Rutin-Mediated Priming of Plant Resistance to Three Bacterial Pathogens Initiating the Early SA Signal Pathway

Integrated endogenous hormones and transcriptome analysis contribute to fruit development related gene mining in Eriobotrya japonica

Loquat has both a delicious taste and natural medicinal effects. Fruit yield is the foundation of loquat production. However, as loquat fruits ripen, the time course changes in endogenous hormones and the transcriptome are still unclear, and the mining of loquat fruit development-related genes is still limited. Pulps from four stages of fruit development, including 70 days after full-blooming (DAF) (Z01), 90 DAF (Z02), 110 DAF (Z03), and 130 DAF (Z04), were collected to detect the contents of endogenous hormones and conduct transcriptome analysis. The results revealed that the pulps thickened continuously at a steady speed, whereas the rapid fruit expansion before the Z02 stage could be attributed to a sharp expansion of seeds. In addition, the endogenous hormone levels of the pulps tended to differ among these four stages. A total of 39,051 genes were obtained, and each sample was compared. Z01-VS-Z02, Z01-VS-Z03, and Z01-VS-Z04 presented 2611, 12,594, and 19,214 differentially expressed genes (DEGs), respectively. We found that there were 259, 49, 47, 70, 169, 47, 22 and 33 DEGs related to Aux, GA, CTK, ABA, Eth, BR, SA and JA, respectively. GO and KEGG enrichment analyses revealed that the most obviously enriched terms were photosynthesis-antenna proteins, starch and sucrose metabolism, and photosynthesis. Cluster analysis of the expression trends of the DEGs revealed that 25 clusters were obtained, 16 of which were highly correlated with 1 to 5 hormones. A total of 25 and 28 core genes were systematically identified from clusters 21 and 25, respectively. Heterologous expression revealed that EjHsc70, a selected core gene, promoted Arabidopsis growth and could be involved in the development process of loquat fruit. This study provides new insights into fruit development in Eriobotrya japonica.

Antiviral activity and mechanisms of action of atropine, rutin, and hypoxanthine against tomato Brown rugose fruit virus

Plant viral diseases cause considerable damage to the agricultural industry and are difficult to control. Recently, botanical biopesticides that are environmentally friendly, safe for non-target organisms, and not prone to developing drug resistance have shown great potential as antiviral agents. In the present study a screening of natural products with antiviral potential was conducted, and three compounds - atropine, rutin, and hypoxanthine - were identified to possess anti-tomato brown rugose fruit virus (ToBRFV) activity. Further, the modes of action of these compounds were investigated. The results of the bioassay revealed that atropine, rutin and hypoxanthine were effective at concentrations of 50, 100 and 150 μg mL-1 in inactivating, inhibiting proliferation and protecting against ToBRFV when combined with atropine and rutin. As the concentration of compounds increased, their antiviral properties were found to be enhanced. These compounds were found to reduce the expression of the coat protein and the replicase genes of ToBRFV. Atropine and rutin, in particular, demonstrated substantial anti-ToBRFV effects with diverse modes of action when used alone or in combination. Hypoxanthine demonstrated a comparatively weaker antiviral effect than the other two compounds, and when combined with the latter, the antiviral activity of the other compounds was also reduced to a certain extent. These results provided key proof that these compounds may represent a promising source of novel antiviral agents for agricultural use.

Integrated transcriptome and metabolome analyses reveals the mechanisms of function loss of Lr29 leaf rust resistance gene at high temperatures in wheat

Leaf rust (LR) is one of the most common diseases of wheat. The resistance gene Lr29 provides wide resistance to LR, but loses its function under high temperatures. Despite the importance of this gene, the mechanism of resistance is unclear. In this study we investigated the resistance mechanism of the Lr29 gene to LR at the seedling stage, as well as the reasons behind the loss of gene function at high temperatures by using integrated transcriptome and metabolome analyses. Results suggests that the pathways of reactive oxygen species (ROS), which could be due to expression of genes including LOX (lipoxygenase), APX (ascorbate peroxidase) and GST (glutathione S-transferase), play a key role in the resistance of Lr29 to LR, furthermore flavonoids, such as epicatechin, cosmosiin, apiin, vitexin and rutin, were identified as the key metabolites linked to Lr29 resistance. We also found that, at high temperatures, Lr29 downregulated the genes and metabolites associated with glycolysis and the tricarboxylic acid (TCA) cycle, while genes and metabolites related to the shikimic acid pathway were upregulated. This study might provide a valuable theoretical foundation for the cloning of the Lr29 gene, the analysis of its disease resistance mechanism, and the understanding of how temperature affects gene function.

Methyl Jasmonate Induces Phenylphenalenone Accumulation, Resulting in Black Leaf Streak Disease Resistance In Banana (Musa acuminata cv. Grand Nain)

This study analyzes the effects of methyl jasmonic acid (MeJA) and salicylic acid (SA) on the defensive responses of banana cv. Grand Nain against Black Leaf Streak Disease (BLSD), caused by Mycosphaerella fijiensis. The metabolic responses were analyzed using HPLC and NMR. With the exception of rutin, all compounds were identified as phenylphenalenones. Application of MeJA and SA resulted in an increase in the level of irenolone and hydroxyanigofurone production. Furthermore, MeJA was observed to induce the de novo synthesis of 2-(4'-hydroxyphenyl)-1,8-naphthalic anhydride, 2-(4'-methoxyphenyl)-1,8-naphthalic anhydride, and 7-(4'-hydroxyphenyl) naphthal-8-formyl-1-carboxylic anhydride. Molecular analysis revealed a significant upregulation of some genes implicated in the phenolic compound synthesis and of lipoxygenase but not the ones of PR proteins. MeJA-treated leaves showed improved resistance to BLSD. The results suggest that MeJA may serve as an effective protective strategy against the most damaging banana disease, providing a potential strategy for protecting banana crops.

Metabolic profiling and antibacterial activity of tree wood extracts obtained under variable extraction conditions

INTRODUCTION

Tree bacterial diseases are a threat in forestry due to their increasing incidence and severity. Understanding tree defence mechanisms requires evaluating metabolic changes arising during infection. Metabolite extraction affects the chemical diversity of the samples and, therefore, the biological relevance of the data. Metabolite extraction has been standardized for several biological models. However, little information is available regarding how it influences wood extract's chemical diversity.

OBJECTIVES

This study aimed to develop a methodological approach to obtain extracts from different tree species with the highest reproducibility and chemical diversity possible, to ensure proper coverage of the trees' metabolome.

METHODS

A full factorial design was used to evaluate the effect of solvent type, extraction temperature and number of extraction cycles on the metabolic profile, chemical diversity and antibacterial activity of four tree species.

RESULTS

Solvent, temperature and their interaction significantly affected the extracts' chemical diversity, while the number of extraction cycles positively correlated with yield and antibacterial activity. Although 60% of the features were recovered in all the tested conditions, differences in the presence and abundance of specific chemical classes per tree were observed, including organooxygen compounds, prenol lipids, carboxylic acids, and flavonoids.

CONCLUSIONS

Each tree species has a unique metabolic profile, which means that no single protocol is universally effective. Extraction at 50 °C for three cycles using 80% methanol or chloroform/methanol/water showed the best results and is suggested for studying wood metabolome. These observations highlight the need to tailor extraction protocols to each tree species to ensure comprehensive metabolome coverage for metabolic profiling.

Applying infectious clones and untargeted metabolite profiling to characterize citrus tristeza virus-induced stem pitting in citrus

Citrus tristeza virus (CTV) causes economically important stem pitting in sensitive citrus types however the exact mechanisms of stem pitting development in citrus remain unclear. In this study, CTV infectious clones were used to study stem pitting induction in 'Duncan' grapefruit and 'Mexican' lime. A panel of open reading frame (ORF) replacement clones was generated focusing on the CTV ORFs implicated in stem pitting development and pathogenicity, namely p33, p18, p13 and p23. ORF replacements from severe- and mild-pitting CTV isolates were introduced into a mild-pitting infectious clone (genotype T36) to determine if stem pitting could be induced. A broad range of stem pitting outcomes were observed with ORF p18 (from isolate T3-KB) and ORF p23 (from isolate GFMS12-1.3) associated with enhanced stem pitting development. Metabolomic trends underlying the different stem pitting outcomes were further assessed by untargeted metabolite profiling. In each citrus host, the metabolite profiling identified statistically significant compounds that differed between stem pitting groups. These compounds were mainly phenolic acids and phenolic glycosides and are known to function as antioxidant and stress-signaling molecules. These metabolites can serve as targets for future time-course observations to potentially use mass spectrometry profiling to inform CTV management practices.

