Redox regulation in plant immune function

Maize and heat stress: Physiological, genetic, and molecular insights

Global mean temperature is increasing at a rapid pace due to the rapid emission of greenhouse gases majorly from anthropogenic practices and predicted to rise up to 1.5°C above the pre-industrial level by the year 2050. The warming climate is affecting global crop production by altering biochemical, physiological, and metabolic processes resulting in poor growth, development, and reduced yield. Maize is susceptible to heat stress, particularly at the reproductive and early grain filling stages. Interestingly, heat stress impact on crops is closely regulated by associated environmental covariables such as humidity, vapor pressure deficit, soil moisture content, and solar radiation. Therefore, heat stress tolerance is considered as a complex trait, which requires multiple levels of regulations in plants. Exploring genetic diversity from landraces and wild accessions of maize is a promising approach to identify novel donors, traits, quantitative trait loci (QTLs), and genes, which can be introgressed into the elite cultivars. Indeed, genome wide association studies (GWAS) for mining of potential QTL(s) and dominant gene(s) is a major route of crop improvement. Conversely, mutation breeding is being utilized for generating variation in existing populations with narrow genetic background. Besides breeding approaches, augmented production of heat shock factors (HSFs) and heat shock proteins (HSPs) have been reported in transgenic maize to provide heat stress tolerance. Recent advancements in molecular techniques including clustered regularly interspaced short palindromic repeats (CRISPR) would expedite the process for developing thermotolerant maize genotypes.

Physiological Mechanisms Underlying Tassel Symptom Formation in Maize Infected with Sporisorium reilianum

Head smut is a soil-borne fungal disease caused by Sporisorium reilianum that infects maize tassels and ears. This disease poses a tremendous threat to global maize production. A previous study found markedly different and stably heritable tassel symptoms in some maize inbred lines with Sipingtou blood after infection with S. reilianum. In the present study, 55 maize inbred lines with Sipingtou blood were inoculated with S. reilianum and classified into three tassel symptom types (A, B, and C). Three maize inbred lines representing these classes (Huangzao4, Jing7, and Chang7-2, respectively) were used as test materials to investigate the physiological mechanisms of tassel formation in infected plants. Changes in enzyme activity, hormone content, and protein expression were analyzed in all three lines after infection and in control plants. The activities of peroxidase (POD), superoxide dismutase (SOD), and phenylalanine-ammonia-lyase (PAL) were increased in the three typical inbred lines after inoculation. POD and SOD activities showed similar trends between lines, with the increase percentage peaking at the V12 stage (POD: 57.06%, 63.19%, and 70.28% increases in Huangzao4, Jing7, and Chang7-2, respectively; SOD: 27.01%, 29.62%, and 47.07% in Huangzao4, Jing7, and Chang7-2, respectively. These were all higher than in the disease-resistant inbred line Mo17 at the same growth stage); this stage was found to be key in tassel symptom formation. Levels of gibberellic acid (GA3), indole-3-acetic acid (IAA), and abscisic acid (ABA) were also altered in the three typical maize inbred lines after inoculation, with changes in GA3 and IAA contents tightly correlated with tassel symptoms after S. reilianum infection. The differentially expressed proteins A5H8G4, P09233, and Q8VXG7 were associated with changes in enzyme activity, whereas P49353, P13689, and P10979 were associated with changes in hormone contents. Fungal infection caused reactive oxygen species (ROS) and nitric oxide (NO) bursts in the three typical inbred lines. This ROS accumulation caused biofilm disruption and altered host signaling pathways, whereas NO signaling triggered strong secondary metabolic responses in the host and altered the activities of defense-related enzymes. These factors together resulted in the formation of varying tassel symptoms. Thus, interactions between S. reilianum and susceptible maize materials were influenced by a variety of signals, enzymes, hormones, and metabolic cycles, encompassing a very complex regulatory network. This study preliminarily identified the physiological mechanisms leading to differences in tassel symptoms, deepening our understanding of S. reilianum-maize interactions.

Comparative RNA-seq analysis of resistant and susceptible banana genotypes reveals molecular mechanisms in response to banana bunchy top virus (BBTV) infection

Bananas hold significant economic importance as an agricultural commodity, serving as a primary livelihood source, a favorite fruit, and a staple crop in various regions across the world. However, Banana bunchy top disease (BBTD), which is caused by banana bunchy top virus (BBTV), poses a considerable threat to banana cultivation. To understand the resistance mechanism and the interplay of host suitability factors in the presence of BBTV, we conducted RNA-seq-based comparative transcriptomics analysis on mock-inoculated and BBTV-inoculated samples from resistant (wild Musa balbisiana) and susceptible (Musa acuminata 'Lakatan') genotypes. We observed common patterns of expression for 62 differentially expressed genes (DEGs) in both genotypes, which represent the typical defense response of bananas to BBTV. Furthermore, we identified 99 DEGs exclusive to the 'Lakatan' banana cultivar, offering insights into the host factors and susceptibility mechanisms that facilitate successful BBTV infection. In parallel, we identified 151 DEGs unique to the wild M. balbisiana, shedding light on the multifaceted mechanisms of BBTV resistance, involving processes such as secondary metabolite biosynthesis, cell wall modification, and pathogen perception. Notably, our validation efforts via RT-qPCR confirmed the up-regulation of the glucuronoxylan 4-O-methyltransferase gene (14.28 fold-change increase), implicated in xylan modification and degradation. Furthermore, our experiments highlighted the potential recruitment of host's substrate adaptor ADO (30.31 fold-change increase) by BBTV, which may play a role in enhancing banana susceptibility to the viral pathogen. The DEGs identified in this work can be used as basis in designing associated gene markers for the precise integration of resistance genes in marker-assisted breeding programs. Furthermore, the findings can be applied to develop genome-edited banana cultivars targeting the resistance and susceptibility genes, thus developing novel cultivars that are resilient to important diseases.

Spraying phenolic acid-modifiedchitooligosaccharide derivatives improves anthocyanin accumulation in grape

Herein, four chitooligosaccharide derivatives (COS-RA, COS-FA, COS-VA, COS-GA) were prepared by laccase-catalyzed chitooligosaccharide modification with rosmarinic acid (RA), ferulic acid (FA), gallic acid (GA), and vanillic acid (VA), and structures were characterized. RA and FA resulted in higher amino-substitution in the chitooligosaccharides than GA and VA. COS-RA and COS-FA had greater DPPH scavenging rates than COS-GA and COS-VA. Compared with COS treatment, spraying 250 mg L-1 COS-RA or COS-VA 6 times (once per 7 days) increased soluble sugar and anthocyanin content by 18.6%-23.2% and 41.7%-46.7%, respectively, from the fruit expansion to harvest stage. COS-RA and COS-VA also enhanced gene expression related to anthocyanin synthesis (PAL, F3H, F3'5'H, DFR, and UFGT) and monomeric anthocyanin accumulation (Mal-3-O-glu, Petu-3-O-ace-glu, Del-3-O-glu). Therefore, chitooligosaccharide derivatives may improve grape fruit anthocyanin accumulation by regulating antioxidant systems, improving the photosynthetic rate and inducing gene expression related to anthocyanin synthesis.

The Past, Present, and Future of Wheat Dwarf Virus Management-A Review

Wheat dwarf disease (WDD) is an important disease of monocotyledonous species, including economically important cereals. The causative pathogen, wheat dwarf virus (WDV), is persistently transmitted mainly by the leafhopper Psammotettix alienus and can lead to high yield losses. Due to climate change, the periods of vector activity increased, and the vectors have spread to new habitats, leading to an increased importance of WDV in large parts of Europe. In the light of integrated pest management, cultivation practices and the use of resistant/tolerant host plants are currently the only effective methods to control WDV. However, knowledge of the pathosystem and epidemiology of WDD is limited, and the few known sources of genetic tolerance indicate that further research is needed. Considering the economic importance of WDD and its likely increasing relevance in the coming decades, this study provides a comprehensive compilation of knowledge on the most important aspects with information on the causal virus, its vector, symptoms, host range, and control strategies. In addition, the current status of genetic and breeding efforts to control and manage this disease in wheat will be discussed, as this is crucial to effectively manage the disease under changing environmental conditions and minimize impending yield losses.

