VTC2) catalyses the conversion of GDP-L-galactose to L-galactose-1-P, a vital step of ascorbic acid (AsA) biosynthesis in plants. AsA is well known for its function in the amelioration of oxidative stress caused by most pathogen infection, but its function against viral infection remains unclear. Here, we have identified a VTC2 gene in wheat named as TaVTC2 and investigated its function in association with the wheat yellow mosaic virus (WYMV) infection. Our results showed that overexpression of TaVTC2 significantly increased viral accumulation, whereas knocking down TaVTC2 inhibited the viral infection in wheat, suggesting a positive regulation on viral infection by TaVTC2. Moreover, less AsA was produced in TaVTC2 knocking down plants (TaVTC2-RNAi) which due to the reduction in TaVTC2 expression and subsequently in TaVTC2 activity, resulting in a reactive oxygen species (ROS) burst in leaves. Furthermore, the enhanced WYMV resistance in TaVTC2-RNAi plants was diminished by exogenously applied AsA. We further demonstrated that WYMV NIb directly bound to TaVTC2 and inhibited TaVTC2 enzymatic activity in vitro. The effect of TaVTC2 on ROS scavenge was suppressed by NIb in a dosage-dependent manner, indicating the ROS scavenging was highly regulated by the interaction of TaVTC2 with NIb. Furthermore, TaVTC2 RNAi plants conferred broad-spectrum disease resistance. Therefore, the data indicate that TaVTC2 recruits WYMV NIb to down-regulate its own enzymatic activity, reducing AsA accumulation to elicit a burst of ROS which confers the resistance to WYMV infection. Thus, a new mechanism of the formation of plant innate immunity was proposed.

Efficacy of Biological Control Agents and Resistance Inducer for Control of Mal Secco Disease

Mal secco, caused by Plenodomus tracheiphilus, is an economically important fungal vascular disease in citrus-growing countries of the Mediterranean basin. Preventing fungal infections usually requires a high number of copper treatments but European legislation imposes the minimization of their accumulation in soil. In our study, biological control agents (BCAs) and a plant resistance inducer (PRI), tested in four different experiments on citrus seedlings under controlled conditions, have resulted in promising strategies to control mal secco disease. Foliar (Experiment I) and soil (Experiment II) applications of two formulations of Bacillus amyloliquefaciens strain D747 (Amylo-X® LC and Amylo-X® WG) provided similar performances in reducing the disease amount (incidence and symptoms severity) over time compared to the untreated control, whereas copper hydroxide (Kocide Opti®) used as standard was the most effective treatment over time. In the third experiment, Pythium oligandrum strain M1 (Polyversum®) and Trichoderma asperellum strain ICC012 + Trichoderma gamsii strain ICC080 (Remedier®) were able to reduce disease incidence and symptoms severity compared to the untreated control. Remedier® provided the best performances in reducing the disease amount, whereas the Polyversum® application was the least effective treatment over time. The effectiveness of the Trichoderma spp. formulation in reducing P. tracheiphilus infections did not significantly differ from the standard copper compound (Kocide Opti®). Comprehensively, in the last experiment (IV), acibenzolar-S-methyl (ASM) alone and in mixture with metalaxyl-M proved as effective as B. amyloliquefaciens strain FZB24, with no dose-response relationships observed. These findings provide important insight for the integrated management of mal secco disease.

Identification of Fusarium oxysporum f. sp. lactucae Race 1 as the Causal Agent of Lettuce Fusarium Wilt in Greece, Commercial Cultivars' Susceptibility, and Temporal Expression of Defense-Related Genes

Fusarium wilt of lettuce is found throughout the world, causing significant yield losses. Lettuce is the most-cultivated leafy vegetable in Greece, affected by a large number of foliar and soil-borne pathogens. In this study, 84 isolates of Fusarium oxysporum, obtained from soil-grown lettuce plants exhibiting wilt symptoms, were characterized as belonging to race 1 of F. oxysporum f. sp. lactucae based on sequence analysis of the translation elongation factor 1-alpha (TEF1-α) gene and the rDNA intergenic spacer (rDNA-IGS) region. The isolates were also assigned to one single race through PCR assays with specific primers targeting race 1 and race 4 of the pathogen. In addition, four representative isolates were confirmed to be associated with race 1 based on the pathogenicity tests with a set of differential lettuce cultivars. Artificial inoculations on the most commonly cultivated lettuce cultivars in Greece revealed that the tested cultivars varied regarding their susceptibility to F. oxysporum f. sp. lactucae race 1. Cultivars (cvs.) "Cencibel" and "Lugano" were found to be highly susceptible, while cvs. "Sandalina" and "Starfighter" were the most resistant ones. Expression analysis of 10 defense-related genes (PRB1, HPL1, LTC1, SOD, ERF1, PAL1, LOX, MPK, BG, and GST) was carried out on artificially inoculated lettuce plants of the four above cultivars at different time points after inoculation. In resistant cultivars, a higher induction rate was observed for all the tested genes in comparison with the susceptible ones. Moreover, in resistant cultivars, all genes except LTC1, MPK, and GST showed their highest induction levels in their earliest stages of infection. The results of this study are expected to contribute to the implementation of an integrated management program to control Fusarium wilt of lettuce, based mainly on the use of resistant cultivars.

Inhibition of ROS-Scavenging Enzyme System Is a Key Event in Tomato Genetic Resistance against Root-Knot Nematodes

