Metabolic reprogramming in plant innate immunity: the contributions of phenylpropanoid and oxylipin pathways

Transcriptome and metabolome analyses reveal molecular insights into waterlogging tolerance in Barley

Waterlogging stress is one of the major abiotic stresses affecting the productivity and quality of many crops worldwide. However, the mechanisms of waterlogging tolerance are still elusive in barley. In this study, we identify key differentially expressed genes (DEGs) and differential metabolites (DM) that mediate distinct waterlogging tolerance strategies in leaf and root of two barley varieties with contrasting waterlogging tolerance under different waterlogging treatments. Transcriptome profiling revealed that the response of roots was more distinct than that of leaves in both varieties, in which the number of downregulated genes in roots was 7.41-fold higher than that in leaves of waterlogging sensitive variety after 72 h of waterlogging stress. We also found the number of waterlogging stress-induced upregulated DEGs in the waterlogging tolerant variety was higher than that of the waterlogging sensitive variety in both leaves and roots in 1 h and 72 h treatment. This suggested the waterlogging tolerant variety may respond more quickly to waterlogging stress. Meanwhile, phenylpropanoid biosynthesis pathway was identified to play critical roles in waterlogging tolerant variety by improving cell wall biogenesis and peroxidase activity through DEGs such as Peroxidase (PERs) and Cinnamoyl-CoA reductases (CCRs) to improve resistance to waterlogging. Based on metabolomic and transcriptomic analysis, we found the waterlogging tolerant variety can better alleviate the energy deficiency via higher sugar content, reduced lactate accumulation, and improved ethanol fermentation activity compared to the waterlogging sensitive variety. In summary, our results provide waterlogging tolerance strategies in barley to guide the development of elite genetic resources towards waterlogging-tolerant crop varieties.

Effect of Elicitor Treatments on Quality Attributes in Blueberry: Implications of Cultivar and Environmental Conditions

Elicitors of plant defence responses can trigger defence mechanisms that are able to protect plant tissues from biotic or abiotic stresses. Since one defence response involves the activation of secondary metabolites' biosynthesis, the purpose of this study was to evaluate the effect of chitosan and melatonin pre-harvest treatments on the quality and the nutritional parameters of the fruits of blueberry (Vaccinium corymbosum L.). Across the two years of experiment, three different cultivars (cv.s. 'Cosmopolitan', 'Hortblue Poppins' and 'Legacy') were treated with 1% chitosan or 100 µM melatonin every two weeks during the ripening season and ripe fruits were progressively harvested and analysed. The treatment with both elicitors had only slight effects on dry matter, soluble solids content, titratable acidity and pH, with a cultivar-dependent response. On the other hand, elicitors significantly affected the levels of phenylpropanoid and antioxidant compounds in all cvs. in both years, with a higher accumulation of total anthocyanins and phenolics and the enhancement of the antioxidant capacity, with positive effects on the nutraceutical quality of fruits. The anthocyanin profile in terms of both absolute concentrations and the relative proportion of single anthocyanins was affected by both harvest year and cv., highlighting the role of the genetic background in the plant response to environmental conditions (with particular reference to summer heat stress) and to elicitor treatments.

Exogenous Melatonin Application Accelerated the Healing Process of Oriental Melon Grafted onto Squash by Promoting Lignin Accumulation

Melatonin (MT) is a vital hormone factor in plant growth and development, yet its potential to influence the graft union healing process has not been reported. In this study, we examined the effects of MT on the healing of oriental melon scion grafted onto squash rootstock. The studies indicate that the exogenous MT treatment promotes the lignin content of oriental melon and squash stems by increasing the enzyme activities of hydroxycinnamoyl CoA ligase (HCT), hydroxy cinnamaldehyde dehydrogenase (HCALDH), caffeic acid/5-hydroxy-conifer aldehyde O-methyltransferase (COMT), caffeoyl-CoA O-methyltransferase (CCoAOMT), phenylalanine ammonia-lyase (PAL), 4-hydroxycinnamate CoA ligase (4CL), and cinnamyl alcohol dehydrogenase (CAD). Using the oriental melon and squash treated with the exogenous MT to graft, the connection of oriental melon scion and squash rootstock was more efficient and faster due to higher expression of wound-induced dedifferentiation 1 (WIND1), cyclin-dependent kinase (CDKB1;2), target of monopteros 6 (TMO6), and vascular-related NAC-domain 7 (VND7). Further research found that the exogenous MT increased the lignin content of the oriental melon scion stem by regulating CmCAD1 expression, and then accelerated the graft healing process. In addition, the root growth of grafted seedlings treated with the exogenous MT was more vigorous.

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.

Gut microbiota and metabolome in sporadic Creutzfeldt-Jakob disease

BACKGROUND

Gut dysbiosis and the resulting changes in the metabolites have been associated with neurological diseases. However, the relationship between the gut microbiota and sporadic Creutzfeldt-Jakob disease (sCJD) need to be clarified. The aim of this study was to evaluate the changes in the composition of gut microbiota and metabolome accompanying sCJD, and determine their correlation with disease severity.

METHODS

Fecal samples were collected from 25 sCJD patients and 23 healthy controls. The composition of the fecal microbiota and metabolites was respectively analyzed by 16S ribosomal RNA sequencing and untargeted metabolomics. The correlation of gut microbiota and metabolites with MMSE, MoCA and MRC scores was analyzed.

RESULTS

The sCJD patients showed significant differences in the composition of gut microbiota and metabolites relative to the healthy controls. Several bacteria taxa in sCJD patients were increased at genus level, such as Turicibacter, norank_f_Christensenellaceae, Eisenbergiella, Bilophila and Holdemania. A total of 547 differential metabolites were identified between these two groups (VIP > 1, FDR p < 0.05). As per KEGG analysis, the metabolites related to the biosynthesis of phenylpropanoids, especially biochanin A, showed the most obvious decrease in the sCJD group. In addition, most metabolites involved in the pathways related to linoleic acid metabolism and steroid hormone biosynthesis were associated with MRC scale.

CONCLUSION

Our findings provide new insights into the relationship between gut microbiota and metabolites and sCJD. Some compounds, especially those related to the biosynthesis of phenylpropanoids were significantly altered in patients with sCJD, and those related to linoleic acid metabolism and steroid hormone biosynthesis might be biomarkers of evaluating disease severity.

Overexpression of Brassica napus COMT1 in Arabidopsis heightens UV-B-mediated resistance to Plutella xylostella herbivory

UV-B radiation regulates numerous morphogenic, biochemical and physiological responses in plants, and can stimulate some responses typically associated with other abiotic and biotic stimuli, including invertebrate herbivory. Removal of UV-B from the growing environment of various plant species has been found to increase their susceptibility to consumption by invertebrate pests, however, to date, little research has been conducted to investigate the effects of UV-B on crop susceptibility to field pests. Here, we report findings from a multi-omic and genetic-based study investigating the mechanisms of UV-B-stimulated resistance of the crop, Brassica napus (oilseed rape), to herbivory from an economically important lepidopteran specialist of the Brassicaceae, Plutella xylostella (diamondback moth). The UV-B photoreceptor, UV RESISTANCE LOCUS 8 (UVR8), was not found to mediate resistance to this pest. RNA-Seq and untargeted metabolomics identified components of the sinapate/lignin biosynthetic pathway that were similarly regulated by UV-B and herbivory. Arabidopsis mutants in genes encoding two enzymes in the sinapate/lignin biosynthetic pathway, CAFFEATE O-METHYLTRANSFERASE 1 (COMT1) and ELICITOR-ACTIVATED GENE 3-2 (ELI3-2), retained UV-B-mediated resistance to P. xylostella herbivory. However, the overexpression of B. napus COMT1 in Arabidopsis further reduced plant susceptibility to P. xylostella herbivory in a UV-B-dependent manner. These findings demonstrate that overexpression of a component of the sinapate/lignin biosynthetic pathway in a member of the Brassicaceae can enhance UV-B-stimulated resistance to herbivory from P. xylostella.

Recent progress on the microbial mitigation of heavy metal stress in soybean: overview and implications

Plants are adapted to defend themselves through programming, reprogramming, and stress tolerance against numerous environmental stresses, including heavy metal toxicity. Heavy metal stress is a kind of abiotic stress that continuously reduces various crops' productivity, including soybeans. Beneficial microbes play an essential role in improving plant productivity as well as mitigating abiotic stress. The simultaneous effect of abiotic stress from heavy metals on soybeans is rarely explored. Moreover, reducing metal contamination in soybean seeds through a sustainable approach is extremely needed. The present article describes the initiation of heavy metal tolerance mediated by plant inoculation with endophytes and plant growth-promoting rhizobacteria, the identification of plant transduction pathways via sensing annotation, and contemporary changes from molecular to genomics. The results suggest that the inoculation of beneficial microbes plays a significant role in rescuing soybeans under heavy metal stress. They create a dynamic, complex interaction with plants via a cascade called plant-microbial interaction. It enhances stress metal tolerance via the production of phytohormones, gene expression, and secondary metabolites. Overall, microbial inoculation is essential in mediating plant protection responses to heavy metal stress produced by a fluctuating climate.

