Deciphering the role of phytoalexins in plant-microorganism interactions and human health

A mechanistic insight into the anticancer potentials of resveratrol: Current perspectives

Resveratrol is a widely recognized polyphenolic phytochemical found in various plants and their fruits, such as peanuts, grapes, and berry fruits. It is renowned for its several health advantages. The phytochemical is well known for its anticancer properties, and a substantial amount of clinical evidence has also established its promise as a chemotherapeutic agent. This study focuses on assessing the anticancer properties of resveratrol and gaining insight into the underlying molecular mechanisms. It also evaluates the biopharmaceutical, toxicological characteristics, and clinical utilization of resveratrol to determine its suitability for further development as a reliable anticancer agent. Therefore, the information about preclinical and clinical studies was collected from different electronic databases up-to-date (2018-2023). Findings from this study revealed that resveratrol has potent therapeutic benefits against various cancers involving different molecular mechanisms, such as induction of oxidative stress, cytotoxicity, inhibition of cell migration and invasion, autophagy, arresting of the S phase of the cell cycle, apoptotic, anti-angiogenic, and antiproliferative effects by regulating different molecular pathways including PI3K/AKT, p38/MAPK/ERK, NGFR-AMPK-mTOR, and so on. However, the compound has poor oral bioavailability due to reduced absorption; this limitation is overcome by applying nanotechnology (nanoformulation of resveratrol). Clinical application also showed therapeutic benefits in several types of cancer with no serious adverse effects. We suggest additional extensive studies to further check the efficacy, safety, and long-term hazards. This could involve a larger number of clinical samples to establish the compound as a reliable drug in the treatment of cancer.

Metabolomics-driven investigation of plant defense response against pest and pathogen attack

The advancement of metabolomics has assisted in the identification of various bewildering characteristics of the biological system. Metabolomics is a standard approach, facilitating crucial aspects of system biology with absolute quantification of metabolites using minimum samples, based on liquid/gas chromatography, mass spectrometry and nuclear magnetic resonance. The metabolome profiling has narrowed the wide gaps of missing information and has enhanced the understanding of a wide spectrum of plant-environment interactions by highlighting the complex pathways regulating biochemical reactions and cellular physiology under a particular set of conditions. This high throughput technique also plays a prominent role in combined analyses of plant metabolomics and other omics datasets. Plant metabolomics has opened a wide paradigm of opportunities for developing stress-tolerant plants, ensuring better food quality and quantity. However, despite advantageous methods and databases, the technique has a few limitations, such as ineffective 3D capturing of metabolites, low comprehensiveness, and lack of cell-based sampling. In the future, an expansion of plant-pathogen and plant-pest response towards the metabolite architecture is necessary to understand the intricacies of plant defence against invaders, elucidation of metabolic pathway operational during defence and developing a direct correlation between metabolites and biotic stresses. Our aim is to provide an overview of metabolomics and its utilities for the identification of biomarkers or key metabolites associated with biotic stress, devising improved diagnostic methods to efficiently assess pest and pathogen attack and generating improved crop varieties with the help of combined application of analytical and molecular tools.

Dirigent isoflavene-forming PsPTS2: 3D structure, stereochemical, and kinetic characterization comparison with pterocarpan-forming PsPTS1 homolog in pea

Pea phytoalexins (-)-maackiain and (+)-pisatin have opposite C6a/C11a configurations, but biosynthetically how this occurs is unknown. Pea dirigent-protein (DP) PsPTS2 generates 7,2'-dihydroxy-4',5'-methylenedioxyisoflav-3-ene (DMDIF), and stereoselectivity toward four possible 7,2'-dihydroxy-4',5'-methylenedioxyisoflavan-4-ol (DMDI) stereoisomers was investigated. Stereoisomer configurations were determined using NMR spectroscopy, electronic circular dichroism, and molecular orbital analyses. PsPTS2 efficiently converted cis-(3R,4R)-DMDI into DMDIF 20-fold faster than the trans-(3R,4S)-isomer. The 4R-configured substrate's near β-axial OH orientation significantly enhanced its leaving group abilities in generating A-ring mono-quinone methide (QM), whereas 4S-isomer's α-equatorial-OH was a poorer leaving group. Docking simulations indicated that the 4R-configured β-axial OH was closest to Asp51, whereas 4S-isomer's α-equatorial OH was further away. Neither cis-(3S,4S)- nor trans-(3S,4R)-DMDIs were substrates, even with the former having C3/C4 stereochemistry as in (+)-pisatin. PsPTS2 used cis-(3R,4R)-7,2'-dihydroxy-4'-methoxyisoflavan-4-ol [cis-(3R,4R)-DMI] and C3/C4 stereoisomers to give 2',7-dihydroxy-4'-methoxyisoflav-3-ene (DMIF). DP homologs may exist in licorice (Glycyrrhiza pallidiflora) and tree legume Bolusanthus speciosus, as DMIF occurs in both species. PsPTS1 utilized cis-(3R,4R)-DMDI to give (-)-maackiain 2200-fold more efficiently than with cis-(3R,4R)-DMI to give (-)-medicarpin. PsPTS1 also slowly converted trans-(3S,4R)-DMDI into (+)-maackiain, reflecting the better 4R configured OH leaving group. PsPTS2 and PsPTS1 provisionally provide the means to enable differing C6a and C11a configurations in (+)-pisatin and (-)-maackiain, via identical DP-engendered mono-QM bound intermediate generation, which PsPTS2 either re-aromatizes to give DMDIF or PsPTS1 intramolecularly cyclizes to afford (-)-maackiain. Substrate docking simulations using PsPTS2 and PsPTS1 indicate cis-(3R,4R)-DMDI binds in the anti-configuration in PsPTS2 to afford DMDIF, and the syn-configuration in PsPTS1 to give maackiain.

Recent advancements in multifaceted roles of flavonoids in plant-rhizomicrobiome interactions

The rhizosphere consists of a plethora of microbes, interacting with each other as well as with the plants present in proximity. The root exudates consist of a variety of secondary metabolites such as strigolactones and other phenolic compounds such as coumarin that helps in facilitating communication and forming associations with beneficial microbes in the rhizosphere. Among different secondary metabolites flavonoids (natural polyphenolic compounds) continuously increasing attention in scientific fields for showing several slews of biological activities. Flavonoids possess a benzo-γ-pyrone skeleton and several classes of flavonoids have been reported on the basis of their basic structure such as flavanones, flavonols, anthocyanins, etc. The mutualistic association between plant growth-promoting rhizobacteria (PGPR) and plants have been reported to help the host plants in surviving various biotic and abiotic stresses such as low nitrogen and phosphorus, drought and salinity stress, pathogen attack, and herbivory. This review sheds light upon one such component of root exudate known as flavonoids, which is well known for nodulation in legume plants. Apart from the well-known role in inducing nodulation in legumes, this group of compounds has anti-microbial and antifungal properties helping in establishing defensive mechanisms and playing a major role in forming mycorrhizal associations for the enhanced acquisition of nutrients such as iron and phosphorus. Further, this review highlights the role of flavonoids in plants for recruiting non-mutualistic microbes under stress and other important aspects regarding recent findings on the functions of this secondary metabolite in guiding the plant-microbe interaction and how organic matter affects its functionality in soil.