Genetic resistance in plants against incompatible pests is expressed by the activation of an immune system; however, the molecular mechanisms of pest recognition and expression of immunity, although long the object of investigation, are far from being fully understood. The immune response triggered by the infection of soil-borne parasites, such as root-knot nematodes (RKNs), to incompatible resistant tomato plants was studied and compared to the compatible response that occurred when RKNs attacked susceptible plants. In compatible interactions, the invading nematode juveniles were allowed to fully develop and reproduce, whilst that was impeded in incompatible interactions. In crude root extracts, a first assay of reactive oxygen species (ROS)-scavenging enzymatic activity was carried out at the earliest stages of tomato-RKN incompatible interaction. Membrane-bound and soluble CAT, which is the most active enzyme in hydrogen peroxide (H₂O₂) scavenging, was found to be specifically inhibited in roots of inoculated resistant plants until 5 days after inoculation, with respect to uninoculated plants. The expression of genes encoding for antioxidant enzymes, such as CAT and glutathione peroxidase (GPX), was not always inhibited in roots of nematode-infected resistant tomato. Therefore, the biochemical mechanisms of CAT inhibition were further investigated. Two CAT isozymes were characterized by size exclusion HPLC as a tetrameric form with a molecular weight of 220,000 dalton and its subunits (55,000 dalton). Fractions containing such isozymes were tested by their sensitivity to both salicylic acid (SA) and H₂O₂. It was evidenced that elevated concentrations of both chemicals led to a partial inactivation of CAT. Elevated concentrations of H₂O₂ in incompatible interactions have been suggested to be produced by membrane-bound superoxide anion generating, SOD, and isoperoxidase-enhanced activities. Such partial inactivation of CAT has been depicted as one of the earliest key metabolic events, which is specifically associated with tomato immunity to RKNs. Enhanced ROS production and the inhibition of ROS-scavenging systems have been considered to trigger all the metabolic events leading to cell death and tissue necrosis developed around the head of the invading juveniles by which this special type of plant resistance is exerted.

Sulfur dioxide improves the thermotolerance of maize seedlings by regulating salicylic acid biosynthesis

Heat stress (HS) has become a serious threat to crop growth and yield. Sulfur dioxide (SO₂) is being verified as a signal molecule in regulating the plant stress response. However, it is unknown whether SO₂ plays a significant role in the plant heat stress response (HSR). Herein, maize seedlings were pretreated with various concentrations of SO₂ and then kept at 45 °C for heat stress treatment, aiming to study the effect of SO₂ pretreatment on HSR in maize by phenotypic, physiological, and biochemical analyses. It was found that SO₂ pretreatment greatly improved the thermotolerance of maize seedlings. The SO₂-pretreated seedlings showed 30-40% lower ROS accumulation and membrane peroxidation, but 55-110% higher activities of antioxidant enzymes than the distilled water-pretreated seedlings under heat stress. Interestingly, endogenous salicylic acid (SA) levels were increased by ∼85% in SO₂-pretreated seedlings, as revealed by phytohormone analyses. Furthermore, the SA biosynthesis inhibitor paclobutrazol markedly reduced SA levels and attenuated SO₂-triggered thermotolerance of maize seedlings. Meanwhile, transcripts of several SA biosynthesis and signaling, and heat stress-responsive genes in SO₂-pretreated seedlings were significantly elevated under HS. These data have demonstrated that SO₂ pretreatment increased endogenous SA levels, which activated the antioxidant machinery and strengthened the stress defense system, thereby improving the thermotolerance of maize seedlings under HS. Our current study provides a new strategy for mitigating heat stress damage for safe crop production.

Lactoferrin and its role in biotechnological strategies for plant defense against pathogens

Agricultural crops are susceptible to many diseases caused by various pathogens, such as viruses, bacteria and fungi. This paper reviews the general principles of plant protection against pathogens, as well as the role of iron and antimicrobial peptide metabolism in plant immunity. The article highlights the principles of antibacterial, fungicidal and antiviral action of lactoferrin, a mammalian secretory glycoprotein, and lactoferrin peptides, and their role in protecting plants from phytopathogens. This review offers a comprehensive analysis and shows potential prospects of using the lactoferrin gene to enhance plant resistance to various phytopathogens, as well as the advantages of this biotechnological approach over existing methods of protecting plants against various diseases.

Host Resistance to Parasitic Plants-Current Knowledge and Future Perspectives

Parasitic flowering plants represent a diverse group of angiosperms, ranging from exotic species with limited distribution to prominent weeds, causing significant yield losses in agricultural crops. The major damage caused by them is related to the extraction of water and nutrients from the host, thus decreasing vegetative growth, flowering, and seed production. Members of the root parasites of the Orobanchaceae family and stem parasites of the genus Cuscuta are among the most aggressive and damaging weeds, affecting both monocotyledonous and dicotyledonous crops worldwide. Their control and eradication are hampered by the extreme seed longevity and persistence in soil, as well as their taxonomic position, which makes it difficult to apply selective herbicides not damaging to the hosts. The selection of resistant cultivars is among the most promising approaches to deal with this matter, although still not widely employed due to limited knowledge of the molecular mechanisms of host resistance and inheritance. The current review aims to summarize the available information on host resistance with a focus on agriculturally important parasitic plants and to outline the future perspectives of resistant crop cultivar selection to battle the global threat of parasitic plants.

An activated form of NB-ARC protein RLS1 functions with cysteine-rich receptor-like protein RMC to trigger cell death in rice

A key event that follows pathogen recognition by a resistance (R) protein containing an NB-ARC (nucleotide-binding adaptor shared by Apaf-1, R proteins, and Ced-4) domain is hypersensitive response (HR)-type cell death accompanied by accumulation of reactive oxygen species and nitric oxide. However, the integral mechanisms that underlie this process remain relatively opaque. Here, we show that a gain-of-function mutation in the NB-ARC protein RLS1 (Rapid Leaf Senescence 1) triggers high-light-dependent HR-like cell death in rice. The RLS1-mediated defense response is largely independent of salicylic acid accumulation, NPR1 (Nonexpressor of Pathogenesis-Related Gene 1) activity, and RAR1 (Required for Mla12 Resistance 1) function. A screen for suppressors of RLS1 activation identified RMC (Root Meander Curling) as essential for the RLS1-activated defense response. RMC encodes a cysteine-rich receptor-like secreted protein (CRRSP) and functions as an RLS1-binding partner. Intriguingly, their co-expression resulted in a change in the pattern of subcellular localization and was sufficient to trigger cell death accompanied by a decrease in the activity of the antioxidant enzyme APX1. Collectively, our findings reveal an NB-ARC-CRRSP signaling module that modulates oxidative state, the cell death process, and associated immunity responses in rice.

Novel 1-Indanone derivatives containing oxime and oxime ether moieties as immune activator to resist plant virus

BACKGROUND

Vegetable viruses are difficult to prevent and control in the field, causing massive economic losses of agricultural production in the world. A new natural product-based antiviral agent would be an effective means to control viral diseases. As a class of natural products, 1-indanones present various pharmacologically actives, while their application in agriculture remains to be found.