Integrative analysis of the multi-omics reveals the stripe rust fungus resistance mechanism of the TaPAL in wheat

Wheat is one of the major food crops in the world. However, stripe rust fungus significantly decreases wheat yield and quality. In the present study, transcriptomic and metabolite analyses were conducted in R88 (resistant line) and CY12 (susceptible cultivar) during Pst-CYR34 infection due to the limited availability of information regarding the underlying mechanisms governing wheat-pathogen interactions. The results revealed that Pst infection promoted the genes and metabolites involved in phenylpropanoid biosynthesis. The key enzyme gene TaPAL to regulate lignin and phenolic synthesis has a positive resistance contribution to Pst in wheat, which was verified by the virus-induced gene silencing (VIGS) technique. The distinctive resistance of R88 is regulated by the selective expression of genes involved in the fine-tuning of wheat-Pst interactions. Furthermore, metabolome analysis suggested that lignin biosynthesis-related metabolite accumulation was significantly affected by Pst. These results help to elucidate the regulatory networks of wheat-Pst interactions and pave the way for durable resistance breeding in wheat, which may ease environmental and food crises around the world.

Transcriptome analysis indicates the involvement of herbicide-responsive and plant-pathogen interaction pathways in the development of resistance to ACCase inhibitors in Apera spica-venti

BACKGROUND

The continuous use of the herbicides contributes to the emergence of the resistant populations of numerous weed species that are tolerant to multiple herbicides with different modes of action (multiple resistance) which is provided by non-target-site resistance mechanisms. In this study, we addressed the question of rapid acquisition of herbicide resistance to pinoxaden (acetyl CoA carboxylase inhibitor) in Apera spica-venti, which endangers winter cereal crops and has high adaptation capabilities to inhabit many rural locations. To this end, de novo transcriptome of Apera spica-venti was assembled and RNA-sequencing analysis of plants resistant and susceptible to pinoxaden treated with this herbicide was performed.

RESULTS

The obtained data showed that the prime candidate genes responsible for herbicide resistance were those encoding 3-ketoacyl-CoA synthase 12-like, UDP-glycosyltransferases (UGT) including UGT75K6, UGT75E2, UGT83A1-like, and glutathione S-transferases (GSTs) such as GSTU1 and GSTU6. Also, such highly accelerated herbicide resistance emergence may result from the enhanced constitutive expression of a wide range of genes involved in detoxification already before herbicide treatment and may also influence response to biotic stresses, which was assumed by the detection of expression changes in genes encoding defence-related proteins, including receptor kinase-like Xa21. Moreover, alterations in the expression of genes associated with methylation in non-treated herbicide-resistant populations were identified.

CONCLUSION

The obtained results indicated genes that may be involved in herbicide resistance. Moreover, they provide valuable insight into the possible effect of resistance on the weed interaction with the other stresses by indicating pathways associated with both abiotic and biotic stresses. © 2023 Society of Chemical Industry.

A chromosome-scale genome assembly of Castanopsis hystrix provides new insights into the evolution and adaptation of Fagaceae species

Fagaceae species dominate forests and shrublands throughout the Northern Hemisphere, and have been used as models to investigate the processes and mechanisms of adaptation and speciation. Compared with the well-studied genus Quercus, genomic data is limited for the tropical-subtropical genus Castanopsis. Castanopsis hystrix is an ecologically and economically valuable species with a wide distribution in the evergreen broad-leaved forests of tropical-subtropical Asia. Here, we present a high-quality chromosome-scale reference genome of C. hystrix, obtained using a combination of Illumina and PacBio HiFi reads with Hi-C technology. The assembled genome size is 882.6 Mb with a contig N50 of 40.9 Mb and a BUSCO estimate of 99.5%, which are higher than those of recently published Fagaceae species. Genome annotation identified 37,750 protein-coding genes, of which 97.91% were functionally annotated. Repeat sequences constituted 50.95% of the genome and LTRs were the most abundant repetitive elements. Comparative genomic analysis revealed high genome synteny between C. hystrix and other Fagaceae species, despite the long divergence time between them. Considerable gene family expansion and contraction were detected in Castanopsis species. These expanded genes were involved in multiple important biological processes and molecular functions, which may have contributed to the adaptation of the genus to a tropical-subtropical climate. In summary, the genome assembly of C. hystrix provides important genomic resources for Fagaceae genomic research communities, and improves understanding of the adaptation and evolution of forest trees.

Molecular regulation of immunity in tea plants

Tea, which is mainly produced using the young leaves and buds of tea plants (Camellia sinensis (L.) O. Kuntze), is one of the most common non-alcoholic beverages consumed in the world. The standard of tea mostly depends on the variety and quality of tea plants, which generally grow in subtropical areas, where the warm and humid conditions are also conducive to the occurrence of diseases. In fighting against pathogens, plants rely on their sophisticated innate immune systems which has been extensively studied in model plants. Many components involved in pathogen associated molecular patterns (PAMPs) triggered immunity (PTI) and effector triggered immunity (ETI) have been found. Nevertheless, the molecular regulating network against pathogens (e.g., Pseudopestalotiopsis sp., Colletotrichum sp. and Exobasidium vexans) causing widespread disease (such as grey blight disease, anthracnose, and blister blight) in tea plants is still unclear. With the recent release of the genome data of tea plants, numerous genes involved in tea plant immunity have been identified, and the molecular mechanisms behind tea plant immunity is being studied. Therefore, the recent achievements in identifying and cloning functional genes/gene families, in finding crucial components of tea immunity signaling pathways, and in understanding the role of secondary metabolites have been summarized and the opportunities and challenges in the future studies of tea immunity are highlighted in this review.

In Vivo Antiphytoviral and Aphid Repellency Activity of Essential Oils and Hydrosols from Mentha suaveolens and Foeniculum vulgare to Control Zucchini Yellow Mosaic Virus and Its Vector Aphis gossypii

In recent years, natural compounds have gained attention in many fields due to their wide-range biological activity. In particular, essential oils and their associated hydrosols are being screened to control plant pests, exerting antiviral, antimycotic and antiparasitic actions. They are more quickly and cheaply produced and are generally considered safer for the environment and non-target organisms than conventional pesticides. In this study, we report the evaluation of the biological activity of two essential oils and their corresponding hydrosols obtained from Mentha suaveolens and Foeniculum vulgare in the control of zucchini yellow mosaic virus and its vector, Aphis gossypii, in Cucurbita pepo plants. The control of the virus was ascertained with treatments applied either concurrently with or after virus infection; choice tests were performed to verify repellency activity against the aphid vector. The results indicated that treatments could decrease virus titer as measured using real-time RT-PCR, while the experiments on the vector showed that the compounds effectively repelled aphids. The extracts were also chemically characterized using gas chromatography-mass spectrometry. Mentha suaveolens and Foeniculum vulgare hydrosol extracts mainly comprised fenchone and decanenitrile, respectively, while essential oils analysis returned a more complex composition, as expected.

Transcriptome mapping related genes encoding PR1 protein involved in necrotic symptoms to soybean mosaic virus infection

Necrosis caused by soybean mosaic virus (SMV) has not been specifically distinguished from susceptible symptoms. The molecular mechanism for the occurrence of necrosis is largely overlooked in soybean genetic research. Field evaluation reveals that SMV disease seriously influences soybean production as indicated by decreasing 22.4% ~ 77.0% and 8.8% ~ 17.0% of yield and quality production, respectively. To expand molecular mechanism behind necrotic reactions, transcriptomic data obtained from the asymptomatic, mosaic, and necrotic pools were assessed. Compared between asymptomatic and mosaic plants, 1689 and 1752 up- and down-regulated differentially expressed genes (DEGs) were specifically found in necrotic plants. Interestingly, the top five enriched pathways with up-regulated DEGs were highly related to the process of the stress response, whereas the top three enriched pathways with down-regulated DEGs were highly related to the process of photosynthesis, demonstrating that defense systems are extensively activated, while the photosynthesis systems were severely destroyed. Further, results of the phylogenetic tree based on gene expression pattern and an amino acid sequence and validation experiments discovered three PR1 genes, Glyma.15G062400, Glyma.15G062500, and Glyma.15G062700, which were especially expressed in necrotic leaves. Meanwhile, exogenous salicylic acid (SA) but not methyl jasmonate (MeJA) could induce the three PR1 gene expressions on healthy leaves. Contrastingly, exogenous SA obviously decreased the expression level of Glyma.15G062400, Glyma.15G062500, and concentration of SMV, but increased Glyma.15G062700 expression in necrotic leaves. These results showed that GmPR1 is associated with the development of SMV-induced necrotic symptoms in soybean. Glyma.15G062400, Glyma.15G062500, and Glyma.15G062700 is up-regulated in necrotic leaves at the transcriptional levels, which will greatly facilitate a better understanding of the mechanism behind necrosis caused by SMV disease.

