The ameliorative effects of exogenous inoculation of Piriformospora indica on molecular, biochemical and physiological parameters of Artemisia annua L. under arsenic stress condition

Synergistic effects of melatonin and 24-epibrassinolide on chickpea water deficit tolerance

BACKGROUND

Water deficiency stress reduces yield in grain legumes, primarily due to a decrease in the pods number. Melatonin (ML) and 24-epibrassinolide (EBL) are recognized for their hormone-like properties that improve plant tolerance to abiotic stresses. This study aimed to assess the impact of different concentrations of ML (0, 100, and 200 µM) and EBL (0, 3, and 6 µM) on the growth, biochemical, and physiological characteristics of chickpea plants under water-stressed conditions.

RESULTS

The study's findings indicated that under water-stressed conditions, a decrease in seed (30%) and pod numbers (31%), 100-seed weight (17%), total chlorophyll content (46%), stomatal conductance (33%), as well as an increase in H2O2 (62%), malondialdehyde content (40%), and electrolyte leakage index (40%), resulted in a 40% reduction in chickpea plants grain yield. Our findings confirmed that under water-stressed conditions, seed oil, seed oil yield, and seed protein yield dropped by 20%, 55%, and 36%, respectively. The concurrent exogenous application of ML and EBL significantly reduces oxidative stress, plasma membrane damage, and reactive oxygen species (ROS) content. This treatment also leads to increased yield and its components, higher pigment content, enhanced oil and protein yield, and improved enzymatic and non-enzymatic antioxidant activities such as catalase, superoxide dismutase, polyphenol oxidase, ascorbate peroxidase, guaiacol peroxidase, flavonoid, and carotenoid. Furthermore, it promotes the accumulation of osmoprotectants such as proline, total soluble protein, and sugars.

CONCLUSIONS

Our study found that ML and EBL act synergistically to regulate plant growth, photosynthesis, osmoprotectants accumulation, antioxidant defense systems, and maintain ROS homeostasis, thereby mitigating the adverse effects of water deficit conditions. ML and EBL are key regulatory network components in stressful conditions, with significant potential for future research and practical applications. The regulation metabolic pathways of ML and EBL in water-stressed remains unknown. As a result, future research should aim to elucidate the molecular mechanisms by employing genome editing, RNA sequencing, microarray, transcriptomic, proteomic, and metabolomic analyses to identify the mechanisms involved in plant responses to exogenous ML and EBL under water deficit conditions. Furthermore, the economical applications of synthetic ML and EBL could be an interesting strategy for improving plant tolerance.

Nutrient and mycoremediation of a global menace 'arsenic': exploring the prospects of phosphorus and Serendipita indica-based mitigation strategies in rice and other crops

KEY MESSAGE

Serendipita indica induced metabolic reprogramming in colonized plants complements phosphorus-management in improving their tolerance to arsenic stress on multifaceted biological fronts. Restoration of the anthropic damage done to our environment is inextricably linked to devising strategies that are not only economically sound but are self-renewing and ecologically conscious. The dilemma of heavy metal (HM) dietary ingestion, especially arsenic (As), faced by humans and animals alike, necessitates the exploitation of such technologies and the cultivation of healthy and abundant crops. The remarkable symbiotic alliance between plants and 'mycorrhizas' has evolved across eons, benefiting growth/yield aspects as well as imparting abiotic/biotic stress tolerance. The intricate interdependence of Serendipita indica (S. indica) and rice plant reportedly reduce As accumulation, accentuating the interest of microbiologists, agriculturists, and ecotoxicological scientists apropos of the remediation mechanisms of As in the soil-AMF-rice system. Nutrient management, particularly of phosphorus (P), is also praised for mitigating As phytotoxicity by deterring the uptake of As molecules due to the rhizospheric cationic competition. Taking into consideration the reasonable prospects of success in minimizing As acquisition by rice plants, this review focuses on the physiological, metabolic, and transcriptional alterations underlying S. indica symbiosis, recuperation of As stress together with nutritional management of P by gathering case studies and presenting successful paradigms. Weaving together a volume of literature, we assess the chemical forms of As and related transport pathways, discuss As-P-rice interaction and the significance of fungi in As toxicity mitigation, predominantly the role of mycorrhiza, as well as survey of the multifaceted impacts of S. indica on plants. A potential strategy for simultaneous S. indica + P administration in paddy fields is proposed, followed by future research orientation to expand theoretic comprehension and encourage field-based implementation.

