Methyl jasmonate conferred Arsenic tolerance in Thymus kotschyanus by DNA hypomethylation, stimulating terpenoid metabolism, and upregulating two cytochrome P450 monooxygenases

Advances in the Biosynthesis of Plant Terpenoids: Models, Mechanisms, and Applications

Plants have evolved complex terpene defenses. Terpenoids accumulate in plant tissues or release as volatile in response to ever-changing environment, playing essential roles in chemo-ecological functions as defense against pathogen and insect, improving pollination and seed dispersal, facilitation plant-to-plant communication. They are also gaining attention in pharmaceuticals, nutraceuticals, fragrance, and biofuels. Here, we highlight the recent progress in the fundamental pathways of terpenoid biosynthesis, key enzymes, and their corresponding genes involved in terpenoid synthesis. We identified the further exploration of biosynthetic networks and the development of novel terpenoid resources, proposed the need for further exploration of biosynthetic networks and the development of novel terpenoid resources. Based on that knowledge, future research should be directed towards the mechanisms governing terpenoid biosynthesis dependent environmental change and molecular breeding.

Selenium nanoparticles affected growth and secondary metabolism in chicory seedlings epigenetically by modifying DNA methylation and transcriptionally by upregulating DREB1A transcription factor and stimulating genes involved in phenylpropanoid metabolism

In this biosafety risk assessment project, the molecular and physiological responses of chicory seedlings to the introduction of selenate (0, 0.1, 0.5, 1, and 5 mgl-1) or nanoscale red elemental Se product (nSe) into the culture medium were investigated. The application of nSe at low concentrations improved the fresh weight of shoots and roots, while 5 mgl-1 nSe caused severe phytotoxicity. Molecular analysis confirmed partially different epigenetic responses to nSe and selenate. DNA hypomethylation is an important mechanism by which Se exerts its influence at the pre-transcriptional level. With increasing nSe concentration, the transcription factor DREB1A (dehydration-responsive element-binding) showed a linear upward trend. The use of nSe contributed to the transcriptional upregulation of the genes for phenylalanine ammonia-lyase (PAL), hydroxycinnamoyl-CoA: quinate-hydroxycinnamoyl transferases (HQT) and hydroxycinnamoyl-CoA: shikimate/quinate-hydroxycinnamoyl transferase (HCT). Proline concentrations were increased in both leaves and roots in response to the nano-supplement. Cytotoxicity of Se at toxic concentrations decreased protein levels, in contrast to the positive nSe treatments, 0.1 and 0.5. Notably, nSe supplementation acted as an efficient elicitor, stimulating the accumulation of phenylpropanoid derivatives, including caffeic acid, chlorogenic acid, and cichoric acid metabolites. The concentration of ascorbate and glutathione displayed a similar upward trend in response to the nSe supplementation. Further comprehensive comparative molecular studies in different stress-sensitive and tolerant species are necessary to gain a better understanding of the underlying mechanisms. This will allow for the optimization of functional protocols for nSe-based supplements to meet the expectations of sustainable agriculture.

Integrated metabolomics, transcriptomic, and phytohormonal analyses to study the effects of water stress and foliar abscisic acid application in Thymus species using LC-MS/MS

Thyme species, including Thymus vulgaris, T. kotschyanus (drought-tolerant) and T. serpyllum (drought-sensitive), are valuable medicinal herbs. They are often grown in arid regions and are increasingly suffering from water stress due to climate change. Here, we analyzed the metabolome and expression of selected genes in leaves of these species under drought stress with and without treatment with the phytohormone abscisic acid (ABA). Among the terpenes, dominant metabolites in thyme, thymol was the most important terpenoid component, followed by thymoquinone, carvacrol and p-cymene in all three species. Drought stress reduced terpene concentrations, while moderate ABA levels increased them. T. kotschyanus showed the highest concentrations of thymol and carvacrol after combined treatment with drought and ABA. Metabolite accumulation was partially correlated with genes related to terpenoid biosynthesis. The combined treatment of drought stress and ABA resulted in a significant reduction of the stress hormone jasmonic acid and an increase of its biosynthetic precursor, OPDA (cis-12-oxophytodienoic acid), in all species. The present research results indicate that ABA treatment at moderate concentrations could be used as a measure to increase the production of some pharmaceutically active phenolic monoterpenes in T. vulgaris, T. serpyllum and T. kotschyanus and increase the stress resistance of the plants.

