Expression of pathogenesis-related proteins in transplastomic tobacco plants confers resistance to filamentous pathogens under field trials

Biochemical changes, antioxidative profile, and efficacy of the bio-stimulant in plant defense response against Sclerotinia sclerotiorum in common bean (Phasaeolus vulgaris L.)

Sclerotinia sclerotiorum, is a highly destructive pathogen with widespread impact on common bean (Phasaeolus vulgaris L.) worldwide. In this work, we investigated the efficacy of microbial consortia in bolstering host defense against sclerotinia rot. Specifically, we evaluated the performance of a microbial consortia comprising of Trichoderma erinaceum (T51) and Trichoderma viride (T52) (referred to as the T4 treatment) in terms of biochemical parameters, alleviation of the ROS induced cellular toxicity, membrane integrity (measured as MDA content), nutrient profiling, and the host defense-related antioxidative enzyme activities. Our findings demonstrate a notable enhancement in thiamine content, exhibiting 1.887 and 1.513-fold higher in the T4 compared to the un-inoculated control and the T1 treatment (only S. sclerotiorum treated). Similarly, the total proline content exhibited 3.46 and 1.24-fold higher and the total phenol content was 4.083 and 2.625-fold higher in the T4 compared to the un-inoculated control and the T1 treatment, respectively. Likewise, a general trend was found for other antioxidative and non-oxidative enzyme activities. However, results found were approximately similar in T2 treatment (bioprimed with T51) or T3 treatments (bioprimed with T52). Further, host defense attribute (survival rate) under the pathogen challenged condition was maximum in the T4 (15.55 % disease incidence) compared to others. Therefore, bio priming with consortia could be useful in reducing the economic losses incited by S. sclerotiorum in common beans.

How plants manage pathogen infection

To combat microbial pathogens, plants have evolved specific immune responses that can be divided into three essential steps: microbial recognition by immune receptors, signal transduction within plant cells, and immune execution directly suppressing pathogens. During the past three decades, many plant immune receptors and signaling components and their mode of action have been revealed, markedly advancing our understanding of the first two steps. Activation of immune signaling results in physical and chemical actions that actually stop pathogen infection. Nevertheless, this third step of plant immunity is under explored. In addition to immune execution by plants, recent evidence suggests that the plant microbiota, which is considered an additional layer of the plant immune system, also plays a critical role in direct pathogen suppression. In this review, we summarize the current understanding of how plant immunity as well as microbiota control pathogen growth and behavior and highlight outstanding questions that need to be answered.

Deciphering the underlying immune network of the potato defense response inhibition by Phytophthora infestans nuclear effector Pi07586 through transcriptome analysis

Phytophthora infestans, a highly destructive plant oomycete pathogen, is responsible for causing late blight in potatoes worldwide. To successfully infect host cells and evade immunity, P. infestans secretes various effectors into host cells and exclusively targets the host nucleus. However, the precise mechanisms by which these effectors manipulate host gene expression and reprogram defenses remain poorly understood. In this study, we focused on a nuclear-targeted effector, Pi07586, which has been implicated in immune suppression. Quantitative real-time PCR (qRT-PCR) analysis showed Pi07586 was significant up-regulation during the early stages of infection. Agrobacterium-induced transient expression revealed that Pi07586 localized in the nucleus of leaf cells. Overexpression of Pi07586 resulted in increased leaf colonization by P. infestans. RNA-seq analysis revealed that Pi07586 effectively suppressed the expression of PR-1C-like and photosynthetic antenna protein genes. Furthermore, high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS) analysis indicated that Pi07586 overexpression led to a substantial decrease in abscisic acid (ABA), jasmonic acid (JA), and jasmonoyl-isoleucine (JA-Ile) levels, while not affecting salicylic acid (SA) and indole-3-acetic acid (IAA) production. These findings shed new light on the modulation of plant immunity by Pi07586 and enhance our understanding of the intricate relationship between P. infestans and host plants.

Comparative Analysis of the Expression of Resistance-Related Genes Respond to the Diversity Foliar Pathogens of Pseudostellaria heterophylla

The foliar disease, which is the primary complex disease of Pseudostellaria heterophylla, can be caused by multiple co-infecting pathogens, resulting in a significant reduction in yield. However, there is a lack of research on the relationship between co-infection of various pathogens and the response of resistance-related genes in P. heterophylla. Through the use of 18S rDNA sequencing and pathogenicity testing, it has been determined that Fusarium oxysporum, Alternaria alternata, Arcopilus aureus, Botrytis cinerea, Nemania diffusa, Whalleya microplaca, and Cladosporium cladosporioides are co-infecting pathogens responsible for foliar diseases in P. heterophylla. Furthermore, the qRT-PCR analysis revealed that F. oxysporum, A. alternata, B. cinerea, A. aureus, N. diffusa, Schizophyllum commune, C. cladosporioides, and Coprinellus xanthothrix upregulated ten, two, three, four, seven, thirteen, five, one, and six resistance-related genes, respectively. These findings suggest that a total of 22 resistance-related genes were implicated in the response to diverse fungi, and the magnitude and frequency of induction of resistance-related genes varied considerably among the different fungi. The aforementioned gene associated with resistance was found to be implicated in the response to multiple fungi, including PhPRP1, PhBDRN15, PhBDRN11, and PhBDRN3, which were found to be involved in the resistance response to nine, five, four, and four fungi, respectively. The findings indicate that the PhPRP1, PhBDRN15, PhBDRN11, and PhBDRN3 genes exhibit a broad-spectrum resistance to various fungi. Furthermore, the avirulence fungi C. xanthothrix, which is known to affect P. heterophylla, was found to prime a wide range of resistance responses in P. heterophylla, thereby enhancing its disease resistance. This study provided insight into the management strategies for foliar diseases of P. heterophylla and new genetic materials for disease-resistant breeding.