Advanced metabolic engineering strategies for increasing artemisinin yield in Artemisia annua L

Artemisinin, also known as 'Qinghaosu', is a chemically sesquiterpene lactone containing an endoperoxide bridge. Due to the high activity to kill Plasmodium parasites, artemisinin and its derivatives have continuously served as the foundation for antimalarial therapies. Natural artemisinin is unique to the traditional Chinese medicinal plant Artemisia annua L., and its content in this plant is low. This has motivated the synthesis of this bioactive compound using yeast, tobacco, and Physcomitrium patens systems. However, the artemisinin production in these heterologous hosts is low and cannot fulfil its increasing clinical demand. Therefore, A. annua plants remain the major source of this bioactive component. Recently, the transcriptional regulatory networks related to artemisinin biosynthesis and glandular trichome formation have been extensively studied in A. annua. Various strategies including (i) enhancing the metabolic flux in artemisinin biosynthetic pathway; (ii) blocking competition branch pathways; (iii) using transcription factors (TFs); (iv) increasing peltate glandular secretory trichome (GST) density; (v) applying exogenous factors; and (vi) phytohormones have been used to improve artemisinin yields. Here we summarize recent scientific advances and achievements in artemisinin metabolic engineering, and discuss prospects in the development of high-artemisinin yielding A. annua varieties. This review provides new insights into revealing the transcriptional regulatory networks of other high-value plant-derived natural compounds (e.g., taxol, vinblastine, and camptothecin), as well as glandular trichome formation. It is also helpful for the researchers who intend to promote natural compounds production in other plants species.

Serendipita indica Promotes the Growth of Tartary Buckwheat by Stimulating Hormone Synthesis, Metabolite Production, and Increasing Systemic Resistance

The main objective of this study was to investigate the influence of Serendipita indica on the growth of Tartary buckwheat plants. This study highlighted that the roots of Tartary buckwheat can be colonized by S. indica and that this fungal endophyte improved plants height, fresh weight, dry weight, and grain yield. In the meantime, the colonization of S. indica in Tartary buckwheat leaves resulted in elevated levels of photosynthesis, plant hormone content, antioxidant enzyme activity, proline content, chlorophyll content, soluble sugars, and protein content. Additionally, the introduction of S. indica to Tartary buckwheat roots led to a substantial rise in the levels of flavonoids and phenols found in the leaves and seeds of Tartary buckwheat. In addition, S. indica colonization reduced the content of malondialdehyde and hydrogen peroxide when compared to non-colonized plants. Importantly, the drought tolerance of Tartary buckwheat plants is increased, which benefits from physiology and bio-chemical changes in plants after S. indica colonized. In conclusion, we have shown that S. indica can improve systematic resistance and promote the growth of Tartary buckwheat by enhancing the photosynthetic capacity of Tartary buckwheat, inducing the production of IAA, increasing the content of secondary metabolites such as total phenols and total flavonoids, and improving the antioxidant enzyme activity of the plant.

Contribution of Serendipita indica on growth improvement, antioxidative capacity of Dracocephalum kotschyi, and its resistance against cadmium stress