RESULTS

A series of novel 1-indanone derivatives were designed and synthesized and the antiviral activities were systematically evaluated. Bioassays showed that most compounds exhibited good protective activities against cucumber mosaic virus (CMV), tomato spotted wilt virus (TSWV), and pepper mild mottle virus (PMMoV). Notably, compound 27 exhibited the best protective effects against PMMoV with EC₅₀ values of 140.5 mg L^-1 , superior to ninanmycin (245.6 mg L^-1 ). Compound 27 induced immunity responses through multilayered regulation on mitogen-activated protein kinase, plant hormone signal transduction and phenylpropanoid biosynthesis pathways.

CONCLUSION

These 1-indanone derivatives especially compound 27 can be considered as potential immune activators to resist plant virus. © 2023 Society of Chemical Industry.

Transcriptome Dynamics in Triticum aestivum Genotypes Associated with Resistance against the Wheat Dwarf Virus

Wheat dwarf virus (WDV) is one of the most important pathogens of cereal crops worldwide. To understand the molecular mechanism of resistance, here we investigated the comparative transcriptome of wheat genotypes with different levels of resistance (Svitava and Fengyou 3) and susceptibility (Akteur) to WDV. We found a significantly higher number of differentially expressed transcripts (DETs) in the susceptible genotype than in the resistant one (e.g., Svitava). The number of downregulated transcripts was also higher in the susceptible genotype than in the resistant one (Svitava) and the opposite was true for the upregulated transcripts. Further functional analysis of gene ontology (GO) enrichment identified a total of 114 GO terms for the DETs. Of these, 64 biological processes, 28 cellular components and 22 molecular function GO terms were significantly enriched. A few of these genes appear to have a specific expression pattern related to resistance or susceptibility to WDV infection. Validation of the expression pattern by RT-qPCR showed that glycosyltransferase was significantly downregulated in the susceptible genotype compared to the resistant genotypes after WDV infection, while CYCLIN-T1-3, a regulator of CDK kinases (cyclin-dependent kinase), was upregulated. On the other hand, the expression pattern of the transcription factor (TF) MYB (TraesCS4B02G174600.2; myeloblastosis domain of transcription factor) was downregulated by WDV infection in the resistant genotypes compared to the susceptible genotype, while a large number of TFs belonging to 54 TF families were differentially expressed due to WDV infection. In addition, two transcripts (TraesCS7A02G341400.1 and TraesCS3B02G239900.1) were upregulated with uncharacterised proteins involved in transport and regulation of cell growth, respectively. Altogether, our findings showed a clear gene expression profile associated with resistance or susceptibility of wheat to WDV. In future studies, we will explore the regulatory network within the same experiment context. This knowledge will broaden not only the future for the development of virus-resistant wheat genotypes but also the future of genetic improvement of cereals for resilience and WDV-resistance breeding.

Evaluating Nicotinamide Adenine Dinucleotide for Its Effects on Halo Blight of Snap Bean

Halo blight, caused by Pseudomonas syringae pv. phaseolicola, is one of the major bacterial diseases on snap bean in Florida, and the outbreaks of this disease have occurred more often in recent years. Current management of this disease primarily depends on application of fixed copper-based bactericides but climate change and resistance development in the pathogen populations still cause hardship for management of this disease, especially in south Florida. In this study, nicotinamide adenine dinucleotide (NAD⁺) was evaluated in the greenhouse for its potential to reduce halo blight on snap bean. When NAD⁺ at 5 mM was applied by soil drench, foliar spray, or leaf infiltration, NAD⁺ significantly (P < 0.05) reduced disease severity of halo blight on snap bean compared with the untreated control. When NAD⁺ was applied by leaf infiltration, among the tested concentrations, NAD⁺ at 0.5 to 1.0 mM was most effective in decreasing halo blight disease. NAD⁺ at 2.5 mM applied as a foliar spray in rotation with Kocide 3000 (copper hydroxide) at 0.5 mg/ml further reduced disease severity compared with Kocide 3000 alone. In the in vitro study, no inhibitory effects of NAD⁺ were detected on the bacterial pathogen P. syringae pv. phaseolicola. Results of real-time PCR showed that the defense-related genes PR1, AZI1, EDS1, SARD1, PDF1.2, and PAL1 were upregulated in the NAD⁺ treatment. Taken together, these data indicated that NAD⁺ significantly suppressed halo blight on snap bean, and application of NAD⁺ has the potential in management of this important disease.

The emerging role for metabolism in fueling neutrophilic inflammation

Neutrophils are a critical element of host defense and are rapidly recruited to inflammatory sites. Such sites are frequently limited in oxygen and/or nutrient availability, presenting a metabolic challenge for infiltrating cells. Long believed to be uniquely dependent on glycolysis, it is now clear that neutrophils possess far greater metabolic plasticity than previously thought, with the capacity to generate energy stores and utilize extracellular proteins to fuel central carbon metabolism and biosynthetic activity. Out-with cellular energetics, metabolic programs have also been implicated in the production of neutrophils and their progenitors in the bone marrow compartment, activation of neutrophil antimicrobial responses, inflammatory and cell survival signaling cascades, and training of the innate immune response. Thus, understanding the mechanisms by which metabolic processes sustain changes in neutrophil effector functions and how these are subverted in disease states provides exciting new avenues for the treatment of dysfunctional neutrophilic inflammation which are lacking in clinical practice to date.

New trends in methyl salicylate sensing and their implications in agriculture

Methyl salicylate (MeSal) is an organic compound present in plants during stress events and is therefore a key marker for early plant disease detection. It has usually been detected by conventional methods that require bulky and costly equipment, such as gas chromatography or mass spectrometry. Currently, however, chemical sensors provide an alternative for MeSal monitoring, showing good performance for its determination in the vapour or liquid phase. The most promising concepts used in MeSal determination include sensors based on electrochemical and conductometric principles, although other technologies based on mass-sensitive, microwave, or spectrophotometric principles also show promise. The receptor elements or sensitive materials are shown to be part of the key elements in these sensing technologies. A literature survey identified a significant contribution of bioreceptors, including enzymes, odourant-binding proteins or peptides, as well as receptors based on polymers or inorganic materials in MeSal determination. This work reviews these concepts and materials and discusses their future prospects and limitations for application in plant health monitoring.