Pathogenesis-Related Proteins (PRs) with Enzyme Activity Activating Plant Defense Responses

Throughout evolution, plants have developed a highly complex defense system against different threats, including phytopathogens. Plant defense depends on constitutive and induced factors combined as defense mechanisms. These mechanisms involve a complex signaling network linking structural and biochemical defense. Antimicrobial and pathogenesis-related (PR) proteins are examples of this mechanism, which can accumulate extra- and intracellular space after infection. However, despite their name, some PR proteins are present at low levels even in healthy plant tissues. When they face a pathogen, these PRs can increase in abundance, acting as the first line of plant defense. Thus, PRs play a key role in early defense events, which can reduce the damage and mortality caused by pathogens. In this context, the present review will discuss defense response proteins, which have been identified as PRs, with enzymatic action, including constitutive enzymes, β-1,3 glucanase, chitinase, peroxidase and ribonucleases. From the technological perspective, we discuss the advances of the last decade applied to the study of these enzymes, which are important in the early events of higher plant defense against phytopathogens.

Characterization and control of Rhizoctonia solani affecting lucky bamboo (Dracaena sanderiana hort. ex. Mast.) using some bioagents

In a survey conducted during the period of March-May 2019 in nurseries, warehouses, and shops at three governorates (Alexandria, El-Behera, and Giza governorates, Egypt), symptoms of root rot, basal stem rot, and wilt disease complex were observed in the lucky bamboo (Dracaena sanderiana hort. ex. Mast.). The highest disease infection percentage was found in lucky bamboo collected from Alexandria City (47.67%), while the highest disease severity was in lucky bamboo collected from El-Behera Governorate (35.19%). Rhizoctonia solani, Fusarium oxysporum, F. solani, Aspergillus niger, and Alternaria alternate were isolated and identified in the infected lucky bamboo samples. R. solani isolates were the most dominant among the recovered fungal species with a percentage of 80.89% of the total isolates (246). Pathogenicity tests showed that R. solani was the most pathogen with 100% disease infection and 76.67% disease severity. Molecular identification characterized R. solani isolate as R. solani AUMC 15120, MZ723906. Meanwhile, four biological control agents (bioagents) were isolated from the healthy lucky bamboo samples and identified based on cultural, morphological, microscopic characteristics, and the molecular phylogenetic analysis as Clonostachys rosea AUMC 15121, OL461708; Bacillus circulans TAG1, MW441316; B. siamensis TAP1, MW441318 and Ochrobactrum anthropi TAM1, MW441317. The four bioagents showed potential inhibition of R. solani in vitro as well as in vivo on lucky bamboo plants in vase treatments compared to the untreated inoculated control as well as certain fungicides and biocides used (Moncut, Rizolex-T, Topsin-M, Bio-Zeid, and Bio-Arc). The bioagent O. anthropi showed the highest inhibition growth (85.11%) of the in vitro R. solani colony, which was not significantly different from the biocide Bio-Arc (83.78%). However, C. rosea, B. siamensis and B. circulans showed inhibition values of 65.33, 64.44, and 60.44%, respectively. On the other hand, the biocide Bio-Zeid showed less inhibitory effect (43.11%), while the lowest growth inhibition was recorded by Rizolex-T (34.22%) and Topsin-M (28.67%). Furthermore, the in vivo experiment supported the in vitro results for the most effective treatments, where all the treatments significantly decreased the percentage of infection and disease severity compared to the inoculated untreated control. Additionally, the bioagent O. anthropi showed the highest effect, i.e., the lowest disease incidence and disease severity being 13.33% and 10%, compared to 100% and 75%, respectively, in the untreated inoculated control. This was not significantly different from the fungicide Moncut (13.33% and 21%) and from the bioagent C. rosea (20% and 15%) treatments for both parameters, respectively. In conclusion, the bioagents O. anthropi MW441317 at 1 × 10⁸ CFU/ml as well as C. rosea AUMC15121 at 1 × 10⁷/ml proved to be efficient to control R. solani causing root rot, and basal stem rot on lucky bamboo, compared to fungicide Moncut and can be used for disease management without the negative impact of the chemical control. Furthermore, this is the first report of the isolation and identification of Rhizoctonia solani, a pathogenic fungus, and four biocontrol agents (Bacillus circulans, B. siamensis, Ochrobactrum anthropi and Clonostachys rosea) associated with the healthy lucky bamboo plants.

Plant growth promotion and differential expression of defense genes in chilli pepper against Colletotrichum truncatum induced by Trichoderma asperellum and T. harzianum

BACKGROUND

Trichoderma asperellum and T. harzianum were assessed in this study as a potential biological control against Colletotrichum truncatum. C. truncatum is a hemibiotrophic fungus that causes anthracnose disease in chilli thereby affecting plant growth and fruit yield. Scanning electron microscope (SEM) technique showed the beneficial interaction between chilli root-Trichoderma spp. inducing the plant growth promotion, mechanical barrier, and defense network under C. truncatum challenged conditions.