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

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

Nitric Oxide in Plant Functioning: Metabolism, Signaling, and Responses to Infestation with Ecdysozoa Parasites

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological processes in plants, including responses to biotic and abiotic stresses. Changes in endogenous NO concentration lead to activation/deactivation of NO signaling and NO-related processes. This paper presents the current state of knowledge on NO biosynthesis and scavenging pathways in plant cells and highlights the role of NO in post-translational modifications of proteins (S-nitrosylation, nitration, and phosphorylation) in plants under optimal and stressful environmental conditions. Particular attention was paid to the interactions of NO with other signaling molecules: reactive oxygen species, abscisic acid, auxins (e.g., indole-3-acetic acid), salicylic acid, and jasmonic acid. In addition, potential common patterns of NO-dependent defense responses against attack and feeding by parasitic and molting Ecdysozoa species such as nematodes, insects, and arachnids were characterized. Our review definitely highlights the need for further research on the involvement of NO in interactions between host plants and Ecdysozoa parasites, especially arachnids.

Novel genomic regions on chromosome 5B controlling wheat powdery mildew seedling resistance under Egyptian conditions

Wheat powdery mildew (PM) causes significant yield losses worldwide. None of the Egyptian wheat cultivars was detected to be highly resistant to such a severe disease. Therefore, a diverse spring wheat panel was evaluated for PM seedling resistance using different Bgt conidiospores collected from Egyptian fields in two growing seasons. The evaluation was done in two separate experiments. Highly significant differences were found between the two experiments suggesting the presence of different isolates populations. Highly significant differences were found among the tested genotypes confirming the ability to improve PM resistance using the recent panel. Genome-wide association study (GWAS) was done for each experiment separately and a total of 71 significant markers located within 36 gene models were identified. The majority of these markers are located on chromosome 5B. Haplotype block analysis identified seven blocks containing the significant markers on chromosome 5B. Five gene models were identified on the short arm of the chromosome. Gene enrichment analysis identified five and seven pathways based on the biological process and molecular functions respectively for the detected gene models. All these pathways are associated with disease resistance in wheat. The genomic regions on 5B seem to be novel regions that are associated with PM resistance under Egyptian conditions. Selection of superior genotypes was done and Grecian genotypes seem to be a good source for improving PM resistance under Egyptian conditions.

Oxylipins and Reactive Carbonyls as Regulators of the Plant Redox and Reactive Oxygen Species Network under Stress

Reactive oxygen species (ROS), and in particular H2O2, serve as essential second messengers at low concentrations. However, excessive ROS accumulation leads to severe and irreversible cell damage. Hence, control of ROS levels is needed, especially under non-optimal growth conditions caused by abiotic or biotic stresses, which at least initially stimulate ROS synthesis. A complex network of thiol-sensitive proteins is instrumental in realizing tight ROS control; this is called the redox regulatory network. It consists of sensors, input elements, transmitters, and targets. Recent evidence revealed that the interplay of the redox network and oxylipins–molecules derived from oxygenation of polyunsaturated fatty acids, especially under high ROS levels–plays a decisive role in coupling ROS generation and subsequent stress defense signaling pathways in plants. This review aims to provide a broad overview of the current knowledge on the interaction of distinct oxylipins generated enzymatically (12-OPDA, 4-HNE, phytoprostanes) or non-enzymatically (MDA, acrolein) and components of the redox network. Further, recent findings on the contribution of oxylipins to environmental acclimatization will be discussed using flooding, herbivory, and establishment of thermotolerance as prime examples of relevant biotic and abiotic stresses.

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.

Salinity Stress Influences the Main Biochemical Parameters of Nepeta racemosa Lam

In this work, the effects of salt stress on Nepeta racemosa Lam. were studied to analyze the possibility of using it as a potential culture for salinity-affected soils. A total of nine concentrations of salts-NaCl (18, 39, and 60 mg/100 g soil), Na₂SO₄ (50, 85, and 120 mg/100 g soil), and a mixture (9 g NaCl + 25 g Na₂SO₄, 19 g NaCl + 43 g Na₂SO₄, and 30 g NaCl + 60 g Na₂SO₄/100 g soil)-simulated real salinity conditions. Environmental electron microscopy offered information about the size and distribution of glandular trichomes, which are very important structures that contain bioactive compounds. The chlorophyll pigments, polyphenols, flavonoids, and antioxidant activity were determined based on spectrophotometric protocols. The results have shown a different impact of salinity depending on the salt type, with an increase in bioactive compound concentrations in some cases. The highest polyphenol concentrations were obtained for Na₂SO₄ variants (47.05 and 46.48 mg GA/g dw for the highest salt concentration in the first and second year, respectively), while the highest flavonoid content was found for the salt mixtures (42.77 and 39.89 mg QE/g dw for the highest concentrations of salt in the first and, respectively, the second year), approximately 100% higher than control. From the Pearson analysis, strong correlations were found between chlorophyll pigments (up to 0.93), antioxidant activity and yield for the first harvest (up to 0.38), and antioxidant activity and flavonoid content for the second harvest (up to 0.95). The results indicate the possibility of growing the studied plants in salt-stress soils, obtaining higher concentrations of bioactive compounds.

Gene fusions, micro-exons and splice variants define stress signaling by AP2/ERF and WRKY transcription factors in the sesame pan-genome

Evolutionary dynamics of AP2/ERF and WRKY genes, the major components of defense response were studied extensively in the sesame pan-genome. Massive variation was observed for gene copy numbers, genome location, domain structure, exon-intron structure and protein parameters. In the pan-genome, 63% of AP2/ERF members were devoid of introns whereas >99% of WRKY genes contained multiple introns. AP2 subfamily was found to be micro-exon rich with the adjoining intronic sequences sharing sequence similarity to many stress-responsive and fatty acid metabolism genes. WRKY family included extensive multi-domain gene fusions where the additional domains significantly enhanced gene and exonic sizes as well as gene copy numbers. The fusion genes were found to have roles in acquired immunity, stress response, cell and membrane integrity as well as ROS signaling. The individual genomes shared extensive synteny and collinearity although ecological adaptation was evident among the Chinese and Indian accessions. Significant positive selection effects were noticed for both micro-exon and multi-domain genes. Splice variants with changes in acceptor, donor and branch sites were common and 6-7 splice variants were detected per gene. The study ascertained vital roles of lipid metabolism and chlorophyll biosynthesis in the defense response and stress signaling pathways. 60% of the studied genes localized in the nucleus while 20% preferred chloroplast. Unique cis-element distribution was noticed in the upstream promoter region with MYB and STRE in WRKY genes while MYC was present in the AP2/ERF genes. Intron-less genes exhibited great diversity in the promoter sequences wherein the predominance of dosage effect indicated variable gene expression levels. Mimicking the NBS-LRR genes, a chloroplast localized WRKY gene, Swetha_24868, with additional domains of chorismate mutase, cAMP and voltage-dependent potassium channel was found to act as a master regulator of defense signaling, triggering immunity and reducing ROS levels.

Circadian Redox Rhythm in Plant-Fungal Pathogen Interactions

Significance: Circadian-controlled cellular growth, differentiation, and metabolism are mainly achieved by a classical transcriptional-translational feedback loop (TTFL), as revealed by investigations in animals, plants, and fungi. Recent Advances: Recently, reactive oxygen species (ROS) have been reported as part of a cellular network synchronizing nontranscriptional oscillators with established TTFL components, adding complexity to regulatory mechanisms of circadian rhythm. Both circadian rhythm and ROS homeostasis have a great impact on plant immunity as well as fungal pathogenicity, therefore interconnections of these two factors are implicit in plant-fungus interactions. Critical Issues: In this review, we aim to summarize the recent advances in circadian-controlled ROS homeostasis, or ROS-modulated circadian clock, in plant-fungus pathosystems, particularly using the rice (Oryza sativa) blast fungus (Magnaporthe oryzae) pathosystem as an example. Understanding of such bidirectional interaction between the circadian timekeeping machinery and ROS homeostasis/signaling would provide a theoretical basis for developing disease control strategies for important plants/crops. Future Directions: Questions remain unanswered about the detailed mechanisms underlying circadian regulation of redox homeostasis in M. oryzae, and the consequent fungal differentiation and death in a time-of-day manner. We believe that the rice-M. oryzae pathobiosystem would provide an excellent platform for investigating such issues in circadian-ROS interconnections in a plant-fungus interaction context. Antioxid. Redox Signal. 37, 726-738.