Naringenin restricts the colonization and growth of Ralstonia solanacearum in tobacco mutant KCB-1

Bacterial wilt severely jeopardizes plant growth and causes enormous economic loss in the production of many crops, including tobacco (Nicotiana tabacum). Here, we first demonstrated that the roots of bacterial wilt-resistant tobacco mutant KCB-1 can limit the growth and reproduction of Ralstonia solanacearum. Secondly, we demonstrated that KCB-1 specifically induced an upregulation of naringenin content in root metabolites and root secretions. Further experiments showed that naringenin can disrupt the structure of R. solanacearum, inhibit the growth and reproduction of R. solanacearum, and exert a controlling effect on bacterial wilt. Exogenous naringenin application activated the resistance response in tobacco by inducing the burst of reactive oxygen species and salicylic acid deposition, leading to transcriptional reprogramming in tobacco roots. Additionally, both external application of naringenin in CB-1 and overexpression of the Nicotiana tabacum chalcone isomerase (NtCHI) gene, which regulates naringenin biosynthesis, in CB-1 resulted in a higher complexity of their inter-root bacterial communities than in untreated CB-1. Further analysis showed that naringenin could be used as a marker for resistant tobacco. The present study provides a reference for analyzing the resistance mechanism of bacterial wilt-resistant tobacco and controlling tobacco bacterial wilt.

Emerging Trends in Non-Protein Amino Acids as Potential Priming Agents: Implications for Stress Management Strategies and Unveiling Their Regulatory Functions

Plants endure the repercussions of environmental stress. As the advancement of global climate change continues, it is increasingly crucial to protect against abiotic and biotic stress effects. Some naturally occurring plant compounds can be used effectively to protect the plants. By externally applying priming compounds, plants can be prompted to trigger their defensive mechanisms, resulting in improved immune system effectiveness. This review article examines the possibilities of utilizing exogenous alpha-, beta-, and gamma-aminobutyric acid (AABA, BABA, and GABA), which are non-protein amino acids (NPAAs) that are produced naturally in plants during instances of stress. The article additionally presents a concise overview of the studies' discoveries on this topic, assesses the particular fields in which they might be implemented, and proposes new avenues for future investigation.

Multi-omics identification of a key glycosyl hydrolase gene FtGH1 involved in rutin hydrolysis in Tartary buckwheat (Fagopyrum tataricum)

Rutin, a flavonoid rich in buckwheat, is important for human health and plant resistance to external stresses. The hydrolysis of rutin to quercetin underlies the bitter taste of Tartary buckwheat. In order to identify rutin hydrolysis genes, a 200 genotypes mini-core Tartary buckwheat germplasm resource was re-sequenced with 30-fold coverage depth. By combining the content of the intermediate metabolites of rutin metabolism with genome resequencing data, metabolite genome-wide association analyses (GWAS) eventually identified a glycosyl hydrolase gene FtGH1, which could hydrolyse rutin to quercetin. This function was validated both in Tartary buckwheat overexpression hairy roots and in vitro enzyme activity assays. Mutation of the two key active sites, which were determined by molecular docking and experimentally verified via overexpression in hairy roots and transient expression in tobacco leaves, exhibited abnormal subcellular localization, suggesting functional changes. Sequence analysis revealed that mutation of the FtGH1 promoter in accessions of two haplotypes might be necessary for enzymatic activity. Co-expression analysis and GWAS revealed that FtbHLH165 not only repressed FtGH1 expression, but also increased seed length. This work reveals a potential mechanism behind rutin metabolism, which should provide both theoretical support in the study of flavonoid metabolism and in the molecular breeding of Tartary buckwheat.

Plant Biostimulant as an Environmentally Friendly Alternative to Modern Agriculture

Ensuring the safety of crop production presents a significant challenge to humanity. Pesticides and fertilizers are commonly used to eliminate external interference and provide nutrients, enabling crops to sustain growth and defense. However, the addition of chemical substances does not meet the environmental standards required for agricultural production. Recently, natural sources such as biostimulants have been found to help plants with growth and defense. The development of biostimulants provides new solutions for agricultural product safety and has become a widely utilized tool in agricultural. The review summarizes the classification of biostimulants, including humic-based biostimulant, protein-based biostimulant, oligosaccharide-based biostimulant, metabolites-based biostimulants, inorganic substance, and microbial inoculant. This review attempts to summarize suitable alternative technology that can address the problems and analyze the current state of biostimulants, summarizes the research mechanisms, and anticipates future technological developments and market trends, which provides comprehensive information for researchers to develop biostimulants.

Intercropping of Narrow-Leafed Lupin (Lupinus angustifolius L.) and Barley (Hordeum vulgare L.) Affects the Flavonoid Composition of Both Crops

Barley (Hordeum vulgare L.) is a common cereal crop in agricultural production and is often included in legume-cereal intercropping. Flavonoids, a major class of secondary metabolites found in barley, are involved in plant defense and protection. However, the effect of intercropping on barley flavonoids remains unknown. Herein, an intercropping system involving barley and lupin (Lupinus angustifolius L.) was studied. Intercropping increased the level of luteolin in lupin roots. Lupin-barley intercropping considerably increased genistein, rutin, and apigenin in barley shoots. Genistein and apigenin were also detected in intercropped barley roots and rhizosphere soil. The three flavonoids have been reported as defense compounds, suggesting that lupin triggers a defense response in barley to strengthen its survival ability.

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

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

Phenylpropanoid Derivatives and Their Role in Plants' Health and as antimicrobials

Phenylpropanoids belong to a wide group of compounds commonly secreted by plants and involved in different roles related with plant growth and development and the defense against plant pathogens. Some key intermediates from shikimate pathway are used to synthesize these compounds. In this way, by the phenylpropanoid pathway several building blocks are achieved to obtain flavonoids, isoflavonoids, coumarins, monolignols, phenylpropenes, phenolic acids, stilbenes and stilbenoids, and lignin, suberin and sporopollenin for plant-microbe interactions, structural support and mechanical strength, organ pigmentation, UV protection and acting against pathogens. Some reviews have revised phenylpropanoid biosynthesis and regulation of the biosynthetic pathways. In this review, the most important chemical structures about phenylpropanoid derivatives are summarized grouping them in different sections according to their structure. We have put special attention on their different roles in plants especially in plant health, growth and development and plant-environment interactions. Their interaction with microorganisms is discussed including their role as antimicrobials. We summarize all new findings about new developed structures and their involvement in plants health.

The Fungal, Nutritional, and Metabolomic Diagnostics of the Oil Palm Elaeis guineensis Affected by Bud Rot Disease in Esmeraldas, Ecuador

The oil palm Elaeis guineensis represents one of the most important crops in Ecuador. Considering that bud rot disease is deadly in Ecuador, more attention has been given to identifying possible causes for palm debility from this disease. We studied the involvement of fungi and nutrients in triggering bud rot disease in E. guineensis. Special emphasis was given to the molecules synthesized by the plant to protect against this devastating disease. Techniques like Diagnosis and Recommendation Integrated System (DRIS) and metagenomic analysis were used to understand the possible implications of biotic and abiotic factors in the development of bud rot disease in oil palm in Ecuador. Liquid chromatography-mass spectrometry (LC-MS) analysis was used to identify the phenolic protection barrier of the palm facing the disease. Our results indicate that fungi from Ascomyceta phylum were found in the tested samples. The species directly involved are different in soil compared with plants. The results indicate a deficiency of chemical elements, such as Ca, Mn, Mg, and Fe, which are responsible for palm debility from bud rot disease. More than 30 compounds with protective roles were identified in the leaves of symptomatic plants from the first stage of the infection.