Supplementary information

The online version contains supplementary material available at 10.1007/s11032-022-01351-3.

New plant immunity elicitors from a sugar beet byproduct protect wheat against Zymoseptoria tritici

The current worldwide context promoting agroecology and green agriculture require the discovery of new ecofriendly and sustainable plant protection tools. Plant resistance inducers, called also elicitors, are one of the most promising alternatives fitting with such requirements. We produced here a set of 30 molecules from pyroglutamic acid, bio-sourced from sugar beet byproducts, and examined for their biological activity on the major agro-economically pathosystem wheat-Zymoseptoria tritici. Foliar application of the molecules provided significant protection rates (up to 63% disease severity reduction) for 16 among them. Structure-activity relationship analysis highlighted the importance of all chemical groups of the pharmacophore in the bioactivity of the molecules. Further investigations using in vitro and in planta antifungal bioassays as well as plant molecular biomarkers revealed that the activity of the molecules did not rely on direct biocide activity towards the pathogen, but rather on the activation of plant defense mechanisms dependent on lipoxygenase, phenylalanine ammonia-lyase, peroxidase, and pathogenesis-related protein pathways. This study reports a new family of bio-sourced resistance inducers and provides new insights into the valorization of agro-resources to develop the sustainable agriculture of tomorrow.

Genome-wide studies of PAL genes in sorghum and their responses to aphid infestation

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.25) plays a crucial role in plant adaptation to biotic and abiotic stresses. However, the current knowledge about PAL proteins in sorghum is essentially lacking. Thus, in this study we aimed to analyze the PAL family genes in sorghum using a genome-wide approach and to explore the role of PAL genes in host plant resistance to aphids via SA-mediated defense signaling. Here, we report gene structural features of 8 PAL (SbPAL) genes in sorghum (Sorghum bicolor), their phylogeny, protein motifs and promoter analysis. Furthermore, we demonstrated that the SbPAL genes were induced by sugarcane aphid (SCA) infestation and SbPAL exhibited differential gene expression in susceptible and resistant genotypes. PAL activity assays further validated upregulated expression of the SbPAL genes in a resistant genotype. In addition, exogenous application of SA reduced plant damage and suppressed aphid population growth and fecundity in susceptible genotype, suggesting that those SbPAL genes act as positive regulator of the SA-mediated defense signaling pathway to combat aphid pests in sorghum. This study provides insights for further examination of the defense role of PAL in sorghum against other pests and pathogens.

Genes Associated with Biological Nitrogen Fixation Efficiency Identified Using RNA Sequencing in Red Clover (Trifolium pratense L.)

Commonly studied in the context of legume-rhizobia symbiosis, biological nitrogen fixation (BNF) is a key component of the nitrogen cycle in nature. Despite its potential in plant breeding and many years of research, information is still lacking as to the regulation of hundreds of genes connected with plant-bacteria interaction, nodulation, and nitrogen fixation. Here, we compared root nodule transcriptomes of red clover (Trifolium pratense L.) genotypes with contrasting nitrogen fixation efficiency, and we found 491 differentially expressed genes (DEGs) between plants with high and low BNF efficiency. The annotation of genes expressed in nodules revealed more than 800 genes not yet experimentally confirmed. Among genes mediating nodule development, four nod-ule-specific cysteine-rich (NCR) peptides were confirmed in the nodule transcriptome. Gene duplication analyses revealed that genes originating from tandem and dispersed duplication are significantly over-represented among DEGs. Weighted correlation network analysis (WGCNA) organized expression profiles of the transcripts into 16 modules linked to the analyzed traits, such as nitrogen fixation efficiency or sample-specific modules. Overall, the results obtained broaden our knowledge about transcriptomic landscapes of red clover's root nodules and shift the phenotypic description of BNF efficiency on the level of gene expression in situ.

Transcriptomic analysis provides insight into defensive strategies in response to continuous cropping in strawberry (Fragaria × ananassa Duch.) plants

BACKGROUND

Strawberries are an important economic fruit crop world-wide. In strawberry cultivation, continuous cropping (CC) can seriously threaten yield and quality. However, our understanding of the gene expression changes in response to CC and during subsequent defense processes is limited. In this study, we analyzed the impact of CC on the transcriptome of strawberry roots using RNA-Seq technology to elucidate the effect of CC and the subsequent molecular changes.

RESULTS

We found that CC significantly affects the growth of strawberry plants. The transcriptome analysis identified 136 differentially expressed genes (DEGs), including 49 up-regulated and 87 down-regulated DEGs. A Gene Ontology (GO) analysis indicated that the up-regulated DEGs were mainly assigned to defense-related GO terms, and most down-regulated DEGs were assigned to nutrient-related GO terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the responsive DEGs were classified in a large number of important biological pathways, such as phenylalanine metabolism, starch and sucrose metabolism, phenylpropanoid biosynthesis, glutathione metabolism and plant-pathogen interaction. We also found that four WRKY transcription factors and three peroxidase genes involved in plant defense pathways were up-regulated in the roots of strawberry plants subjected to CC.

CONCLUSION

Several unigenes involved in plant defense processes, such as CNGCs, WRKY transcription factors, PR1, and peroxidase genes with highly variable expression levels between non-CC and CC treatments may be involved in the regulation of CC in strawberry. These results indicate that strawberry roots reallocate development resources to defense mechanisms in response to CC. This study will further deepen our understanding of the fundamental regulatory mechanisms of strawberry resource reallocation in response to CC.

Transcriptomic insights into the molecular mechanism of wheat response to stripe rust fungus

The wheat crop (Triticum aestivum L.) is the widely cultivated and most important staple foods of worlds. Stripe (yellow) rust is prompted by Puccinia striiformis f. sp. tritici (Pst) to reduces the yield and grain quality of the wheat significantly. Although many resistant cultivars have been successfully used in wheat breeding, the size of the regulating network and the underlying molecular mechanisms of wheat to response Pst still unknown. Therefore, in order to identify differentially expression genes (DEGs) and the regulate network related to Pst resistance, 15 cDNA libraries were constructed from wheat with CYR34 infection. In this study, a highly susceptible cv. Chuanyu12 (CY12) was used to study the transcriptome profiles after being inoculated with Pst physiological race CYR34. The DEGs were investigated at 24h, 48h, 72h, and 7 days post-inoculation. Certain key genes and pathways of response for Pst-CYR34 in CY12 were identified. The results revealed that Pst-CYR34 inhibited the DEGs related to energy metabolism, biosynthesis, carbon fixation, phenylalanine metabolism, and plant hormone signaling pathways after post-inoculation at 24h, 48h, 72h, and 7d. Light-harvesting chlorophyll protein complex in photosystem I and photosystem II; F-type ATPase, cytochrome b6/f/complex, and photosynthetic electron transport; ethylene, salicylic acid (SA), and jasmonic acid (JA); and lignin and flavonoids biosynthesis in CY12 are among the down-regulated DEGs. The expression patterns of these DEGs were verified via Quantitative Real-time PCR analysis. Our results give insights into the foundation for further exploring the molecular mechanisms regulating networks of Pst response and opens the door for bread wheat Pst resistance breeding.

Antioxidant activation, cell wall reinforcement, and reactive oxygen species regulation promote resistance to waterlogging stress in hot pepper (Capsicum annuum L.)

BACKGROUND

Hot pepper (Capsicum annuum L.) is one of the world's oldest domesticated crops. It has poor waterlogging tolerance, and flooding frequently results in plant death and yield reduction. Therefore, understanding the molecular mechanisms associated with pepper waterlogging tolerance is essential to grow new varieties with stronger tolerance.

RESULTS

In this study, we discovered that after 5 days of flooding, the growth rate of waterlogging-tolerant pepper cultivars did not reduce to a large extent. Physiological data revealed that chlorophyll concentration was not significantly affected by flooding; however, stomatal conductance was altered considerably 0-5 days after flooding, and the net photosynthesis rate changed substantially 5-10 days after flooding. In addition, the root activity of waterlogging-tolerant varieties was substantially higher after flooding for 10 days than that of the control. This implies that the effect of flooding is associated with changes in the root environment, which ultimately affects photosynthesis. We evaluated changes in gene expression levels between two pepper types at the same time point and the same pepper variety at different time points after flooding stress treatment and performed a screening for multiple potential genes. These differentially expressed genes (DEGs) were further analyzed for functional enrichment, and the results revealed that antioxidase genes, cell wall synthesis pathway genes, and calcium ion regulation pathway genes might be associated with waterlogging tolerance. Other genes identified in peppers with waterlogging tolerance included those associated with lignin synthesis regulation, reactive oxygen species (ROS) regulation pathways, and others associated with stress resistance. Considerable changes in the expression levels of these genes were recorded 5 days after waterlogging, which was consistent with a considerable increase in oxidase content that was also noted on the fifth day after flooding. The quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) findings revealed that among the 20 selected DEGs, including genes such as mitogen-activated protein kinase 3 (MPK3) and calcium-binding protein 4 (CML4), approximately 80% of the gene expression patterns were consistent with our RNA-seq dataset.