Natural phytoalexins inspired the discovery of new biphenyls as potent antifungal agents for treatment of invasive fungal infections

With the aim of discovering novel and effective antifungal agents derived from natural sources, a series of new biphenyls based on natural biphenyl phytoalexins were designed, synthesized and evaluated for their antifungal activities against four invasive fungi. By modifying the two benzene rings of noraucuparin, a well-known biphenyl phytoantitoxin, some promising compounds with remarkable antifungal activity were discovered. Notably, compounds 23a, 23e and 23h exhibited potent activities and a broad antifungal spectrum with low MICs of 0.25-16 μg/mL, which were 8-256-fold more potent than that of the lead compound noraucuparin. Particularly, they displayed comparable potency to the positive control amphotericin B against Cryptococcus neoformans. Some interesting structure-activity relationships have also been discussed. Preliminary mechanism studies revealed that compound 23h might achieve its rapid fungicidal activity by disrupting the fungal cell membrane. Moreover, compound 23h exhibited significant inhibition against some virulence factors of Cryptococcus neoformans, low toxicity to normal human cells, as well as favorable pharmacokinetic and drug-like properties. The above results evidenced that the development of new antifungal candidates derived from natural phytoalexins was a bright and promising strategy.

Combined effects of two phytoalexins, brassinin and camalexin, on the cells of colorectal origin

Brassinin and camalexin belong to phytoalexins, plant compounds generated in the response to stress. Both compounds are known to be cytotoxic to several cancer cell lines, mainly by inducing oxidative stress and subsequent apoptosis. In the presented study, cytotoxic effects of brassinin and camalexin, individually and, for the first time, after combined exposure, on the cells of normal (CCD-Co18) and cancer (Caco-2) lines originated from colorectal tissues and their proapoptotic impact on Caco-2 cells were studied. The determined IC50 values indicate a clearly higher sensitivity of cancer cells to the tested substances, as well as a stronger cytotoxic effect of camalexin than brassinin. The synergistic effect of both phytoalexins was also demonstrated. Caspase-dependent and independent mechanisms were involved in the final effects. Both tested phytoalexins caused evident, concentration-dependent symptoms of oxidative stress in cancer cells, leading to apoptosis, but in the highest concentrations, also to necrosis. In case of camalexin, signs of pyroptosis were additionally detected.

Leveraging the Persistent Radical Effect in the Synthesis of trans-2,3-Diaryl Dihydrobenzofurans

A simple method for accessing trans-2,3-diaryl dihydrobenzofurans is reported. This approach leverages the equilibrium between quinone methide dimers and their persistent radicals. This equilibrium is disrupted by phenols that yield comparatively transient phenoxyl radicals, leading to cross-coupling between the persistent and transient radicals. The resultant quinone methides with pendant phenols rapidly cyclize to form dihydrobenzofurans (DHBs). This putative biomimetic access to dihydrobenzofurans provides superb functional group tolerance and a unified approach for the synthesis of resveratrol-based natural products.

Anti-Inflammatory Effects of Olive Leaf Extract and Its Bioactive Compounds Oleacin and Oleuropein-Aglycone on Senescent Endothelial and Small Airway Epithelial Cells

Olive tree by-products have been deeply studied as an invaluable source of bioactive compounds. Several in vitro and in vivo studies showed that olive leaf extract (OLE) has anti-inflammatory and antioxidant properties. Here, we wanted to assess the valuable benefits of two less-studied OLE components-3,4-DHPEA-EDA (Oleacin, OC) and 3,4-DHPEA-EA (Oleuropein-Aglycone, OA)-directly purified from OLE using a cost-effective and environmentally sustainable method, in line with the principles of circular economy. OLE, OC and OA were then tested in human cellular models involved in acute and chronic inflammation and in the pathogenesis of viral infections, i.e., lipopolysaccharide (LPS)-treated monocyte/macrophages (THP-1) and endothelial cells (HUVECs), senescent HUVECs and Poly(I:C)-treated small airway epithelial cells (hSAECs). Results showed that OC and OA are efficient in ameliorating almost all of the pro-inflammatory readouts (IL-1β, TNF-α, IL-8, ICAM, VCAM) and reducing the release of IL-6 in all the cellular models. In hSAECs, they also modulate the expression of SOD2, NF-kB and also ACE2 and TMPRSS2, whose expression is required for SARS-CoV-2 virus entry. Overall, these data suggest the usefulness of OLE, OC and OA in controlling or preventing inflammatory responses, in particular those associated with viral respiratory infections and aging.

Biliatresone induces cholangiopathy in C57BL/6J neonates

Exposure to plant toxins or microbiota that are able to digest common food ingredients to toxic structures might be responsible for biliary atresia (BA). An isoflavonoid, biliatresone is known to effectively alter the extrahepatic bile duct (EHBD) development in BALB/c mice. Biliatresone causes a reduction of Glutathione (GSH) levels, SOX17 downregulation and is effectively countered with N-Acetyl-L-cysteine treatment in vitro. Therefore, reversing GSH-loss appears to be a promising treatment target for a translational approach. Since BALB/c mice have been described as sensitive in various models, we evaluated the toxic effect of biliatresone in robust C57BL/6J mice and confirmed its toxicity. Comparison between BALB/c and C57BL/6J mice revealed similarity in the toxic model. Affected neonates exhibited clinical symptoms of BA, such as jaundice, ascites, clay-colored stools, yellow urine and impaired weight gain. The gallbladders of jaundiced neonates were hydropic and EHBD were twisted and enlarged. Serum and histological analysis proved cholestasis. No anomalies were seen in the liver and EHBD of control animals. With our study we join a chain of evidence confirming that biliatresone is an effective agent for cross-lineage targeted alteration of the EHBD system.

A Metabolome Analysis and the Immunity of Phlomis purpurea against Phytophthora cinnamomi

Phlomis purpurea grows spontaneously in the southern Iberian Peninsula, namely in cork oak (Quercus suber) forests. In a previous transcriptome analysis, we reported on its immunity against Phytophthora cinnamomi. However, little is known about the involvement of secondary metabolites in the P. purpurea defense response. It is known, though, that root exudates are toxic to this pathogen. To understand the involvement of secondary metabolites in the defense of P. purpurea, a metabolome analysis was performed using the leaves and roots of plants challenged with the pathogen for over 72 h. The putatively identified compounds were constitutively produced. Alkaloids, fatty acids, flavonoids, glucosinolates, polyketides, prenol lipids, phenylpropanoids, sterols, and terpenoids were differentially produced in these leaves and roots along the experiment timescale. It must be emphasized that the constitutive production of taurine in leaves and its increase soon after challenging suggests its role in P. purpurea immunity against the stress imposed by the oomycete. The rapid increase in secondary metabolite production by this plant species accounts for a concerted action of multiple compounds and genes on the innate protection of Phlomis purpurea against Phytophthora cinnamomi. The combination of the metabolome with the transcriptome data previously disclosed confirms the mentioned innate immunity of this plant against a devastating pathogen. It suggests its potential as an antagonist in phytopathogens' biological control. Its application in green forestry/agriculture is therefore possible.

Evaluation of inducing activity of CIP elicitors from diverse sources based on monosaccharide composition and physiological indicators

Application of elicitors can greatly enhance plant immune resistance against pathogens. However, it is still obscure whether elicitor activity is influenced by diverse sources. This study investigated the effect of foliar spraying of 19 batches of Chrysanthemum indicum polysaccharides (CIPs) on the disease resistance of Atractylodes macrocephala Koidz. (A. macrocephala) and explored the main reasons for the differences of inducing activity of CIP elicitors. PCA, OPLS-DA, grey relational analysis and entropy weight method had good predictability for the activity evaluation of CIP elicitors and other plant-derived elicitors. The results showed that 19 batches of CIPs had definite regional differences in inducing activity and monosaccharide content. CIP elicitors with high inducing activity could significantly increase the accumulation of Atractylenolide Ⅱ and Atractylenolide Ⅲ, the mRNA relative transcription level of CAT, POD, PAL genes, the amount of pH change in the medium and effectively reduce the disease index of A. macrocephala. Furthermore, CIP with high inducing activity exhibited the high contents of Rha, Ara and GalA, which might be the main contributor to their high activity. The evaluation procedure developed in this work can be applied for screening CIP elicitors with high inducing activity, and it lays a foundation for identifying more functional elicitors related to plant immune resistance.