Identification of Novel Genes Associated with Partial Resistance to Aphanomyces Root Rot in Field Pea by BSR-Seq Analysis

Aphanomyces root rot, caused by Aphanomyces euteiches, causes severe yield loss in field pea (Pisum sativum). The identification of a pea germplasm resistant to this disease is an important breeding objective. Polygenetic resistance has been reported in the field pea cultivar '00-2067'. To facilitate marker-assisted selection (MAS), bulked segregant RNA-seq (BSR-seq) analysis was conducted using an F8 RIL population derived from the cross of 'Carman' × '00-2067'. Root rot development was assessed under controlled conditions in replicated experiments. Resistant (R) and susceptible (S) bulks were constructed based on the root rot severity in a greenhouse study. The BSR-seq analysis of the R bulks generated 44,595,510~51,658,688 reads, of which the aligned sequences were linked to 44,757 genes in a reference genome. In total, 2356 differentially expressed genes were identified, of which 44 were used for gene annotation, including defense-related pathways (jasmonate, ethylene and salicylate) and the GO biological process. A total of 344.1 K SNPs were identified between the R and S bulks, of which 395 variants were located in 31 candidate genes. The identification of novel genes associated with partial resistance to Aphanomyces root rot in field pea by BSR-seq may facilitate efforts to improve management of this important disease.

De Novo Transcriptome Analysis of R. nigrum cv. Aldoniai in Response to Blackcurrant Reversion Virus Infection

The most damaging pathogen in blackcurrant plantations is mite-transmitted blackcurrant reversion virus (BRV). Some Ribes species have an encoded genetic resistance to BRV. We performed RNA sequencing analysis of BRV-resistant blackcurrant cv. Aldoniai to evaluate the molecular mechanisms related to the BRV infection response. The RNA of virus-inoculated and mock-inoculated microshoots was sequenced, and the transcriptional changes at 2- and 4-days post inoculation (dpi) were analyzed. The accumulation and expression of BRV RNA1 were detected in infected plants. In total, 159,701 transcripts were obtained and 30.7% were unigenes, annotated in 7 databases. More than 25,000 differentially expressed genes (DEGs) according to FPKM were upregulated or downregulated. We observed 221 and 850 DEGs at 2 and 4 dpi, respectively, in BRV-infected microshoots related to the stress response. The proportion of upregulated DEGs at 4 dpi was about 3.5 times higher than at 2 dpi. Pathways of the virus defense response were activated, and key candidate genes were identified. The phenylpropanoid and the cutin, suberine, and wax biosynthesis pathways were activated in infected plants. Our comparative de novo analysis of the R. nigrum transcriptome provides clues not only for understanding the molecular BRV resistance mechanisms but also for breeding BRV-tolerant genotypes.

Transcriptome Meta-Analysis Identifies Candidate Hub Genes and Pathways of Pathogen Stress Responses in Arabidopsis thaliana

Simple Summary

Meta-analysis and systems-biology analysis revealed molecular plant defense responses in Arabidopsis thaliana when attacked by various pathogens. Differentially expressed genes were involved in several biosynthetic metabolic pathways, including those responsible for the biosynthesis of secondary metabolites and pathways central to photosynthesis and plant–pathogen interactions. In addition, WRKY40, WRKY46, and STZ transcription factors served as major points in protein–protein interactions. Overall, the findings highlighted genes that are commonly expressed during plant–pathogen interactions and will be useful in the development of novel genetic resistance strategies.

Abstract

Following a pathogen attack, plants defend themselves using multiple defense mechanisms to prevent infections. We used a meta-analysis and systems-biology analysis to search for general molecular plant defense responses from transcriptomic data reported from different pathogen attacks in Arabidopsis thaliana. Data from seven studies were subjected to meta-analysis, which revealed a total of 3694 differentially expressed genes (DEGs), where both healthy and infected plants were considered. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis further suggested that the DEGs were involved in several biosynthetic metabolic pathways, including those responsible for the biosynthesis of secondary metabolites and pathways central to photosynthesis and plant–pathogen interactions. Using network analysis, we highlight the importance of WRKY40, WRKY46 and STZ, and suggest that they serve as major points in protein–protein interactions. This is especially true regarding networks of composite-metabolic responses by pathogens. In summary, this research provides a new approach that illuminates how different mechanisms of transcriptome responses can be activated in plants under pathogen infection and indicates that common genes vary in their ability to regulate plant responses to the pathogens studied herein.

Low Temperature Plasma Strategies for Xylella fastidiosa Inactivation

The quarantine bacterium Xylella fastidiosa was first detected in Salento (Apulia, Italy) in 2013 and caused severe symptoms in olives, leading to plant death. The disease, named Olive Quick Decline Syndrome (OQDS), is caused by the strain “De Donno” ST53 of the subspecies pauca of this bacterium (XfDD), which is spread by the insect Philaenus spumarius. The epidemic poses a serious threat to the agricultural economy and the landscape, as X. fastidiosa infects several plant species and there is yet no recognized solution. Research on OQDS is focused on finding strategies to control its spread or mitigate its symptoms. As a perspective solution, we investigated the efficacy of the low-temperature plasma and plasma-activated water to kill bacterial cells. Experiments were conducted in vitro to test the biocidal effect of the direct application of a Surface Dielectric Barrier Discharge (SDBD) plasma on bacteria cells and Plasma Activated Water (PAW). PAW activity was tested as a possible biocidal agent that can move freely in the xylem network paving the way to test the strategy on infected plants. The results showed a high decontamination rate even for cells of XfDD embedded in biofilms grown on solid media and complete inactivation in liquid culture medium.

Heat Stress-Mediated Constraints in Maize (Zea mays) Production: Challenges and Solutions

An increase in temperature and extreme heat stress is responsible for the global reduction in maize yield. Heat stress affects the integrity of the plasma membrane functioning of mitochondria and chloroplast, which further results in the over-accumulation of reactive oxygen species. The activation of a signal cascade subsequently induces the transcription of heat shock proteins. The denaturation and accumulation of misfolded or unfolded proteins generate cell toxicity, leading to death. Therefore, developing maize cultivars with significant heat tolerance is urgently required. Despite the explored molecular mechanism underlying heat stress response in some plant species, the precise genetic engineering of maize is required to develop high heat-tolerant varieties. Several agronomic management practices, such as soil and nutrient management, plantation rate, timing, crop rotation, and irrigation, are beneficial along with the advanced molecular strategies to counter the elevated heat stress experienced by maize. This review summarizes heat stress sensing, induction of signaling cascade, symptoms, heat stress-related genes, the molecular feature of maize response, and approaches used in developing heat-tolerant maize varieties.

Photosynthesis-related genes induce resistance against soybean mosaic virus: Evidence for involvement of the RNA silencing pathway

Increasing lines of evidence indicate that chloroplast-related genes are involved in plant-virus interactions. However, the involvement of photosynthesis-related genes in plant immunity is largely unexplored. Analysis of RNA-Seq data from the soybean cultivar L29, which carries the Rsv3 resistance gene, showed that several chloroplast-related genes were strongly induced in response to infection with an avirulent strain of soybean mosaic virus (SMV), G5H, but were weakly induced in response to a virulent strain, G7H. For further analysis, we selected the PSaC gene from the photosystem I and the ATP-synthase α-subunit (ATPsyn-α) gene whose encoded protein is part of the ATP-synthase complex. Overexpression of either gene within the G7H genome reduced virus levels in the susceptible cultivar Lee74 (rsv3-null). This result was confirmed by transiently expressing both genes in Nicotiana benthamiana followed by G7H infection. Both proteins localized in the chloroplast envelope as well as in the nucleus and cytoplasm. Because the chloroplast is the initial biosynthesis site of defence-related hormones, we determined whether hormone-related genes are involved in the ATPsyn-α- and PSaC-mediated defence. Interestingly, genes involved in the biosynthesis of several hormones were up-regulated in plants infected with SMV-G7H expressing ATPsyn-α. However, only jasmonic and salicylic acid biosynthesis genes were up-regulated following infection with the SMV-G7H expressing PSaC. Both chimeras induced the expression of several antiviral RNA silencing genes, which indicate that such resistance may be partially achieved through the RNA silencing pathway. These findings highlight the role of photosynthesis-related genes in regulating resistance to viruses.

Functions of Redox Signaling in Pollen Development and Stress Response

Cellular redox homeostasis is crucial for normal plant growth and development. Each developmental stage of plants has a specific redox mode and is maintained by various environmental cues, oxidants, and antioxidants. Reactive oxygen species (ROS) and reactive nitrogen species are the chief oxidants in plant cells and participate in cell signal transduction and redox balance. The production and removal of oxidants are in a dynamic balance, which is necessary for plant growth. Especially during reproductive development, pollen development depends on ROS-mediated tapetal programmed cell death to provide nutrients and other essential substances. The deviation of the redox state in any period will lead to microspore abortion and pollen sterility. Meanwhile, pollens are highly sensitive to environmental stress, in particular to cell oxidative burst due to its peculiar structure and function. In this regard, plants have evolved a series of complex mechanisms to deal with redox imbalance and oxidative stress damage. This review summarizes the functions of the main redox components in different stages of pollen development, and highlights various redox protection mechanisms of pollen in response to environmental stimuli. In continuation, we also discuss the potential applications of plant growth regulators and antioxidants for improving pollen vigor and fertility in sustaining better agriculture practices.