Polyethylene nanoplastics affected morphological, physiological, and molecular indices in tomato (Solanum lycopersicum L.)

This study explored morphological, physiological, molecular, and epigenetic responses of tomatoes (Solanum lycopersicum) to soil contamination with polyethylene nanoplastics (PENP; 0.01, 0.1, and 1 gkg-1 soil). The PENP pollution led to severe changes in plant morphogenesis. The PENP treatments were associated with decreased plant biomass, reduced internode length, delayed flowering, and prolonged fruit ripening. Abnormal inflorescences, flowers, and fruits observed in the PENP-exposed seedlings support genetic changes and meristem dysfunction. Exposure of seedlings to PENP increased H2O2 accumulation and damaged membranes, implying oxidative stress. The PENP treatments induced activities of catalase (EC1.11.1.6), peroxidase (EC1.11.1.7), and phenylalanine ammonia-lyase (EC4.3.1.24) enzymes. Soil contamination with PENP also decreased the net photosynthesis, maximum photosystem efficiency, stomatal conductance, and transpiration rate. The nano-pollutant upregulated the expression of the histone deacetylase (HDA3) gene and R2R3MYB transcription factor. However, the AP2a gene was down-regulated in response to the PENP treatment. Besides, EPNP epigenetically contributed to changes in DNA methylation. The concentrations of proline, soluble phenols, and flavonoids also displayed an upward trend in response to the applied PENP treatments. The long-term exposure of seedlings to PENP influenced fruit biomass, firmness, ascorbate, lycopene, and flavonoid content. These findings raise concerns about the hazardous aspects of PENP to agricultural ecosystems and food security.

Emerging roles of N6-methyladenosine in arsenic-induced toxicity

Arsenic can cause extensive toxic damage after entering the body of humans and animals by altering a variety of events. As the most common form of methylation modification of RNA in eukaryotic cells, N6-methyladenosine (m6A) is widely involved in regulating RNA processing, translation and degradation, thus playing important role in various pathophysiological processes. Emerging studies have demonstrated that m6A modification is synergistically mediated by methyltransferases, demethylases and methyl-binding proteins. Recently, emerging studies have shown that m6A modification and its regulatory proteins play important roles in arsenic toxicity through mediating various key signaling pathways. We comprehensively analyzed the mechanisms by which m6A modification and its regulatory proteins contribute to arsenic toxicity. Our reviews offer a scientific foundation for the development of preventive and control strategies to mitigate arsenic-induced toxicity, with an emphasis on an epigenetic approach.

Elicitors fortifies the plant resilience against metal and metalloid stress

This review addresses plant interactions with HMs, emphasizing defence mechanisms and the role of chelating agents, antioxidants and various elicitor molecules in mitigating metal toxicity in plants. To combat soil contamination with HMs, chelate assisted phytoextraction using application of natural or synthetic aminopolycarboxylic acids is an effective strategy. Plants also employ diverse signaling pathways, including hormones, calcium, reactive oxygen species, nitric oxide, and Mitogen-Activated Protein Kinases influencing gene expression and defence mechanisms to counter HM stress. Phytohormones enhance the enzymatic and non-enzymatic antioxidant defence mechanism and the level of secondary metabolites in plants when exposed to HM stress. Also it activates genes responsible for DNA repair mechanism. In addition, the plant hormones can also regulate the activity of several transporters of HMs, thereby preventing their entry into the cell. Elicitor molecules regulate metal and metalloid absorption, sequestration and transport in plants. Combining of different elicitors like jasmonic acid, calcium, salicylic acid etc. effectively mitigates metal and metalloid stress in plants. Moreover, microbes including bacteria and fungi, offer eco-friendly and efficient solution for HM remediation. Understanding these elicitors, microbes and various signaling pathways is crucial for developing strategies to enhance plant resilience to metal and metalloid stress.