A Proteomics Insight into Advancements in the Rice-Microbe Interaction

Rice is one of the most-consumed foods worldwide. However, the productivity and quality of rice grains are severely constrained by pathogenic microbes. Over the last few decades, proteomics tools have been applied to investigate the protein level changes during rice-microbe interactions, leading to the identification of several proteins involved in disease resistance. Plants have developed a multi-layered immune system to suppress the invasion and infection of pathogens. Therefore, targeting the proteins and pathways associated with the host's innate immune response is an efficient strategy for developing stress-resistant crops. In this review, we discuss the progress made thus far with respect to rice-microbe interactions from side views of the proteome. Genetic evidence associated with pathogen-resistance-related proteins is also presented, and challenges and future perspectives are highlighted in order to understand the complexity of rice-microbe interactions and to develop disease-resistant crops in the future.

Efficiency of breeding olives for resistance to Verticillium wilt

Olive trees are the most cultivated evergreen trees in the Mediterranean Basin, where they have deep historical and socioeconomic roots. The fungus Verticillium dahliae develops inside the vascular bundles of the host, and there are no effective applicable treatments, making it difficult to control the disease. In this sense, the use of integrated disease management, specifically the use of resistant cultivars, is the most effective means to alleviate the serious damage that these diseases are causing and reduce the expansion of this pathogen. In 2008, the University of Cordoba started a project under the UCO Olive Breeding Program whose main objective has been to develop new olive cultivars with high resistance to Verticillium wilt. Since 2008, more than 18,000 genotypes from 154 progenies have been evaluated. Only 19.9% have shown some resistance to the disease in controlled conditions and only 28 have been preselected due to their resistance in field condition and remarkable agronomic characteristics. The results of this study represent an important advancement in the generation of resistant olive genotypes that will become commercial cultivars currently demanded by the olive growing sector. Our breeding program has proven successful, allowing the selection of several new genotypes with high resistance to the disease and agronomical performance. It also highlights the need for long-term field evaluations for the evaluation of resistance and characterization of olive genotypes.

Insights into the Bioinformatics and Transcriptional Analysis of the Elongator Complexes (ELPs) Gene Family of Wheat: TaELPs Contribute to Wheat Abiotic Stress Tolerance and Leaf Senescence

Elongator complexes (ELPs) are the protein complexes that promote transcription through histone acetylation in eukaryotic cells and interact with elongating RNA polymerase II (RNAPII). ELPs' role in plant growth and development, signal transduction, and response to biotic and abiotic stresses have been confirmed in model plants. However, the functions of the wheat ELP genes are not well documented. The present study identified 18 members of the ELPs from the wheat genome with a homology search. Further, bioinformatics and transcription patterns in response to different stress conditions were analyzed to dissect their potential regulatory mechanisms in wheat. Gene duplication analysis showed that 18 pairs of ELP paralogous genes were derived from segmental duplication, which was divided into six clades by protein phylogenetic and cluster analysis. The orthologous analysis of wheat TaELP genes showed that TaELP genes may have evolved from orthologous genes of other plant species or closely related plants. Moreover, a variety of cis-acting regulatory elements (CAREs) related to growth and development, hormone response, and biotic and abiotic stresses were identified in the TaELPs' promoter regions. The qRT-PCR analysis showed that the transcription of TaELPs was induced under hormone, salt, and drought stress and during leaf senescence. The TaELP2 gene was silenced with BSMV-VIGS, and TaELP2 was preliminarily verified to be involved in the regulation of wheat leaf senescence. Overall, TaELP genes might be regulated by hormone signaling pathways and response to abiotic stress and leaf senescence, which could be investigated further as potential candidate genes for wheat abiotic stress tolerance and yield improvement.

Trained Immunity, BCG and SARS-CoV-2 General Outline and Possible Management in COVID-19

The Bacillus Calmette-Guérin (BCG) vaccine has been in use for over 100 years. It protects against severe, blood-borne forms of tuberculosis. Observations indicate that it also increases immunity against other diseases. The mechanism responsible for this is trained immunity, an increased response of non-specific immune cells in repeated contact with a pathogen, not necessarily of the same species. In the following review, we present the current state of knowledge on the molecular mechanisms responsible for this process. We also seek to identify the challenges facing science in this area and consider the application of this phenomenon in managing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic.

Geminiviral C4/AC4 proteins: An emerging component of the viral arsenal against plant defence

Virus infection triggers a plethora of defence reactions in plants to incapacitate the intruder. Viruses, in turn, have added additional functions to their genes so that they acquire capabilities to neutralize the above defence reactions. In plant-infecting viruses, the family Geminiviridae comprises members, majority of whom encode 6-8 genes in their small single-stranded DNA genomes. Of the above genes, one which shows the most variability in its amino acid sequence is the C4/AC4. Recent studies have uncovered evidence, which point towards a wide repertoire of functions performed by C4/AC4 revealing its role as a major player in suppressing plant defence. This review summarizes the various plant defence mechanisms against viruses and highlights how C4/AC4 has evolved to counter most of them.

In vivo surface-enhanced Raman scattering nanosensor for the real-time monitoring of multiple stress signalling molecules in plants

When under stress, plants release molecules to activate their defense system. Detecting these stress-related molecules offers the possibility to address stress conditions and prevent the development of diseases. However, detecting endogenous signalling molecules in living plants remains challenging due to low concentrations of these analytes and interference with other compounds; additionally, many methods currently used are invasive and labour-intensive. Here we show a non-destructive surface-enhanced Raman scattering (SERS)-based nanoprobe for the real-time detection of multiple stress-related endogenous molecules in living plants. The nanoprobe, which is placed in the intercellular space, is optically active in the near-infrared region (785 nm) to avoid interferences from plant autofluorescence. It consists of a Si nanosphere surrounded by a corrugated Ag shell modified by a water-soluble cationic polymer poly(diallyldimethylammonium chloride), which can interact with multiple plant signalling molecules. We measure a SERS enhancement factor of 2.9 × 10⁷ and a signal-to-noise ratio of up to 64 with an acquisition time of ~100 ms. To show quantitative multiplex detection, we adopted a binding model to interpret the SERS intensities of two different analytes bound to the SERS hot spot of the nanoprobe. Under either abiotic or biotic stress, our optical nanosensors can successfully monitor salicylic acid, extracellular adenosine triphosphate, cruciferous phytoalexin and glutathione in Nasturtium officinale, Triticum aestivum L. and Hordeum vulgare L.-all stress-related molecules indicating the possible onset of a plant disease. We believe that plasmonic nanosensor platforms can enable the early diagnosis of stress, contributing to a timely disease management of plants.