Ethylene and Jasmonates Signaling Network Mediating Secondary Metabolites under Abiotic Stress

Plants are sessile organisms that face environmental threats throughout their life cycle, but increasing global warming poses an even more existential threat. Despite these unfavorable circumstances, plants try to adapt by developing a variety of strategies coordinated by plant hormones, resulting in a stress-specific phenotype. In this context, ethylene and jasmonates (JAs) present a fascinating case of synergism and antagonism. Here, Ethylene Insensitive 3/Ethylene Insensitive-Like Protein1 (EIN3/EIL1) and Jasmonate-Zim Domain (JAZs)-MYC2 of the ethylene and JAs signaling pathways, respectively, appear to act as nodes connecting multiple networks to regulate stress responses, including secondary metabolites. Secondary metabolites are multifunctional organic compounds that play crucial roles in stress acclimation of plants. Plants that exhibit high plasticity in their secondary metabolism, which allows them to generate near-infinite chemical diversity through structural and chemical modifications, are likely to have a selective and adaptive advantage, especially in the face of climate change challenges. In contrast, domestication of crop plants has resulted in change or even loss in diversity of phytochemicals, making them significantly more vulnerable to environmental stresses over time. For this reason, there is a need to advance our understanding of the underlying mechanisms by which plant hormones and secondary metabolites respond to abiotic stress. This knowledge may help to improve the adaptability and resilience of plants to changing climatic conditions without compromising yield and productivity. Our aim in this review was to provide a detailed overview of abiotic stress responses mediated by ethylene and JAs and their impact on secondary metabolites.

Decoding Metabolic Reprogramming in Plants under Pathogen Attacks, a Comprehensive Review of Emerging Metabolomics Technologies to Maximize Their Applications

In their environment, plants interact with a multitude of living organisms and have to cope with a large variety of aggressions of biotic or abiotic origin. What has been known for several decades is that the extraordinary variety of chemical compounds the plants are capable of synthesizing may be estimated in the range of hundreds of thousands, but only a fraction has been fully characterized to be implicated in defense responses. Despite the vast importance of these metabolites for plants and also for human health, our knowledge about their biosynthetic pathways and functions is still fragmentary. Recent progress has been made particularly for the phenylpropanoids and oxylipids metabolism, which is more emphasized in this review. With an increasing interest in monitoring plant metabolic reprogramming, the development of advanced analysis methods should now follow. This review capitalizes on the advanced technologies used in metabolome mapping in planta, including different metabolomics approaches, imaging, flux analysis, and interpretation using bioinformatics tools. Advantages and limitations with regards to the application of each technique towards monitoring which metabolite class or type are highlighted, with special emphasis on the necessary future developments to better mirror such intricate metabolic interactions in planta.

Cocultivation of pigeon pea hairy root cultures and Aspergillus for the enhanced production of cajaninstilbene acid

Pigeon pea hairy root cultures (PPHRCs) have been proven to be a promising alternative for the production of health-beneficial phenolic compounds, such as the most important health-promoting compound, i.e., cajaninstilbene acid (CSA). In this study, PPHRCs were cocultured with live Aspergillus fungi for further improving phenolic productivity via biological elicitation. Aspergillus oryzae CGMCC 3.951 (AO 3.951) was found to be the optimal fungus that could achieve the maximum increment of CSA (10.73-fold increase) in 42-day-old PPHRCs under the inoculum size of mycelia 0.50% and cocultivation time 36 h. More precisely, the contents of CSA in hairy roots and culture media after fungal elicitation increased by 9.87- and 62.18-fold over control, respectively. Meanwhile, the contents of flavonoid glycosides decreased, while aglycone yields increased upon AO 3.951 elicitation. Moreover, AO 3.951 could trigger the oxidative stress and pathogen defense response thus activating the expression of biosynthesis- and ABC transporter-related genes, which contributed to the intracellular accumulation and extracellular secretion of phenolic compounds (especially CSA) in PPHRCs. And PAL2, 4CL2, STS1, and I3'H were likely to be the potential key enzyme genes regulating the biosynthesis of CSA, and ABCB11X1-1, ABCB11, and ABCG24X2 were closely related to the transmembrane transport of CSA. Overall, the cocultivation approach could make PPHRCs more commercially attractive for the production of high-value phenolic compounds such as CSA and flavonoid aglycones in nutraceutical/medicinal fields. And the elucidation of crucial biosynthesis and transport genes was important for systematic metabolic engineering aimed at increasing CSA productivity. KEY POINTS: • Cocultivation of PPHRCs and live fungi was to enhance CSA production and secretion. • PPHRCs augmented CSA productivity 10.73-fold when cocultured with AO 3.951 mycelia. • Several biosynthesis and transport genes related to CSA production were clarified.

Traditional, Therapeutic Uses and Phytochemistry of Terrestrial European Orchids and Implications for Conservation

The Orchidaceae family accounts for about 28,000 species, and most of them are mentioned in the folk medicine of nations around the world. The use of terrestrial orchids in European and Mediterranean regions has been reported since ancient times, but little information is available on their medicinal properties, as well as on their phytochemicals and biological activities. However, plant collection for human use is still listed as one of the main threats for terrestrial orchids, alongside other menacing factors such as wrong habitat management and disturbance to symbionts, such as pollinators and mycorrhizal fungi. Therefore, the primary aim of this review was to resume and discuss available information regarding the past and current popular uses of European orchids. We then grouped phytochemical data to evaluate the presence of bioactive compounds of pharmacological relevance, and we discussed whether these could support the therapeutic employment of the different organs. Finally, we briefly debated the sustainability of orchid utilizations, considering the different threatening factors and conservation actions including plant propagation methods.

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.

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

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

Lack of antagonism between salicylic acid and jasmonate signalling pathways in poplar

Salicylic acid (SA) and jasmonic acid (JA) often play distinct roles in plant defence against pathogens. Research from Arabidopsis thaliana has established that SA- and JA-mediated defences are more effective against biotrophs and necrotrophs, respectively. These two hormones often interact antagonistically in response to particular attackers, with the induction of one leading to suppression of the other. Here, we report a contrasting pattern in the woody perennial Populus: positive SA-JA interplay. Using genetically engineered high SA lines of black poplar and wild-type lines after exogenous hormone application, we quantified SA and JA metabolites, signalling gene transcripts, antifungal flavonoids and resistance to rust (Melampsora larici-populina). Salicylic acid and JA metabolites were induced concurrently upon rust infection in poplar genotypes with varying resistance levels. Analysis of SA-hyperaccumulating transgenic poplar lines showed increased jasmonate levels, elevated flavonoid content and enhanced rust resistance, but no discernible reduction in growth. Exogenous application of either SA or JA triggered the accumulation of the other hormone. Expression of pathogenesis-related (PR) genes, frequently used as markers for SA signalling, was not correlated with SA content, but rather activated in proportion to pathogen infection. We conclude that SA and JA pathways interact positively in poplar resulting in the accumulation of flavonoid phytoalexins.