CONCLUSIONS

The findings of this study suggest that ROS modulation, increased antioxidase activity, lignin formation, and the expression of stress resistance genes help peppers with waterlogging tolerance resist flooding stress in the early stages. These findings provide a basis for further investigation of the molecular mechanisms responsible for waterlogging tolerance in pepper and may be a critical reference for the breeding of hot pepper.

A Panoramic View on Grapevine Trunk Diseases Threats: Case of Eutypa Dieback, Botryosphaeria Dieback, and Esca Disease

Grapevine trunk diseases (GTD) are currently one of the most devastating and challenging diseases in viticulture, leading to considerable yield losses and a remarkable decline in grapevine quality. The identification of the causal agents is the cornerstone of an efficient approach to fighting against fungal diseases in a sustainable, non-chemical manner. This review attempts to describe and expose the symptoms of each pathology related to GTD, the modes of transmission, and the harmfulness of recently reported agents. Special attention was given to new diagnostic tests and technologies, grapevine defense mechanisms, molecular mechanisms of endophytes fungal colonization, and management strategies used to control these threats. The present extended review is, therefore, an updated state-of-the-art report on the progress in the management of vineyards.

In vivo Antiphytoviral Activity of Essential Oils and Hydrosols From Origanum vulgare, Thymus vulgaris, and Rosmarinus officinalis to Control Zucchini Yellow Mosaic Virus and Tomato Leaf Curl New Delhi Virus in Cucurbita pepo L

In the last decades, the interest in biological activity of natural compounds has been growing. In plant protection, essential oils have been reported to exhibit antiviral, antimycotic, and antiparasitic activities, and are regarded as promising for the formulation of safe antimicrobial agents. Attention has also been focused on hydrosols, the by-products of hydro-distillation of essential oils. Their production is easy, fast, and cheap, and they seem to arise less concern for human health than essential oils. Plant viruses represent a major concern for agricultural crops since no treatment compound is available for virus control. This work was aimed at evaluating the antiphytoviral effectiveness of treatments with three essential oils and corresponding hydrosols extracted from Origanum vulgare, Thymus vulgaris, and Rosmarinus officinalis on Cucurbita pepo plants infected by zucchini yellow mosaic virus or tomato leaf curl New Delhi virus. Treatments were applied either concurrently or after virus inoculation to ascertain an inhibition or curative activity, respectively. Symptoms were observed and samplings were performed weekly. Virus titer and expression levels of phenylalanine ammonia lyase gene (PAL) were measured on treated and untreated infected plants by real-time PCR. PAL gene plays an important role in plant defense response as it is involved in tolerance/resistance to phytopathogens. Results indicated that treatments were effective against tomato leaf curl New Delhi virus whether applied simultaneously with the inoculation or after. A major inhibition was observed with O. vulgare essential oil and hydrosol, resulting in 10^–4-fold decrease of virus titer 3 weeks after treatment. Curative activity gave maximum results with all three essential oils and T. vulgaris and R. officinalis hydrosols, recording from 10^–2-fold decrease to virus not detected 4 weeks after treatment. An induction of PAL gene expression was recorded at 12 d.p.i. and then was restored to the levels of untreated control. This allows to hypothesize an early plant defense response to virus infection, possibly boosted by treatments. Plant extracts’ composition was characterized by gas chromatography-mass spectrometry. Phenols were largely main components of O. vulgare and T. vulgaris extracts (carvacrol and thymol, respectively), while extracts from R. officinalis were based on monoterpene hydrocarbons (essential oil) and oxygenated monoterpenes (hydrosol).

Tryptophan Levels as a Marker of Auxins and Nitric Oxide Signaling

The aromatic amino acid tryptophan is the main precursor for indole-3-acetic acid (IAA), which involves various parallel routes in plants, with indole-3-acetaldoxime (IAOx) being one of the most common intermediates. Auxin signaling is well known to interact with free radical nitric oxide (NO) to perform a more complex effect, including the regulation of root organogenesis and nitrogen nutrition. To fathom the link between IAA and NO, we use a metabolomic approach to analyze the contents of low-molecular-mass molecules in cultured cells of Arabidopsis thaliana after the application of S-nitrosoglutathione (GSNO), an NO donor or IAOx. We separated the crude extracts of the plant cells through ion-exchange columns, and subsequent fractions were analyzed by gas chromatography-mass spectrometry (GC-MS), thus identifying 26 compounds. A principal component analysis (PCA) was performed on N-metabolism-related compounds, as classified by the Kyoto Encyclopedia of Genes and Genomes (KEGG). The differences observed between controls and treatments are mainly explained by the differences in Trp contents, which are much higher in controls. Thus, the Trp is a shared response in both auxin- and NO-mediated signaling, evidencing some common signaling mechanism to both GSNO and IAOx. The differences in the low-molecular-mass-identified compounds between GSNO- and IAOx-treated cells are mainly explained by their concentrations in benzenepropanoic acid, which is highly associated with IAA levels, and salicylic acid, which is related to glutathione. These results show that the contents in Trp can be a marker for the study of auxin and NO signaling.

Role of Promising Secondary Metabolites to Confer Resistance Against Environmental Stresses in Crop Plants: Current Scenario and Future Perspectives

Plants often face incompatible growing environments like drought, salinity, cold, frost, and elevated temperatures that affect plant growth and development leading to low yield and, in worse circumstances, plant death. The arsenal of versatile compounds for plant consumption and structure is called metabolites, which allows them to develop strategies to stop enemies, fight pathogens, replace their competitors and go beyond environmental restraints. These elements are formed under particular abiotic stresses like flooding, heat, drought, cold, etc., and biotic stress such as a pathogenic attack, thus associated with survival strategy of plants. Stress responses of plants are vigorous and include multifaceted crosstalk between different levels of regulation, including regulation of metabolism and expression of genes for morphological and physiological adaptation. To date, many of these compounds and their biosynthetic pathways have been found in the plant kingdom. Metabolites like amino acids, phenolics, hormones, polyamines, compatible solutes, antioxidants, pathogen related proteins (PR proteins), etc. are crucial for growth, stress tolerance, and plant defense. This review focuses on promising metabolites involved in stress tolerance under severe conditions and events signaling the mediation of stress-induced metabolic changes are presented.

Alzheimer's disease as an autoimmune disorder of innate immunity endogenously modulated by tryptophan metabolites

Introduction

Alzheimer's disease (AD) is characterized by neurotoxic immuno-inflammation concomitant with cytotoxic oligomerization of amyloid beta (Aβ) and tau, culminating in concurrent, interdependent immunopathic and proteopathic pathogeneses.

Methods

We performed a comprehensive series of in silico, in vitro, and in vivo studies explicitly evaluating the atomistic-molecular mechanisms of cytokine-mediated and Aβ-mediated neurotoxicities in AD.  Next, 471 new chemical entities were designed and synthesized to probe the pathways identified by these molecular mechanism studies and to provide prototypic starting points in the development of small-molecule therapeutics for AD.

Results

In response to various stimuli (e.g., infection, trauma, ischemia, air pollution, depression), Aβ is released as an early responder immunopeptide triggering an innate immunity cascade in which Aβ exhibits both immunomodulatory and antimicrobial properties (whether bacteria are present, or not), resulting in a misdirected attack upon "self" neurons, arising from analogous electronegative surface topologies between neurons and bacteria, and rendering them similarly susceptible to membrane-penetrating attack by antimicrobial peptides (AMPs) such as Aβ. After this self-attack, the resulting necrotic (but not apoptotic) neuronal breakdown products diffuse to adjacent neurons eliciting further release of Aβ, leading to a chronic self-perpetuating autoimmune cycle.  AD thus emerges as a brain-centric autoimmune disorder of innate immunity. Based upon the hypothesis that autoimmune processes are susceptible to endogenous regulatory processes, a subsequent comprehensive screening program of 1137 small molecules normally present in human brain identified tryptophan metabolism as a regulator of brain innate immunity and a source of potential endogenous anti-AD molecules capable of chemical modification into multi-site therapeutic modulators targeting AD's complex immunopathic-proteopathic pathogenesis.

Discussion

 Conceptualizing AD as an autoimmune disease, identifying endogenous regulators of this autoimmunity, and designing small molecule drug-like analogues of these endogenous regulators represents a novel therapeutic approach for AD.