Plant immune inducer ZNC promotes rutin accumulation and enhances resistance to Botrytis cinerea in tomato

Gray mold is a destructive disease caused by Botrytis cinerea, a pervasive plant pathogen, which poses a threat to both tomato growth and postharvest storage. The utilization of induced resistance presents a potential strategy for combating plant pathogenic attacks. ZNC (zhinengcong), an extract derived from the endophytic fungus Paecilomyces variotii, has been discovered to play a vital role in preventing diverse forms of bacterial infections. Nevertheless, the precise mechanism behind its ability to enhance tomato resistance to fungi remains unclear. In this study, we found that the exogenous spraying of ZNC could significantly improve the resistance of tomato plants to B. cinerea. The results of both the metabolomic analysis and high-performance liquid chromatography (HPLC) demonstrated that tomato plants responded to ZNC treatment by accumulating high levels of rutin. Additional transcriptome analysis uncovered that rutin enhances tomato resistance possible by initiating the generation of reactive oxygen species (ROS) and phosphorylation of mitogen-activated protein kinases (MPKs) related genes expression during the initial phase of invasion by B. cinerea. In addition, we also found that rutin might activate plant immunity by eliciting ethylene (ET) and jasmonic acid (JA)-mediated pathways. Therefore, plant immune inducer ZNC and rutin has bright application prospects and high utilization value to control gray mold.

Multiomics analysis reveals the molecular mechanisms underlying virulence in Rhizoctonia and jasmonic acid-mediated resistance in Tartary buckwheat (Fagopyrum tataricum)

Rhizoctonia solani is a devastating soil-borne pathogen that seriously threatens the cultivation of economically important crops. Multiple strains with a very broad host range have been identified, but only 1 (AG1-IA, which causes rice sheath blight disease) has been examined in detail. Here, we analyzed AG4-HGI 3 originally isolated from Tartary buckwheat (Fagopyrum tataricum), but with a host range comparable to AG1-IA. Genome comparison reveals abundant pathogenicity genes in this strain. We used multiomic approaches to improve the efficiency of screening for disease resistance genes. Transcriptomes of the plant-fungi interaction identified differentially expressed genes associated with virulence in Rhizoctonia and resistance in Tartary buckwheat. Integration with jasmonate-mediated transcriptome and metabolome changes revealed a negative regulator of jasmonate signaling, cytochrome P450 (FtCYP94C1), as increasing disease resistance probably via accumulation of resistance-related flavonoids. The integration of resistance data for 320 Tartary buckwheat accessions identified a gene homolog to aspartic proteinase (FtASP), with peak expression following R. solani inoculation. FtASP exhibits no proteinase activity but functions as an antibacterial peptide that slows fungal growth. This work reveals a potential mechanism behind pathogen virulence and host resistance, which should accelerate the molecular breeding of resistant varieties in economically essential crops.

Effects of tomato inoculation with the entomopathogenic fungus Metarhizium brunneum on spider mite resistance and the rhizosphere microbial community

Entomopathogenic fungi have been well exploited as biocontrol agents that can kill insects through direct contact. However, recent research has shown that they can also play an important role as plant endophytes, stimulating plant growth, and indirectly suppressing pest populations. In this study, we examined the indirect, plant-mediated, effects of a strain of entomopathogenic fungus, Metarhizium brunneum on plant growth and population growth of two-spotted spider mites (Tetranychus urticae) in tomato, using different inoculation methods (seed treatment, soil drenching and a combination of both). Furthermore, we investigated changes in tomato leaf metabolites (sugars and phenolics), and rhizosphere microbial communities in response to M. brunneum inoculation and spider mite feeding. A significant reduction in spider mite population growth was observed in response to M. brunneum inoculation. The reduction was strongest when the inoculum was supplied both as seed treatment and soil drench. This combination treatment also yielded the highest shoot and root biomass in both spider mite-infested and non-infested plants, while spider mite infestation increased shoot but reduced root biomass. Fungal treatments did not consistently affect leaf chlorogenic acid and rutin concentrations, but M. brunneum inoculation via a combination of seed treatment and soil drenching reinforced chlorogenic acid (CGA) induction in response to spider mites and under these conditions the strongest spider mite resistance was observed. However, it is unclear whether the M. brunneum-induced increase in CGA contributed to the observed spider mite resistance, as no general association between CGA levels and spider mite resistance was observed. Spider mite infestation resulted in up to two-fold increase in leaf sucrose concentrations and a three to five-fold increase in glucose and fructose concentrations, but these concentrations were not affected by fungal inoculation. Metarhizium, especially when applied as soil drench, impacted the fungal community composition but not the bacterial community composition which was only affected by the presence of spider mites. Our results suggest that in addition to directly killing spider mites, M. brunneum can indirectly suppress spider mite populations on tomato, although the underlying mechanism has not yet been resolved, and can also affect the composition of the soil microbial community.

Quick Decline and Stem Pitting Citrus tristeza virus Isolates Induce a Distinct Metabolomic Profile and Antioxidant Enzyme Activity in the Phloem Sap of Two Citrus Species

Susceptibility to the severe Citrus tristeza virus (CTV), T36, is higher for Citrus macrophylla (CM) than for C. aurantium (CA). How host-virus interactions are reflected in host physiology is largely unknown. In this study, the profile of metabolites and the antioxidant activity in the phloem sap of healthy and infected CA and CM plants were evaluated. The phloem sap of quick decline (T36) and stem pitting (T318A) infected citrus, and control plants was collected by centrifugation, and the enzymes and metabolites analyzed. The activity of the antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), in infected plants increased significantly in CM and decreased in CA, compared to the healthy controls. Using LC-HRMS² a metabolic profile rich in secondary metabolites was assigned to healthy CA, compared to healthy CM. CTV infection of CA caused a drastic reduction in secondary metabolites, but not in CM. In conclusion, CA and CM have a different response to severe CTV isolates and we propose that the low susceptibility of CA to T36 may be related to the interaction of the virus with the host's metabolism, which reduces significantly the synthesis of flavonoids and antioxidant enzyme activity.

Visualizing the distribution of flavonoids in litchi (Litchi chinenis) seeds through matrix-assisted laser desorption/ionization mass spectrometry imaging

Flavonoids are one of the most important bioactive components in litchi (Litchi chinensis Sonn.) seeds and have broad-spectrum antiviral and antitumor activities. Litchi seeds have been shown to inhibit the proliferation of cancer cells and induce apoptosis, particularly effective against breast and liver cancers. Elucidating the distribution of flavonoids is important for understanding their physiological and biochemical functions and facilitating their efficient extraction and utilization. However, the spatial distribution patterns and expression states of flavonoids in litchi seeds remain unclear. Herein, matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) was used for in situ detection and imaging of the distribution of flavonoids in litchi seed tissue sections for the first time. Fifteen flavonoid ion signals, including liquiritigenin, apigenin, naringenin, luteolin, dihydrokaempferol, daidzein, quercetin, taxifolin, kaempferol, isorhamnetin, myricetin, catechin, quercetin 3-β-d-glucoside, baicalin, and rutin, were successfully detected and imaged in situ through MALDI-MSI in the positive ion mode using 2-mercaptobenzothiazole as a matrix. The results clearly showed the heterogeneous distribution of flavonoids, indicating the potential of litchi seeds for flavonoid compound extraction. MALDI-MS-based multi-imaging enhanced the visualization of spatial distribution and expression states of flavonoids. Thus, apart from improving our understanding of the spatial distribution of flavonoids in litchi seeds, our findings also facilitate the development of MALDI-MSI-based metabolomics as a novel effective molecular imaging tool for evaluating the spatial distribution of endogenous compounds.

Ziziphus spina-christi extract-stabilized novel silver nanoparticle synthesis for combating Fusarium oxysporum-causing pepper wilt disease: in vitro and in vivo studies

The novelty of the present study is studying the ability of aqueous Ziziphus spina-christi leaves' extract (ZSCE) to produce eco-friendly and cost-effective silver nanoparticles (Ag NPs) against Fusarium wilt disease. Phytochemical screening of ZSCE by HPLC showed that they contain important antimicrobial substances such as Rutin, Naringin, Myricetin, Quercetin, Kaempferol, Hesperidin, Syringeic, Eugenol, Pyrogallol, Gallic and Ferulic. Characterization methods reveal a stable Ag NPs with a crystalline structure, spherical in shape with average particle size about 11.25 nm. ZSCE and Ag NPs showed antifungal potential against F. oxysporum at different concentrations with MIC of Ag NPs as 0.125 mM. Ag NPs treatment was the most effective, as it gave the least disease severity (20.8%) and the highest protection rate (75%). The application of ZSCE or Ag NPs showed a clear recovery, and its effectiveness was not limited for improving growth and metabolic characteristics only, but also inducing substances responsible for defense against pathogens and activating plant immunity (such as increasing phenols and strong expression of peroxidase and polyphenol oxidase as well as isozymes). Owing to beneficial properties such as antifungal activity, and the eco-friendly approach of cost and safety, they can be applied in agricultural field as novel therapeutic nutrients.