METHODS

Seeds bio-primed with T. asperellum, T. harzianum, and T. asperellum + T. harzianum promoted the plant growth parameters and strengthening of physical barrier via lignification on the wall of vascular tissues. Seed primed with bioagents were used for exploring the molecular mechanism of defense response in pepper against anthracnose to assess the temporal expression of six defense genes in the Surajmukhi variety of Capsicum annuum. QRT-PCR demonstrated induction of defense responsive genes in chilli pepper bioprimed with Trichoderma spp. such as plant defensin 1.2 (CaPDF1.2), superoxide dismutase (SOD), ascorbate peroxidase (APx), guaiacol peroxidase (GPx), pathogenesis related proteins PR-2 and PR-5.

RESULTS

The results showed that bioprimed seeds were assessed for T. asperellum, T. harzianum, and T. asperellum + T. harzianum-chilli root colonization interaction under in vivo conditions. The results of the scanning electron microscope revealed that T. asperellum, T. harzianum and T. asperellum + T. harzianum interact with chilli roots directly via the development of plant-Trichoderma interaction system. Seeds bio-primed with bioagents promoted the plant growth parameters, fresh and dry weight of shoot and root, plant height, leaf area index, number of leaves, stem diameter and strengthening of physical barrier via lignification on the wall of vascular tissues and expression of six defense related genes in pepper against anthracnose.

CONCLUSIONS

Application of T. asperellum and T. harzianum and in combination of treatments enhanced the plant growth. Further, as seeds bioprimed with T. asperellum, T. harzianum and in combination with treatment of T. asperellum + T. harzianum induced the strengthening of the cell wall by lignification and expression of six defense related genes CaPDF1.2, SOD, APx, GPx, PR-2 and PR-5 in pepper against C. truncatum. Our study contributed for better disease management through biopriming with T. asperellum, T. harzianum and T. asperellum + T. harzianum. The biopriming possess enormous potential to promote plant growth, modulate the physical barrier, and induced the defense related genes in chilli pepper against anthracnose.

Whole-Genome Resequencing Deciphers New Insight Into Genetic Diversity and Signatures of Resistance in Cultivated Cotton Gossypium hirsutum

Cotton is an important crop that produces fiber and cottonseed oil for the textile and oil industry. However, cotton leaf curl virus disease (CLCuD) stress is limiting its yield in several Asian countries. In this study, we have sequenced Mac7 accession, a Gossypium hirsutum resistance source against several biotic stresses. By aligning with the Gossypium hirsutum (AD1) 'TM-1' genome, a total of 4.7 and 1.2 million SNPs and InDels were identified in the Mac7 genome. The gene ontology and metabolic pathway enrichment indicated SNPs and InDels role in nucleotide bindings, secondary metabolite synthesis, and plant-pathogen interaction pathways. Furthermore, the RNA-seq data in different tissues and qPCR expression profiling under CLCuD provided individual gene roles in resistant and susceptible accessions. Interestingly, the differential NLR genes demonstrated higher expression in resistant plants rather than in susceptible plants expression. The current resequencing results may provide primary data to identify DNA resistance markers which will be helpful in marker-assisted breeding for development of Mac7-derived resistance lines.

Cloning and Characterization of Two Novel PR4 Genes from Picea asperata

Pathogenesis-related (PR) proteins are important in plant pathogenic resistance and comprise 17 families, including the PR4 family, with antifungal and anti-pathogenic functions. PR4 proteins contain a C-terminal Barwin domain and are divided into Classes I and II based on the presence of an N-terminal chitin-binding domain (CBD). This study is the first to isolate two PR4 genes, PaPR4-a and PaPR4-b, from Picea asperata, encoding PaPR4-a and PaPR4-b, respectively. Sequence analyses suggested that they were Class II proteins, owing to the presence of an N-terminal signal peptide and a C-terminal Barwin domain, but no CBD. Tertiary structure analyses using the Barwin-like protein of papaya as a template revealed structural similarity, and therefore, functional similarity between the proteins. Predictive results revealed an N-terminal transmembrane domain, and subcellular localization studies confirmed its location on cell membrane and nuclei. Real-time quantitative PCR (RT-qPCR) demonstrated that PaPR4-a and PaPR4-b expression levels were upregulated following infection with Lophodermium piceae. Additionally, PaPR4-a and PaPR4-b were induced in Escherichia coli, where the recombinant proteins existed in inclusion bodies. The renatured purified proteins showed antifungal activity. Furthermore, transgenic tobacco overexpressing PaPR4-a and PaPR4-b exhibited improved resistance to fungal infection. The study can provide a basis for further molecular mechanistic insights into PR4-induced defense responses.

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.