Cadmium pollution is a severe issue worldwide which causes an elevated concern in agriculture. The utilization of plant-microbial interactions offers a promising approach for the remediation of cadmium-polluted soils. To elucidate the mechanism of Serendipita indica-mediated cadmium stress tolerance, a potting experiment was conducted to study the impact of S. indica on Dracocephalum kotschyi plants grown under different cadmium concentrations (0, 5, 10, and 20 mg/kg). The effects of cadmium and S. indica on plant growth, antioxidant enzyme activities, and accumulation of cadmium were investigated. The results showed that cadmium stress significantly decreases biomass, photosynthetic pigments, and carbohydrate content concomitantly with increasing antioxidant activities, electrolyte leakage, and hydrogen peroxide, proline, and cadmium content. Inoculation with S. indica alleviated the adverse effect of cadmium stress by enhancing shoot and root dry weight, photosynthetic pigments, and carbohydrate, proline, and catalase activity. Unlike cadmium stress, the presence of fungus led to a reduction in electrolyte leakage and hydrogen peroxide content as well as the content of cadmium in D. kotschyi leaf which mitigates cadmium-induced oxidative stress. Our findings demonstrated S. indica inoculation alleviates the adverse effects of cadmium stress in D. kotschyi plants which could prolong their survival under stressful conditions. Due to the importance of D. kotschyi and the effect of biomass increase on the amount of its medicinal substances, exploiting S. indica not only promotes plant growth, but also may be used as a potential eco-friendly method for relieving the phytotoxicity of Cd and remediating Cd-contaminated soil.

Serendipita indica-A Review from Agricultural Point of View

Fulfilling the food demand of a fast-growing population is a global concern, resulting in increased dependence of the agricultural sector on various chemical formulations for enhancing crop production. This leads to an overuse of chemicals, which is not only harmful to human and animal health, but also to the environment and the global economy. Environmental safety and sustainable production are major responsibilities of the agricultural sector, which is inherently linked to the conservation of the biodiversity, the economy, and human and animal health. Scientists, therefore, across the globe are seeking to develop eco-friendly and cost-effective strategies to mitigate these issues by putting more emphasis on the use of beneficial microorganisms. Here, we review the literature on Serendipita indica, a beneficial endophytic fungus, to bring to the fore its properties of cultivation, the ability to enhance plant growth, improve the quality of produced crops, mitigate various plant stresses, as well as protect the environment. The major points in this review are as follows: (1) Although various plant growth promoting microorganisms are available, the distinguishing character of S. indica being axenically cultivable with a wide range of hosts makes it more interesting for research. (2) S. indica has numerous functions, ranging from promoting plant growth and quality to alleviating abiotic and biotic stresses, suggesting the use of this fungus as a biofertiliser. It also improves the soil quality by limiting the movement of heavy metals in the soil, thus, protecting the environment. (3) S. indica's modes of action are due to interactions with phytohormones, metabolites, photosynthates, and gene regulation, in addition to enhancing nutrient and water absorption. (4) Combined application of S. indica and nanoparticles showed synergistic promotion in crop growth, but the beneficial effects of these interactions require further investigation. This review concluded that S. indica has a great potential to be used as a plant growth promoter or biofertiliser, ensuring sustainable crop production and a healthy environment.

Symbiotic System Establishment between Piriformospora indica and Glycine max and Its Effects on the Antioxidant Activity and Ion-Transporter-Related Gene Expression in Soybean under Salt Stress

The utilization of symbiosis with beneficial microorganisms has considerable potential for increasing growth and resistance under abiotic stress. The endophytic root fungus Piriformospora indica has been shown to improve plant growth under salt and drought stress in diverse plant species, while there have been few reports of the interaction of P. indica with soybean under salt stress. In this study, the symbiotic system of P. indica and soybean (Glycine max L.) was established, and the effect of P. indica on soybean growth and salt tolerance was investigated. The colonized and non-colonized soybeans were subjected to salt stress (200 mmol/L NaCl), and the impairments in chlorophyll and increasing relative conductivity that can be caused by salt stress were alleviated in the P. indica-colonized plants. The accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O2−) were lower than that in non-colonized plants under salt treatment, whereas the activities of antioxidant enzymes were significantly increased by P. indica colonization, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR). Importantly, without salt treatment, the Na+ concentration was lower, and the K+ concentration was higher in the roots compared with non-colonized plants. Differential expressions of ion transporter genes were found in soybean roots after P. indica colonization. The P. indica colonization positively regulated the transcription level of PM H+-ATPase, SOS1, and SOS2. The study shows that P. indica enhances the growth and salt tolerance of soybean, providing a strategy for the agricultural production of soybean plants in saline-alkali soils.