Universal gene co-expression network reveals receptor-like protein genes involved in broad-spectrum resistance in pepper (Capsicum annuum L.)

Receptor-like proteins (RLPs) on plant cells have been implicated in immune responses and developmental processes. Although hundreds of RLP genes have been identified in plants, only a few RLPs have been functionally characterized in a limited number of plant species. Here, we identified RLPs in the pepper (Capsicum annuum) genome and performed comparative transcriptomics coupled with the analysis of conserved gene co-expression networks (GCNs) to reveal the role of core RLP regulators in pepper-pathogen interactions. A total of 102 RNA-seq datasets of pepper plants infected with four pathogens were used to construct CaRLP-targeted GCNs (CaRLP-GCNs). Resistance-responsive CaRLP-GCNs were merged to construct a universal GCN. Fourteen hub CaRLPs, tightly connected with defense-related gene clusters, were identified in eight modules. Based on the CaRLP-GCNs, we evaluated whether hub CaRLPs in the universal GCN are involved in the biotic stress response. Of the nine hub CaRLPs tested by virus-induced gene silencing, three genes (CaRLP264, CaRLP277, and CaRLP351) showed defense suppression with less hypersensitive response-like cell death in race-specific and non-host resistance response to viruses and bacteria, respectively, and consistently enhanced susceptibility to Ralstonia solanacearum and/or Phytophthora capsici. These data suggest that key CaRLPs are involved in the defense response to multiple biotic stresses and can be used to engineer a plant with broad-spectrum resistance. Together, our data show that generating a universal GCN using comprehensive transcriptome datasets can provide important clues to uncover genes involved in various biological processes.

Dual RNA-Seq Analysis of the Interaction Between Edible Fungus Morchella sextelata and Its Pathogenic Fungus Paecilomyces penicillatus Uncovers the Candidate Defense and Pathogenic Factors

Morels (Morchella spp.) are economically important mushrooms cultivated in many countries. However, their production and quality are hindered by white mold disease because of Paecilomyces penicillatus infection. In this study, we aimed to understand the genetic mechanisms of interactions between P. penicillatus and Morchella. M. sextelata, the most prevalent species of Morchella in China, was inoculated with P. penicillatus; then, the expression profiles of both fungi were determined simultaneously at 3 and 6 days post-inoculation (dpi) using a dual RNA-Seq approach. A total of 460 and 313 differentially expressed genes (DEGs) were identified in P. penicillatus and M. sextelata, respectively. The CAZymes of β-glucanases and mannanases, as well as subtilase family, were upregulated in P. penicillatus, which might be involved in the degradation of M. sextelata cell walls. Chitin recognition protein, caffeine-induced death protein, and putative apoptosis-inducing protein were upregulated, while cyclin was downregulated in infected M. sextelata. This indicates that P. penicillatus could trigger programmed cell death in M. sextelata after infection. Laccase-2, tyrosinases, and cytochrome P450s were also upregulated in M. sextelata. The increased expression levels of these genes suggest that M. sextelata could detoxify the P. penicillatus toxins and also form a melanin barrier against P. penicillatus invasion. The potential pathogenic mechanisms of P. penicillatus on M. sextelata and the defense mechanisms of M. sextelata against P. penicillatus were well described.

Multilayer regulatory landscape during pattern-triggered immunity in rice

Upon fungal and bacterial pathogen attack, plants launch pattern-triggered immunity (PTI) by recognizing pathogen-associated molecular patterns (PAMPs) to defend against pathogens. Although PTI-mediated response has been widely studied, a systematic understanding of the reprogrammed cellular processes during PTI by multi-omics analysis is lacking. In this study, we generated metabolome, transcriptome, proteome, ubiquitome and acetylome data to investigate rice (Oryza sativa) PTI responses to two PAMPs, the fungi-derived chitin and the bacteria-derived flg22. Integrative multi-omics analysis uncovered convergence and divergence of rice responses to these PAMPs at multiple regulatory layers. Rice responded to chitin and flg22 in a similar manner at the transcriptome and proteome levels, but distinct at the metabolome level. We found that this was probably due to post-translational regulation including ubiquitination and acetylation, which reshaped gene expression by modulating enzymatic activities, and possibly led to distinct metabolite profiles. We constructed regulatory atlas of metabolic pathways, including the defence-related phenylpropanoid and flavonoid biosynthesis and linoleic acid derivative metabolism. The multi-level regulatory network generated in this study sets the foundation for in-depth mechanistic dissection of PTI in rice and potentially in other related poaceous crop species.

Redox sensor QSOX1 regulates plant immunity by targeting GSNOR to modulate ROS generation

Reactive oxygen signaling regulates numerous biological processes, including stress responses in plants. Redox sensors transduce reactive oxygen signals into cellular responses. Here, we present biochemical evidence that a plant quiescin sulfhydryl oxidase homolog (QSOX1) is a redox sensor that negatively regulates plant immunity against a bacterial pathogen. The expression level of QSOX1 is inversely correlated with pathogen-induced reactive oxygen species (ROS) accumulation. Interestingly, QSOX1 both senses and regulates ROS levels by interactingn with and mediating redox regulation of S-nitrosoglutathione reductase, which, consistent with previous findings, influences reactive nitrogen-mediated regulation of ROS generation. Collectively, our data indicate that QSOX1 is a redox sensor that negatively regulates plant immunity by linking reactive oxygen and reactive nitrogen signaling to limit ROS production.

Four chromosome scale genomes and a pan-genome annotation to accelerate pecan tree breeding

Genome-enabled biotechnologies have the potential to accelerate breeding efforts in long-lived perennial crop species. Despite the transformative potential of molecular tools in pecan and other outcrossing tree species, highly heterozygous genomes, significant presence-absence gene content variation, and histories of interspecific hybridization have constrained breeding efforts. To overcome these challenges, here, we present diploid genome assemblies and annotations of four outbred pecan genotypes, including a PacBio HiFi chromosome-scale assembly of both haplotypes of the 'Pawnee' cultivar. Comparative analysis and pan-genome integration reveal substantial and likely adaptive interspecific genomic introgressions, including an over-retained haplotype introgressed from bitternut hickory into pecan breeding pedigrees. Further, by leveraging our pan-genome presence-absence and functional annotation database among genomes and within the two outbred haplotypes of the 'Lakota' genome, we identify candidate genes for pest and pathogen resistance. Combined, these analyses and resources highlight significant progress towards functional and quantitative genomics in highly diverse and outbred crops.

Redox Regulation in Diazotrophic Bacteria in Interaction with Plants

Plants interact with a large number of microorganisms that greatly influence their growth and health. Among the beneficial microorganisms, rhizosphere bacteria known as Plant Growth Promoting Bacteria increase plant fitness by producing compounds such as phytohormones or by carrying out symbioses that enhance nutrient acquisition. Nitrogen-fixing bacteria, either as endophytes or as endosymbionts, specifically improve the growth and development of plants by supplying them with nitrogen, a key macro-element. Survival and proliferation of these bacteria require their adaptation to the rhizosphere and host plant, which are particular ecological environments. This adaptation highly depends on bacteria response to the Reactive Oxygen Species (ROS), associated to abiotic stresses or produced by host plants, which determine the outcome of the plant-bacteria interaction. This paper reviews the different antioxidant defense mechanisms identified in diazotrophic bacteria, focusing on their involvement in coping with the changing conditions encountered during interaction with plant partners.