Identification of Candidate Genes Associated With Tolerance to Apple Replant Disease by Genome-Wide Transcriptome Analysis

Apple replant disease (ARD) is a worldwide economic risk in apple cultivation for fruit tree nurseries and fruit growers. Several studies on the reaction of apple plants to ARD are documented but less is known about the genetic mechanisms behind this symptomatology. RNA-seq analysis is a powerful tool for revealing candidate genes that are involved in the molecular responses to biotic stresses in plants. The aim of our work was to find differentially expressed genes in response to ARD in Malus. For this, we compared transcriptome data of the rootstock ‘M9’ (susceptible) and the wild apple genotype M. ×robusta 5 (Mr5, tolerant) after cultivation in ARD soil and disinfected ARD soil, respectively. When comparing apple plantlets grown in ARD soil to those grown in disinfected ARD soil, 1,206 differentially expressed genes (DEGs) were identified based on a log2 fold change, (LFC) ≥ 1 for up– and ≤ −1 for downregulation (p < 0.05). Subsequent validation revealed a highly significant positive correlation (r = 0.91; p < 0.0001) between RNA-seq and RT-qPCR results indicating a high reliability of the RNA-seq data. PageMan analysis showed that transcripts of genes involved in gibberellic acid (GA) biosynthesis were significantly enriched in the DEG dataset. Most of these GA biosynthesis genes were associated with functions in cell wall stabilization. Further genes were related to detoxification processes. Genes of both groups were expressed significantly higher in Mr5, suggesting that the lower susceptibility to ARD in Mr5 is not due to a single mechanism. These findings contribute to a better insight into ARD response in susceptible and tolerant apple genotypes. However, future research is needed to identify the defense mechanisms, which are most effective for the plant to overcome ARD.

Camalexin accumulation as a component of plant immunity during interactions with pathogens and beneficial microbes

This review provides an overview on the role of camalexin in plant immunity taking into account various plant-pathogen and beneficial microbe interactions, regulation mechanisms and the contribution in basal and induced plant resistance. In a hostile environment, plants evolve complex and sophisticated defense mechanisms to counteract invading pathogens and herbivores. Several lines of evidence support the assumption that secondary metabolites like phytoalexins which are synthesized de novo, play an important role in plant defenses and contribute to pathogens' resistance in a wide variety of plant species. Phytoalexins are synthesized and accumulated in plants upon pathogen challenge, root colonization by beneficial microbes, following treatment with chemical elicitors or in response to abiotic stresses. Their protective properties against pathogens have been reported in various plant species as well as their contribution to human health. Phytoalexins are synthesized through activation of particular sets of genes encoding specific pathways. Camalexin (3'-thiazol-2'-yl-indole) is the primary phytoalexin produced by Arabidopsis thaliana after microbial infection or abiotic elicitation and an iconic representative of the indole phytoalexin family. The synthesis of camalexin is an integral part of cruciferous plant defense mechanisms. Although the pathway leading to camalexin has been largely elucidated, the regulatory networks that control the induction of its biosynthetic steps by pathogens with different lifestyles or by beneficial microbes remain mostly unknown. This review thus presents current knowledge regarding camalexin biosynthesis induction during plant-pathogen and beneficial microbe interactions as well as in response to microbial compounds and provides an overview on its regulation and interplay with signaling pathways. The contribution of camalexin to basal and induced plant resistance and its detoxification by some pathogens to overcome host resistance are also discussed.

Rhizosphere Signaling: Insights into Plant-Rhizomicrobiome Interactions for Sustainable Agronomy

Rhizospheric plant-microbe interactions have dynamic importance in sustainable agriculture systems that have a reduced reliance on agrochemicals. Rhizosphere signaling focuses on the interactions between plants and the surrounding symbiotic microorganisms that facilitate the development of rhizobiome diversity, which is beneficial for plant productivity. Plant-microbe communication comprises intricate systems that modulate local and systemic defense mechanisms to mitigate environmental stresses. This review deciphers insights into how the exudation of plant secondary metabolites can shape the functions and diversity of the root microbiome. It also elaborates on how rhizosphere interactions influence plant growth, regulate plant immunity against phytopathogens, and prime the plant for protection against biotic and abiotic stresses, along with some recent well-reported examples. A holistic understanding of these interactions can help in the development of tailored microbial inoculants for enhanced plant growth and targeted disease suppression.

The Complexity of Sesquiterpene Chemistry Dictates Its Pleiotropic Biologic Effects on Inflammation

Sesquiterpenes (SQs) are volatile compounds made by plants, insects, and marine organisms. SQ have a large range of biological properties and are potent inhibitors and modulators of inflammation, targeting specific components of the nuclear factor-kappaB (NF-κB) signaling pathway and nitric oxide (NO) generation. Because SQs can be isolated from over 1600 genera and 2500 species grown worldwide, they are an attractive source of phytochemical therapeutics. The chemical structure and biosynthesis of SQs is complex, and the SQ scaffold represents extraordinary structural variety consisting of both acyclic and cyclic (mono, bi, tri, and tetracyclic) compounds. These structures can be decorated with a diverse range of functional groups and substituents, generating many stereospecific configurations. In this review, the effect of SQs on inflammation will be discussed in the context of their complex chemistry. Because inflammation is a multifactorial process, we focus on specific aspects of inflammation: the inhibition of NF-kB signaling, disruption of NO production and modulation of dendritic cells, mast cells, and monocytes. Although the molecular targets of SQs are varied, we discuss how these pathways may mediate the effects of SQs on inflammation.

Grapevine rootstock and soil microbiome interactions: Keys for a resilient viticulture

Soil microbiota has increasingly been shown to play an integral role in viticulture resilience. The emergence of new metagenomic and culturomic technologies has led to significant advances in the study of microbial biodiversity. In the agricultural sector, soil and plant microbiomes have been found to significantly improve resistance to environmental stressors and diseases, as well as influencing crop yields and fruit quality thus improving sustainability under shifting environments. Grapevines are usually cultivated as a scion grafted on rootstocks, which are selected according to pedoclimatic conditions and cultural practices, known as terroir. The rootstock connects the surrounding soil to the vine's aerial part and impacts scion growth and berry quality. Understanding rootstock and soil microbiome dynamics is a relevant and important field of study, which may be critical to improve viticulture sustainability and resilience. This review aims to highlight the relationship between grapevine roots and telluric microbiota diversity and activity. In addition, this review explores the concept of core microbiome regarding potential applications of soil microbiome engineering with the goal of enhancing grapevine adaptation to biotic and abiotic stress.

Transformation of Major Peanut (Arachis hypogaea) Stilbenoid Phytoalexins Caused by Selected Microorganisms

The peanut plant accumulates defensive stilbenoid phytoalexins in response to the presence of soil fungi, which in turn produce phytoalexin-detoxifying enzymes for successfully invading the plant host. Aspergillus spp. are opportunistic pathogens that invade peanut seeds; most common fungal species often produce highly carcinogenic aflatoxins. The purpose of the present research was to evaluate the in vitro dynamics of peanut phytoalexin transformation/detoxification by important fungal species. This work revealed that in feeding experiments, Aspergillus spp. from section Flavi were capable of degrading the major peanut phytoalexin, arachidin-3, into its hydroxylated homolog, arachidin-1, and a benzenoid, SB-1. However, Aspergillus niger from section Nigri as well as other fungal and bacterial species tested, which are not known to be involved in the infection of the peanut plant, were incapable of changing the structure of arachidin-3. The results of feeding experiments with arachidin-1 and resveratrol are also reported. The research provided new knowledge on the dynamics of peanut stilbenoid transformations by essential fungi. These findings may contribute to the elucidation of the phytoalexin detoxification mechanism involved in the infection of peanut by important toxigenic Aspergillus spp.

Specialized metabolites: Physiological and biochemical role in stress resistance, strategies to improve their accumulation, and new applications in crop breeding and management

Specialized plant metabolites (SPMs), traditionally referred to as 'secondary metabolites', are chemical compounds involved in a broad range of biological functions, including plant responses to abiotic and biotic stresses. Moreover, some of them have a role in end-product quality with potential health benefits in humans. For this reason, they became an important target of studies focusing on their mechanisms of action and use in crop breeding and management. In this review we summarize the specific role of SPMs in physiological processes and in plant resistance to abiotic and biotic stresses, and the different strategies to enhance their production/accumulation in plant tissues under stress, including genetic approaches (marker-assisted selection and biotechnological tools) and agronomic management (fertilizer applications, cultivation method and beneficial microorganisms). New crop management strategies based on the direct application of the most promising compounds in form of plant residuals or liquid formulations are also described.