Mapping and functional analysis of high-copper accumulation mutant oshc1 in rice

Copper (Cu) is an essential but potentially toxic element in rice. Little is known about the mechanism of rice grain Cu accumulation. In this study, we identified a high copper accumulation in grain 1 (oshc1) mutant from the wild type indica rice cultivar 9311 (WT) mutant bank. Compared with those in WT, more Cu was shown to accumulate in the shoots of seedlings and the above-ground tissues except nodes although less total Cu content in oshc1. Further analysis showed that the mutant had an accelerated Cu transport ratio from roots to shoots and higher Cu concentration in xylem sap than WT. This phenomenon in oshc1 was controlled by a single recessive gene, which was identified as BGIOSGA007732, and named OsHMA4. The eight base frame-shift from 1021 to 1028 bp in the coding sequence of OsHMA4 led to a modification after the 341st amino acid and resulted in premature translation termination of OsHMA4 at the 377th amino acid. This may change the function of OsHMA4. Furthermore, the up-regulated OsCOPT7 and OsATX1 and down-regulated OsHMA4 probably decrease Cu compartmentalization in roots of oshc1. In summary, the frame-shift in OsHMA4 changes the function of OsHMA4 and the expression of genes relative to Cu transport in the mutant, which leads to more Cu transport upward and higher Cu accumulation in the rice grains. Moreover, oshc1 was more tolerance to Cu-shortage than WT, while more sensitive to Cu excess exposure than WT. However, RNA-Seq analysis shown that changes in transcription levels of genes in oshc1 involving in molecular function of ions binding and biological processes of cell wall organization and defense response to bio-stress. Which indicates that oshc1 is advantage to Cu limited condition than WT. This work reveals the mechanism of high Cu accumulation in the grains of oshc1 and provides a material to breed new cultivars with optimum levels of Cu in brown rice by crossing with other dominant varieties, which can be planted in different soils to ensure the yield and quality of rice.

Strawberry Proteome Responses to Controlled Hot and Cold Stress Partly Mimic Post-harvest Storage Temperature Effects on Fruit Quality

To determine the effect of different temperature on strawberry after harvest, physiological indicator analysis and proteomics analysis were conducted on ripened strawberry (“Sweet Charlie”) fruit stored at 4, 23, and 37°C for 10 or 20 days. Results showed that 4°C maintained a better visual quality of strawberry, and the weight loss and firmness remained stable within 3 days. Low temperature negatively affected anthocyanin but positively affected soluble sugars. Though anthocyanin content was higher with increasing temperature, anthocyanin synthesis related proteins were downregulated. Higher indole-acetic acid (IAA) content in seeds and lower abscisic acid (ABA) content were found in berry at 4°C. Antioxidant related proteins were upregulated during storage, showing a significant up-regulation of peroxidase (POD) at 4°C, and ascorbate-glutathione (AsA-GSH) cycle related proteins and heat shock proteins (HSPs) at 37°C. In addition, overexpressed sugar phosphate/phosphate translocator, 1-aminocyclopropane-1-carboxylate oxidase, and aquaporin PIP2-2 had a positive effect in response to low temperature stress for containing higher protopectin content and POD activity.

Meta-Analysis of Common and Differential Transcriptomic Responses to Biotic and Abiotic Stresses in Arabidopsis thaliana

Environmental stresses adversely affect crop growth and yield, resulting in major losses to plants. These stresses occur simultaneously in nature, and we therefore conducted a meta-analysis in this study to identify differential and shared genes, pathways, and transcriptomic mechanisms involved in Arabidopsis response to biotic and abiotic stresses. The results showed a total of 436/21 significant up-/downregulated differentially expressed genes (DEGs) in response to biotic stresses, while 476 and 71 significant DEGs were respectively up- and downregulated in response to abiotic stresses in Arabidopsis thaliana. In addition, 21 DEGs (2.09%) were commonly regulated in response to biotic and abiotic stresses. Except for WRKY45 and ATXTH22, which were respectively up-/down- and down-/upregulated in response to biotic and abiotic stresses, other common DEGs were upregulated in response to all biotic and abiotic treatments. Moreover, the transcription factors (TFs) bHLH, MYB, and WRKY were the common TFs in response to biotic and abiotic stresses. In addition, ath-miR414 and ath-miR5658 were identified to be commonly expressed in response to both biotic and abiotic stresses. The identified common genes and pathways during biotic and abiotic stresses may provide potential candidate targets for the development of stress resistance breeding programs and for the genetic manipulation of crop plants.

Transcriptomic and Metabolomic Analysis of Wheat Kernels in Response to the Feeding of Orange Wheat Blossom Midges (Sitodiplosis mosellana) in the Field

The orange wheat blossom midge (Sitodiplosis mosellana Géhin) is an insect pest that feeds on wheat (Triticum aestivum L.). The resistance mechanisms of wheat to S. mosellana infestation are largely unknown. In this study, the wheat varieties LX99 and 6218 were identified as highly resistant and susceptible, respectively, via field investigations conducted over two consecutive years. Morphological and microstructural observations of mature wheat kernels following S. mosellana infestation revealed that the degree of cell structure damage in resistant LX99 grains was less than that in susceptible 6218 grains. Transcriptomic and metabolomic analyses of seeds following S. mosellana feeding showed that the differentially expressed genes and differentially accumulated metabolites from LX99 were mostly enriched in several primary and secondary metabolic pathways, including phenylpropanoid biosynthesis, flavonoid biosynthesis, and phenylalanine biosynthesis. Additionally, phenylpropanoid- and flavonoid-related gene expression was significantly upregulated following S. mosellana infestation in LX99 relative to that in 6218. Some metabolites involved in phenylpropanoid/flavonoid pathways, such as cinnamic acid, coumarin, epigallocatechin, and naringenin, were only induced in infested LX99 kernels. These results suggest that phenylpropanoid/flavonoid pathways play important roles in wheat kernel resistance to S. mosellana attack and provide useful insights for the breeding and utilization of resistant varieties.

Molecular cloning and functional characterization of NtWRKY41a in the biosynthesis of phenylpropanoids in Nicotiana tabacum

Phenylpropanoids are important secondary metabolites that have multifaceted effects on plant growth, development, and environmental adaptation. WRKY41 has been shown to repress anthocyanins synthesis in Arabidopsis, but its full roles in regulating plant phenylpropanoids metabolism still remains to be further studied. Here, we cloned two NtWRKY41 genes from N. tabacum genome, and NtWRKY41a showed higher expression levels than NtWRKY41b genes in all the tobacco tissues examined. Overexpression and knock-out of NtWRKY41a gene revealed that NtWRKY41a promoted the biosynthesis of Chlorogenic acid (CGA) and lignin, but repressed the accumulation of scopoletin and flavonoids in tobacco. Transcriptome analysis found 7 phenylpropanoids related differentially expressed genes (DEGs) between WT and NtWRKY41a-OE plants, among which the transcription of NtCCoAOMT and NtHST was significantly induced by posttranslational activation of NtWRKY41a, while those of NtF6'H1 and NtGT3 was significantly repressed by NtWRKY41a. Chromatin immunoprecipitation and Dual-Luc assays further indicated that NtWRKY41a could bind to the promoter regions of these four genes to regulate their transcription. Moreover, ectopic expression of NtWRKY41a also promoted the transcription of several NtLOX and NtHPL genes, which encode key enzymes involved in the oxylipin pathway. Our findings revealed new functions of NtWRKY41a in modulating the distribution of metabolism flux in phenylpropanoids pathway, and provided a promising target for manipulating phenylpropanoids contents in tobacco.

Integrative transcriptomic and gene co-expression network analysis of host responses upon Verticillium dahliae infection in Gossypium hirsutum

Worldwide, Verticillium wilt is among the major harmful diseases in cotton production, causing substantial reduction in yields. While this disease has been extensively researched at the molecular level of the pathogen, the molecular basis of V. dahliae host response association is yet to be thoroughly investigated. In this study, RNA-seq analysis was carried out on V. dahliae infected two Gossypium hirsutum L. cultivars, Xinluzao-36 (susceptible) and Zhongzhimian-2 (disease resistant) for 0 h, 24 h, 72 h and 120 h time intervals. Statistical analysis revealed that V. dahliae infection elicited differentially expressed gene responses in the two cotton varieties, but more intensely in the susceptible cultivar than in the resistant cultivars. Data analysis revealed 4241 differentially expressed genes (DEGs) in the LT variety across the three treatment timepoints whereas 7657 in differentially expressed genes (DEGs) in the Vd592 variety across the three treatment timepoints. Six genes were randomly selected for qPCR validation of the RNA-Seq data. Numerous genes encompassed in disease resistance and defense mechanisms were identified. Further, RNA-Seq dataset was utilized in construction of the weighted gene co-expression network and 11 hub genes were identified, that encode for different proteins associated with lignin and immune response, Auxin response factor, cell wall and vascular development, microtubule, Ascorbate transporter, Serine/threonine kinase and Immunity and drought were identified. This significant research will aid in advancing crucial knowledge on virus-host interactions and identify key genes intricate in G. hirsutum L. resistance to V. dahliae infection.