Biocontrol of Plant Diseases Using Glycyrrhiza glabra Leaf Extract

The growing concern regarding the potential risks of pesticides and their impact on nontarget organisms stimulates the development and application of alternative, environmentally friendly products. It seems necessary to develop alternatives for conventional products and for those already widely used in organic agriculture, e.g., copper. Very importantly, such alternative products should not limit the productivity and profitability of agriculture. In this study, we examined the efficacy of licorice (Glycyrrhiza glabra) leaf extract as such an alternative. We tested its impact on the virulence of Pseudomonas syringae toward the model plant Arabidopsis thaliana and the crop plant tomato (Solanum lycopersicum) as well as of Clavibacter michiganensis, Xanthomonas campestris, and Phytophthora infestans toward tomato, at multiple levels. We demonstrate that licorice leaf extract acts as a direct fungicide and bactericide. Moreover, it acts against a metalaxyl-resistant P. infestans strain. In addition, the extract from licorice leaves influences the plant immune system, modulating the plant responses to the challenge with pathogen(s); this involves both salicylic acid and ethylene-based responses. Our results show that in addition to the well-known use of licorice root extract in medicine, the leaf extract can be an effective alternative in organic and integrated farming, contributing to copper reduction and resistance management.[Formula: see text] Copyright © 2022 The Author(s). This is an open-access article distributed under the CC BY 4.0 International license.

Naringenin confers defence against Phytophthora nicotianae through antimicrobial activity and induction of pathogen resistance in tobacco

Tobacco black shank caused by Phytophthora nicotianae is a serious disease in tobacco cultivation. We found that naringenin is a key factor that causes different sensitivity to P. nicotianae between resistant and susceptible tobacco. The level of basal flavonoids in resistant tobacco was distinct from that in susceptible tobacco. Of all flavonoids with different content, naringenin showed the best antimicrobial activity against mycelial growth and sporangia production of P. nicotianae in vitro. However, naringenin showed very low or no antimicrobial activity to other plant pathogens. We found that naringenin induced not only the accumulation of reactive oxygen species, but also the expression of salicylic acid biosynthesis-related genes. Naringenin induced the expression of the basal pathogen resistance gene PR1 and the SAR8.2 gene that contributes to plant resistance to P. nicotianae. We then interfered with the expression of the chalcone synthase (NtCHS) gene, the key gene of the naringenin synthesis pathway, to inhibit naringenin biosynthesis. NtCHS-RNAi rendered tobacco highly sensitive to P. nicotianae, but there was no change in susceptibility to another plant pathogen, Ralstonia solanacearum. Finally, exogenous application of naringenin on susceptible tobacco enhanced resistance to P. nicotianae and naringenin was very stable in this environment. Our findings revealed that naringenin plays a core role in the defence against P. nicotianae and expanded the possibilities for the application of plant secondary metabolites in the control of P. nicotianae.

Role of Phenylpropanoids and Flavonoids in Plant Resistance to Pests and Diseases

Phenylpropanoids and flavonoids are specialized metabolites frequently reported as involved in plant defense to biotic or abiotic stresses. Their biosynthetic accumulation may be constitutive and/or induced in response to external stimuli. They may participate in plant signaling driving plant defense responses, act as a physical or chemical barrier to prevent invasion, or as a direct toxic weapon against microbial or insect targets. Their protective action is described as the combinatory effect of their localization during the host's interaction with aggressors, their sustained availability, and the predominance of specific compounds or synergy with others. Their biosynthesis and regulation are partly deciphered; however, a lot of gaps in knowledge remain to be filled. Their mode of action on microorganisms and insects probably arises from an interference with important cellular machineries and structures, yet this is not fully understood for all type of pests and pathogens. We present here an overview of advances in the state of the art for both phenylpropanoids and flavonoids with the objective of paving the way for plant breeders looking for natural sources of resistance to improve plant varieties. Examples are provided for all types of microorganisms and insects that are targeted in crop protection. For this purpose, fields of phytopathology, phytochemistry, and human health were explored.

Impact of Foliar Application of Amino Acids on Essential Oil Content, Odor Profile, and Flavonoid Content of Different Mint Varieties in Field Conditions

Mint is an industrial plant that is a good source of essential oil and many phenolic compounds that have several positive benefits to human health and can be used to prevent the development of many diseases. The aim of this research was to investigate the possibility of increasing essential oil and flavonoid content, changing the chemical composition of these compounds in different mint cultivars under foliar application with precursors (phenylalanine, tryptophan, and tyrosine) at two concentrations, 100 and 200 mg L^-1, to enable the possibilities for wider use of these plants when they are grown in field conditions. Spraying with phenylalanine at 100 mg L^-1 concentration increased essential oil content in Mentha piperita 'Granada' plants by 0.53 percentage units. Foliar application with tyrosine solutions at 100 mg L^-1 concentration most effectively influenced the essential oil odor profile Mentha spicata 'Crispa'. The highest number of total flavonoids was in Mentha piperita 'Swiss' sprayed with tyrosine at 100 mg L^-1 concentration. The flavonoid content depended on the mint cultivar, amino acids, and their concentration. The results showed that the effect of amino acid solutions on different secondary metabolites' quantitative and qualitative composition differed depending on the mint cultivar; therefore, amino acids and their concentrations must be selected based on the cultivar they are targeting.

Rutin Stimulates the Green Alga Chromochloris zofingiensis for Improved Biomass and Astaxanthin Production

Chromochloris zofingiensis represents a potential algal producer of the value-added ketocarotenoid astaxanthin. Here, rutin, a low-cost flavonoid compound, was evaluated regarding its roles in C. zofingiensis production under astaxanthin-inducing conditions via physiological, biochemical, and transcriptomics analyses. The rutin treatment allowed C. zofingiensis to achieve 81.2% more biomass and 20.5% greater astaxanthin content under nitrogen deprivation, leading to more than doubled astaxanthin production. The rutin-treated C. zofingiensis had higher levels of chlorophylls, proteins, and lipids and lower carbohydrate level than the control. Rutin promoted the intracellular abscisic acid (ABA) level, which could be restored by the ABA biosynthesis inhibitor, accompanied by the restoration of biomass concentration and astaxanthin content. The application of exogenous ABA to C. zofingiensis also furthered biomass concentration and astaxanthin accumulation. Together with the comparative transcriptomics analysis, our study provides implications into the involvement of ABA in rutin-mediated stimulation of C. zofingiensis growth and astaxanthin accumulation and highlights a feasible strategy of combining stress and chemical induction for improved microalgal production.

A Novel Guanine Elicitor Stimulates Immunity in Arabidopsis and Rice by Ethylene and Jasmonic Acid Signaling Pathways

Rice sheath blight (ShB) caused by Rhizoctonia solani is one of the most destructive diseases in rice. Fungicides are widely used to control ShB in agriculture. However, decades of excessive traditional fungicide use have led to environmental pollution and increased pathogen resistance. Generally, plant elicitors are regarded as environmentally friendly biological pesticides that enhance plant disease resistance by triggering plant immunity. Previously, we identified that the plant immune inducer ZhiNengCong (ZNC), a crude extract of the endophyte, has high activity and a strong ability to protect plants against pathogens. Here, we further found that guanine, which had a significant effect on inducing plant resistance to pathogens, might be an active component of ZNC. In our study, guanine activated bursts of reactive oxygen species, callose deposition and mitogen-activated protein kinase phosphorylation. Moreover, guanine-induced plant resistance to pathogens depends on ethylene and jasmonic acid but is independent of the salicylic acid signaling pathway. Most importantly, guanine functions as a new plant elicitor with broad-spectrum resistance to activate plant immunity, providing an efficient and environmentally friendly biological elicitor for bacterial and fungal disease biocontrol.