D-Tagatose-Based Product Triggers Sweet Immunity and Resistance of Grapevine to Downy Mildew, but Not to Gray Mold Disease

The use of natural bio-based compounds becomes an eco-friendly strategy to control plant diseases. Rare sugars would be promising compounds as inducers of plant “sweet immunity”. The present study aimed to investigate the induced resistance of grapevine leaves against Plasmopara viticola and Botrytis cinerea by a rare sugar-based product (IFP48) and its active ingredient D-tagatose (TAG), in order to elucidate molecular mechanism involved in defense-related metabolic regulations before and after pathogen challenge. Data showed that spraying leaves with IFP48 and TAG lead to a significant reduction of downy mildew, but not of gray mold disease. The induced protection against P. viticola relies on IFP48’s and to a lesser extent TAG’s ability to potentiate the activation of salicylic acid- and jasmonic acid/ethylene-responsive genes and stilbene phytoalexin accumulation. Most of defense responses remained upregulated in IFP48-treated plants after infection with P. viticola, but inconsistent following challenge with B. cinerea. The beneficial effects of IFP48 were associated with an enhanced accumulation of tagatose inside leaf tissues compared to TAG treatment. Meanwhile, the amounts of sugars, glucose, fructose, maltose, galactose and trehalose remained unchanged or decreased in IFP48-treated leaves after P. viticola infection, although only a few genes involved in sugar transport and metabolism showed transcriptional regulation. This suggests a contribution of sugar homeostasis to the IFP48-induced sweet immune response and priming plants for enhanced resistance to P. viticola, but not to B. cinerea.

Biosynthesis and antifungal activity of fungus-induced O-methylated flavonoids in maize

Fungal infection of grasses, including rice (Oryza sativa), sorghum (Sorghum bicolor), and barley (Hordeum vulgare), induces the formation and accumulation of flavonoid phytoalexins. In maize (Zea mays), however, investigators have emphasized benzoxazinoid and terpenoid phytoalexins, and comparatively little is known about flavonoid induction in response to pathogens. Here, we examined fungus-elicited flavonoid metabolism in maize and identified key biosynthetic enzymes involved in the formation of O-methylflavonoids. The predominant end products were identified as two tautomers of a 2-hydroxynaringenin-derived compound termed xilonenin, which significantly inhibited the growth of two maize pathogens, Fusarium graminearum and Fusarium verticillioides. Among the biosynthetic enzymes identified were two O-methyltransferases (OMTs), flavonoid OMT 2 (FOMT2), and FOMT4, which demonstrated distinct regiospecificity on a broad spectrum of flavonoid classes. In addition, a cytochrome P450 monooxygenase (CYP) in the CYP93G subfamily was found to serve as a flavanone 2-hydroxylase providing the substrate for FOMT2-catalyzed formation of xilonenin. In summary, maize produces a diverse blend of O-methylflavonoids with antifungal activity upon attack by a broad range of fungi.

Metabolomics Insights into Chemical Convergence in Xanthomonas perforans and Metabolic Changes Following Treatment with the Small Molecule Carvacrol

Microbes are natural chemical factories and their metabolome comprise diverse arrays of chemicals. The genus Xanthomonas comprises some of the most important plant pathogens causing devastating yield losses globally and previous studies suggested that species in the genus are untapped chemical minefields. In this study, we applied an untargeted metabolomics approach to study the metabolome of a globally spread important xanthomonad, X. perforans. The pathogen is difficult to manage, but recent studies suggest that the small molecule carvacrol was efficient in disease control. Bacterial strains were treated with carvacrol, and samples were taken at time intervals (1 and 6 h). An untreated control was also included. There were five replicates for each sample and samples were prepared for metabolomics profiling using the standard procedure. Metabolomics profiling was carried out using a thermo Q-Exactive orbitrap mass spectrometer with Dionex ultra high-performance liquid chromatography (UHPLC) and an autosampler. Annotation of significant metabolites using the Metabolomics Standards Initiative level 2 identified an array of novel metabolites that were previously not reported in Xanthomonas perforans. These metabolites include methoxybrassinin and cyclobrassinone, which are known metabolites of brassicas; sarmentosin, a metabolite of the Passiflora-heliconiine butterfly system; and monatin, a naturally occurring sweetener found in Sclerochiton ilicifolius. To our knowledge, this is the first report of these metabolites in a microbial system. Other significant metabolites previously identified in non-Xanthomonas systems but reported in this study include maculosin; piperidine; β-carboline alkaloids, such as harman and derivatives; and several important medically relevant metabolites, such as valsartan, metharbital, pirbuterol, and ozagrel. This finding is consistent with convergent evolution found in reported biological systems. Analyses of the effect of carvacrol in time-series and associated pathways suggest that carvacrol has a global effect on the metabolome of X. perforans, showing marked changes in metabolites that are critical in energy biosynthesis and degradation pathways, amino acid pathways, nucleic acid pathways, as well as the newly identified metabolites whose pathways are unknown. This study provides the first insight into the X. perforans metabolome and additionally lays a metabolomics-guided foundation for characterization of novel metabolites and pathways in xanthomonad systems.

Resveratrol shortens the chronological lifespan of Saccharomyces cerevisiae by a pro-oxidant mechanism

The antioxidant phenotype caused by resveratrol has been recognized as a key piece in the health benefits exerted by this phytochemical in diseases related to aging. It has recently been proposed that a mitochondrial pro-oxidant mechanism could be the cause of resveratrol antioxidant properties. In this regard, the hypothesis that resveratrol impedes electron transport to complex III of the electron transport chain as its main target suggests that resveratrol could increase reactive oxygen species (ROS) generation through reverse electron transport or by the semiquinones formation. This idea also explains that cells respond to resveratrol oxidative damage, inducing their antioxidant systems. Moreover, resveratrol pro-oxidant properties could accelerate the aging process, according to the free radical theory of aging, which postulates that organism's age due to the accumulation of the harmful effects of ROS in cells. Nonetheless, there is no evidence linking the chronological lifespan (CLS) shorten occasioned by resveratrol with a pro-oxidant mechanism. Hence, this study aimed to evaluate whether resveratrol shortens the CLS of Saccharomyces cerevisiae due to a pro-oxidant activity. Herein, we provide evidence that supplementation with 100 μM of resveratrol at 5% glucose: (1) shortened the CLS of ctt1Δ and yap1Δ strains; (2) decreased ROS levels and increased the catalase activity in WT strain; (3) maintained unaffected the ROS levels and did not change the catalase activity in ctt1Δ strain; and (4) lessened the exponential growth of ctt1Δ strain, which was restored with the adding of reduced glutathione. These results indicate that resveratrol decreases CLS by a pro-oxidant mechanism.

Effect of tebuconazole and trifloxystrobin on Ceratocystis fimbriata to control black rot of sweet potato: processes of reactive oxygen species generation and antioxidant defense responses

Black rot, caused by Ceratocystis fimbriata, is one of the most destructive disease of sweet potato worldwide, resulting in significant yield losses. However, a proper management system can increase resistance to this disease. Therefore, this study investigated the potential of using tebuconazole (TEB) and trifloxystrobin (TRI) to improve the antioxidant defense systems in sweet potato as well as the inhibitory effects on the growth of and antioxidant activity in C. fimbriata. Four days after inoculating cut surfaces of sweet potato disks with C. fimbriata, disease development was reduced by different concentrations of TEB + TRI. Infection by C. fimbriata increased the levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and electrolyte leakage (EL), and the activity of lipoxygenase (LOX) by 138, 152, 73, and 282%, respectively, in sweet potato disks, relative to control. In the sweet potato disks, C. fimbriata reduced the antioxidant enzyme activities as well as the contents of ascorbate (AsA) and reduced glutathione (GSH) by 82 and 91%, respectively, compared with control. However, TEB + TRI reduced the oxidative damage in the C. fimbriata-inoculated sweet potato disks by enhancing the antioxidant defense systems. On the other hand, applying TEB + TRI increased the levels of H₂O₂, MDA, and EL, and increased the activity of LOX in C. fimbriata, in which the contents of AsA and GSH decreased, and therefore, inhibited the growth of C. fimbriata. These results suggest that TEB + TRI can significantly control black rot disease in sweet potato by inhibiting the growth of C. fimbriata.