Plant Synthetic Promoters: Advancement and Prospective

Native/endogenous promoters have several fundamental limitations in terms of their size, Cis-elements distribution/patterning, and mode of induction, which is ultimately reflected in their insufficient transcriptional activity. Several customized synthetic promoters were designed and tested in plants during the past decade to circumvent such constraints. Such synthetic promoters have a built-in capacity to drive the expression of the foreign genes at their maximum amplitude in plant orthologous systems. The basic structure and function of the promoter has been discussed in this review, with emphasis on the role of the Cis-element in regulating gene expression. In addition to this, the necessity of synthetic promoters in the arena of plant biology has been highlighted. This review also provides explicit information on the two major approaches for developing plant-based synthetic promoters: the conventional approach (by utilizing the basic knowledge of promoter structure and Cis-trans interaction) and the advancement in gene editing technology. The success of plant genetic manipulation relies on the promoter efficiency and the expression level of the transgene. Therefore, advancements in the field of synthetic promoters has enormous potential in genetic engineering-mediated crop improvement.

The Key Roles of ROS and RNS as a Signaling Molecule in Plant-Microbe Interactions

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play a pivotal role in the dynamic cell signaling systems in plants, even under biotic and abiotic stress conditions. Over the past two decades, various studies have endorsed the notion that these molecules can act as intracellular and intercellular signaling molecules at a very low concentration to control plant growth and development, symbiotic association, and defense mechanisms in response to biotic and abiotic stress conditions. However, the upsurge of ROS and RNS under stressful conditions can lead to cell damage, retarded growth, and delayed development of plants. As signaling molecules, ROS and RNS have gained great attention from plant scientists and have been studied under different developmental stages of plants. However, the role of RNS and RNS signaling in plant-microbe interactions is still unknown. Different organelles of plant cells contain the enzymes necessary for the formation of ROS and RNS as well as their scavengers, and the spatial and temporal positions of these enzymes determine the signaling pathways. In the present review, we aimed to report the production of ROS and RNS, their role as signaling molecules during plant-microbe interactions, and the antioxidant system as a balancing system in the synthesis and elimination of these species.

GmWAK1, Novel Wall-Associated Protein Kinase, Positively Regulates Response of Soybean to Phytophthora sojae Infection

Phytophthora root rot is a destructive soybean disease worldwide, which is caused by the oomycete pathogen Phytophthora sojae (P. sojae). Wall-associated protein kinase (WAK) genes, a family of the receptor-like protein kinase (RLK) genes, play important roles in the plant signaling pathways that regulate stress responses and pathogen resistance. In our study, we found a putative Glycine max wall-associated protein kinase, GmWAK1, which we identified by soybean GmLHP1 RNA-sequencing. The expression of GmWAK1 was significantly increased by P. sojae and salicylic acid (SA). Overexpression of GmWAK1 in soybean significantly improved resistance to P. sojae, and the levels of phenylalanine ammonia-lyase (PAL), SA, and SA-biosynthesis-related genes were markedly higher than in the wild-type (WT) soybean. The activities of enzymatic superoxide dismutase (SOD) and peroxidase (POD) antioxidants in GmWAK1-overexpressing (OE) plants were significantly higher than those in in WT plants treated with P. sojae; reactive oxygen species (ROS) and hydrogen peroxide (H₂O₂) accumulation was considerably lower in GmWAK1-OE after P. sojae infection. GmWAK1 interacted with annexin-like protein RJ, GmANNRJ4, which improved resistance to P. sojae and increased intracellular free-calcium accumulation. In GmANNRJ4-OE transgenic soybean, the calmodulin-dependent kinase gene GmMPK6 and several pathogenesis-related (PR) genes were constitutively activated. Collectively, these results indicated that GmWAK1 interacts with GmANNRJ4, and GmWAK1 plays a positive role in soybean resistance to P. sojae via a process that might be dependent on SA and involved in alleviating damage caused by oxidative stress.

Epigenetic malleability at core promoter initiates tobacco PR-1a expression post salicylic acid treatment

BACKGROUND

Tobacco's PR-1a gene is induced by pathogen attack or exogenous application of salicylic acid (SA). Nucleosome mapping and chromatin immunoprecipitation assay were used to delineate the histone modifications on the PR-1a promoter. However, the epigenetic modifications of the inducible promoter of the PR-1a gene are not fully understood yet.

METHODS AND RESULTS

Southern approach was used to scan the promoter of PR-1a to identify presence of nucleosomes, ChIP assays were performed using anti-histones antibodies of repressive chromatin by di- methylated at H3K9 and H4K20 or active chromatin by acetylated H3K9/14 and H4K16 to find epigenetic malleability of nucleosome over core promoter in uninduced or induced state post SA treatment. Class I and II mammalian histone deacetylase (HDAC) inhibitor TSA treatment was used to enhance the expression of PR-1a by facilitating the histone acetylation post SA treatment. Here, we report correlated consequences of the epigenetic modifications correspond to disassembly of the nucleosome (spans from - 102 to + 55 bp, masks TATA and transcription initiation) and repressor complex from core promoter, eventually initiates the transcription of PR-1a gene post SA treatment. While active chromatin marks di and trimethylation of H3K4, acetylation of H3K9 and H4K16 are increased which are associated to the transcription initiation of PR-1a following SA treatment. However, in uninduced state constitutive expression of a negative regulator (SNI1) of AtPR1, suppresses AtPR1 expression by six-fold in Arabidopsis thaliana. Further, we report 50-to-1000-fold increased expression of AtPR1 in uninduced lsd1 mutant plants, up to threefold increased expression of AtPR1 in uninduced histone acetyl transferases (HATs) mutant plants, SNI1 dependent negative regulation of AtPR1, all together our results suggest that inactive state of PR-1a is indeed maintained by a repressive complex.

CONCLUSION

The study aimed to reveal the mechanism of transcription initiation of tobacco PR-1a gene in presence or absence of SA. This is the first study that reports nucleosome and repressor complex over core promoter region maintains the inactivation of gene in uninduced state, and upon induction disassembling of both initiates the downstream gene activation process.