Contrasting effects of soil microbial interactions on growth-defence relationships between early- and mid-successional plant communities

Plants allocate resources to processes related to growth and enemy defence. Simultaneously, they interact with complex soil microbiomes that also affect plant performance. While the influence of individual microbial groups on single plants is increasingly studied, effects of microbial interactions on growth, defence and growth-defence relationships remain unknown, especially at the plant community level. We investigated how three microbial groups (bacteria, fungi, protists), alone and in full-factorial combinations, affect plant performance and potential growth-defence relationships by measuring phenolics composition in early- and mid-successional grass and forb communities in a glasshouse experiment. Microbial groups did not affect plant growth and only fungi increased defence compounds in early- and mid-successional forbs, while grasses were not affected. Shoot biomass-defence relationships were negatively correlated in most microbial treatments in early-successional forbs, but positively in several microbial treatments in mid-successional forbs. The growth-defence relationship was generally negative in early-successional but not in mid-successional grasses. The presence of different microbiomes commonly removed the observed growth-defence relationships. We conclude that soil microorganisms and their interactions can shift growth-defence relationships differentially for plant functional groups and the relationships vary between successional stages. Microbial interaction-induced growth-defence shifts might therefore underlie distinct plant strategies and fitness.

Different Fruit-Specific Promoters Drive AtMYB12 Expression to Improve Phenylpropanoid Accumulation in Tomato

Tomato is an economically crucial vegetable/fruit crop globally. Tomato is rich in nutrition and plays an essential role in a healthy human diet. Phenylpropanoid, a critical compound in tomatoes, reduces common degenerative and chronic diseases risk caused by oxidative stress. As an MYB transcription factor, ATMYB12 can increase phenylpropanoid content by activating phenylpropanoid synthesis related genes, such as PAL, C4H, 4CL, CHS. However, the heterologous expression of AtMYB12 in tomatoes can be altered through transgenic technologies, such as unstable expression vectors and promoters with different efficiency. In the current study, the efficiency of other fruit-specific promoters, namely E8S, 2A12, E4, and PG, were compared and screened, and we determined that the expression efficiency of AtMYB12 was driven by the E8S promoter was the highest. As a result, the expression of phenylpropanoid synthesis related genes was regulated by AtMYB12, and the phenylpropanoid accumulation in transgenic tomato fruits increased 16 times. Additionally, the total antioxidant capacity of fruits was measured through Trolox equivalent antioxidant capacity (TEAC) assay, which was increased by 2.4 times in E8S transgenic lines. TEAC was positively correlated with phenylpropanoid content. Since phenylpropanoid plays a crucial role in the human diet, expressing AtMYB12 with stable and effective fruit-specific promoter E8S could improve tomato’s phenylpropanoid and nutrition content and quality. Our results can provide genetic resources for the subsequent improvement of tomato varieties and quality, which is significant for human health.

Integrated Transcriptome and Metabolome Analysis Revealed That Flavonoid Biosynthesis May Dominate the Resistance of Zanthoxylum bungeanum against Stem Canker

Stem canker of Zanthoxylum bungeanum is a devastating disease that seriously affects the plantation and industrial development of Z. bungeanum due to a lack of effective control measures. The objective of this study was to screen out resistant Z. bungeanum varieties and further explore their resistance mechanisms against stem canker. Results showed that the most resistant and susceptible varieties were, respectively, Doujiao (DJ) and Fengxian Dahongpao (FD). Combining transcriptomic and metabolomic analyses, we found that the genes and metabolites associated with the phenylpropanoid metabolism, especially flavonoid biosynthesis, were highly significantly enriched in DJ following pathogen infection compared with that in FD, which indicated that the flavonoid metabolism may positively dominate the resistance of Z. bungeanum. This finding was further confirmed by quantitative real-time polymerase chain reaction analysis, through which higher expression levels of core genes involved in flavonoid metabolism in resistant variety were observed. Moreover, by analyzing the differences in the flavonoid content in the stems of resistant and susceptible varieties and the antifungal activities of flavonoids extracted from Z. bungeanum stems, the conclusion that flavonoid metabolism positively regulates the resistance of Z. bungeanum was further supported. Our results not only aid in better understanding the resistance mechanisms of Z. bungeanum against stem canker but also promote the breeding and utilization of resistant varieties.

Naringenin Induces Pathogen Resistance Against Pseudomonas syringae Through the Activation of NPR1 in Arabidopsis

Flavonoids are well known for the coloration of plant organs to protect UV and ROS and to attract pollinators as well. Flavonoids also play roles in many aspects of physiological processes including pathogen resistance. However, the molecular mechanism to explain how flavonoids play roles in pathogen resistance was not extensively studied. In this study, we investigated how naringenin, the first intermediate molecule of the flavonoid biosynthesis, functions as an activator of pathogen resistances. The transcript levels of two pathogenesis-related (PR) genes were increased by the treatment with naringenin in Arabidopsis. Interestingly, we found that naringenin triggers the monomerization and nuclear translocation of non-expressor of pathogenesis-related genes 1 (NPR1) that is a transcriptional coactivator of PR gene expression. Naringenin can induce the accumulation of salicylic acid (SA) that is required for the monomerization of NPR1. Furthermore, naringenin activates MPK6 and MPK3 in ROS-dependent, but SA-independent manners. By using a MEK inhibitor, we showed that the activation of a MAPK cascade by naringenin is also required for the monomerization of NPR1. These results suggest that the pathogen resistance by naringenin is mediated by the MAPK- and SA-dependent activation of NPR1 in Arabidopsis.

Transcriptome profiling reveals response genes for downy mildew resistance in cucumber

We discovered a potential defense pathway of cucumber to downy mildew. The signaling that activates the pathways of ROS and lignin accumulation may play an important role in the defense response. Many resistance genes were identified by transcriptome analysis. Downy mildew (DM), caused by Pseudoperonospora cubensis, is one of the most destructive diseases and causes severe yield losses of cucumber. However, the genes and pathways involved in regulating DM resistance were still poorly understood. In our study, we observed that the highly sensitive inbred line 53 (IL53) exhibited more severe disease symptoms than the highly resistant inbred line 51 (IL51) under P. cubensis infection. Furthermore, lignin, limiting the germination and extension of P. cubensis, and H₂O₂, as a signaling molecule during the resistant process, were both shown to increase, indicating that the signaling that activates these pathways might be responsible for the resistance divergence between IL51 and IL53. Transcriptome analysis, using the resistant and susceptible pools in F₂ populations with IL51 and IL53 as parents, showed that a series of differentially expressed genes was involved in multiple functions of defense response: pathogen-associated molecular pattern recognition, signal transduction, reactive oxygen species and lignin accumulation, and transcription regulators. Combining physiological data with transcriptomes, we predicted a potential molecular mechanism of cucumber resistance to DM. Our research provided a foundation for further studies on the mechanism of cucumber resistance to DM.

Strategies to Manage Rice Sheath Blight: Lessons from Interactions between Rice and Rhizoctonia solani

Rhizoctonia solani is an important phytopathogenic fungus with a wide host range and worldwide distribution. The anastomosis group AG1 IA of R. solani has been identified as the predominant causal agent of rice sheath blight, one of the most devastating diseases of crop plants. As a necrotrophic pathogen, R. solani exhibits many characteristics different from biotrophic and hemi-biotrophic pathogens during co-evolutionary interaction with host plants. Various types of secondary metabolites, carbohydrate-active enzymes, secreted proteins and effectors have been revealed to be essential pathogenicity factors in R. solani. Meanwhile, reactive oxygen species, phytohormone signaling, transcription factors and many other defense-associated genes have been identified to contribute to sheath blight resistance in rice. Here, we summarize the recent advances in studies on molecular interactions between rice and R. solani. Based on knowledge of rice-R. solani interactions and sheath blight resistance QTLs, multiple effective strategies have been developed to generate rice cultivars with enhanced sheath blight resistance.