Metabolomic and Confocal Laser Scanning Microscopy (CLSM) Analyses Reveal the Important Function of Flavonoids in Amygdalus pedunculata Pall Leaves With Temporal Changes

Amygdalus pedunculata Pall [Rosaceae, Prunus, Prunus pedunculata (Pall.) Maxim.] belongs to the Rosaceae family and is resistant to cold and drought. Ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry and metabolomics were used to track the changes in bioactive metabolites during several stages of Amygdalus pedunculata Pall growth. A total of 827 different metabolites were detected, including 169 flavonoids, 68 organic acids, 35 terpenoids and 2 tannins. Flavonoid biosynthesis and flavone and flavonol biosynthesis were the main synthetic sources of flavonoids. Quercetin, isoquercitrin, and epicatechin as biomarkers related to growth and development were found. Quercetin connects the biosynthesis of flavonoids and the biosynthesis of flavones and flavonols. The contents of isoquercitrin and epicatechin increased uniformly during the whole growth process from the flowering stage to the fruit ripening stage, indicating that play key roles in the fruit growth and ripening stages of this plant. The tissue location and quantitative analysis of flavonoids in leaves at different stages were performed by confocal laser scanning microscopy. The flavonoids were mainly distributed in the palisade tissue and spongy tissue, indicating the need for protection of these sensitive tissues in particular. Through comprehensive and systematic analysis, the temporal distribution of flavonoids in the process of their leaves growth was determined. These results clarify the important role of flavonoids in the developmental process of Amygdalus pedunculata Pall.

Molecular Targets and Biological Functions of cAMP Signaling in Arabidopsis

Cyclic AMP (cAMP) is a pivotal signaling molecule existing in almost all living organisms. However, the mechanism of cAMP signaling in plants remains very poorly understood. Here, we employ the engineered activity of soluble adenylate cyclase to induce cellular cAMP elevation in Arabidopsis thaliana plants and identify 427 cAMP-responsive genes (CRGs) through RNA-seq analysis. Induction of cellular cAMP elevation inhibits seed germination, disturbs phytohormone contents, promotes leaf senescence, impairs ethylene response, and compromises salt stress tolerance and pathogen resistance. A set of 62 transcription factors are among the CRGs, supporting a prominent role of cAMP in transcriptional regulation. The CRGs are significantly overrepresented in the pathways of plant hormone signal transduction, MAPK signaling, and diterpenoid biosynthesis, but they are also implicated in lipid, sugar, K⁺, nitrate signaling, and beyond. Our results provide a basic framework of cAMP signaling for the community to explore. The regulatory roles of cAMP signaling in plant plasticity are discussed.

Phaseolin Attenuates Lipopolysaccharide-Induced Inflammation in RAW 264.7 Cells and Zebrafish

Kushen (Radix Sophorae flavescentis) is used to treat ulcerative colitis, tumors, and pruritus. Recently, phaseolin, formononetin, matrine, luteolin, and quercetin, through a network pharmacology approach, were tentatively identified as five bioactive constituents responsible for the anti-inflammatory effects of S. flavescentis. However, the role of phaseolin (one of the primary components of S. flavescentis) in the direct regulation of inflammation and inflammatory processes is not well known. In this study, the beneficial role of phaseolin against inflammation was explored in lipopolysaccharide (LPS)-induced inflammation models of RAW 264.7 macrophages and zebrafish larvae. Phaseolin inhibited LPS-mediated production of nitric oxide (NO) and the expression of inducible nitric oxide synthase (iNOS), without affecting cell viability. In addition, phaseolin suppressed pro-inflammatory mediators such as cyclooxygenase 2 (COX-2), interleukin-1β (IL-1β), tumor necrosis factor α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), and interleukin-6 (IL-6) in a dose-dependent manner. Furthermore, phaseolin reduced matrix metalloproteinase (MMP) activity as well as macrophage adhesion in vitro and the recruitment of leukocytes in vivo by downregulating Ninjurin 1 (Ninj1), an adhesion molecule. Finally, phaseolin inhibited the nuclear translocation of nuclear factor-kappa B (NF-κB). In view of the above, our results suggest that phaseolin could be a potential therapeutic candidate for the management of inflammation.

Synthesis and Biological Evaluation of 2,3,4-Triaryl-1,2,4-oxadiazol-5-ones as p38 MAPK Inhibitors

A series of azastilbene derivatives, characterized by the presence of the 1,2,4-oxadiazole-5-one system as a linker of the two aromatic rings of stilbenes, have been prepared as novel potential inhibitors of p38 MAPK. Biological assays indicated that some of the synthesized compounds are endowed with good inhibitory activity towards the kinase. Molecular modeling data support the biological results showing that the designed compounds possess a reasonable binding mode in the ATP binding pocket of p38α kinase with a good binding affinity.

Amino acid-derived defense metabolites from plants: A potential source to facilitate novel antimicrobial development

For millennia, humanity has relied on plants for its medicines, and modern pharmacology continues to reexamine and mine plant metabolites for novel compounds and to guide improvements in biological activity, bioavailability, and chemical stability. The critical problem of antibiotic resistance and increasing exposure to viral and parasitic diseases has spurred renewed interest into drug treatments for infectious diseases. In this context, an urgent revival of natural product discovery is globally underway with special attention directed toward the numerous and chemically diverse plant defensive compounds such as phytoalexins and phytoanticipins that combat herbivores, microbial pathogens, or competing plants. Moreover, advancements in “omics,” chemistry, and heterologous expression systems have facilitated the purification and characterization of plant metabolites and the identification of possible therapeutic targets. In this review, we describe several important amino acid–derived classes of plant defensive compounds, including antimicrobial peptides (e.g., defensins, thionins, and knottins), alkaloids, nonproteogenic amino acids, and phenylpropanoids as potential drug leads, examining their mechanisms of action, therapeutic targets, and structure–function relationships. Given their potent antibacterial, antifungal, antiparasitic, and antiviral properties, which can be superior to existing drugs, phytoalexins and phytoanticipins are an excellent resource to facilitate the rational design and development of antimicrobial drugs.

Genome-scale analyses of polyketide synthases in banana: Phylogenetics and expression profiling forecast their candidacy in specialized metabolism

Plant type III polyketide synthases (PKSs) are associated with various functions in plant growth, development and defense by providing a multitude of polyketide scaffolds for diverse specialized metabolic pathways (SMPs). To decipher banana PKSs involved in specialized metabolism, genome-wide comparative analyses were conducted with A (Musa acuminata) and B (Musa balbisiana) genomes of banana. Both genomes retained eight chalcone synthases (CHSs), seven curcumin synthases (CURSs), three diketidyl-CoA synthases (DCSs) and one anther specific CHS (ASC). Segmental (42%) and tandem (37%) duplication events majorly flourished the banana PKS family. Six of 19 PKSs of A genome (designated as MaPKSs) showed relatively a higher expression in the root, corm, sheath, leaf and embryogenic cell suspension (ECS) of banana. To determine the defense response of MaPKSs and to highlight their candidacy in various SMPs, expression profiling was conducted by qPCR in ECSs treated with 100/200 μM of jasmonic acid (JA) and salicylic acid (SA) at 24/48 h. Maximum and subordinate expression induction of MaPKSs was apparent respectively against JA and SA treatments. Notably, most MaPKSs achieved their peak expression within 24 h of JA and the total flavonoid content was reached maximum within 24 h of JA/SA elicitations. Considering the homology, phylogeny, and expression levels in each analyzed sample (n = 13), three CHSs, three DCSs along with three CURSs and one ASC were selected as most promising candidates respectively for flavonoids, phenylphenalenones and sporopollenin biosynthesis in banana. Our findings provide a first-line resource to disclose the functions of banana PKSs involved in distinct SMPs.