Effect of copper stress on Phaseolus coccineus in the presence of exogenous methyl jasmonate and/or Serratia plymuthica from the Spitsbergen soil

Copper stress in the presence of exogenous methyl jasmonate and Serratia plymuthica in a complete trifactorial design with copper (0, 50 µM), methyl jasmonate (0, 1, 10 µM) and Serratia plymuthica (without and with inoculation) was studied on the physiological parameters of Phaseolus coccineus. Copper application reduced biomass and allantoin content, but increased chlorophyll and carotenoids contents as well as catalase and peroxidases activities. Jasmonate did not modify biomass and organic acids levels under copper treatment, but additional inoculation elevated biomass and content of tartrate, malate and succinate. Jasmonate used alone or in combination with bacteria increased superoxide dismutase activity in copper application. With copper, allantoin content elevated at lower jasmonate concentration, but with additional inoculation - at higher jasmonate concentration. Under copper stress, inoculation resulted in higher accumulation of tartrate, malate and citrate contents in roots, which corresponded with lower allantoin concentration in roots. Combined with copper, inoculation reduced catalase and guaiacol peroxidase activities, whereas organic acids content was higher. Under metal stress, with bacteria, jasmonate reduced phenolics content, elevated superoxide dismutase and guaiacol peroxidase activities. The data indicate that jasmonate and S. plymuthica affected most physiological parameters of P. coccineus grown with copper and revealed some effect on biomass.

2D-DIGE based proteome analysis of wheat-Thinopyrum intermedium 7XL/7DS translocation line under drought stress

Background

Drought stress is the most limiting factor for plant growth and crop production worldwide. As a major cereal crop, wheat is susceptible to drought. Thus, discovering and utilizing drought-tolerant gene resources from related species are highly important for improving wheat drought resistance. In this study, the drought tolerance of wheat Zhongmai 8601-Thinopyrum intermedium 7XL/7DS translocation line YW642 was estimated under drought stress, and then two-dimensional difference gel electrophoresis (2D-DIGE) based proteome analysis of the developing grains was performed to uncover the drought-resistant proteins.

Results

The results showed that 7XL/7DS translocation possessed a better drought-tolerance compared to Zhongmai 8601. 2D-DIGE identified 146 differential accumulation protein (DAP) spots corresponding to 113 unique proteins during five grain developmental stages of YW642 under drought stress. Among them, 55 DAP spots corresponding to 48 unique proteins displayed an upregulated expression, which were mainly involved in stress/defense, energy metabolism, starch metabolism, protein metabolism/folding and transport. The cis-acting element analysis revealed that abundant stress-related elements were present in the promoter regions of the drought-responsive protein genes, which could play important roles in drought defense. RNA-seq and RT-qPCR analyses revealed that some regulated DAP genes also showed a high expression level in response to drought stress.

Conclusions

Our results indicated that Wheat-Th. intermedium 7XL/7DS translocation line carried abundant drought-resistant proteins that had potential application values for wheat drought tolerance improvement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08599-1.

Potential of biosynthesized zinc oxide nanoparticles to control Fusarium wilt disease in eggplant (Solanum melongena) and promote plant growth

In this study, a novel, non-toxic, eco-friendly zinc oxide nanoparticles (ZnO-NPs) was used instead of the synthetic fungicides widely used to control the destructive phytopathogenic fungus Fusarium oxysporum, the causative agent of wilt disease in Solanum melongena L. Herein, the biosynthesized ZnO-NPs was carried out by Penicillium expansum ATCC 7861. In vitro, mycosynthesized ZnO-NPs exhibited antifungal activity against Fusarium oxysporum. In vivo, ZnO-NPs suppressed Fusarium wilt disease in cultivated Solanum melongena L. by decreasing the disease severity with 75% of plant protection. Moreover, ZnO-NPs stimulated the recovery of eggplant as an indicated by improving of morphological and metabolic indicators including plant height(152.5%), root length(106.6%), plant fresh biomass (146%), chlorophyll a (102.8%), chlorophyll b (67.86%), total soluble carbohydrates (48.5%), total soluble protein (81.8%), phenol (10.5%), antioxidant activity and isozymes compared with infected control. Therefore, this study suggests using mycosynthesized ZnO-NPs as an alternative to synthetic fungicides not only to eradicate the Fusarium wilt disease in cultivated eggplant (Solanum melongena) but also to promote the growth parameters and metabolic aspects.

Trichoderma: The Current Status of Its Application in Agriculture for the Biocontrol of Fungal Phytopathogens and Stimulation of Plant Growth

Rhizosphere filamentous fungi of the genus Trichoderma, a dominant component of various soil ecosystem mycobiomes, are characterized by the ability to colonize plant roots. Detailed knowledge of the properties of Trichoderma, including metabolic activity and the type of interaction with plants and other microorganisms, can ensure its effective use in agriculture. The growing interest in the application of Trichoderma results from their direct and indirect biocontrol potential against a wide range of soil phytopathogens. They act through various complex mechanisms, such as mycoparasitism, the degradation of pathogen cell walls, competition for nutrients and space, and induction of plant resistance. With the constant exposure of plants to a variety of pathogens, especially filamentous fungi, and the increased resistance of pathogens to chemical pesticides, the main challenge is to develop biological protection alternatives. Among non-pathogenic microorganisms, Trichoderma seems to be the best candidate for use in green technologies due to its wide biofertilization and biostimulatory potential. Most of the species from the genus Trichoderma belong to the plant growth-promoting fungi that produce phytohormones and the 1-aminocyclopropane-1-carboxylate (ACC) deaminase enzyme. In the present review, the current status of Trichoderma is gathered, which is especially relevant in plant growth stimulation and the biocontrol of fungal phytopathogens.