Digital gene expression analysis of the response to Ralstonia solanacearum between resistant and susceptible tobacco varieties

Tobacco bacterial wilt (TBW) caused by Ralstonia solanacearum is the most serious soil-borne disease of tobacco. However, molecular mechanism information of R. solanacearum resistance is limited to tobacco, hindering better breeding of resistant tobacco. In this study, the expression profiles of the rootstalks of Yunyan87 (susceptible cultivar) and Fandi3 (resistant cultivar) at different stages after R. solanacearum infection were compared to explore molecular mechanisms of tobacco resistance against the bacterium. Findings from gene-expression profiling indicated that the number of upregulated differentially expressed genes (DEGs) at 3 and 7 days post-inoculation (dpi) increased significantly in the resistant cultivar. WRKY6 and WRKY11 family genes in WRKY transcription factors, ERF5 and ERF15 family genes in ERFs transcription factors, and genes encoding PR5 were significantly upregulated in the resistant cultivar response to the infection. For the first time, WRKY11 and ERF15 were found to be possibly involved in disease-resistance. The Kyoto Encyclopedia of Genes and Genomes analysis demonstrated glutathione metabolism and phenylpropane pathways as primary resistance pathways to R. solanacearum infection. In the resistant cultivar, DEGs encoding CYP450, TCM, CCoAOMT, 4CL, PAL, CCR, CSE, and CADH, involved in the synthesis of plant antitoxins such as flavonoids, stilbenoids, and lignins, enriched in the phenylpropane pathway were upregulated at 3 and 7 dpi. Furthermore, a pot experiment was performed to verify the role of flavonoids in controlling TBW. This study will strongly contribute to a better understanding of molecular interactions between tobacco plants and R. solanacearum.

Plant Endophytic Fungus Extract ZNC Improved Potato Immunity, Yield, and Quality

Endophytic fungi play an important role in plant survival and reproduction, but the role of their metabolites in plant growth and immunity, as well as in crop quality formation, is poorly understood. Zhinengcong (ZNC) is a crude ethanol extract from the endophytic fungus Paecilomyces variotii, and previous studies have shown that it can improve the growth and immunity in Arabidopsis thaliana. The aim of the study was to reveal the trade-off balance between plant growth and immunity by evaluating the mechanisms of ZNC on potato growth, yield, and priming immunity against the oomycete Phytophthora infestans indoors and in the field. ZNC maintained a good balance between plant growth and resistance against P. infestans with high activity. It induced the reactive oxygen species (ROS) production, promoted plant growth, yield and quality parameters, enhanced the expression of indoleacetic acid (IAA) related genes, and increased the absorption of nitrogen from the soil. Moreover, the plant endophytic fungus extract ZNC stimulated the pathogen-associated molecular pattern (PAMP) triggered immunity (PTI) pathway and contributed to the ZNC-mediated defense response. Two years of field trials have shown that irrigation with ZNC at one of two optimal concentrations of 1 or 10ng/ml could significantly increase the output by 18.83% or more. The quality of potato tubers was also greatly improved, in which the contents of vitamin C, protein, and starch were significantly increased, especially the sugar content was increased by 125%. Spray application of ZNC onto potato plants significantly reduced the occurrence of potato blight disease with 66.49% of control efficacy at 200ng/ml and increased the potato yield by 66.68% or more in the field. In summary, plant endophytic fungus extract ZNC promoted potato immunity, yield, and quality and presented excellent potential in agricultural applications.

OsHsfB4d Binds the Promoter and Regulates the Expression of OsHsp18.0-CI to Resistant Against Xanthomonas Oryzae

BACKGROUND

Bacterial leaf streak (BLS) and bacterial blight (BB) are two major prevalent and devastating rice bacterial diseases caused by the Gram-negative bacteria of Xanthomonas oryzae pv. oryzicola (Xoc) and Xanthomonas oryzae pv. oryzae (Xoo), respectively. Previously, we identified a defence-related (DR) gene encoding a small heat shock protein, OsHsp18.0-CI, that positively regulates BLS and BB resistance in rice.

RESULTS

To reveal the regulatory mechanism of the OsHsp18.0-CI response to Xoc and Xoo, we characterized the class B heat shock factor (Hsf), OsHsfB4d, through transcriptional analysis and a transgenic study. OsHsfB4d is upregulated post inoculation by either the Xoc strain RS105 or Xoo strain PXO99a in Zhonghua 11 (wild type, ZH11) as well as in OsHsp18.0-CI overexpressing rice plants. Transient expression of OsHsfB4d can activate the expression of green fluorescent protein (GFP) and luciferase (Luc) via the OsHsp18.0-CI promoter. Rice plants overexpressing OsHsfB4d exhibited enhanced resistance to RS105 and PXO99a as well as increased expression of OsHsp18.0-CI and pathogenesis-related genes. Furthermore, we found that OsHsfB4d directly binds to a DNA fragment carrying the only perfect heat shock element (HSE) in the promoter of OsHsp18.0-CI.

CONCLUSION

Overall, we reveal that OsHsfB4d, a class B Hsf, acts as a positive regulator of OsHsp18.0-CI to mediate BLS and BB resistance in rice.

UV-B Induced Flavonoids Contribute to Reduced Biotrophic Disease Susceptibility in Lettuce Seedlings

Biotrophic disease is one of the largest causes of decreased yield in agriculture. While exposure to ultraviolet B (UV-B) light (280-320 nm) has been previously observed to reduce plant susceptibility to disease, there is still a paucity of information regarding underlying biological mechanisms. In addition, recent advances in UV-LED technology raise the prospect of UV light treatments in agriculture which are practical and efficient. Here, we characterized the capability of UV-B LED pre-treatments to reduce susceptibility of a range of lettuce (Lactuca sativa) cultivars to downy mildew disease caused by the obligate biotroph Bremia lactucae. Innate cultivar susceptibility level did not seem to influence the benefit of a UV-B induced disease reduction with similar reductions as a percentage of the control observed (54-62% decrease in conidia count) across all susceptible cultivars. UV-B-induced reductions to conidia counts were sufficient to significantly reduce the infectivity of the diseased plant. Secondary infections caused by UV-B pre-treated plants exhibited yet further (67%) reduced disease severity. UV-B-induced flavonoids may in part mediate this reduced disease severity phenotype, as B. lactucae conidia counts of lettuce plants negatively correlated with flavonoid levels in a UV-B-dependent manner (r = -0.81). Liquid chromatography-mass spectrometry (LC-MS) was used to identify metabolic features which contribute to this correlation and, of these, quercetin 3-O-(6"-O-malonyl)-b-D-glucoside had the strongest negative correlation with B. lactucae conidia count (r = -0.68). When quercetin 3-O-(6"-O-malonyl)-b-D-glucoside was directly infiltrated into lettuce leaves, with those leaves subsequently infected, the B. lactucae conidia count was reduced (25-39%) in two susceptible lettuce cultivars. We conclude that UV-B induced phenolics, in particular quercetin flavonoids, may act as phytoanticipins to limit the establishment of biotrophic pathogens thus delaying or reducing their sporulation as measured by conidia count. These findings highlight the opportunity for UV-B morphogenesis to be exploited through the application of UV-LED technology, as part of the development of next-generation, sustainable disease control tools.

Transcriptomic Insights into Innate Immunity Responding to Red Rot Disease in Red Alga Pyropia yezoensis

Pyropia yezoensis, one of the most economically important marine algae, suffers from the biotic stress of the oomycete necrotrophic pathogen Pythium porphyrae. However, little is known about the molecular defensive mechanisms employed by Pyr. yezoensis during the infection process. In the present study, we defined three stages of red rot disease based on histopathological features and photosynthetic physiology. Transcriptomic analysis was carried out at different stages of infection to identify the genes related to the innate immune system in Pyr. yezoensis. In total, 2139 up-regulated genes and 1672 down-regulated genes were identified from all the infected groups. Pathogen receptor genes, including three lectin genes (pattern recognition receptors (PRRs)) and five genes encoding typical plant R protein domains (leucine rich repeat (LRR), nucleotide binding site (NBS), or Toll/interleukin-1 receptor (TIR)), were found to be up-regulated after infection. Several defense mechanisms that were typically regarded as PAMP-triggered immunity (PTI) in plants were induced during the infection. These included defensive and protective enzymes, heat shock proteins, secondary metabolites, cellulase, and protease inhibitors. As a part of the effector-triggered immunity (ETI), the expression of genes related to the ubiquitin-proteasome system (UPS) and hypersensitive cell death response (HR) increased significantly during the infection. The current study suggests that, similar to plants, Pyr. yezoensis possesses a conserved innate immune system that counters the invasion of necrotrophic pathogen Pyt. porphyrae. However, the innate immunity genes of Pyr. yezoensis appear to be more ancient in origin compared to those in higher plants.