Biosynthetic Mechanisms of Secondary Metabolites Promoted by the Interaction Between Endophytes and Plant Hosts

Endophytes is a kind of microorganism resource with great potential medicinal value. The interactions between endophytes and host not only promote the growth and development of each other but also drive the biosynthesis of many new medicinal active substances. In this review, we summarized recent reports related to the interactions between endophytes and hosts, mainly regarding the research progress of endophytes affecting the growth and development of host plants, physiological stress and the synthesis of new compounds. Then, we also discussed the positive effects of multiomics analysis on the interactions between endophytes and their hosts, as well as the application and development prospects of metabolites synthesized by symbiotic interactions. This review may provide a reference for the further development and utilization of endophytes and the study of their interactions with their hosts.

Plants-Microorganisms-Based Bioremediation for Heavy Metal Cleanup: Recent Developments, Phytoremediation Techniques, Regulation Mechanisms, and Molecular Responses

Rapid industrialization, mine tailings runoff, and agricultural activities are often detrimental to soil health and can distribute hazardous metal(loid)s into the soil environment, with harmful effects on human and ecosystem health. Plants and their associated microbes can be deployed to clean up and prevent environmental pollution. This green technology has emerged as one of the most attractive and acceptable practices for using natural processes to break down organic contaminants or accumulate and stabilize metal pollutants by acting as filters or traps. This review explores the interactions between plants, their associated microbiomes, and the environment, and discusses how they shape the assembly of plant-associated microbial communities and modulate metal(loid)s remediation. Here, we also overview microbe-heavy-metal(loid)s interactions and discuss microbial bioremediation and plants with advanced phytoremediation properties approaches that have been successfully used, as well as their associated biological processes. We conclude by providing insights into the underlying remediation strategies' mechanisms, key challenges, and future directions for the remediation of metal(loid)s-polluted agricultural soils with environmentally friendly techniques.

Recent Developments in Microbe-Plant-Based Bioremediation for Tackling Heavy Metal-Polluted Soils

Soil contamination with heavy metals (HMs) is a serious concern for the developing world due to its non-biodegradability and significant potential to damage the ecosystem and associated services. Rapid industrialization and activities such as mining, manufacturing, and construction are generating a huge quantity of toxic waste which causes environmental hazards. There are various traditional physicochemical techniques such as electro-remediation, immobilization, stabilization, and chemical reduction to clean the contaminants from the soil. However, these methods require high energy, trained manpower, and hazardous chemicals make these techniques costly and non-environment friendly. Bioremediation, which includes microorganism-based, plant-based, microorganism-plant associated, and other innovative methods, is employed to restore the contaminated soils. This review covers some new aspects and dimensions of bioremediation of heavy metal-polluted soils. The bioremediation potential of bacteria and fungi individually and in association with plants has been reviewed and critically examined. It is reported that microbes such as Pseudomonas spp., Bacillus spp., and Aspergillus spp., have high metal tolerance, and bioremediation potential up to 98% both individually and when associated with plants such as Trifolium repens, Helianthus annuus, and Vallisneria denseserrulata. The mechanism of microbe's detoxification of metals depends upon various aspects which include the internal structure, cell surface properties of microorganisms, and the surrounding environmental conditions have been covered. Further, factors affecting the bioremediation efficiency and their possible solution, along with challenges and future prospects, are also discussed.

Targeting Cd coping mechanisms for stress tolerance in Brassica napus under spiked-substrate system: from physiology to remediation perspective