Chitosan nanoparticles (CSNPs) conferred salinity tolerance in maize by upregulating E3 ubiquitin-protein ligase, P5CS1, HKT1, NHX1, and PMP3 genes

This study explored the transcriptional behaviors of several candidate genes in response to the application of CSNPs (50 and 100 mgl-1) in maize seedlings grown under two salinity levels (NaCl of 0.07 and 0.14 gkg-1soil). Employing CSNPs at both concentrations mitigated the inhibitory role of salinity on the leaf and root fresh weights. The application of CSNPs enhanced the transcription of the E3 ubiquitin-protein ligase gene by an average of threefold, contrasted with the salinity controls. The Δ1-pyrroline-5-carboxylate synthetase (P5CS1) gene was upregulated in response to both individual and mixed treatments of CSNPs and salinity. The transcription of the high-affinity K+ transporter (HKT1) gene displayed an upward trend in response to the CSNPs and salinity treatments. The Na+/H+ exchangers (NHX1) gene exhibited a similar trend to that of the HKT1 gene. The utilization of CSNPs was accompanied by an upregulation in the plasma membrane proteolipid 3 (PMP3) gene, contrasted with the salinity controls. The phenylalanine ammonia-lyase (PAL) activity displayed an upward trend in response to the foliar application of CSNPs. The CSNPs at the 100 mgl-1 concentration were more capable of inducing the ascorbate peroxidase enzyme under both salinity conditions than the 50 mgl-1 dose. The simultaneous exposure of maize seedlings to CSNPs and salinity resulted in the drastic upregulation of the catalase activities. This study provides novel insights into the major mechanisms underlying the stress-mitigating effects of CSNPs, thereby providing a suitable platform for their application in sustainable agricultural practices.

Silicon nanoparticles (SiNPs) stimulated secondary metabolism and mitigated toxicity of salinity stress in basil (Ocimum basilicum) by modulating gene expression: a sustainable approach for crop protection

The underlying mechanisms through which silicon oxide nanoparticles (SiNPs) can confer salinity resistance to plants are poorly understood. This study explored the efficacy of supplementing nutrient solution with SiNPs (20-30 nm; 10 mg kg-1 soil) to stimulate metabolism and alleviate the risks associated with salinity (0.73 g kg-1 soil) in basil seedlings. For this purpose, variations in photosynthetic indices, proline osmoprotectant, antioxidant markers, phenylpropanoid metabolism, and transcriptional behaviors of genes were investigated. SiNPs increased shoot fresh weight (38%) and mitigated the risk associated with the salinity stress by 14%. SiNPs alleviated the inhibitory effects of salinity on the total chlorophyll concentration by 15%. The highest increase (twofold) in proline content was recorded in the SiNP-treated seedlings grown under salinity. The nano-supplement enhanced the activity of enzymatic antioxidants, including peroxidase (2.5-fold) and catalase (4.7-fold). SiNPs induced the expression of gamma-cadinene synthase (CDS) and caffeic acid O-methyltransferase (COMT) genes by 6.5- and 18.3-fold, respectively. SiNPs upregulated the eugenol synthase (EGS1) and fenchol synthase (FES) genes by six- and nine-fold, respectively. Salinity transcriptionally downregulated the geraniol synthase (GES) gene, while this gene displayed an upward trend in response to SiNPs by eight-fold. The nano-supplement transcriptionally stimulated the R-linalool synthase (LIS) gene by 3.3-fold. The terpinolene synthase (TES) gene displayed a similar trend to that of the GES gene. The highest expression (25-fold) of the phenylalanine ammonia-lyase (PAL) gene was recorded in seedlings supplemented with SiNPs. The physiological and molecular assessments demonstrated that employing SiNPs is a sustainable strategy for improving plant primary/secondary metabolism and crop protection.