Engineering plant immune circuit: walking to the bright future with a novel toolbox

Plant pathogens destroy crops and cause severe yield losses, leading to an insufficient food supply to sustain the human population. Apart from relying on natural plant immune systems to combat biological agents or waiting for the appropriate evolutionary steps to occur over time, researchers are currently seeking new breakthrough methods to boost disease resistance in plants through genetic engineering. Here, we summarize the past two decades of research in disease resistance engineering against an assortment of pathogens through modifying the plant immune components (internal and external) with several biotechnological techniques. We also discuss potential strategies and provide perspectives on engineering plant immune systems for enhanced pathogen resistance and plant fitness.

Innate Immune Memory in Macrophages

Macrophages have been recognized as the primary mediators of innate immunity starting from embryonic/fetal development. Macrophage-mediated defenses may not be as antigen-specific as adaptive immunity, but increasing information suggests that these responses do strengthen with repeated immunological triggers. The concept of innate memory in macrophages has been described as "trained immunity" or "innate immune memory (IIM)." As currently understood, this cellular memory is rooted in epigenetic and metabolic reprogramming. The recognition of IIM may be particularly important in the fetus and the young neonate who are yet to develop protective levels of adaptive immunity, and could even be of preventive/therapeutic importance in many disorders. There may also be a possibility of therapeutic enhancement with targeted vaccination. This article presents a review of the properties, mechanisms, and possible clinical significance of macrophage-mediated IIM.

Biotechnological approaches for reducing fruit losses caused by pathogenic infection

Fruit loss due to disease occurs in both the field and postharvest. Knowledge of host immune responses and pathogen virulence is enabling the formulation of increasingly sophisticated strategies for disease control. Traditional genetic modification, typically involving overexpression of genes involved in pathogen perception and defence responses, is beginning to be superseded by CRISPR-Cas9 manipulation of host susceptibility targets. Moreover, the refinement of RNA interference (RNAi) strategies, including spray-induced gene silencing (SIGS), is allowing more nuanced control options. These latter approaches have the advantage over earlier technologies in that either they do not result in the generation of genetically modified organisms (RNAi-based SIGS), or the genetic manipulation used leaves no trace of introduced genetic material (gene editing). Thus, these strategies may be more widely acceptable for deployment for future disease control.

Genetic requirements for infection-specific responses in conferring disease resistance in Arabidopsis

Immunity in plants arises from defense regulatory circuits that can be conceptualized as modules. Both the types (and isolates) of pathogen and the repertoire of plant receptors may cause different modules to be activated and affect the magnitude of activation. Two major defense enzymes of Arabidopsis are ALD1 and ICS1/SID2. ALD1 is an aminotransferase needed for producing the metabolites pipecolic acid, hydroxy-pipecolic acid, and possibly other defense signals. ICS1/SID2 produces isochorismate, an intermediate in the synthesis of salicylic acid (SA) and SA-derivatives. Metabolites resulting from the activation of these enzymes are found in petiole exudates and may serve as priming signals for systemic disease resistance in Arabidopsis. Mutants lacking ALD1 are known to have reduced SA accumulation. To further investigate the role of ALD1 in relation to the SA-related module, immunity phenotypes of double mutants that disrupt ALD1 and ICS1/SID2 or SA perception by NPR1 were compared with each single mutant after infection by different Pseudomonas strains. Exudates collected from these mutants after infection were also evaluated for their ability to confer disease resistance when applied to wild-type plants. During infection with virulent or attenuated strains, the loss of ALD1 does not increase the susceptibility of npr1 or sid2 mutants, suggesting the main role of ALD1 in this context is in amplifying the SA-related module. In contrast, after an infection that leads to strong pathogen recognition via the cytoplasmic immune receptor RPS2, ALD1 acts additively with both NPR1 and ICS1/SID2 to suppress pathogen growth. The additive effects are observed in early basal defense responses as well as SA-related events. Thus, there are specific conditions that dictate whether the modules independently contribute to immunity to provide additive protection during infection. In the exudate experiments, intact NPR1 and ICS1/SID2, but not ALD1 in the donor plants were needed for conferring immunity. Mixing exudates showed that loss of SID2 yields exudates that suppress active exudates from wild-type or ald1 plants. This indicates that ICS1/SID2 may not only lead to positive defense signals, but also prevent a suppressive signal(s).

Phosphorylation of a wheat aquaporin at two sites enhances both plant growth and defense

Eukaryotic aquaporins share the characteristic of functional multiplicity in transporting distinct substrates and regulating various processes, but the underlying molecular basis for this is largely unknown. Here, we report that the wheat (Triticum aestivum) aquaporin TaPIP2;10 undergoes phosphorylation to promote photosynthesis and productivity and to confer innate immunity against pathogens and a generalist aphid pest. In response to elevated atmospheric CO₂ concentrations, TaPIP2;10 is phosphorylated at the serine residue S280 and thereafter transports CO₂ into wheat cells, resulting in enhanced photosynthesis and increased grain yield. In response to apoplastic H₂O₂ induced by pathogen or insect attacks, TaPIP2;10 is phosphorylated at S121 and this phosphorylated form transports H₂O₂ into the cytoplasm, where H₂O₂ intensifies host defenses, restricting further attacks. Wheat resistance and grain yield could be simultaneously increased by TaPIP2;10 overexpression or by expressing a TaPIP2;10 phosphomimic with aspartic acid substitutions at S121 and S280, thereby improving both crop productivity and immunity.

Walking through crossroads-rice responses to heat and biotic stress interactions

Rice, the most important source of calories for humans is prone to severe yield loss due to changing climate including heat stress. Additionally, rice encounters biotic stresses in conjunction with heat stress, which exacerbates the adverse effects, and exponentially increase such losses. Several investigations have identified biotic and heat stress-related quantitative trait loci (QTLs) that may contribute to improved tolerance to these stresses. However, a significant knowledge gap exists in identifying the genomic regions imparting tolerance against combined biotic and heat stress. Hereby, we are presenting a conceptual meta-analysis identifying genomic regions that may be promising candidates for enhancing combined biotic and heat stress tolerance in rice. Fourteen common genomic regions were identified along chromosomes 1, 2, 3, 4, 6, 10 and 12, which harbored 1265 genes related to heat stress and defense responses in rice. Further, the meta expression analysis revealed 24 differentially expressed genes (DEGs) involved in calcium-mediated stress signaling including transcription factors Myb, bHLH, ROS signaling, molecular chaperones HSP110 and pathogenesis related proteins. Additionally, we also proposed a hypothetical model based on GO and MapMan analysis representing the pathways intersecting heat and biotic stresses. These DEGs can be potential candidate genes for improving tolerance to combined biotic and heat stress in rice. We present a framework highlighting plausible connecting links (QTLs/genes) between rice response to heat stress and different biotic factors associated with yield, that can be extended to other crops.