Identification of a novel NPR1 homolog gene, OsNH5N16, which contributes to broad-spectrum resistance in rice

Over half of the earth's population consumes rice as the primary food crop for dietary calories. However, severe loss of rice yield occurs due to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) and bakanae disease caused by Fusarium fujikuroi (F. fujikuroi). Therefore, broad-spectrum resistance (BSR) to these pathogens is essential for rice cultivation. The Nonexpressor of Pathogenesis-Related Genes1 (NPR1), which is related to the signal molecule salicylic acid (SA) and the expression of pathogenesis-related (PR) genes, is a key regulator of systemic acquired resistance (SAR). Although five NPR1 homologs (NHs) have been identified in rice thus far, their cellular and biological functions remain largely unexplored. In this study, we identified a novel rice NH gene from Oryza sativa L. cv. Dongjin. The genetic variation of single nucleotide polymorphisms in OsNH5 caused a single amino acid substitution of asparagine for serine at residue 16. OsNH5N16 was mainly located in the nucleus, and its transcription was induced by Xoo. We generated transgenic rice lines constitutively expressing OsNH5N16 to investigate its function. Plants that overexpressed OsNH5N16 displayed enhanced BSR to Xoo and F. fujikuroi compared with wild varieties, and the transcription of PR genes such as OsPR1, GLUC, and CHIT2 was considerably upregulated. Moreover, we revealed that SA increases the transcription of OsNH5N16 and the promoter activity of OsPR1 regulated by OsNH5N16. These results showed that OsNH5N16 enhances BSR by regulating the expression of PR genes related to SAR and it is controlled by SA at the transcriptional and post-translational levels. This is the first report on the innate immune response conferring BSR associated with NH5.

Early transcriptome changes induced by the Geminivirus C4 oncoprotein: setting the stage for oncogenesis

BACKGROUND

The Beet curly top virus C4 oncoprotein is a pathogenic determinant capable of inducing extensive developmental abnormalities. No studies to date have investigated how the transcriptional profiles differ between plants expressing or not expressing the C4 oncoprotein.

RESULTS

We investigated early transcriptional changes in Arabidopsis associated with expression of the Beet curly top virus C4 protein that represent initial events in pathogenesis via a comparative transcriptional analysis of mRNAs and small RNAs. We identified 48 and 94 differentially expressed genes at 6- and 12-h post-induction versus control plants. These early time points were selected to focus on direct regulatory effects of C4 expression. Since previous evidence suggested that the C4 protein regulated the brassinosteroid (BR)-signaling pathway, differentially expressed genes could be divided into two groups: those responsive to alterations in the BR-signaling pathway and those uniquely responsive to C4. Early transcriptional changes that disrupted hormone homeostasis, 18 and 19 differentially expressed genes at both 6- and 12-hpi, respectively, were responsive to C4-induced regulation of the BR-signaling pathway. Other C4-induced differentially expressed genes appeared independent of the BR-signaling pathway at 12-hpi, including changes that could alter cell development (4 genes), cell wall homeostasis (5 genes), redox homeostasis (11 genes) and lipid transport (4 genes). Minimal effects were observed on expression of small RNAs.

CONCLUSION

This work identifies initial events in genetic regulation induced by a geminivirus C4 oncoprotein. We provide evidence suggesting the C4 protein regulates multiple regulatory pathways and provides valuable insights into the role of the C4 protein in regulating initial events in pathogenesis.

Recent advances in the regulation of plant immunity by S-nitrosylation

S-nitrosylation, the addition of a nitric oxide (NO) moiety to a reactive protein cysteine (Cys) thiol, to form a protein S-nitrosothiol (SNO), is emerging as a key regulatory post-translational modification (PTM) to control the plant immune response. NO also S-nitrosylates the antioxidant tripeptide, glutathione, to form S-nitrosoglutathione (GSNO), both a storage reservoir of NO bioactivity and a natural NO donor. GSNO and, by extension, S-nitrosylation, are controlled by GSNO reductase1 (GSNOR1). The emerging data suggest that GSNOR1 itself is a target of NO-mediated S-nitrosylation, which subsequently controls its selective autophagy, regulating cellular protein SNO levels. Recent findings also suggest that S-nitrosylation may be deployed by pathogen-challenged host cells to counteract the effect of delivered microbial effector proteins that promote pathogenesis and by the pathogens themselves to augment virulence. Significantly, it also appears that S-nitrosylation may regulate plant immune functions by controlling SUMOylation, a peptide-based PTM. In this context, global SUMOylation is regulated by S-nitrosylation of SUMO conjugating enzyme 1 (SCE1) at Cys139. This redox-based PTM has also been shown to control the function of a key zinc finger transcriptional regulator during the establishment of plant immunity. Here, we provide an update of these recent advances.

Nitric oxide production and signalling in algae

Nitric oxide (NO) was the first identified gaseous messenger and is now well established as a major ubiquitous signalling molecule. The rapid development of our understanding of NO biology in embryophytes came with the partial characterization of the pathways underlying its production and with the decrypting of signalling networks mediating its effects. Notably, the identification of proteins regulated by NO through nitrosation greatly enhanced our perception of NO functions. In comparison, the role of NO in algae has been less investigated. Yet, studies in Chlamydomonas reinhardtii have produced key insights into NO production through the identification of NO-forming nitrite reductase and of S-nitrosated proteins. More intriguingly, in contrast to embryophytes, a few algal species possess a conserved nitric oxide synthase, the main enzyme catalysing NO synthesis in metazoans. This latter finding paves the way for a deeper characterization of novel members of the NO synthase family. Nevertheless, the typical NO-cyclic GMP signalling module transducing NO effects in metazoans is not conserved in algae, nor in embryophytes, highlighting a divergent acquisition of NO signalling between the green and the animal lineages.

The effect of NADPH oxidase inhibitor diphenyleneiodonium (DPI) and glutathione (GSH) on Isatis cappadocica, under Arsenic (As) toxicity

The present work was conducted to assess the effects of arsenic (As, 1000 µM), diphenyleneiodonium (DPI, 10 µM) and reduced glutathione (GSH, 500 µM) on Isatis cappadocica. As treatment decreased plant growth and fresh and dry weight of shoot and root and also enhanced the accumulation of As. As stress also enhanced the oxidative stress biomarkers, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content. However, the application of GSH decreased the content of H₂O₂ and MDA by 43% and 55%, respectively, as compared to As treatment. The antioxidants like superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione S-transferase (GST) also enhanced with As stress. NADPH oxidase inhibitor, the DPI, enhances the effect of As toxicity by increasing the accumulation of As, H₂O₂, MDA. DPI also enhances the activity of antioxidant enzymes except GR and GST, However, the application GSH increased the plant growth and biomass yield, decreases accumulation of As, H₂O₂ and MDA content in As as well as As + DPI treated plants. The thiols content [total thiol (TT), non-protein thiol (NPT) protein thiols (PT), and glutathione (GSH)] were decreased in the As + DPI treatment but supplementation of GSH enhanced them. Novelty statement: The study reveals the beneficial role of GSH in mitigating the deleterious effects of Arsenic toxicity through its active involvement in the antioxidant metabolism, thiol synthesis and osmolyte accumulation. Apart from As, We provided the plants NADPH oxidase inhibitor, the diphenyleneiodonium (DPI), which boosts the As toxicity. At present, there is dearth of information pertaining to the effects of DPI on plants growth and their responses under heavy metal stress.GSH application reversed the effect of diphenyleneiodonium (DPI) under As stress preventing the oxidative damage to biomolecules through the modulation of different antioxidant enzymes. The application of GSH for As stressed soil could be a sustainable approach for crop production.

Comparison of the chemical diversity of Vitis rotundifolia and Vitis vinifera cv. ‘Cabernet Sauvignon’

Grapevine is one of the most important fruit plants in the world, mainly due to its grapes and related products, with a highly economic and cultural importance. Every year, vineyards are affected by several pathogen outbreaks and the only way to control them is through preventive applications of agrochemicals every 12 to 15 days. This approach is not sustainable and not always effective. The Vitis genus comprise different species that exhibit varying levels of resistance to pathogens, thus the understanding of the innate resistance/susceptibility mechanisms of these different Vitis species is crucial to cope with these threats. In this work, an untargeted metabolomics approach was followed, using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS), to analyse the metabolic chemical diversity of two Vitis species: Vitis rotundifolia (resistant to pathogens) and V. vinifera cv. ‘Cabernet Sauvignon’ (susceptible to pathogens). Chemical formulas from both Vitis were used to build Van Krevelen diagrams and compositional space plots, which do not require full metabolite identification and provide an easy comparison method. Based only on these visualization tools, it was shown that the V. rotundifolia metabolome is more complex than the metabolome of V. vinifera cv. ‘Cabernet Sauvignon’. Moreover, the regions that present a higher density are associated to lipids, polyketides and carbohydrates. Also, V. rotundifolia metabolome presented a higher ratio O/C compounds.