Genome-Wide Identification and Functions against Tomato Spotted Wilt Tospovirus of PR-10 in Solanum lycopersicum

Tomato spotted wilt virus impacts negatively on a wide range of economically important plants, especially tomatoes. When plants facing any pathogen attack or infection, increase the transcription level of plant genes that are produced pathogenesis-related (PR) proteins. The aim of this study is a genome-wide identification of PR-10 superfamily and comparative analysis of PR-10 and Sw-5b gene functions against tomato responses to biotic stress (TSWV) to systemic resistance in tomato. Forty-five candidate genes were identified, with a length of 64–210 amino acid residues and a molecular weight of 7.6–24.4 kDa. The PR-10 gene was found on ten of the twelve chromosomes, and it was determined through a genetic ontology that they were involved in six biological processes and molecular activities, and nine cellular components. Analysis of the transcription level of PR-10 family members showed that the PR-10 gene (Solyc09g090980) has high expression levels in some parts of the tomato plant. PR-10 and Sw-5b gene transcription and activity in tomato leaves were strongly induced by TSWV infection, whereas H8 plants having the highest significantly upregulated expression of PR-10 and Sw-5b gene after the inoculation of TSWV, and TSWV inoculated in M82 plants showed significantly upregulated expression of PR-10 gene comparatively lower than H8 plants. There was no significant expression of Sw-5b gene of TSWV inoculated in M82 plants and then showed highly significant correlations between PR-10 and Sw-5b genes at different time points in H8 plants showed significant correlations compared to M82 plants after the inoculation of TSWV; a heat map showed that these two genes may also participate in regulating the defense response after the inoculation of TSWV in tomato.

Putative Genes of Pathogenesis-Related Proteins and Coronatine-Insensitive Protein 1 in Ribes spp

In response to pathogen attacks, plants activate a complex of defense mechanisms including an accumulation of the endogenous signaling compounds salicylic acid and jasmonic acid. The activity of pathogenesis-related genes (PRs) and coronatine-insensitive 1 (COI1) in defense-response pathways are established in plants. The aim of this study was to identify homologs of the PRs and COI1 in blackcurrants. Primers with degenerate nucleotides were designed based on the most conservative parts of PR1 and COI1 genes from other plants and applied for amplification of specific fragments of PRs and COI1 in Ribes spp. Seven heterogeneous sequences of PR with a diversity of 66.0-98.3% at nucleic acid level were found. The phylogenetic analysis revealed the dependence of R. nigrum PR homologs on the PR1 and PR6 families. Four heterogeneous sequences of R. nigrum COI1 with an identity of 95.9-98.8% at nucleic acid level were isolated. Specific primers for newly detected genes' homologs were designed in this study and could be useful for evaluating the defense response to pathogen attacks in blackcurrants.

Growth-defense trade-offs and yield loss in plants with engineered cell walls

As a major component of plant secondary cell walls, lignin provides structural integrity and rigidity, and contributes to primary defense by providing a physical barrier to pathogen ingress. Genetic modification of lignin biosynthesis has been adopted to reduce the recalcitrance of lignified cell walls to improve biofuel production, tree pulping properties and forage digestibility. However, lignin-modification is often, but unpredictably, associated with dwarf phenotypes. Hypotheses suggested to explain this include: collapsed vessels leading to defects in water and solute transport; accumulation of molecule(s) that are inhibitory to plant growth or deficiency of metabolites that are critical for plant growth; activation of defense pathways linked to cell wall integrity sensing. However, there is still no commonly accepted underlying mechanism for the growth defects. Here, we discuss recent data on transcriptional reprogramming in plants with modified lignin content and their corresponding suppressor mutants, and evaluate growth-defense trade-offs as a factor underlying the growth phenotypes. New approaches will be necessary to estimate how gross changes in transcriptional reprogramming may quantitatively affect growth. Better understanding of the basis for yield drag following cell wall engineering is important for the biotechnological exploitation of plants as factories for fuels and chemicals.

A Genome-Wide Analysis of Pathogenesis-Related Protein-1 (PR-1) Genes from Piper nigrum Reveals Its Critical Role during Phytophthora capsici Infection

Black pepper (Piper nigrum L.) is a prominent spice that is an indispensable ingredient in cuisine and traditional medicine. Phytophthora capsici, the causative agent of footrot disease, causes a drastic constraint in P. nigrum cultivation and productivity. To counterattack various biotic and abiotic stresses, plants employ a broad array of mechanisms that includes the accumulation of pathogenesis-related (PR) proteins. Through a genome-wide survey, eleven PR-1 genes that belong to a CAP superfamily protein with a caveolin-binding motif (CBM) and a CAP-derived peptide (CAPE) were identified from P. nigrum. Despite the critical functional domains, PnPR-1 homologs differ in their signal peptide motifs and core amino acid composition in the functional protein domains. The conserved motifs of PnPR-1 proteins were identified using MEME. Most of the PnPR-1 proteins were basic in nature. Secondary and 3D structure analyses of the PnPR-1 proteins were also predicted, which may be linked to a functional role in P. nigrum. The GO and KEGG functional annotations predicted their function in the defense responses of plant-pathogen interactions. Furthermore, a transcriptome-assisted FPKM analysis revealed PnPR-1 genes mapped to the P. nigrum-P. capsici interaction pathway. An altered expression pattern was detected for PnPR-1 transcripts among which a significant upregulation was noted for basic PnPR-1 genes such as CL10113.C1 and Unigene17664. The drastic variation in the transcript levels of CL10113.C1 was further validated through qRT-PCR and it showed a significant upregulation in infected leaf samples compared with the control. A subsequent analysis revealed the structural details, phylogenetic relationships, conserved sequence motifs and critical cis-regulatory elements of PnPR-1 genes. This is the first genome-wide study that identified the role of PR-1 genes during P. nigrum-P. capsici interactions. The detailed in silico experimental analysis revealed the vital role of PnPR-1 genes in regulating the first layer of defense towards a P. capsici infection in Panniyur-1 plants.