Biofilms and nanoparticles: applications in agriculture

A profound need to explore eco-friendly methods to practice sustainable agriculture leads to the research and exploration of plant growth-promoting rhizobacteria (PGPRs). Biofilms are assemblages of microbial communities within a self-secreted exopolymeric matrix, adhering to different biotic and abiotic surfaces and performing a variety of desired and undesired functions. Biofilm formation by PGPRs is governed by effective root colonization of the host plant in providing plant growth promotion and stress management. Biofilms can also provide a suitable environment for the synthesis and entrapment of nanoparticles. Together, nanoparticles and PGPRs may contribute towards biocontrol and crop management. This review discusses the significance of biofilms in agriculture and their confluence with different types of nanoparticles for plant protection and improved crop production.

Application of UPLC-QTOF-MS Based Untargeted Metabolomics in Identification of Metabolites Induced in Pathogen-Infected Rice

Metabolomics is a useful tool for comparing metabolite changes in plants. Because of its high sensitivity, metabolomics combined with high-resolution mass spectrometry (HR-MS) is the most widely accepted metabolomics tools. In this study, we compared the metabolites of pathogen-infected rice (Oryza sativa) with control rice using an untargeted metabolomics approach. We profiled the mass features of two rice groups using a liquid chromatography quadrupole time-of-flight mass spectrometry (QTOF-MS) system. Twelve of the most differentially induced metabolites in infected rice were selected through multivariate data analysis and identified through a mass spectral database search. The role of these compounds in metabolic pathways was finally investigated using pathway analysis. Our study showed that the most frequently induced secondary metabolites are prostanoids, a subclass of eicosanoids, which are associated with plant defense metabolism against pathogen infection. Herein, we propose a new untargeted metabolomics approach for understanding plant defense system at the metabolic level.

Phytostilbenes as agrochemicals: biosynthesis, bioactivity, metabolic engineering and biotechnology

Covering: 1976 to 2020. Although constituting a limited chemical family, phytostilbenes represent an emblematic group of molecules among natural compounds. Ever since their discovery as antifungal compounds in plants and their ascribed role in human health and disease, phytostilbenes have never ceased to arouse interest for researchers, leading to a huge development of the literature in this field. Owing to this, the number of references to this class of compounds has reached the tens of thousands. The objective of this article is thus to offer an overview of the different aspects of these compounds through a large bibliography analysis of more than 500 articles. All the aspects regarding phytostilbenes will be covered including their chemistry and biochemistry, regulation of their biosynthesis, biological activities in plants, molecular engineering of stilbene pathways in plants and microbes as well as their biotechnological production by plant cell systems.

Relationships between Plant Defense Inducer Activities and Molecular Structure of Gallomolecules

Plant defense inducers (PDIs) are booming and attractive protection agents designed to immunostimulate the plant to reduce subsequent pathogen colonization. The structure-PDI activity relationships of four flavan-3-ols: Epicatechin (EC), Epigallocatechin (EGC), Epicatechin gallate (ECG), Epigallocatechin gallate (EGCG) and Gallotannic acid (GTA) were investigated in both whole plant and suspension cell systems. ECG, EGCG, and GTA displayed elicitor activities. Their infiltration into tobacco leaves induced hypersensitive reaction-like lesions with topical scopoletin and PR-target transcript accumulations. On the contrary, EC and EGC infiltrations fail to trigger the biochemical changes in tobacco tissues. The tobacco BY-2 cells challenged with ECG, EGCG, or GTA led to alkalinization of the BY-2 extracellular medium while EC and EGC did not trigger any pH variation. This work provides evidence that the esterified gallate pattern is as an essential flavonoid entity to induce plant defense reactions in tobacco. The phytoprotective properties of the esterified gallate-free EC and the esterified gallate-rich GTA were evaluated on the tobacco/Phytophthora parasitica var. nicotianae (Ppn) pathosystem. Tobacco treatment with EC did not induce significant protection against Ppn compared to GTA which shows antimicrobial properties on Ppn and decreases the infection on GTA-infiltrated and -sprayed wild-type leaves. GTA protection was impaired in the transgenic NahG tobacco plants, suggesting that protection was mediated by salicylic acid.

Plant growth-stimulating rhizobacteria capable of producing L-amino acids

Pseudomonas putida BIRD-1 is a microorganism that inhabits the rhizosphere and solubilizes phosphate and iron and produces indolacetic acid [Roca, A., Pizarro-Tobías, P., Udaondo, Z., Fernández, M., Matilla, M.A., Molina-Henares, M.A., et al. (2013) Analysis of plant growth-promoting properties encoded by the genome of the rhizobacterium Pseudomonas putida BIRD-1. Environ Microbiol 15: 780-794]. In this study, we generated mutant strains that are capable of producing the plant growth stimulating compounds L-tryptophan and L-phenylalanine. We prepared clones that overproduce L-tryptophan by first mutagenizing P. putida BIRD-1, then by selecting for clones in the presence of inhibitory concentrations of 5-fluoro-D,L-tryptophan. The production of this aromatic amino acid was confirmed by chemical analysis and cross-feeding experiments with auxotrophs. One of the mutants, named P. putida BIRD-1-12, was mutagenized again to isolate clones that are also able to grow in the presence of inhibitory concentrations of p-fluoro-D,L-phenylalanine. One of these resulting clones was then isolated and named BIRD-1-12F. Our analysis revealed that the strains that either overproduce L-tryptophan, or L-tryptophan and L-phenylalanine, excel at promoting the growth of a number of plant crops of agricultural interest.

Natural products as inspiration for the development of bacterial antibiofilm agents

Natural products have historically been a rich source of diverse chemical matter with numerous biological activities, and have played an important role in drug discovery in many areas including infectious disease. Synthetic and medicinal chemistry have been, and continue to be, important tools to realize the potential of natural products as therapeutics and as chemical probes. The formation of biofilms by bacteria in an infection setting is a significant factor in the recalcitrance of many bacterial infections, conferring increased tolerance to many antibiotics and to the host immune response, and as yet there are no approved therapeutics for combatting biofilm-based bacterial infections. Small molecules that interfere with the ability of bacteria to form and maintain biofilms can overcome antibiotic tolerance conferred by the biofilm phenotype, and have the potential to form combination therapies with conventional antibiotics. Many natural products with anti-biofilm activity have been identified from plants, microbes, and marine life, including: elligic acid glycosides, hamamelitannin, carolacton, skyllamycins, promysalin, phenazines, bromoageliferin, flustramine C, meridianin D, and brominated furanones. Total synthesis and medicinal chemistry programs have facilitated structure confirmation, identification of critical structural motifs, better understanding of mechanistic pathways, and the development of more potent, more accessible, or more pharmacologically favorable derivatives of anti-biofilm natural products.