More Than the Sum of Its Parts: Microbiome Biodiversity as a Driver of Plant Growth and Soil Health

Microorganisms drive several processes needed for robust plant growth and health. Harnessing microbial functions is thus key to productive and sustainable food production. Molecular methods have led to a greater understanding of the soil microbiome composition. However, translating species or gene composition into microbiome functionality remains a challenge. Community ecology concepts such as the biodiversity–ecosystem functioning framework may help predict the assembly and function of plant-associated soil microbiomes. Higher diversity can increase the number and resilience of plant-beneficial functions that can be coexpressed and unlock the expression of plant-beneficial traits that are hard to obtain from any species in isolation. We combine well-established community ecology concepts with molecular microbiology into a workable framework that may enable us to predict and enhance soil microbiome functionality to promote robust plant growth in a global change context.

Identification of the phytosulfokine receptor 1 (OsPSKR1) confers resistance to bacterial leaf streak in rice

A rice allele of PSKR1 functioning in resistance to bacterial leaf streak was identified. Phytosulfokine (PSK), a disulfated pentapeptide encoded by precursor genes that are ubiquitously present in higher plants, belongs to the group of plant peptide growth factors. The PSK receptor PSKR1 in Arabidopsis thaliana is an active kinase and has guanylate cyclase activity resulting in dual-signaling outputs. Here, the LOC_Os02g41890 out of three candidates completely rescued root growth and susceptible to Pseudomonas syringae pv. DC3000 in the Arabidopsis pskr1-3 mutant and was identified as OsPSKR1. This protein was localized to plasma membrane similar to AtPSKR1. The expression of OsPSKR1 was upregulated upon inoculation with RS105, a strain of Xanthomonas oryzae pv. oryzicola (Xoc) that cause bacterial leaf streak in rice. OsPSKR1 overexpression (OE) lines had greater resistance to RS105 than the wild type. Consistently, the expression of pathogenesis-related genes involved in the salicylic acid (SA) pathway was upregulated in the transgenic lines. Overall, OsPSKR1 functions as a candidate PSK receptor and regulates resistance to Xoc by activating the expression of pathogenesis-related genes involved in the SA pathway in rice.

Rice sulfoquinovosyltransferase SQD2.1 mediates flavonoid glycosylation and enhances tolerance to osmotic stress

Sulfoquinovosyltransferase 2 (SQD2) catalyses the final step in the sulfoquinovosyldiacylglycerol (SQDG) biosynthetic pathway. It is involved in the phosphate starvation response. Here, we show that rice SQD2.1 has dual activities catalysing SQDG synthesis and flavonoid glycosylation. SQD2.1 null mutants (sqd2.1) in rice had decreased levels of glycosidic flavonoids, particularly apigenin 7-O-glucoside (A7G), whereas these metabolites were increased in rice plants overexpressing SQD2.1. The sqd2.1 mutants and SQD2.1 overexpressing lines showed reduced and enhanced, respectively, tolerance to salinity and drought. Treating the sqd2.1 mutants with A7G decreased oxidative damage and restored stress tolerance to the wild-type levels. These findings demonstrate that SQD2.1 has a novel function in the glycosylation of flavonoids that is required for osmotic stress tolerance in rice. The novel activity of SQD2.1 in the production of glycosidic flavonoids improves scavenging of reactive oxygen species and protects against excessive oxidation.

Accumulation of amino acids and flavonoids in hairy root cultures of common buckwheat (Fagopyrum esculentum)

Transformed hairy root culture in common buckwheat (Fagopyrum esculentum Moench Rubra cultivar) was investigated for accumulation of amino acids and specific flavonoids. Leaves and stems of F. esculentum were used a starting material for induction of hairy roots via the Agrobacterium rhizogenes A4 strain. The transformed lines were confirmed by PCR detection of rol B gene, and their capability to continuously form hairy roots. Three lines from each explant types depending upon growth kinetics were observed. The hairy root lines were used to measure the contents of 17 amino acids and 3 flavonoids. Overall, the hairy root lines exhibited elevated accumulation of semi-essential amino acids such as lysine, isoleucine, valine, histidine and phenylalanine. Content of proline was increased 3-5 times, likely due to the biotic stress reaction induced with A. rhizogenes. Determination of flavonoids by high-performance liquid chromatography, hesperidine and kaempferol-3-rutinoside, were accumulated in hairy root cultures and didn't detected in non-transformed root. The increase in flavonoids positively correlated with the antioxidant capacity of the hairy root cultures.

Comparative metabolomics analysis of different resistant rice varieties in response to the brown planthopper Nilaparvata lugens Hemiptera: Delphacidae

INTRODUCTION

The brown planthopper (BPH, Nilaparvata lugens Stål, Hemiptera: Delphacidae) is one of the most devastating insect pests of the crucially important cereal crop, rice (Oryza sativa L.). Currently, multiple BPH-resistant rice varieties have been cultivated and generalized to control BPH. However, the defence metabolic responses and their modes of action against BPH in different rice cultivars remain uncharacterized.

OBJECTIVE

We used a non-biased metabolomics approach to explore the differences in metabolite profiles in response to BPH infestation in the susceptible TN1 rice cultivar and two resistant cultivars (IR36 and IR56).

METHODS

The metabolomic detection based on gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) was performed to investigate the content changes of identified metabolites in TN1, IR36 and IR56 rice varieties at various time points (0 h, 24 h, 48 h and 96 h) post BPH feeding. The differentially expressed metabolites were screened and the corresponding metabolic pathways were further enriched.

RESULTS

The results showed that compared to that in TN1, the content changes of most primary metabolites were more stable, but the concentration alterations of some defence-related metabolites were more acute and persistent in IR36 and IR56. Furthermore, the differentially expressed pathways analysis revealed that cyanoamino acids and lipids metabolism was persistently induced in IR36, but changes in thiamine, taurine and hypotaurine metabolism were more significant in IR56 during BPH infestation. Besides, the contents of quercetin and spermidine which were harmful to BPH fitness, were significantly elevated by BPH in TN1 and IR36, and the quercetin level was significantly decreased during BPH feeding in IR56.

CONCLUSION

The results of the differences in metabolite profiles in response to BPH infestation in different rice cultivars were useful to clarify the metabolic mechanism of rice plants during BPH infestation and to provide new resources to control this insect pest.

Suppression of UV-B stress induced flavonoids by biotic stress: Is there reciprocal crosstalk?

Plants respond to abiotic UV-B stress with enhanced expression of genes for flavonoid production, especially the key-enzyme chalcone synthase (CHS). Some flavonoids are antioxidative, antimicrobial and/or UV-B protective secondary metabolites. However, when plants are challenged with concomitant biotic stress (simulated e.g. by the bacterial peptide flg22, which induces MAMP triggered immunity, MTI), the production of flavonoids is strongly suppressed in both Arabidopsis thaliana cell cultures and plants. On the other hand, flg22 induces the production of defense related compounds, such as the phytoalexin scopoletin, as well as lignin, a structural barrier thought to restrict pathogen spread within the host tissue. Since all these metabolites require the precursor phenylalanine for their production, suppression of the flavonoid production appears to allow the plant to focus its secondary metabolism on the production of pathogen defense related compounds during MTI. Interestingly, several flavonoids have been reported to display anti-microbial activities. For example, the plant flavonoid phloretin targets the Pseudomonas syringae virulence factors flagella and type 3 secretion system. That is, suppression of flavonoid synthesis during MTI might have also negative side-effects on the pathogen defense. To clarify this issue, we deployed an Arabidopsis flavonoid mutant and obtained genetic evidence that flavonoids indeed contribute to ward off the virulent bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000. Finally, we show that UV-B attenuates expression of the flg22 receptor FLS2, indicating that there is negative and reciprocal interaction between this abiotic stress and the plant-pathogen defense responses.