Identification of virulence associated milRNAs and their bidirectional targets in Rhizoctonia solani and maize during infection

BACKGROUND

Anastomosis group 1 IA (AG1-IA) of Rhizoctonia solani is the major agent of banded leaf and sheath blight (BLSB) disease that causes severe yield loss in many worldwide crops. MicroRNAs (miRNAs) are ~ 22 nt non-coding RNAs that negatively regulate gene expression levels by mRNA degradation or translation inhibition. A better understanding of miRNA function during AG1-IA infection can expedite to elucidate the molecular mechanisms of fungi-host interactions.

RESULTS

In this study, we sequenced three small RNA libraries obtained from the mycelium of AG1-IA isolate, non-infected maize sheath and mixed maize sheath 3 days after inoculation. In total, 137 conserved and 34 novel microRNA-like small RNAs (milRNAs) were identified from the pathogen. Among these, one novel and 17 conserved milRNAs were identified as potential virulence-associated (VA) milRNAs. Subsequently, the prediction of target genes for these milRNAs was performed in both AG1-IA and maize, while functional annotation of these targets suggested a link to pathogenesis-related biological processes. Further, expression patterns of these virulence-associated milRNAs demonstrated that theyparticipate in the virulence of AG1-IA. Finally, regulation of one maize targeting gene, GRMZM2G412674 for Rhi-milRNA-9829-5p, was validated by dual-luciferase assay and identified to play a positive role in BLSB resistance in two maize mutants. These results suggest the global differentially expressed milRNAs of R. solani AG1-IA that participate in the regulation of target genes in both AG1-IA and maize to reinforce its pathogenicity.

CONCLUSIONS

Our data have provided a comprehensive overview of the VA-milRNAs of R. solani and identified that they are probably the virulence factors by directly interfered in host targeting genes. These results offer new insights on the molecular mechanisms of R.solani-maize interactions during the process of infection.

Overexpression of a plasma membrane protein generated broad-spectrum immunity in soybean

Plants fight-off pathogens and pests by manifesting an array of defence responses using their innate immunity mechanisms. Here we report the identification of a novel soybean gene encoding a plasma membrane protein, transcription of which is suppressed following infection with the fungal pathogen, Fusarium virguliforme. Overexpression of the protein led to enhanced resistance against not only against F. virguliforme, but also against spider mites (Tetranychus urticae, Koch), soybean aphids (Aphis glycines, Matsumura) and soybean cyst nematode (Heterodera glycines). We, therefore, name this protein as Glycine max disease resistance 1 (GmDR1; Glyma.10g094800). The homologues of GmDR1 have been detected only in legumes, cocoa, jute and cotton. The deduced GmDR1 protein contains 73 amino acids. GmDR1 is predicted to contain an ecto- and two transmembrane domains. Transient expression of the green fluorescent protein fused GmDR1 protein in soybean leaves showed that it is a plasma membrane protein. We investigated if chitin, a pathogen-associated molecular pattern (PAMP), common to all pathogen and pests considered in this study, can significantly enhance defence pathways among the GmDR1-overexpressed transgenic soybean lines. Chitin induces marker genes of the salicylic- and jasmonic acid-mediated defence pathways, but suppresses the defence pathway regulated by ethylene. Chitin induced SA- and JA-regulated defence pathways may be one of the mechanisms involved in generating broad-spectrum resistance among the GmDR1-overexpressed transgenic soybean lines against two serious pathogens and two pests including spider mites, against which no known resistance genes have been identified in soybean and among the most other crop species.

Phytohormone Priming of Tomato Plants Evoke Differential Behavior in Rhizoctonia solani During Infection, With Salicylate Priming Imparting Greater Tolerance Than Jasmonate

In the field of phytohormone defense, the general perception is that salicylate (SA)-mediated defense is induced against biotrophic pathogens while jasmonate (JA)-mediated defense functions against necrotrophic pathogens. Our goals were to observe the behavior of the necrotrophic pathogen Rhizoctonia solani in the vicinity, on the surface, and within the host tissue after priming the host with SA or JA, and to see if priming with these phytohormones would affect the host defense differently upon infection. It was observed for the first time, that R. solani could not only distinguish between JA versus SA-primed tomato plants from a distance, but surprisingly avoided SA-primed plants more than JA-primed plants. To corroborate these findings, early infection events were monitored and compared through microscopy, Scanning Electron Microscopy, and Confocal Laser Scanning Microscopy using transformed R. solani expressing green fluorescence protein gene (gfp). Different histochemical and physiological parameters were compared between the unprimed control, JA-primed, and SA-primed plants after infection. The expression of a total of fifteen genes, including the appressoria-related gene of the pathogen and twelve marker genes functioning in the SA and JA signaling pathways, were monitored over a time course during early infection stages. R. solani being traditionally designated as a necrotroph, the major unexpected observations were that Salicylate priming offered better tolerance than Jasmonate priming and that it was mediated through the activation of SA-mediated defense during the initial phase of infection, followed by JA-mediated defense in the later phase. Hence, the present scenario of biphasic SA-JA defense cascades during R. solani infection, with SA priming imparting maximum tolerance, indicate a possible hemibiotrophic pathosystem that needs to be investigated further.