Reticine A, a new potent natural elicitor: isolation from the fruit peel of Citrus reticulate and induction of systemic resistance against tobacco mosaic virus and other plant fungal diseases

BACKGROUND

Systemic acquired resistance (SAR) induced by elicitors is a highly satisfying form of resistance that protects plants against invading pathogens. Exploration and development of new elicitors is a promising alternative to conventional biocides in resistant pest management. In our previous broad screening, fruit peel extract of Citrus reticulata Blanco exhibited the ability to induce SAR in tobacco.

RESULT

A new potent elicitor reticine A was isolated from the fruit peel extract of industrial crop C. reticulate and its structure was well elucidated. In vivo assays showed that reticine A had considerable control efficacies at 100 and 500 μg mL-1 , being superior to commercial elicitor benzothiadiazole (BTH) (100 μg mL-1 ). Reticine A had no significant impact on the virulence of tobacco mosaic virus (TMV) particles under in vitro conditions. Application of reticine A induced a local hypersensitive reaction (HR), systemic accumulation of H2 O2 and salicylic acid (SA), systemic increase in defensive enzyme activities and systemic upregulated expression of pathogenesis-related (PR) proteins, suggesting its induction of SAR in tobacco. The expression of NPR1 and SA biosynthesis genes ICS and PAL were systemically upregulated.

CONCLUSION

SAR induced by reticine A against TMV in tobacco was demonstrated and the mechanism might be attributed to activating the expression of several defensive genes mediated by an SA signal. This study highlights the potential of reticine A which is recommended to be applied directly or as an active ingredient in the crude extract formulation ahead of time in the field, as well as being a potential lead compound for further optimization.

Glucosinolate Biosynthesis and the Glucosinolate–Myrosinase System in Plant Defense

Insect pests represent a major global challenge to important agricultural crops. Insecticides are often applied to combat such pests, but their use has caused additional challenges such as environmental contamination and human health issues. Over millions of years, plants have evolved natural defense mechanisms to overcome insect pests and pathogens. One such mechanism is the production of natural repellents or specialized metabolites like glucosinolates. There are three types of glucosinolates produced in the order Brassicales: aliphatic, indole, and benzenic glucosinolates. Upon insect herbivory, a “mustard oil bomb” consisting of glucosinolates and their hydrolyzing enzymes (myrosinases) is triggered to release toxic degradation products that act as insect deterrents. This review aims to provide a comprehensive summary of glucosinolate biosynthesis, the “mustard oil bomb”, and how these metabolites function in plant defense against pathogens and insects. Understanding these defense mechanisms will not only allow us to harness the benefits of this group of natural metabolites for enhancing pest control in Brassicales crops but also to transfer the “mustard oil bomb” to non-glucosinolate producing crops to boost their defense and thereby reduce the use of chemical pesticides.

The Chloroplast Reactive Oxygen Species-Redox System in Plant Immunity and Disease

Pathogen infections limit plant growth and productivity, thus contributing to crop losses. As the site of photosynthesis, the chloroplast is vital for plant productivity. This organelle, communicating with other cellular compartments challenged by infection (e.g., apoplast, mitochondria, and peroxisomes), is also a key battlefield in the plant-pathogen interaction. Here, we focus on the relation between reactive oxygen species (ROS)-redox signaling, photosynthesis which is governed by redox control, and biotic stress response. We also discuss the pathogen strategies to weaken the chloroplast-mediated defense responses and to promote pathogenesis. As in the next decades crop yield increase may depend on the improvement of photosynthetic efficiency, a comprehensive understanding of the integration between photosynthesis and plant immunity is required to meet the future food demand.

Transcriptome analysis of xa5-mediated resistance to bacterial leaf streak in rice (Oryza sativa L.)

Bacterial leaf steak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) is a devastating disease in rice production. The resistance to BLS in rice is a quantitatively inherited trait, of which the molecular mechanism is still unclear. It has been proved that xa5, a recessive bacterial blast resistance gene, is the most possible candidate gene of the QTL qBlsr5a for BLS resistance. To study the molecular mechanism of xa5 function in BLS resistance, we created transgenic lines with RNAi of Xa5 (LOC_Os05g01710) and used RNA-seq to analyze the transcriptomes of a Xa5-RNAi line and the wild-type line at 9 h after inoculation with Xoc, with the mock inoculation as control. We found that Xa5-RNAi could (1) increase the resistance to BLS as expected from xa5; (2) alter (mainly up-regulate) the expression of hundreds of genes, most of which were related to disease resistance; and (3) greatly enhance the response of thousands of genes to Xoc infection, especially of the genes involved in cell death pathways. The results suggest that xa5 is the cause of BLS-resistance of QTL qBlsr5a and it displays BLS resistance effect probably mainly because of the enhanced response of the cell death-related genes to Xoc infection.

A Meta-Analysis of Quantitative Trait Loci Associated with Multiple Disease Resistance in Rice (Oryza sativa L.)

Rice blast, sheath blight and bacterial leaf blight are major rice diseases found worldwide. The development of resistant cultivars is generally perceived as the most effective way to combat these diseases. Plant disease resistance is a polygenic trait where a combinatorial effect of major and minor genes affects this trait. To locate the source of this trait, various quantitative trait loci (QTL) mapping studies have been performed in the past two decades. However, investigating the congruency between the reported QTL is a daunting task due to the heterogeneity amongst the QTLs studied. Hence, the aim of our study is to integrate the reported QTLs for resistance against rice blast, sheath blight and bacterial leaf blight and objectively analyze and consolidate the location of QTL clusters in the chromosomes, reducing the QTL intervals and thus identifying candidate genes within the selected meta-QTL. A total of twenty-seven studies for resistance QTLs to rice blast (8), sheath blight (15) and bacterial leaf blight (4) was compiled for QTL projection and analyses. Cumulatively, 333 QTLs associated with rice blast (114), sheath blight (151) and bacterial leaf blight (68) resistance were compiled, where 303 QTLs could be projected onto a consensus map saturated with 7633 loci. Meta-QTL analysis on 294 QTLs yielded 48 meta-QTLs, where QTLs with membership probability lower than 60% were excluded, reducing the number of QTLs within the meta-QTL to 274. Further, three meta-QTL regions (MQTL2.5, MQTL8.1 and MQTL9.1) were selected for functional analysis on the basis that MQTL2.5 harbors the highest number of QTLs; meanwhile, MQTL8.1 and MQTL9.1 have QTLs associated with all three diseases mentioned above. The functional analysis allows for determination of enriched gene ontology and resistance gene analogs (RGAs) and other defense-related genes. To summarize, MQTL2.5, MQTL8.1 and MQTL9.1 have a considerable number of R-genes that account for 10.21%, 4.08% and 6.42% of the total genes found in these meta-QTLs, respectively. Defense genes constitute around 3.70%, 8.16% and 6.42% of the total number of genes in MQTL2.5, MQTL8.1 and MQTL9.1, respectively. This frequency is higher than the total frequency of defense genes in the rice genome, which is 0.0096% (167 defense genes/17,272 total genes). The integration of the QTLs facilitates the identification of QTL hotspots for rice blast, sheath blight and bacterial blight resistance with reduced intervals, which helps to reduce linkage drag in breeding. The candidate genes within the promising regions could be utilized for improvement through genetical engineering.

Hydrogen sulfide regulates the activity of antioxidant enzymes through persulfidation and improves the resistance of tomato seedling to Copper Oxide nanoparticles (CuO NPs)-induced oxidative stress

Hydrogen sulfide (H₂S), a small gaseous signaling molecule, regulates antioxidase activity and improves plant tolerance to oxidative stress. The phytotoxic effect of Copper Oxide (II) nanoparticles (CuO NPs) is due to oxidative stress. Here, we show that H₂S-mediated persulfidation of antioxidase is essential for an effective stress response of tomato exposed to CuO NPs. The CuO NP-induced increase in hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels was significantly reduced by treatment with the H₂S donor NaHS. In vivo, NaHS increased superoxide dismutase (SOD), ascorbate peroxidase (APX) and peroxidase (POD) activities under CuO NP stress. In vitro, NaHS increased APX and POD activities but decreased catalase (CAT) activity. Persulfidation existed in recombinant SlCAT1, SlcAPX1 and SlPOD5 proteins. The persulfidatied cysteine (Cys) residues were verified by liquid chromatography-tandem mass spectrometry (LC-MS/MS), revealing their position on the protein surface. Cys234 of SlCAT1 is located in the immune-responsive domain and close to the enzyme activity domain. Cys234 of SlcAPX1 and Cys 61 SlPOD5 are located in the enzyme activity domain. Persulfidation increased SlcAPX1 and SlPOD5 activities but decreased SlCAT1 activity. These data indicate that H₂S-mediated persulfidation posttranslationally regulates the activities of CAT, APX and POD, thereby enhancing the plant's response to oxidative stress. Additionally, this work provides an experimental approach for the study of persulfidation in plants.