MdWRKY75e enhances resistance to Alternaria alternata in Malus domestica

The Alternaria alternata apple pathotype adversely affects apple (Malus domestica Borkh.) cultivation. However, the molecular mechanisms underlying enhanced resistance to this pathogen in apple remain poorly understood. We have previously reported that MdWRKY75 expression is upregulated by A. alternata infection in 'Sushuai' apples. In this study, we discovered that overexpression of MdWRKY75e increased the resistance of transgenic apple lines to A. alternata infection, whereas silencing this gene enhanced susceptibility to A. alternata infection. Furthermore, we found that MdWRKY75e directly binds to the MdLAC7 promoter to regulate the biosynthesis of laccase and increase the biosynthesis of lignin during A. alternata infection. Moreover, the thickening of the cell wall enhanced the mechanical defense capabilities of apple. In addition, we found that jasmonic acid remarkably induced MdWRKY75e expression, and its levels in transgenic apple lines were elevated. These results indicate that MdWRKY75e confers resistance to the A. alternata apple pathotype mainly via the jasmonic acid pathway and that pathogenesis-related genes and antioxidant-related enzyme activity are involved in the disease resistance of MdWRKY75e transgenic plants. In conclusion, our findings provide insights into the importance of MdWRKY75e for resistance to A. alternata infection in apples.

Constitutive Defense Strategy of Coffee Under Field Conditions: A Comparative Assessment of Resistant and Susceptible Cultivars to Rust

Coffea arabica is the most economically important coffee species worldwide. However, its production is severely limited by diseases such as rust. The mechanisms underlying constitutive defense responses in coffee are still poorly understood, compared with induced defense mechanisms. We aimed to characterize constitutive defense responses of thirteen cultivars of C. arabica. Cultivars were classified under field conditions according to the level of resistance to rust: resistant (R), moderately resistant (MR), and susceptible (S). Based on this classification, the stability of eight reference genes (RGs) was evaluated. The most stable RGs were EF1α, APT1, and 24S. We also evaluated the expression of CaWRKY1, CaPAL1, CaCAD1, and CaPOX1, and activities of PAL, CAD, and POX, which are involved in lignin biosynthesis, and leaf content of total phenolic compounds and lignin. Gene expression and enzymatic activity were not correlated with defense metabolites in the R cultivar group but showed a negative correlation with phenolic compounds in MR cultivars. Cultivar S showed positive correlations of gene expression and enzyme activity with phenolic compounds. These results may assist coffee breeding programs regarding selection of genotypes and in optimization of rust resistance.

The phenylpropanoid pathway inhibitor piperonylic acid induces broad-spectrum pest and disease resistance in plants

Although many phenylpropanoid pathway-derived molecules act as physical and chemical barriers to pests and pathogens, comparatively little is known about their role in regulating plant immunity. To explore this research field, we transiently perturbed the phenylpropanoid pathway through application of the CINNAMIC ACID-4-HYDROXYLASE (C4H) inhibitor piperonylic acid (PA). Using bioassays involving diverse pests and pathogens, we show that transient C4H inhibition triggers systemic, broad-spectrum resistance in higher plants without affecting growth. PA treatment enhances tomato (Solanum lycopersicum) resistance in field and laboratory conditions, thereby illustrating the potential of phenylpropanoid pathway perturbation in crop protection. At the molecular level, transcriptome and metabolome analyses reveal that transient C4H inhibition in tomato reprograms phenylpropanoid and flavonoid metabolism, systemically induces immune signalling and pathogenesis-related genes, and locally affects reactive oxygen species metabolism. Furthermore, C4H inhibition primes cell wall modification and phenolic compound accumulation in response to root-knot nematode infection. Although PA treatment induces local accumulation of the phytohormone salicylic acid, the PA resistance phenotype is preserved in tomato plants expressing the salicylic acid-degrading NahG construct. Together, our results demonstrate that transient phenylpropanoid pathway perturbation is a conserved inducer of plant resistance and thus highlight the crucial regulatory role of this pathway in plant immunity.

The novel pathogen-responsive glycosyltransferase UGT73C7 mediates the redirection of phenylpropanoid metabolism and promotes SNC1-dependent Arabidopsis immunity

Recent studies have shown that global metabolic reprogramming is a common event in plant innate immunity; however, the relevant molecular mechanisms remain largely unknown. Here, we identified a pathogen-induced glycosyltransferase, UGT73C7, that plays a critical role in Arabidopsis disease resistance through mediating redirection of the phenylpropanoid pathway. Loss of UGT73C7 function resulted in significantly decreased resistance to Pseudomonas syringae pv. tomato DC3000, whereas constitutive overexpression of UGT73C7 led to an enhanced defense response. UGT73C7-activated immunity was demonstrated to be dependent on the upregulated expression of SNC1, a Toll/interleukin 1 receptor-type NLR gene. Furthermore, in vitro and in vivo assays indicated that UGT73C7 could glycosylate p-coumaric acid and ferulic acid, the upstream metabolites in the phenylpropanoid pathway. Mutations that lead to the loss of UGT73C7 enzyme activities resulted in the failure to induce SNC1 expression. Moreover, glycosylation activity of UGT73C7 resulted in the redirection of phenylpropanoid metabolic flux to biosynthesis of hydroxycinnamic acids and coumarins. The disruption of the phenylpropanoid pathway suppressed UGT73C7-promoted SNC1 expression and the immune response. This study not only identified UGT73C7 as an important regulator that adjusts phenylpropanoid metabolism upon pathogen challenge, but also provided a link between phenylpropanoid metabolism and an NLR gene.

Transcriptome and metabolome analyses revealing the potential mechanism of seed germination in Polygonatum cyrtonema

Polygonatum cyrtonema Hua (Huangjing, HJ) has medicinal and edible value in China. However, the seeds of this plant are naturally difficult to germinate. Therefore, to elucidate the mechanism underlying the germination of this plant in order to meet the market demand, the metabolomic and transcriptomic analyses were performed in this study. We observed that plant hormones and α-amylase activity were differentially regulated when comparing germinated and un-germinated seeds. In addition, the metabolites related to phenylpropanoid and flavonoid biosynthesis were significantly up-accumulated in germinated seeds. Hydroxycinnamoyl derivatives and organic acids were observed to be significantly decreased during germination. The results of this study suggested that compared to un-germinated seeds, germinated seeds promote flavonoid synthesis and inhibit lignin synthesis which could be beneficial to the germination of HJ seeds. Furthermore, these results suggested that starch if hydrolyzed into glucose, which could provide the necessary energy for germination. Our results may help to establish a foundation for further research investigating the regulatory networks of seed germination and may facilitate the propagation of HJ seeds.

Comparative biochemical and transcriptome analyses in tomato and eggplant reveal their differential responses to Tuta absoluta infestation

Tomato is more prone to Tuta absoluta invasion and damages as compared to other host plants but the mechanism behind this preference has not been elucidated. Here, two contrasting host preference plants, tomato and eggplant, were used to investigate biochemical and transcriptomic modifications induced by T. absoluta infestation. Biochemical analysis at 0-72 h post T. absoluta infestation revealed significantly reduced concentrations of amino acid, fructose, sucrose, jasmonic acid, salicylic acid, and total phenols in tomato compared to eggplant, mainly at 48 h post T. absoluta infestation. Transcriptome analysis showed higher transcript changes in infested eggplant than tomato. Signaling genes had significant contributions to mediate plant immunity against T. absoluta, specifically genes associated with salicylic acid in eggplant. Genes from PR1b1, NPR1, NPR3, MAPKs, and ANP1 families play important roles to mitigate T. absoluta infestation. Our results will facilitate the development of control strategies against T. absoluta for sustainable tomato production.

Three Types of Elicitors Induce Grapevine Resistance against Downy Mildew via Common and Specific Immune Responses

Three recognized plant defense stimulators (PDS), methyl jasmonate (MeJA), benzothiadiazole (BTH) and phosphonates (PHOS), were sprayed on grapevine Vitis vinifera cuttings and conferred resistance to the biotrophic pathogen Plasmopara viticola. The effects on molecular defense-related genes and polyphenol content (stilbenes and flavanols) were revealed at 6 and 8 days post-elicitation. The transcript accumulation was consistent with the signaling pathway specific to the elicitor, salicylic acid for BTH, and jasmonic acid for MeJA, with some cross-talks. PHOS tended to modulate the defense responses like BTH. Moreover, in response to a downy mildew inoculation, the leaves pre-treated with PHOS and BTH overproduced pterostilbene, and after MeJA treatment, piceids and ε-viniferin, compared to uninoculated elicitor-treated leaves. These results provide evidence of the different modes of action of PDS and their role in sustainable viticulture.