Molecular mechanism of nanochitin whisker elicits plant resistance against Phytophthora and the receptors in plants

Rod-like nanochitin (NC) whisker with cationic nature has a strong synergistic effect with fungicides on inhibition of tobacco root rot disease. This study we explored the activity of NC against Phytophthora and the mechanism for eliciting plant defense response and the receptors in planta. P. capsici isolates, model Nicotiana benthamiana plants and Arabidopsis thaliana were treated with 0.005% of NC suspension and 1 μM of flg22. Infection control efficacy against P. capsici isolates, biosynthetic enzyme activities and the PR genes expression were determined at different hours post treatment in plant. The infection control efficacy, ROS generation, and PTI maker gene expression were re-analyzed in A. thaliana Col-0, bak1 and cerk1 mutants. The results showed that NC did not exhibit inhibitory effect on vegetative growth of P. capsici, but enhanced the resistance against P. capsici by systemically enhanced phenylalanine ammonia-lyase activity and PR gene expression. P. capsici resistance, PTI maker gene promotion, and ROS production in A. thaliana induced by NC depended not only on chitin receptor CERK1, but also BAK1. NC and flg22 induced oomycete immunity through a mechanism of a cross-microbe protection via the BAK1-CERK1 pathway in plant, pointing to the complexity of the plant immunity system.

N-acyl homoserine lactone-mediated modulation of plant growth and defense against Pseudoperonospora cubensis in cucumber

N-acyl-homoserine lactones (AHLs), a well-described group of quorum sensing molecules, may modulate plant defense responses and plant growth. However, there is limited knowledge regarding the defense responses of non-model crops to AHLs and the mechanism of action responsible for the modulation of defense responses against microbial pathogens. In the present study, long-chain N-3-oxo-tetradecanoyl-l-homoserine lactone (oxo-C14-HSL) was shown to have a distinct potential to prime cucumber for enhanced defense responses against the biotrophic oomycete pathogen Pseudoperonospora cubensis and the hemibiotrophic bacterium Pseudomonas syringae pv. lachrymans. We provide evidence that AHL-mediated enhanced defense against downy mildew disease is based on cell wall reinforcement by lignin and callose deposition, the activation of defense-related enzymes (peroxidase, β-1,3-glucanase, phenylalanine ammonia-lyase), and the accumulation of reactive oxygen species (hydrogen peroxide, superoxide) and phenolic compounds. Quantitative analysis of salicylic acid and jasmonic acid, and transcriptional analysis of several of genes associated with these phytohormones, revealed that defense priming with oxo-C14-HSL is commonly regulated by the salicylic acid signaling pathway. We also show that treatment with short- (N-hexanoyl-l-homoserine lactone) and medium-chain (N-3-oxo-decanoyl-l-homoserine lactone) AHLs promoted primary root elongation and modified root architecture, respectively, resulting in enhanced plant growth.

Chitosan induces jasmonic acid production leading to resistance of ripened fruit against Botrytis cinerea infection

Chitosan can function a key role in plant resistant against Botrytis cinerea infection, while its mechanism is unclear in ripened fruits. In this study, we investigated the chitosan effect on two type of ripened fruits including strawberry and grapes (Kyoho and Shine-Muscat) when were infected with B. cinerea. Results showed that chitosan inhibited B. cinerea growth, increased phenolic compounds and cell wall composition, modulated oxidative stress and induced jasmonic acid (JA) production in ripened fruits. Data-independent acquisition (DIA) showed that 224 and 171 proteins were upregulated 1.5-fold by chitosan in Kyoho and Shine-Muscat grape, respectively. Topless-related protein 3 (TPR3) were identified and interacted with histone deacetylase 19 (HDAC19) and negatively regulated by JA and chitosan. Meanwhile, overexpression of VvTPR3 and VvHDAC19 reduced the stability of cell wall against B. cinerea in strawberry. Taken together, chitosan induces defense related genes and protect the fruit quality against Botrytis infection through JA signaling.

Combinatorial Control of Plant Specialized Metabolism: Mechanisms, Functions, and Consequences

Plants constantly perceive internal and external cues, many of which they need to address to safeguard their proper development and survival. They respond to these cues by selective activation of specific metabolic pathways involving a plethora of molecular players that act and interact in complex networks. In this review, we illustrate and discuss the complexity in the combinatorial control of plant specialized metabolism. We hereby go beyond the intuitive concept of combinatorial control as exerted by modular-acting complexes of transcription factors that govern expression of specialized metabolism genes. To extend this discussion, we also consider all known hierarchical levels of regulation of plant specialized metabolism and their interfaces by referring to reported regulatory concepts from the plant field. Finally, we speculate on possible yet-to-be-discovered regulatory principles of plant specialized metabolism that are inspired by knowledge from other kingdoms of life and areas of biological research.