Redox Electrochemistry to Interrogate and Control Biomolecular Communication

Cells often communicate by the secretion, transport, and perception of molecules. Information conveyed by molecules is encoded, transmitted, and decoded by cells within the context of the prevailing microenvironments. Conversely, in electronics, transmission reliability and message validation are predictable, robust, and less context dependent. In turn, many transformative advances have resulted by the formal consideration of information transfer. One way to explore this potential for biological systems is to create bio-device interfaces that facilitate bidirectional information transfer between biology and electronics. Redox reactions enable this linkage because reduction and oxidation mediate communication within biology and can be coupled with electronics. By manipulating redox reactions, one is able to combine the programmable features of electronics with the ability to interrogate and modulate biological function. In this review, we examine methods to electrochemically interrogate the various components of molecular communication using redox chemistry and to electronically control cell communication using redox electrogenetics.

Regulating the regulator: nitric oxide control of post-translational modifications

Nitric oxide (NO) is perfectly suited for the role of a redox signalling molecule. A key route for NO bioactivity occurs via protein S-nitrosation, and involves the addition of a NO moiety to a protein cysteine (Cys) thiol (-SH) to form an S-nitrosothiol (SNO). This process is thought to underpin a myriad of cellular processes in plants that are linked to development, environmental responses and immune function. Here we collate emerging evidence showing that NO bioactivity regulates a growing number of diverse post-translational modifications including SUMOylation, phosphorylation, persulfidation and acetylation. We provide examples of how NO orchestrates these processes to mediate plant adaptation to a variety of cellular cues.

Exploring sunflower responses to Sclerotinia head rot at early stages of infection using RNA-seq analysis

Sclerotinia head rot (SHR), caused by the necrotrophic fungus Sclerotinia sclerotiorum, is one of the most devastating sunflower crop diseases. Despite its worldwide occurrence, the genetic determinants of plant resistance are still largely unknown. Here, we investigated the Sclerotinia-sunflower pathosystem by analysing temporal changes in gene expression in one susceptible and two tolerant inbred lines (IL) inoculated with the pathogen under field conditions. Differential expression analysis showed little overlapping among ILs, suggesting genotype-specific control of cell defense responses possibly related to differences in disease resistance strategies. Functional enrichment assessments yielded a similar pattern. However, all three ILs altered the expression of genes involved in the cellular redox state and cell wall remodeling, in agreement with current knowledge about the initiation of plant immune responses. Remarkably, the over-representation of long non-coding RNAs (lncRNA) was another common feature among ILs. Our findings highlight the diversity of transcriptional responses to SHR within sunflower breeding lines and provide evidence of lncRNAs playing a significant role at early stages of defense.

Transcriptome Analysis of Solanum Tuberosum Genotype RH89-039-16 in Response to Chitosan

Potato (Solanum tuberosum L.) is the worldwide most important nongrain crop after wheat, rice, and maize. The autotetraploidy of the modern commercial potato makes breeding of new resistant and high-yielding cultivars challenging due to complicated and time-consuming identification and selection processes of desired crop features. On the other hand, plant protection of existing cultivars using conventional synthetic pesticides is increasingly restricted due to safety issues for both consumers and the environment. Chitosan is known to display antimicrobial activity against a broad range of plant pathogens and shows the ability to trigger resistance in plants by elicitation of defense responses. As chitosan is a renewable, biodegradable and nontoxic compound, it is considered as a promising next-generation plant-protecting agent. However, the molecular and cellular modes of action of chitosan treatment are not yet understood. In this study, transcriptional changes in chitosan-treated potato leaves were investigated via RNA sequencing. Leaves treated with a well-defined chitosan polymer at low concentration were harvested 2 and 5 h after treatment and their expression profile was compared against water-treated control plants. We observed 32 differentially expressed genes (fold change ≥ 1; p-value ≤ 0.05) 2 h after treatment and 83 differentially expressed genes 5 h after treatment. Enrichment analysis mainly revealed gene modulation associated with electron transfer chains in chloroplasts and mitochondria, accompanied by the upregulation of only a very limited number of genes directly related to defense. As chitosan positively influences plant growth, yield, and resistance, we conclude that activation of electron transfer might result in the crosstalk of different organelles via redox signals to activate immune responses in preparation for pathogen attack, concomitantly resulting in a generally improved metabolic state, fostering plant growth and development. This conclusion is supported by the rapid and transient production of reactive oxygen species in a typical oxidative burst in the potato leaves upon chitosan treatment. This study furthers our knowledge on the mode of action of chitosan as a plant-protecting agent, as a prerequisite for improving its ability to replace or reduce the use of less environmentally friendly agro-chemicals.

Synchronised regulation of disease resistance in primed finger millet plants against the blast disease

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Varied phytohormone levels was recorded in the primed plants infected with Magnoporthe grisea.

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The role of MAPK was studied for the first time in finger millet-blast disease response.

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Callose deposition at the site of pathogen entry in the primed plants indicating its role during plant defense.

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Temporal accumulation of lipoxygenase (LOX) activity confirms its role during jasmonate synthesis in the plant cells.

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The study has portrayed the SA mediated defense mechanism involved in finger millet plants against blast pathogen M. grisea.

Plants, being sessile, are exposed to an array of abiotic and biotic stresses. To adapt towards the changing environments, plants have evolved mechanisms that help in perceiving stress signals wherein phytohormones play a critical role. They have the ability to network enabling them to mediate defense responses. These endogenous signals, functioning at low doses are a part of all the developmental stages of the plant. Phytohormones possess specific functions as they interact with each other positively or negatively through cross-talks. In the present study, variations in the amount of phytohormones produced during biotic stress caused due to Magnoporthe grisea infection was studied through targeted metabolomics in both primed and control finger millet plants. Histochemical studies revealed callose deposition at the site of pathogen entry in the primed plants indicating its role during plant defense. The knowledge on the genetic makeup during infection was obtained by quantification of MAP kinase kinases 1 and 2 (MKK1/2) and lipoxygenase (LOX) genes, wherein the expression levels were high in the primed plants at 6 hours post-inoculation (hpi) compared to mock-control. Studies indicate the pivotal role of mitogen-activated protein kinase (MAPK or MAP kinases) during defense signalling. It is the first report to be studied on MAPK role in finger millet-blast disease response. Temporal accumulation of LOX enzyme along with its activity was also investigated due to its significant role during jasmonate synthesis in the plant cells. Results indicated its highest activity at 12 hpi. This is the first report on the variation in phytohormone levels in fingermillet - M. grisea pathosystem upon priming which were substantiated through salicylic acid (SA) pathway.

Proteomic analysis upon peach fruit infection with Monilinia fructicola and M. laxa identify responses contributing to brown rot resistance

Brown rot, caused by Monilinia spp., is a major peach disease worldwide. In this study, the response of peach cultivars Royal Glory (RG) and Rich Lady (RL) to infection by Monilinia fructicola or Monilinia laxa, was characterized. Phenotypic data, after artificial inoculations, revealed that ‘RL’ was relatively susceptible whereas ‘RG’ was moderately resistant to Monilinia spp. Comparative proteomic analysis identified mesocarp proteins of the 2 cultivars whose accumulation were altered by the 2 Monilinia species. Functional analysis indicated that pathogen-affected proteins in ‘RG’ were mainly involved in energy and metabolism, while, differentially accumulated proteins by the pathogen presence in ‘RL’ were involved in disease/defense and metabolism. A higher number of proteins was differentiated in ‘RG’ fruit compared to ‘RL’. Upon Monilinia spp. infection, various proteins were-down accumulated in ‘RL’ fruit. Protein identification by mass spectrometric analysis revealed that several defense-related proteins including thaumatin, formate dehydrogenase, S-formylglutathione hydrolase, CBS domain-containing protein, HSP70, and glutathione S-transferase were up-accumulated in ‘RG’ fruit following inoculation. The expression profile of selected defense-related genes, such as major latex allergen, 1-aminocyclopropane-1-carboxylate deaminase and UDP-glycoltransferase was assessed by RT-PCR. This is the first study deciphering differential regulations of peach fruit proteome upon Monilinia infection elucidating resistance responses.