Cadmium (Cd) is a prevalent, non-essential, carcinogenic, and hazardous heavy metal that reduces plant productivity and capacity of arable land area around the globe. In the present substrate-based pot study, seedlings of Brassica napus 180015 were grown equidistantly in the spiked-substrate medium for 60 days under increasing concentrations of Cd (0, 10, 20, 30, 40, 50 mg kg^-1). Following harvest, the morpho-physio-biochemical, antioxidative, and Cd-induced tolerance responses were evaluated in B. napus under an increasing Cd stress regime. Additionally, these parameters were also investigated to select the plant's threshold tolerance limit for Cd under the spiked-substrate system. B. napus showed dynamic behavior regarding morpho-physio-biochemical attributes, including agronomic features, biomass, photosynthetic pigments, relative water content under increased Cd toxicity. Cd stress-induced hydrogen peroxide (H₂O₂) production with high MDA contents and passive EL, followed by the orchestration of both enzymatic (SOD, POD, APX, CAT, and GR) and non-enzymatic antioxidants (flavonoids, TPC, TPA, proline, and total soluble protein) up to a certain limit. In addition, Cd-induced stress upregulated transcriptional levels of antioxidative enzyme SOD, POD, APX, GR, and MT encoded genes in B. napus. The increasing trend of Cd accumulation in different tissues at the highest Cd concentration was as follows: root > leaf > stem. In spiked substrate system, B. napus demonstrated improved metal extractability performance and a high potential for phyto-management of low to moderate Cd contamination, implying that this study could be used for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.Novelty statementThis study provides an insight into Cd-coping mechanisms of oilseed rape involved in alleviating toxicity and simultaneous phyto-management of increasing Cd concentration under spiked substrate system. The current study is the first scientific evidence of using a Cd-spiked soilless substrate medium. The present study will further strengthen our understanding of Cd-instigated positive responses in B. napus. Furthermore, it will provide a useful basis for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.

Phytoremediation: a sustainable environmental technology for heavy metals decontamination

Toxic metal contamination of soil is a major environmental hazard. Chemical methods for heavy metal's (HMs) decontamination such as heat treatment, electroremediation, soil replacement, precipitation and chemical leaching are generally very costly and not be applicable to agricultural lands. However, many strategies are being used to restore polluted environments. Among these, phytoremediation is a promising method based on the use of hyper-accumulator plant species that can tolerate high amounts of toxic HMs present in the environment/soil. Such a strategy uses green plants to remove, degrade, or detoxify toxic metals. Five types of phytoremediation technologies have often been employed for soil decontamination: phytostabilization, phytodegradation, rhizofiltration, phytoextraction and phytovolatilization. Traditional phytoremediation method presents some limitations regarding their applications at large scale, so the application of genetic engineering approaches such as transgenic transformation, nanoparticles addition and phytoremediation assisted with phytohormones, plant growth-promoting bacteria and AMF inoculation has been applied to ameliorate the efficacy of plants as candidates for HMs decontamination. In this review, aspects of HMs toxicity and their depollution procedures with focus on phytoremediation are discussed. Last, some recent innovative technologies for improving phytoremediation are highlighted.

Piriformospora indica augments arsenic tolerance in rice (Oryza sativa) by immobilizing arsenic in roots and improving iron translocation to shoots

Arsenic (As) toxicity can be a hazardous threat to sustainable agriculture and human health. Piriformospora indica (P. indica), as a beneficial endophytic fungus, is involved in the plant tolerance to stressful conditions. Here, the biochemical and molecular responses of rice plants to As (50 μM) phytotoxicity and P. indica inoculation as well as the role of P. indica in improving rice adaptation to As stress were evaluated. The results showed that As stress reduced chlorophylls content, chlorophyll fluorescence yield (Fv/Fm), electron transport rate (ETR) and growth. However, P. indica restored chlorophyll content and growth. P. indica decreased the contents of methylglyoxal and malondialdehyde by improving the activity of enzymes involved in the glyoxalase pathway and modulating the redox state of the ascorbic acid-glutathione cycle, and consequently, increased the plant tolerance to As toxicity. P. indica, by downregulating Lsi2 expression (involved in As translocation to the shoot) and upregulating PCS1 and PCS2 expression (involved in As sequestration in vacuoles), immobilized As in the roots and reduced damage to photosynthetic organs. P. indica increased iron (Fe) accumulation in the shoot under As toxicity by upregulating the expression of IRO2, YSL2 and FRDL1 genes. The results of the present study augmented our knowledge in using P. indica symbiosis in improving the tolerance of rice plants against As toxicity for sustainable agriculture.