Identification and validation of early genetic biomarkers for apple replant disease

Apple replant disease (ARD) is a serious threat to producers of apple trees and fruits worldwide. The ARD etiology is not unraveled and managing options are either economically not applicable or environmentally harmful. Thus, interest is given in biomarkers that allow to indicate ARD situations at early time points in order to classify soils according to ARD severity but also to analyze the effectiveness to potential countermeasures. This study aimed at (i) identifying ARD biomarkers on the transcriptional level in root tissue by analyzing the expression of previously identified candidate genes in ARD soils of different origin and texture and (ii) testing the specificity of these marker genes to ARD. In vitro propagated M26 plantlets were submitted to a bio-test with three ARD soils, either untreated or disinfected by γ-irradiation. Expression of seven candidate genes identified in a previous transcriptomic study was investigated by RT-qPCR in a time course experiment. Already three days after planting, a prominent upregulation of the phytoalexin biosynthesis genes biphenyl synthase 3 (BIS3) and biphenyl 4-hydroxylase (B4Hb) was observed in the untreated ARD variants of all three soils. The phytoalexin composition in roots was comparable for all three soils and the total phytoalexin content correlated with the expression of BIS3 and B4Hb. The third promising candidate gene that was upregulated under ARD conditions was the ethylene-responsive transcription factor 1B-like (ERF1B). In a second experiment M26 plantlets were exposed to different abiotic stressors, namely heat, salt and nutrient starvation, and candidate gene expression was determined in the roots. The expression levels of BIS3 and B4Hb were highly and specifically upregulated in ARD soil, but not upon the abiotic stress conditions, whereas ERF1B also showed higher expression under heat stress. In conclusion, BIS3 and B4Hb are recommended as early ARD biomarkers due to their high expression levels and their high specificity.

Resveratrol and Resveratrol-Aspirin Hybrid Compounds as Potent Intestinal Anti-Inflammatory and Anti-Tumor Drugs

Resveratrol (3,4,5-Trihydroxy-trans-stilbene) is a naturally occurring polyphenol that exhibits beneficial pleiotropic health effects. It is one of the most promising natural molecules in the prevention and treatment of chronic diseases and autoimmune disorders. One of the key limitations in the clinical use of resveratrol is its extensive metabolic processing to its glucuronides and sulfates. It has been estimated that around 75% of this polyphenol is excreted via feces and urine. To possibly alleviate the extensive metabolic processing and improve bioavailability, we have added segments of acetylsalicylic acid to resveratrol in an attempt to maintain the functional properties of both. We initially characterized resveratrol-aspirin derivatives as products that can inhibit cytochrome P450 Family 1 Subfamily A Member 1 (CYP1A1) activity, DNA methyltransferase (DNMT) activity, and cyclooxygenase (COX) activity. In this study, we provide a detailed analysis of how resveratrol and its aspirin derivatives can inhibit nuclear factor kappa B (NFκB) activation, cytokine production, the growth rate of cancer cells, and in vivo alleviate intestinal inflammation and tumor growth. We identified resveratrol derivatives C3 and C11 as closely preserving resveratrol bioactivities of growth inhibition of cancer cells, inhibition of NFκB activation, activation of sirtuin, and 5’ adenosine monophosphate-activated protein kinase (AMPK) activity. We speculate that the aspirin derivatives of resveratrol would be more metabolically stable, resulting in increased efficacy for treating immune disorders and as an anti-cancer agent.

Identification of Fusarium solani f. sp. pisi (Fsp) Responsive Genes in Pisum sativum

Pisum sativum (pea) is rapidly emerging as an inexpensive and significant contributor to the plant-derived protein market. Due to its nitrogen-fixation capability, short life cycle, and low water usage, pea is a useful cover-and-break crop that requires minimal external inputs. It is critical for sustainable agriculture and indispensable for future food security. Root rot in pea, caused by the fungal pathogen Fusarium solani f. sp. pisi (Fsp), can result in a 15-60% reduction in yield. It is urgent to understand the molecular basis of Fsp interaction in pea to develop root rot tolerant cultivars. A complementary genetics and gene expression approach was undertaken in this study to identify Fsp-responsive genes in four tolerant and four susceptible pea genotypes. Time course RNAseq was performed on both sets of genotypes after the Fsp challenge. Analysis of the transcriptome data resulted in the identification of 42,905 differentially expressed contigs (DECs). Interestingly, the vast majority of DECs were overexpressed in the susceptible genotypes at all sampling time points, rather than in the tolerant genotypes. Gene expression and GO enrichment analyses revealed genes coding for receptor-mediated endocytosis, sugar transporters, salicylic acid synthesis, and signaling, and cell death were overexpressed in the susceptible genotypes. In the tolerant genotypes, genes involved in exocytosis, and secretion by cell, the anthocyanin synthesis pathway, as well as the DRR230 gene, a pathogenesis-related (PR) gene, were overexpressed. The complementary genetic and RNAseq approach has yielded a set of potential genes that could be targeted for improved tolerance against root rot in P. sativum. Fsp challenge produced a futile transcriptomic response in the susceptible genotypes. This type of response is hypothesized to be related to the speed at which the pathogen infestation advances in the susceptible genotypes and the preexisting level of disease-preparedness in the tolerant genotypes.

Light: An Alternative Method for Physical Control of Postharvest Rotting Caused by Fungi of Citrus Fruit

Solar light has fundamental roles in vast chemical, biochemical, and physical process in biosphere and hence been declared as “source of life.” Solar light is further classified into a broad range of electromagnetic waves, and each region in the solar spectrum bears its unique actions in the universe or biosphere. Since centuries, solar light is believed as a potent source of killing pathogens causing postharvest losses on food products as well as human skin diseases. Citrus fruit crops are widely produced and consumed across the world, but due to their higher juicy contents, Penicillium italicum (blue mold) and Penicillium digitatum (green mold) make their entry to decay fruits and cause approximately 80% and 30% fruit losses, respectively. Agrochemicals or synthetic fungicides are highly efficient to control these postharvest fungal pathogens but have certain health concerns due to toxic environmental residues. Therefore, the scientific community is ever looking for some physical ways to eradicate such postharvest fungal pathogens and reduce the yield losses along with maintaining the public health concerns. This review article presents and discusses existing available information about the positive and negative impacts of different spectrums of solar light exposure on the postharvest storage of citrus fruits, especially to check citrus postharvest rotting caused by Penicillium italicum (blue mold) and Penicillium digitatum (green mold). Moreover, a special focus shall be paid to blue light (390–500 nm), which efficiently reduces the decay of fruits, while keeping the host tissues/cells healthy with no known cytotoxicity, killing the fungal pathogen probably by ferroptosis, but indepth knowledge is scanty. The study defines how to develop commercial applications of light in the postharvest citrus industry.

Inducing Plant Defense Reactions in Tobacco Plants with Phenolic-Rich Extracts from Red Maple Leaves: A Characterization of Main Active Ingredients

Red maple leaf extracts (RME) were tested for their plant defense inducer (PDI) properties. Two extracts were obtained and compared by different approaches: RME1 using ethanol–water (30–70%, v/v, 0.5% HCl 1N) and RME2 using pure water. Both extracts titrated at 1.9 g L−1 in polyphenols and infiltrated into tobacco leaves efficiently induced hypersensitive reaction-like lesions with topical accumulation of auto-fluorescent compounds noted under UV and scopoletin titration assays. The antimicrobial marker PR1, β−1,3-glucanase PR2, chitinase PR3, and osmotin PR5 target genes were all upregulated in tobacco leaves following RME1 treatment. The alkaline hydrolysis of RME1 and RME2 combined with HPLC titration of gallic acid revealed that gallate functions were present in both extracts at levels comprised between 185 and 318 mg L−1. HPLC-HR-MS analyses and glucose assay identified four gallate derivatives consisting of a glucose core linked to 5, 6, 7, and 8 gallate groups. These four galloyl glucoses possessed around 46% of total gallate functions. Their higher concentration in RME suggested that they may contribute significantly to PDI activity. These findings define the friendly galloyl glucose as a PDI and highlight a relevant methodology for combining plant assays and chemistry process to their potential quantification in crude natural extracts.