Glutathione-dependent denitrosation of GSNOR1 promotes oxidative signalling downstream of H2 O2

Photorespiratory hydrogen peroxide (H₂ O₂ ) plays key roles in pathogenesis responses by triggering the salicylic acid (SA) pathway in Arabidopsis. However, factors linking intracellular H₂ O₂ to activation of the SA pathway remain elusive. In this work, the catalase-deficient Arabidopsis mutant, cat2, was exploited to elucidate the impact of S-nitrosoglutathione reductase 1 (GSNOR1) on H₂ O₂ -dependent signalling pathways. Introducing the gsnor1-3 mutation into the cat2 background increased S-nitrosothiol levels and abolished cat2-triggered cell death, SA accumulation, and associated gene expression but had little additional effect on the major components of the ascorbate-glutathione system or glycolate oxidase activities. Differential transcriptome profiles between gsnor1-3 and cat2 gsnor1-3 together with damped ROS-triggered gene expression in cat2 gsnor1-3 further indicated that GSNOR1 acts to mediate the SA pathway downstream of H₂ O₂ . Up-regulation of GSNOR activity was compromised in cat2 cad2 and cat2 pad2 mutants in which glutathione accumulation was genetically prevented. Experiments with purified recombinant GSNOR revealed that the enzyme is posttranslationally regulated by direct denitrosation in a glutathione-dependent manner. Together, our findings identify GSNOR1-controlled nitrosation as a key factor in activation of the SA pathway by H₂ O₂ and reveal that glutathione is required to maintain this biological function.

Surface Dielectric Barrier Discharge plasma: a suitable measure against fungal plant pathogens

Fungal diseases seriously affect agricultural production and the food industry. Crop protection is usually achieved by synthetic fungicides, therefore more sustainable and innovative technologies are increasingly required. The atmospheric pressure low-temperature plasma is a novel suitable measure. We report on the effect of plasma treatment on phytopathogenic fungi causing quantitative and qualitative losses of products both in the field and postharvest. We focus our attention on the in vitro direct inhibitory effect of non-contact Surface Dielectric Barrier Discharge on conidia germination of Botrytis cinerea, Monilinia fructicola, Aspergillus carbonarius and Alternaria alternata. A few minutes of treatment was required to completely inactivate the fungi on an artificial medium. Morphological analysis of spores by Scanning Electron Microscopy suggests that the main mechanism is plasma etching due to Reactive Oxygen Species or UV radiation. Spectroscopic analysis of plasma generated in humid air gives the hint that the rotational temperature of gas should not play a relevant role being very close to room temperature. In vivo experiments on artificially inoculated cherry fruits demonstrated that inactivation of fungal spores by the direct inhibitory effect of plasma extend their shelf life. Pre-treatment of fruits before inoculation improve the resistance to infections maybe by activating defense responses in plant tissues.

The strange case of polyphenols inhibiting the Briggs-Rauscher reaction: pH-modulated reactivity of the superoxide radical

Superoxide radical is one of the main players when it comes to oxidative stress. Even if in itself is moderately reactive and can cause the degradation of very few biologically relevant macromolecules, it can dismutate to hydrogen peroxide followed by a possible conversion to hydroxyl radical. In order to protect the internal environment against reactive oxygen species, plants have evolved a line of defence made from secondary metabolites with versatile redox properties, such as flavonoids and phenolic acids. Their characteristics are highly modulated by pH, as they turn into prooxidant compounds as it increases. Reported here are the behaviour and clear patterns in reactivity towards superoxide anion radical of four classes of plant phenolics as a pH function. The reactivity towards superoxide radical in acidic conditions has been studied by use of oscillating Briggs-Rauscher reaction with a new spectroelectrochemical experimental setup, by recording the absorbance in high quality for the first time. Some mechanistic intricacies have also been explored with regard to this method. Reactivity modulation at neutral and slightly basic pH has been assayed by superoxide radical scavenging ability using nitroblue tetrazolium as a substrate. For stronger alkaline pHs studies, Electron Paramagnetic Resonance was exploited. Hydroxybenzoic acids tend to be the least reactive species at all tested pH values. Hydroxycinnamic acids have their activity towards superoxide radical decreased as the pH increases, whereas flavonoids act vice versa.

The Trithorax Group Factor ULTRAPETALA1 Regulates Developmental as Well as Biotic and Abiotic Stress Response Genes in Arabidopsis

In eukaryotes, Polycomb group (PcG) and trithorax group (trxG) factors oppositely regulate gene transcription during development through histone modifications, with PcG factors repressing and trxG factors activating the expression of their target genes. Although plant trxG factors regulate many developmental and physiological processes, their downstream targets are poorly characterized. Here we use transcriptomics to identify genome-wide targets of the Arabidopsis thaliana trxG factor ULTRAPETALA1 (ULT1) during vegetative and reproductive development and compare them with those of the PcG factor CURLY LEAF (CLF). We find that genes involved in development and transcription regulation are over-represented among ULT1 target genes. In addition, stress response genes and defense response genes such as those in glucosinolate metabolic pathways are enriched, revealing a previously unknown role for ULT1 in controlling biotic and abiotic response pathways. Finally, we show that many ULT1 target genes can be oppositely regulated by CLF, suggesting that ULT1 and CLF may have antagonistic effects on plant growth and development in response to various endogenous and environmental cues.

Using a transcriptome sequencing approach to explore candidate resistance genes against stemphylium blight in the wild lentil species Lens ervoides

BACKGROUND

Stemphylium blight (SB), caused by Stemphylium botryosum, is a devastating disease in lentil production. Although it is known that accessions of Lens ervoides possess superior SB resistance at much higher frequency than the cultivated lentil species, very little is known about the molecular basis regulating SB resistance in L. ervoides. Therefore, a comprehensive molecular study of SB resistance in L. ervoides was needed to exploit this wild resource available at genebanks for use by plant breeders in resistance breeding.

RESULTS

Microscopic and qPCR quantification of fungal growth revealed that 48, 96, and 144 h post-inoculation (hpi) were interesting time points for disease development in L. ervoides recombinant inbred lines (RILs) LR-66-637 (resistant to SB) and LR-66-577 (susceptible to SB). Results of transcriptome sequencing at 0, 48, 96 and 144 hpi showed that 8810 genes were disease-responsive genes after challenge by S. botryosum. Among them, 7526 genes displayed a similar expression trend in both RILs, and some of them were likely involved in non-host resistance. The remaining 1284 genes were differentially expressed genes (DEGs) between RILs. Of those, 712 DEGs upregulated in LR-66-637 were mostly enriched in 'carbohydrate metabolic process', 'cell wall organization or biogenesis', and 'polysaccharide metabolic process'. In contrast, there were another 572 DEGs that were upregulated in LR-66-577, and some of them were enriched in 'oxidation-reduction process', 'asparagine metabolic process' and 'asparagine biosynthetic process'. After comparing DEGs to genes identified in previously described quantitative trait loci (QTLs) for resistance to SB, nine genes were common and three of them showed differential gene expression between a resistant and a susceptible bulk consisting of five RILs each. Results showed that two genes encoding calcium-transporting ATPase and glutamate receptor3.2 were candidate resistance genes, whereas one gene with unknown function was a candidate susceptibility gene.

CONCLUSION

This study provides new insights into the mechanisms of resistance and susceptibility in L. ervoides RILs responding to S. botryosum infection. Furthermore, we identified candidate resistance or susceptibility genes which warrant further gene function analyses, and which could be valuable for resistance breeding, if their role in resistance or susceptibility can be confirmed.

Nitric oxide and hydrogen sulfide in plants: which comes first?

Nitric oxide (NO) is a signal molecule regarded as being involved in myriad functions in plants under physiological, pathogenic, and adverse environmental conditions. Hydrogen sulfide (H2S) has also recently been recognized as a new gasotransmitter with a diverse range of functions similar to those of NO. Depending on their respective concentrations, both these molecules act synergistically or antagonistically as signals or damage promoters in plants. Nevertheless, available evidence shows that the complex biological connections between NO and H2S involve multiple pathways and depend on the plant organ and species, as well as on experimental conditions. Cysteine-based redox switches are prone to reversible modification; proteomic and biochemical analyses have demonstrated that certain target proteins undergo post-translational modifications such as S-nitrosation, caused by NO, and persulfidation, caused by H2S, both of which affect functionality. This review provides a comprehensive update on NO and H2S in physiological processes (seed germination, root development, stomatal movement, leaf senescence, and fruit ripening) and under adverse environmental conditions. Existing data suggest that H2S acts upstream or downstream of the NO signaling cascade, depending on processes such as stomatal closure or in response to abiotic stress, respectively.