Identification of a Novel Semi-Dominant Spotted-Leaf Mutant with Enhanced Resistance to Xanthomonas oryzae pv. oryzae in Rice

Many spotted-leaf mutants show enhanced disease resistance to multiple pathogen attacks; however, the mechanisms are largely unknown. Here, we reported a novel semi-dominant spotted-leaf mutant 24 (spl24) obtained from an ethyl methane sulfonate (EMS)-induced IR64 mutant bank. spl24 developed tiny brown lesions on the leaf tip and spread down gradually to the leaf base as well as the sheath at the early heading stage. The performances of major agronomic traits such as the plant height, panicle length, number of panicles/plant, and 1000-grain weight were significantly altered in spl24 when compared to the wild-type IR64. Furthermore, spl24 exhibited a premature senescing phenotype with degeneration of nuclear acids, significantly reduced soluble protein content, increased level of malonaldehyde (MDA), and lowered activities of reactive oxygen species (ROS) scavenging enzymes. Disease evaluation indicated that spl24 showed enhanced resistance to multiple races of Xanthomonas oryzae pv. oryzae, the causal pathogen of bacterial leaf blight in rice, with elevated expression of pathogenesis-related genes, salicylic acid (SA) signaling pathway-associated genes revealed by real-time quantitative PCR and high-throughput RNA sequencing analysis. Genetic analysis and gene mapping indicated that the lesion mimic phenotype was controlled by a novel semi-dominant nuclear gene. The mutation, tentatively termed as OsSPL24, was in a 110 kb region flanked by markers Indel-33 and Indel-12 in chromosome 11. Together, our data suggest that spl24 is a novel lesion mimic mutant with enhanced innate immunity and would facilitate the isolation and functional characterization of the target gene.

Degradation of chlorophyll and synthesis of flavonols during autumn senescence-the story told by individual leaves

Autumn senescence of deciduous trees is characterized by chlorophyll degradation and flavonoid synthesis. In the present study, chlorophyll and flavonol contents were measured every morning and evening during the whole autumn with a non-destructive method from individual leaves of Sorbus aucuparia, Acer platanoides, Betula pendula and Prunus padus. In most of the studied trees, the chlorophyll content of each individual leaf remained constant until a phase of rapid degradation commenced. The fast phase lasted only ~1 week and ended with abscission. In S. aucuparia, contrary to the other species, the chlorophyll content of leaflets slowly but steadily decreased during the whole autumn, but rapid chlorophyll degradation commenced only prior to leaflet abscission also in this species. An increase in flavonols commonly accompanied the rapid degradation of chlorophyll. The results may suggest that each individual tree leaf retains its photosynthetic activity, reflected by a high chlorophyll content, until a rapid phase of chlorophyll degradation and flavonoid synthesis begins. Therefore, in studies of autumn senescence, leaves whose chlorophyll content is decreasing and leaves with summertime chlorophyll content (i.e. the leaves that have not yet started to degrade chlorophyll) should be treated separately.

Characterization of p-Coumaric acid-induced soluble and cell wall-bound phenolic metabolites in relation to disease resistance to Xanthomonas campestris pv. campestris in Chinese cabbage

To characterize the p-coumaric acid (pCA)-induced phenolic metabolites in relation to the disease resistance against Xanthomonas campestris pv. campestris (Xcc.), the responses of soluble- and cell wall-bound flavonoid and hydroxycinnamic acids compounds to the pretreatment of pCA or the inhibitor of the 4-coumarate-CoA ligase, 3,4-(methylenedioxy) cinnamic acid (MDCA), following Xcc inoculation were assessed, and the resulting data were interpreted with regard to susceptibility to Xcc in Chinese cabbage (Brassica rapa var. pekinensis). At 12 days post-inoculation (DPI) with Xcc, disease symptom development could be distinguished by necrotic lesions, and characterized by an enhanced lipid peroxidation. Overall, pCA acts as a positive stimulus for an accumulation of hydroxycinnamic acids and flavonoids, while MDCA acts as a negative regulator. Pretreatment with pCA resulted in an accumulation of specific hydroxycinnamic acids, pCA, ferulic acid (FA), and sinapic acid (SiA) in both soluble and cell wall-bound forms in Xcc-inoculated leaves, while MDCA pretreatment decreased accumulation in a dose-dependent manner. Two flavonoid compounds, epigallocatechin (EGC) and epigallocatechin gallate (EGCG), showed a similar response to pCA and MDCA pretreatments. These results indicate that a lower disease symptom development in pCA-pretreated leaves was associated with a higher accumulation of hydroxycinnamic acids and flavonoids, and vice-versa in MDCA- and non-pretreated (control) leaves.

UPLC-QTOF-MS metabolomics analysis revealed the contributions of metabolites to the pathogenesis of Rhizoctonia solani strain AG-1-IA

To explore the pathogenesis of Rhizoctonia solani and its phytotoxin phenylacetic acid (PAA) on maize leaves and sheaths, treated leaf and sheath tissues were analyzed and interpreted by ultra-performance liquid chromatography-mass spectrometry combined with chemometrics. The PAA treatment had similar effects to those of R. solani on maize leaves regarding the metabolism of traumatin, phytosphingosine, vitexin 2'' O-beta-D-glucoside, rutin and DIBOA-glucoside, which were up-regulated, while the synthesis of OPC-8:0 and 12-OPDA, precursors for the synthesis of jasmonic acid, a plant defense signaling molecule, was down-regulated under both treatments. However, there were also discrepancies in the influences exhibited by R. solani and PAA as the metabolic concentration of zeaxanthin diglucoside in the R. solani infected leaf group decreased. Conversely, in the PAA-treated leaf group, the synthesis of zeaxanthin diglucoside was enhanced. Moreover, although the synthesis of 12 metabolites were suppressed in both the R. solani- and PAA-treated leaf tissues, the inhibitory effect of R. solani was stronger than that of PAA. An increased expression of quercitrin and quercetin 3-O-glucoside was observed in maize sheaths treated by R. solani, while their concentrations were not changed significantly in the PAA-treated sheaths. Furthermore, a significant decrease in the concentration of L-Glutamate, which plays important roles in plant resistance to necrotrophic pathogens, only occurred in the R. solani-treated sheath tissues. The differentiated metabolite levels may be the partial reason of why maize sheaths were more susceptible to R. solani than leaves and may explain the underlying mechanisms of R. solani pathogenesis.

A substitution mutation in OsPELOTA confers bacterial blight resistance by activating the salicylic acid pathway

We previously reported a spotted-leaf mutant pelota (originally termed HM47) in rice displaying arrested growth and enhanced resistance to multiple races of Xanthomonas oryzae pv. oryzae. Here, we report the map-based cloning of the causal gene OsPELOTA (originally termed spl^HM47 ). We identified a single base substitution from T to A at position 556 in the coding sequence of OsPELOTA, effectively mutating phenylalanine to isoleucine at position 186 in the translated protein sequence. Both functional complementation and over-expression could rescue the spotted-leaf phenotype. OsPELOTA, a paralogue to eukaryotic release factor 1 (eRF1), shows high sequence similarity to Drosophila Pelota and also localizes to the endoplasmic reticulum and plasma membrane. OsPELOTA is constitutively expressed in roots, leaves, sheaths, stems, and panicles. Elevated levels of salicylic acid and decreased level of jasmonate were detected in the pelota mutant. RNA-seq analysis confirmed that genes responding to salicylic acid were upregulated in the mutant. Our results indicate that the rice PELOTA protein is involved in bacterial leaf blight resistance by activating the salicylic acid metabolic pathway.

Arabidopsis thalianaACS8 plays a crucial role in the early biosynthesis of ethylene elicited by Cu2+ ions

Cu²⁺ ions are required by all living organisms and play important roles in many bactericides and fungicides. We previously reported that Cu²⁺ can elicit defense responses, which are dependent on the ethylene signaling pathway in Arabidopsis However, the mechanism by which Cu²⁺ elicits the biosynthesis of ethylene remains unclear. Here, we show that CuSO₄ treatment rapidly increases the production of ethylene. In addition, it upregulates the expression of several defense-related genes and ethylene biosynthesis genes, including genes encoding S-adenosylmethionine synthase, 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase. Among these genes, Arabidopsis thaliana (At)ACS8 was identified as essential for the defense response and early ethylene biosynthesis induced by Cu²⁺ Furthermore, Cu²⁺-induced AtACS8 expression depended on the copper-response cis-element (CuRE) in the promoter of AtACS8 Our study indicates that Cu²⁺ specifically activates the expression of AtACS8 to promote the early biosynthesis of ethylene that elicits plant immunity in Arabidopsis plants.