Melatonin and Its Homologs Induce Immune Responses via Receptors trP47363-trP13076 in Nicotiana benthamiana

Melatonin (N-acetyl-5-methoxytryptamine), a naturally occurring small molecule, can protect plants against abiotic stress after exogenous treatmenting with it. It is not known if melatonin homologs, such as 5-methoxytryptamine and 5-methoxyindole, that are easy and more cost-effective to synthesize can stimulate the plant immune system in the same manner as melatonin. In the present study, we assessed the biological activity of the melatonin homologs, 5-methoxytryptamin and 5-methoxyindole. The results showed that melatonin and its homologs all induced disease resistance against Phytophthora nicotianae in Nicotiana benthamiana plants. The application of all three compounds also induced stomatal closure and the production of reactive oxygen species. Gene expression analysis indicated that the expression of genes involved in hydrogen peroxide (H₂O₂), nitric oxide (NO) production, and salicylic acid (SA) biosynthesis was significantly upregulated by all three compounds. Four homologs of the melatonin receptors were identified by blasting search with the phytomelatonin receptor in Arabidopsis. Molecular docking studies were also used to identify four putative melatonin receptors in N. benthamiana. Further experimentation revealed that silencing of the melatonin receptors trP47363 and trP13076 in N. benthamiana compromised the induction of stomatal closure, PR-1a gene expression and SA accumulation by all three compounds. Collectively, our data indicate that the induction of defense responses in N. benthamiana by melatonin, 5-methoxytryptamine, and 5-methoxyindole involves the melatonin receptors trP47363 and trP13076.

Phosphate deficiency enhances cotton resistance to Verticillium dahliae through activating jasmonic acid biosynthesis and phenylpropanoid pathway

Living in natural environment, plants often suffer from various biotic and abiotic stresses. Phosphate deficiency is a common factor affecting crop production in field, while pathogen invasion is another serious problem. Here we report that Pi-deficient cotton plants exhibit enhanced resistance to Verticillium dahliae. Transcriptomic and histochemical analysis revealed that cotton phenylpropanoid pathway was activated under phosphate deficiency, including lignin and flavonoid biosynthesis. Metabolomic data showed that Pi-deficient cotton accumulates many flavonoids metabolites and displays obvious anti-fungi activity in terms of methanolic extract. Additionally, JA biosynthesis was activated under phosphate deficiency and the Pi-deficiency induced disease resistance was significantly attenuated in GhAOS knock down plants. Taken together, our study demonstrated that phosphate deficiency enhanced cotton resistance to V. dahliae through activating phenylpropanoid pathway and JA biosynthesis, providing new insights into how phosphate deficiency affects plant disease resistance.

Local Responses and Systemic Induced Resistance Mediated by Ectomycorrhizal Fungi

Ectomycorrhizal fungi (EMF) grow as saprotrophs in soil and interact with plants, forming mutualistic associations with roots of many economically and ecologically important forest tree genera. EMF ensheath the root tips and produce an extensive extramatrical mycelium for nutrient uptake from the soil. In contrast to other mycorrhizal fungal symbioses, EMF do not invade plant cells but form an interface for nutrient exchange adjacent to the cortex cells. The interaction of roots and EMF affects host stress resistance but uncovering the underlying molecular mechanisms is an emerging topic. Here, we focused on local and systemic effects of EMF modulating defenses against insects or pathogens in aboveground tissues in comparison with arbuscular mycorrhizal induced systemic resistance. Molecular studies indicate a role of chitin in defense activation by EMF in local tissues and an immune response that is induced by yet unknown signals in aboveground tissues. Volatile organic compounds may be involved in long-distance communication between below- and aboveground tissues, in addition to metabolite signals in the xylem or phloem. In leaves of EMF-colonized plants, jasmonate signaling is involved in transcriptional re-wiring, leading to metabolic shifts in the secondary and nitrogen-based defense metabolism but cross talk with salicylate-related signaling is likely. Ectomycorrhizal-induced plant immunity shares commonalities with systemic acquired resistance and induced systemic resistance. We highlight novel developments and provide a guide to future research directions in EMF-induced resistance.

Overexpression of OsCM alleviates BLB stress via phytohormonal accumulation and transcriptional modulation of defense-related genes in Oryza sativa

Xanthomonas oryzae is a serious pathogen causing bacterial leaf blight (BLB) disease in rice, markedly reducing its yield. In this study, the rice chorismate mutase (OsCM) gene was overexpressed in a bacterial leaf blight-susceptible rice line to investigate the functional role of OsCM in response to bacterial leaf blight stress. We reported that overexpression of OsCM altered the downstream pathway of aromatic amino acids, mitigating pathogen stress by altering stress-responsive genes and hormonal accumulation. Phenotypic evaluation showed that the lesion length in the transgenic line was significantly lesser than that in the wild-type, suggesting greater resistance in the transgenic line. Further analysis revealed that OsCM expression induced phenylalanine accumulation and suppressed tyrosine accumulation in response to bacterial leaf blight stress. Furthermore, bacterial leaf blight stress induced genes downstream of the phenylpropanoid pathway in conjunction with OsCM, suggesting that the phenylpropanoid pathway is dependent on OsCM gene expression. We reported high SA and low JA accumulation in response to bacterial leaf blight stress in the transgenic line. This higher SA accumulation suggested that SA induces immune responses by functioning as a promoter of nonexpresser pathogenesis-related genes 1 (NPR1) transcriptional regulation. Xa7 expression was induced with increase in nonexpresser pathogenesis-related genes 1, which is thought to be responsible for Xa7 expression, which is responsible for mitigating bacterial leaf blight stress.

TCA cycle signalling and the evolution of eukaryotes

A major question remaining in the field of evolutionary biology is how prokaryotic organisms made the leap to complex eukaryotic life. The prevailing theory depicts the origin of eukaryotic cell complexity as emerging from the symbiosis between an α-proteobacterium, the ancestor of present-day mitochondria, and an archaeal host (endosymbiont theory). A primary contribution of mitochondria to eukaryogenesis has been attributed to the mitochondrial genome, which enabled the successful internalisation of bioenergetic membranes and facilitated remarkable genome expansion. It has also been postulated that a key contribution of the archaeal host during eukaryogenesis was in providing 'archaeal histones' that would enable compaction and regulation of an expanded genome. Yet, how the communication between the host and the symbiont evolved is unclear. Here, we propose an evolutionary concept in which mitochondrial TCA cycle signalling was also a crucial player during eukaryogenesis enabling the dynamic control of an expanded genome via regulation of DNA and histone modifications. Furthermore, we discuss how TCA cycle remodelling is a common evolutionary strategy invoked by eukaryotic organisms to coordinate stress responses and gene expression programmes, with a particular focus on the TCA cycle-derived metabolite itaconate.

Bacillus licheniformis strain POT1 mediated polyphenol biosynthetic pathways genes activation and systemic resistance in potato plants against Alfalfa mosaic virus

Alfalfa mosaic virus (AMV) is a worldwide distributed virus that has a very wide host range and causes significant crop losses of many economically important crops, including potato (Solanum tuberosum L.). In this study, the antiviral activity of Bacillus licheniformis strain POT1 against AMV on potato plants was evaluated. The dual foliar application of culture filtrate (CF), 24 h before and after AMV-inoculation, was the most effective treatment that showed 86.79% reduction of the viral accumulation level and improvement of different growth parameters. Moreover, HPLC analysis showed that a 20 polyphenolic compound was accumulated with a total amount of 7,218.86 and 1606.49 mg/kg in POT1-treated and non-treated plants, respectively. Additionally, the transcriptional analysis of thirteen genes controlling the phenylpropanoid, chlorogenic acid and flavonoid biosynthetic pathways revealed that most of the studied genes were induced after POT1 treatments. The stronger expression level of F3H, the key enzyme in flavonoid biosynthesis in plants, (588.133-fold) and AN2, anthocyanin 2 transcription factor, (97.005-fold) suggested that the accumulation flavonoid, especially anthocyanin, might play significant roles in plant defense against viral infection. Gas chromatography-mass spectrometry (GC-MS) analysis showed that pyrrolo[1,2-a]pyrazine-1,4-dione is the major compound in CF ethyl acetate extract, that is suggesting it acts as elicitor molecules for induction of systemic acquired resistance in potato plants. To our knowledge, this is the first study of biological control of AMV mediated by PGPR in potato plants.

Genome-wide characterization and expression profiling of MAPK cascade genes in Salvia miltiorrhiza reveals the function of SmMAPK3 and SmMAPK1 in secondary metabolism

Background

The contribution of mitogen-activated protein kinase (MAPK) cascades to plant growth and development has been widely studied, but this knowledge has not yet been extended to the medicinal plant Salvia miltiorrhiza, which produces a number of pharmacologically active secondary metabolites.