β-Glucan and its nanocomposites in sustainable agriculture and environment: an overview of mechanisms and applications

β-Glucan is an eco-friendly, biodegradable, and economical biopolymer with important roles for acquiring adaptations to mitigate climate change in crop plants. β-Glucan plays a crucial role in the activation of functional plant innate immune system by triggering the downward signaling cascade/s, resulting in the accumulation of different pathogenesis-related proteins (PR-proteins), reactive oxygen species (ROS), antioxidant defense enzymes, Ca2+-influx as well as activation of mitogen-activated protein kinase (MAPK) pathway. Recent experimental studies have shown that β-glucan recognition is mediated by co-receptor LysMPRR (lysin motif pattern recognition receptor)-CERK1 (chitin elicitor receptor kinase 1), LYK4, and LYK5 (LysM-containing receptor-like kinase), as well as different receptor systems in plants that could be plant species-specific and/or age and/or tissue-dependent. Transgenic overexpression of β-glucanase, chitinase, and/or in combination with other PR-proteins like cationic peroxidase, AP24,thaumatin-likeprotein 1 (TLP-1) has also been achieved for improving plant disease resistance in crop plants, but the transgenic methods have some ethical and environmental concerns. In this regard, elicitation of plant immunity using biopolymer like β-glucan and chitosan offers an economical, safe, and publicly acceptable method. The β-glucan and chitosan nanocomposites have proven to be useful for the activation of plant defense pathways and to enhance plant response/systemic acquired resistance (SAR) against broad types of plant pathogens and mitigating multiple stresses under the changing climate conditions.

A "Candidatus Liberibacter asiaticus"-secreted polypeptide suppresses plant immune responses in Nicotiana benthamiana and Citrus sinensis

Citrus Huanglongbing (HLB), known as the most economically devastating disease in citrus industry, is mainly caused by phloem-restricted Gram-negative bacterium "Candidatus Liberibacter asiaticus" (CLas). To date, CLas is still unculturable in vitro, which has been dramatically delaying the research on its pathogenesis, and only few Sec-dependent effectors (SDEs) have been identified to elucidate the pathogenesis of CLas. Here, we confirmed that a CLas-secreted Sec-dependent polypeptide, namely SECP8 (CLIBASIA_05330), localized in nucleus, cytoplasm and cytoplasmic membrane, and showed remarkably higher transcript abundance in citrus than in psyllids. Potato virus X (PVX)-mediated transient expression assays indicated that mSECP8 (the mature form of SECP8) suppressed pro-apoptotic mouse protein BAX and Phytophthora infestans elicitin INF1-triggered hypersensitive response (HR) associated phenotypes, including cell death, H2O2 accumulation and callose deposition. Intriguingly, mSECP8 also inhibited SDE1 (CLIBASIA_05315)-induced water-soaked and dwarfing symptoms in Nicotiana benthamiana. In addition, mSECP8 can promote the susceptibility of transgenic Wanjincheng orange (Citrus sinensis) to CLas invasion and further HLB symptom development, and it contributes to the proliferation of Xanthomonas citri subsp. citri (Xcc). Moreover, the expression of ten immunity-related genes were significantly down-regulated in mSECP8 transgenic citrus than those in wide-type (WT) plants. Overall, we propose that mSECP8 may serve as a novel broad-spectrum suppressor of plant immunity, and provide the first evidence counteractive effect among CLas effectors. This study will enrich and provide new evidences for elucidating the pathogenic mechanisms of CLas in citrus host.

Transcriptome analysis reveals pathogenesis-related gene 1 pathway against salicylic acid treatment in grapevine (Vitis vinifera L)

Salicylic acid (SA) is a well-studied phenolic plant hormone that plays an important role in plant defense against the hemi-biothrophic and biothrophic pathogens and depends on the living cells of host for the successful infection. In this study, a pathogenesis test was performed between Vitis davidii and V. vinifera cultivars against grape white rot disease (Coniella diplodiella). V. davidii was found to be resistant against this disease. SA contents were found to be higher in the resistant grape cultivar after different time points. RNA-seq analysis was conducted on susceptible grapevine cultivars after 12, 24, and 48 h of SA application with the hypothesis that SA may induce defense genes in susceptible cultivars. A total of 511 differentially expressed genes (DEGs) were identified from the RNA-seq data, including some important genes, VvWRKY1/2, VvNPR1, VvTGA2, and VvPR1, for the SA defense pathway. DEGs related to phytohormone signal transduction and flavonoid biosynthetic pathways were also upregulated. The quantitative real-time PCR (qRT-PCR) results of the significantly expressed transcripts were found to be consistent with the transcriptome data, with a high correlation between the two analyses. The pathogenesis-related gene 1 (VvPR1), which is an important marker gene for plant defense, was selected for further promoter analysis. The promoter sequence showed that it contains some important cis-elements (W-box, LS7, as-1, and TCA-element) to recruit the transcription factors VvWRKY, VvNPR1, and VvTGA2 to express the VvPR1 gene in response to SA treatment. Furthermore, the VvPR1 promoter was serially deleted into different fragments (-1,837, -1,443, -1,119, -864, -558, -436, and -192 ) bp and constructed vectors with the GUS reporter gene. Deletion analysis revealed that the VvPR1 promoter between -1837 bp to -558 bp induced significant GUS expression with respect to the control. On the basis of these results, the -558 bp region was assumed to be an important part of the VvPR1 promoter, and this region contained the important cis-elements related to SA, such as TCA-element (-1,472 bp), LS7 (-1,428 bp), and as-1 (-520 bp), that recruit the TFs and induce the expression of the VvPR1 gene. This study expanded the available information regarding SA-induced defense in susceptible grapes and recognized the molecular mechanisms through which this defense might be mediated.