Characterization of the wheat cultivars against Tilletia controversa Kühn, causal agent of wheat dwarf bunt

Wheat is one of the most important staple crops. Tilletia controversa Kühn is the causal agent of wheat dwarf bunt. In this study, a resistant wheat cultivar displayed significantly higher expression of pathogenesis-related genes than a susceptible cultivar at 7 days post inoculation (DPI) with T. controversa. Similarly, the expression was high in the resistant cultivar after exogenous application of phytohormones, including salicylic acid. The expression of pathogenesis-related genes, especially chitinase 4, was high in the resistant cultivar, while LPT-1 was down regulated after T. controversa infection. Callose deposition was greater in the resistant cultivar than in the susceptible cultivar at 10 DPI. Confocal microscopy was used to track the fungal hyphae in both cultivars in anther and ovary cells. The anthers and ovaries of the susceptible cultivar were infected by T. controversa at 7 and 15 DPI. There were no fungal hyphae in anther and ovary cells in the resistant cultivar until 10 and 23 DPI, respectively. Moreover, anther length and width were negatively influenced by T. controversa at 16 DPI. The plant height was also affected by fungal infection. Ultimately, resistance to T. controversa was achieved in cultivars via the regulation of the expression of defense-related and pathogenesis-related genes.

Metabolic adjustments during compatible interaction between barley genotypes and stripe rust pathogen

Stripe rust is a fungal disease that has devastated the barley production for a long time. The present study focused on the role of β-glucan, PR proteins, diamine oxidase (DAO), polyamine oxidase (PAO), key enzymes and metabolites of phenol and proline metabolism in the stripe rust resistance of barley. RD2901 with resistant behavior against stripe rust showed increased levels of PR proteins, phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL) along with the accumulation of β-glucan and lignin which strengthen the plant cell wall during plant-pathogen interaction. It also depicted the enhanced activities of glutamate dehydrogenase (GDH) and ornithine aminotransferase (OAT) coupled with the increased amounts of proline, glycine betaine and choline after infection with M-race of P. striiformis f. sp. hordei. On the contrary, the sensitive genotype Jyoti was unable to enhance the activities of most of these enzymes except PAL and OAT so that it showed an increase in lignin and choline contents only. Secondly, the increase in lignin content was less as compared to the tolerant genotype. Hence, it can be inferred that these key metabolites and enzymes of various metabolic pathways may contribute to the resistance of barley against stripe rust pathogen. This study suggested that these key enzymes and their metabolites could serve as markers for the characterization of plant defensive state that is essential for crop protection.

Bacterial Isolate Inhabiting Spitsbergen Soil Modifies the Physiological Response of Phaseolus coccineus in Control Conditions and under Exogenous Application of Methyl Jasmonate and Copper Excess

The aim of the study was to demonstrate the potential of the promotion and regulation of plant physiology and growth under control and copper stress conditions, and the impact of the exogenous application of methyl jasmonate on this potential. Runner bean plants were treated with methyl jasmonate (1 or 10 µM) (J; J1 or J10) and Cu (50 µM), and inoculated with a bacterial isolate (S17) originating from Spitsbergen soil, and identified as Pseudomonas luteola using the analytical profile index (API) test. Above- and under-ground plant parts were analyzed. The growth parameters; the concentration of the photosynthetic pigments, elements, flavonoids (FLAVO), phenolics (TPC), allantoin (ALLA), and low molecular weight organic acids (LMWOAs); the activity of antioxidant enzymes and enzymes of resistance induction pathways (e.g., superoxide dismutase (SOD), catalase (CAT), ascorbate (APX) and guaiacol (GPX) peroxidase, glucanase (GLU), and phenylalanine (PAL) and tyrosine ammonia-lyase (TAL)), and the antioxidant capacity (AC) were studied. The leaves exhibited substantially higher ALLA and LMWOA concentrations as well as PAL and TAL activities, whereas the roots mostly had higher activities for a majority of the enzymes tested (i.e., SOD, CAT, APX, GPX, and GLU). The inoculation with S17 mitigated the effect of the Cu stress. Under the Cu stress and in the presence of J10, isolate S17 caused an elevation of the shoot fresh weight, K concentration, and TAL activity in the leaves, and APX and GPX (also at J1) activities in the roots. In the absence of Cu, isolate S17 increased the root length and the shoot-to-root ratio, but without statistical significance. In these conditions, S17 contributed to a 236% and 34% enhancement of P and Mn, respectively, in the roots, and a 19% rise of N in the leaves. Under the Cu stress, S17 caused a significant increase in FLAVO and TPC in the leaves. Similarly, the levels of FLAVO, TPC, and AC were enhanced after inoculation with Cu and J1. Regardless of the presence of J, inoculation at Cu excess caused a reduction of SOD and CAT activities, and an elevation of GPX. The effects of inoculation were associated with the application of Cu and J, which modified plant response mainly in a concentration-dependent manner (e.g., PAL, TAL, and LMWOA levels). The conducted studies demonstrated the potential for isolate S17 in the promotion of plant growth.