Results

In this study, we performed a genome-wide survey and identified six MAPKKK kinases (MAPKKKKs), 83 MAPKK kinases (MAPKKKs), nine MAPK kinases (MAPKKs) and 18 MAPKs in the S. miltiorrhiza genome. Within each class of genes, a small number of subfamilies were recognized. A transcriptional analysis revealed differences in the genes’ behaviour with respect to both their site of transcription and their inducibility by elicitors and phytohormones. Two genes were identified as strong candidates for playing roles in phytohormone signalling. A gene-to-metabolite network was constructed based on correlation analysis, highlighting the likely involvement of two of the cascades in the synthesis of two key groups of pharmacologically active secondary metabolites: phenolic acids and tanshinones.

Conclusion

The data provide insight into the functional diversification and conservation of MAPK cascades in S. miltiorrhiza.

Phenylalanine increases chrysanthemum flower immunity against Botrytis cinerea attack

Flowers are the most vulnerable plant organ to infection by the necrotrophic fungus Botrytis cinerea. Here we show that pre-treatment of chrysanthemum (Chrysanthemum morifolium) flowers with phenylalanine (Phe) significantly reduces their susceptibility to B. cinerea. To comprehend how Phe treatment induces resistance, we monitored the dynamics of metabolites (by GC/LC-MS) and transcriptomes (by RNAseq) in flowers after Phe treatment and B. cinerea infection. Phe treatment resulted in accumulation of 3-phenyllactate and benzaldehyde, and in particular induced the expression of genes related to Ca²⁺ signaling and receptor kinases, implicating an induction of the defense response. Interestingly, the main effects of Phe treatment were observed in flowers exposed to B. cinerea infection, stabilizing the global fluctuations in the levels of metabolites and transcripts while reducing susceptibility to the fungus. We suggest that Phe-induced resistance is associated to cell priming, enabling rapid and targeted reprogramming of cellular defense responses to resist disease development. After Phe pre-treatment, the levels of the anti-fungal volatiles phenylacetaldehyde and eugenol were maintained and the level of coniferin, a plausible monolignol precursor in cell wall lignification, was strongly increased. In addition, Phe pre-treatment reduced ROS generation, prevented ethylene emission, and caused changes in the expression of a minor number of genes related to cell wall biogenesis, encoding the RLK THESEUS1, or involved in Ca²⁺ and hormonal signaling processes. Our findings point to Phe pre-treatment as a potential orchestrator of a broad-spectrum defense response which may not only provide an ecologically friendly pest control strategy but also offers a promising way of priming plants to induce defense responses against B. cinerea.

Role of laccase gene in wheat NILs differing at QTL-Fhb1 for resistance against Fusarium head blight

Fusarium head blight (FHB), caused mainly by Fusarium graminearum (Fg), is one of the most severe diseases of wheat. It affects grain yield and quality due to mycotoxin contamination, which is harmful for both human and livestock consumption. Cell wall lignification, following pathogen invasion, is one of the innate defense responses. Plant laccases are known to lignify the secondary cell walls. A metabolo-genomics study identified laccase as one of the candidate genes in QTL-Fhb1 of wheat NILs derived from Sumai 3*5/Thatcher cross. Based on phylogenetics, it was named as TaLAC4. Real-time qPCR revealed a strongly induced expression of TaLAC4 in NIL-R. The VIGS based transient silencing of TaLAC4 in NIL-R resulted in an increased susceptibility leading to Fg spread within the entire spike in 15dpi, contrasting to non-silenced where the infection was limited to inoculated spikelets. Histopathology revealed thickened cell walls, mainly due to G-lignin, in non-silenced NIL-R, relative to silenced, in conjunction with higher total lignin content. Metabolic profiling of TaLAC4 silenced NILs identified the accumulation of several precursor metabolites higher in abundances upstream TaLAC4. These results confirm that the resistance function of TaLAC4 in NIL-R is due to pathogen-induced lignification of secondary cell walls in the rachis.

Insights on the Structural and Metabolic Resistance of Potato (Solanum tuberosum) Cultivars to Tuber Black Dot (Colletotrichum coccodes)

Black dot is a blemish disease of potato tubers caused by the phytopathogenic fungus Colletotrichum coccodes. Qualitative resistance (monogenic) that leads to the hypersensitive response has not been reported against black dot, but commercial potato cultivars show different susceptibility levels to the disease, indicating that quantitative resistance (polygenic) mechanisms against this pathogen exist. Cytological studies are essential to decipher pathogen colonization of the plant tissue, and untargeted metabolomics has been shown effective in highlighting resistance-related metabolites in quantitative resistance. In this study, we used five commercial potato cultivars with different susceptibility levels to black dot, and studied the structural and biochemical aspects that correlate with resistance to black dot using cytological and untargeted metabolomics methods. The cytological approach using semithin sections of potato tuber periderm revealed that C. coccodes colonizes the tuber periderm, but does not penetrate in cortical cells. Furthermore, skin thickness did not correlate with disease susceptibility, indicating that other factors influence quantitative resistance to black dot. Furthermore, suberin amounts did not correlate with black dot severity, and suberin composition was similar between the five potato cultivars studied. On the other hand, the untargeted metabolomics approach allowed highlighting biomarkers of infection, as well as constitutive and induced resistance-related metabolites. Hydroxycinnamic acids, hydroxycinnamic acid amides and steroidal saponins were found to be biomarkers of resistance under control conditions, while hydroxycoumarins were found to be specifically induced in the resistant cultivars. Notably, some of these biomarkers showed antifungal activity in vitro against C. coccodes. Altogether, our results show that quantitative resistance of potatoes to black dot involves structural and biochemical mechanisms, including the production of specialized metabolites with antifungal properties.

Integrated Omics Analyses Identify Key Pathways Involved in Petiole Rigidity Formation in Sacred Lotus

Sacred lotus (Nelumbo nucifera Gaertn.) is a relic aquatic plant with two types of leaves, which have distinct rigidity of petioles. Here we assess the difference from anatomic structure to the expression of genes and proteins in two petioles types, and identify key pathways involved in petiole rigidity formation in sacred lotus. Anatomically, great variation between the petioles of floating and vertical leaves were observed. The number of collenchyma cells and thickness of xylem vessel cell wall was higher in the initial vertical leaves’ petiole (IVP) compared to the initial floating leaves’ petiole (IFP). Among quantified transcripts and proteins, 1021 and 401 transcripts presented 2-fold expression increment (named DEGs, genes differentially expressed between IFP and IVP) in IFP and IVP, 421 and 483 proteins exhibited 1.5-fold expression increment (named DEPs, proteins differentially expressed between IFP and IVP) in IFP and IVP, respectively. Gene function and pathway enrichment analysis displayed that DEGs and DEPs were significantly enriched in cell wall biosynthesis and lignin biosynthesis. In consistent with genes and proteins expressions in lignin biosynthesis, the contents of lignin monomers precursors were significantly different in IFP and IVP. These results enable us to understand lotus petioles rigidity formation better and provide valuable candidate genes information on further investigation.

Transcriptome and metabolite analysis reveal the drought tolerance of foxtail millet significantly correlated with phenylpropanoids-related pathways during germination process under PEG stress

BACKGROUND

Foxtail millet [Setaria italica (L.) P. Beauv.] is an excellent crop known for its superior level of drought tolerance across the world. Especially, less water is needed during its germination period than the other cereal crops. However, the knowledge of the mechanisms underlying the abiotic stress effects on seed germination of foxtail millet is largely unknown.

RESULTS

The water uptake pattern of foxtail millet seeds was ploted during germination period, according to which the germination time course of millet was separated into three phases. We sequenced the transcriptome of foxtail millet seeds, which were treated by PEG during different germination phases after sowing. The transcriptional studies revealed that more DEGs were identified during the further increase in water uptake period (phase III) than during the rapid initial uptake period (phase I) and the plateau period (phase II) under PEG stress. The pathway analysis of DEGs showed that the highly enriched categories were related to phenylpropanoid biosynthesis, plant hormone signal transduction and phenylalanine metabolism during phase III. The 20 phenylpropanoids-related genes of germinating foxtail millet were found to be down-regulated during the further increase in water uptake period under PEG stress. Further expression analysis identified 4 genes of phenylalanine ammonia-lyase, 4-coumarate-CoA ligase 3, cinnamoyl-CoA reductase 1, cationic peroxidase SPC4 in phenylpropanoids-related pathway, which played important roles in foxtail millet in response to PEG stress during different germination periods. The studies of metabolites in phenylpropanoid biosynthesis pathway revealed that higher amount of cinnamic acid was accumulated in germinating seeds under PEG stress, while the contents of p-coumaric acid, caffeic acid, ferulic acid and sinapic acid were decreased. And the effects of five phenolic compounds on germination and growth of foxtail millet showed that 1 mM concentration of cinnamic acid inhibited shoot and root growth, especially root development. Ferulic acid, caffeic acid, sinapic acid and p-coumaric acid could increase the root length and root/sprout in lower concentration.

CONCLUSIONS

These findings suggest that key genes and metabolites of foxtail millet related with phenylpropanoids pathway may play prominent roles in the regulation of resistance to drought during germination. Foxtail millet can probably avoid drought by regulating the levels of endogenous allelochemicals.