Physiological and metabolic analyses provide insight into soybean seed resistance to fusarium fujikuroi causing seed decay

Seed-borne pathogens cause diverse diseases at the growth, pre- and post-harvest stage of soybean resulting in a large reduction in yield and quality. The physiological and metabolic aspects of seeds are closely related to their defense against pathogens. Recently, Fusarium fujikuroi has been identified as the dominant seed-borne fungi of soybean seed decay, but little information on the responses of soybean seeds induced by F. fujikuroi is available. In this study, a time-course symptom development of seed decay was observed after F. fujikuroi inoculation through spore suspension soaking. The germination rate and the contents of soluble sugar and soluble protein were significantly altered over time. Both chitinase and β-1,3-glucanase as important fungal cell wall-degrading enzymes of soybean seeds were also rapidly and transiently activated upon the early infection of F. fujikuroi. Metabolic profile analysis showed that the metabolites in glycine, serine, and threonine metabolism and tryptophan metabolism were clearly induced by F. fujikuroi, but different metabolites were mostly enriched in isoflavone biosynthesis, flavone biosynthesis, and galactose pathways. Interestingly, glycitein and glycitin were dramatically upregulated while daidzein, genistein, genistin, and daidzin were largely downregulated. These results indicate a combination of physiological responses, cell wall-related defense, and the complicated metabolites of soybean seeds contributes to soybean seed resistance against F. fujikuroi, which are useful for soybean resistance breeding.

Integrated Omic Approaches Reveal Molecular Mechanisms of Tolerance during Soybean and Meloidogyne incognita Interactions

The root-knot nematode (RKN), Meloidogyne incognita, is a devastating soybean pathogen worldwide. The use of resistant cultivars is the most effective method to prevent economic losses caused by RKNs. To elucidate the mechanisms involved in resistance to RKN, we determined the proteome and transcriptome profiles from roots of susceptible (BRS133) and highly tolerant (PI 595099) Glycine max genotypes 4, 12, and 30 days after RKN infestation. After in silico analysis, we described major defense molecules and mechanisms considered constitutive responses to nematode infestation, such as mTOR, PI3K-Akt, relaxin, and thermogenesis. The integrated data allowed us to identify protein families and metabolic pathways exclusively regulated in tolerant soybean genotypes. Among them, we highlighted the phenylpropanoid pathway as an early, robust, and systemic defense process capable of controlling M. incognita reproduction. Associated with this metabolic pathway, 29 differentially expressed genes encoding 11 different enzymes were identified, mainly from the flavonoid and derivative pathways. Based on differential expression in transcriptomic and proteomic data, as well as in the expression profile by RT-qPCR, and previous studies, we selected and overexpressed the GmPR10 gene in transgenic tobacco to assess its protective effect against M. incognita. Transgenic plants of the T₂ generation showed up to 58% reduction in the M. incognita reproduction factor. Finally, data suggest that GmPR10 overexpression can be effective against the plant parasitic nematode M. incognita, but its mechanism of action remains unclear. These findings will help develop new engineered soybean genotypes with higher performance in response to RKN infections.

Defense Mechanisms of Cotton Fusarium and Verticillium Wilt and Comparison of Pathogenic Response in Cotton and Humans

Cotton is an important economic crop. Fusarium and Verticillium are the primary pathogenic fungi that threaten both the quality and sustainable production of cotton. As an opportunistic pathogen, Fusarium causes various human diseases, including fungal keratitis, which is the most common. Therefore, there is an urgent need to study and clarify the resistance mechanisms of cotton and humans toward Fusarium in order to mitigate, or eliminate, its harm. Herein, we first discuss the resistance and susceptibility mechanisms of cotton to Fusarium and Verticillium wilt and classify associated genes based on their functions. We then outline the characteristics and pathogenicity of Fusarium and describe the multiple roles of human neutrophils in limiting hyphal growth. Finally, we comprehensively compare the similarities and differences between animal and plant resistance to Fusarium and put forward new insights into novel strategies for cotton disease resistance breeding and treatment of Fusarium infection in humans.

Transcriptomic and Metabolomic Analysis of a Pseudomonas-Resistant versus a Susceptible Arabidopsis Accession

Accessions of one plant species may show significantly different levels of susceptibility to stresses. The Arabidopsis thaliana accessions Col-0 and C24 differ significantly in their resistance to the pathogen Pseudomonas syringae pv. tomato (Pst). To help unravel the underlying mechanisms contributing to this naturally occurring variance in resistance to Pst, we analyzed changes in transcripts and compounds from primary and secondary metabolism of Col-0 and C24 at different time points after infection with Pst. Our results show that the differences in the resistance of Col-0 and C24 mainly involve mechanisms of salicylic-acid-dependent systemic acquired resistance, while responses of jasmonic-acid-dependent mechanisms are shared between the two accessions. In addition, arginine metabolism and differential activity of the biosynthesis pathways of aliphatic glucosinolates and indole glucosinolates may also contribute to the resistance. Thus, this study highlights the difference in the defense response strategies utilized by different genotypes.

The TGA Transcription Factors from Clade II Negatively Regulate the Salicylic Acid Accumulation in Arabidopsis

Salicylic acid (SA) is a hormone that modulates plant defenses by inducing changes in gene expression. The mechanisms that control SA accumulation are essential for understanding the defensive process. TGA transcription factors from clade II in Arabidopsis, which include the proteins TGA2, TGA5, and TGA6, are known to be key positive mediators for the transcription of genes such as PR-1 that are induced by SA application. However, unexpectedly, stress conditions that induce SA accumulation, such as infection with the avirulent pathogen P. syringae DC3000/AvrRPM1 and UV-C irradiation, result in enhanced PR-1 induction in plants lacking the clade II TGAs (tga256 plants). Increased PR-1 induction was accompanied by enhanced isochorismate synthase-dependent SA production as well as the upregulation of several genes involved in the hormone’s accumulation. In response to avirulent P. syringae, PR-1 was previously shown to be controlled by both SA-dependent and -independent pathways. Therefore, the enhanced induction of PR-1 (and other defense genes) and accumulation of SA in the tga256 mutant plants is consistent with the clade II TGA factors providing negative feedback regulation of the SA-dependent and/or -independent pathways. Together, our results indicate that the TGA transcription factors from clade II negatively control SA accumulation under stress conditions that induce the hormone production. Our study describes a mechanism involving old actors playing new roles in regulating SA homeostasis under stress.