Root-endophytic Chaetomium cupreum chemically enhances aluminium tolerance in Miscanthus sinensis via increasing the aluminium detoxicants, chlorogenic acid and oosporein

Transgenic soybean of GsMYB10 shapes rhizosphere microbes to promote resistance to aluminum (Al) toxicity

Plant resistance genes could affect rhizosphere microbiota, which in turn enhanced plant resistance to stresses. Our previous study found that overexpression of the GsMYB10 gene led to enhanced tolerance of soybean plants to aluminum (Al) toxicity. However, whether GsMYB10 gene could regulate rhizosphere microbiota to mitigate Al toxicity remains unclear. Here, we analyzed the rhizosphere microbiomes of HC6 soybean (WT) and transgenic soybean (trans-GsMYB10) at three Al concentrations, and constructed three different synthetic microbial communities (SynComs), including bacterial, fungal and cross-kingdom (bacteria and fungi) SynComs to verify their role in improving Al tolerance of soybean. Trans-GsMYB10 shaped the rhizosphere microbial communities and harbored some beneficial microbes, such as Bacillus, Aspergillus and Talaromyces under Al toxicity. Fungal and cross-kingdom SynComs showed a more effective role than the bacterial one in resistance to Al stress, and these SynComs helped soybean resist Al toxicity via affecting some functional genes that involved cell wall biosynthesis and organic acid transport etc. Overall, this study reveals the mechanism of soybean functional genes regulating the synergistic resistance of rhizosphere microbiota and plants to Al toxicity, and also highlights the possibility of focusing on the rhizobial microbial community as a potential molecular breeding target to produce crops.

Study on the Potential for Stimulating Mulberry Growth and Drought Tolerance of Plant Growth-Promoting Fungi

Drought stress often leads to heavy losses in mulberry planting, especially for fruits and leaves. Application of plant growth-promoting fungi (PGPF) endows various plant beneficial traits to overcome adverse environmental conditions, but little is known about the effects on mulberry under drought stress. In the present study, we isolated 64 fungi from well-growing mulberry trees surviving periodical drought stress, and Talaromyces sp. GS1, Pseudeurotium sp. GRs12, Penicillium sp. GR19, and Trichoderma sp. GR21 were screened out due to their strong potential in plant growth promotion. Co-cultivation assay revealed that PGPF stimulated mulberry growth, exhibiting increased biomass and length of stems and roots. Exogenous application of PGPF could alter fungal community structures in the rhizosphere soils, wherein Talaromyces was obviously enhanced after inoculation of Talaromyces sp. GS1, and Peziza was increased in the other treatments. Moreover, PGPF could promote iron and phosphorus absorption of mulberry as well. Additionally, the mixed suspensions of PGPF induced the production of catalase, soluble sugar, and chlorophyll, which in turn enhanced the drought tolerance of mulberry and accelerated their growth recovery after drought. Collectively, these findings might provide new insights into improving mulberry drought tolerance and further boosting mulberry fruit yields by exploiting interactions between hosts and PGPF.

Isoavenaciol and 7-hydroxy-isoavenaciol: Zn-chelating metallophores produced by root-endophytic Pezicula ericae in a Zn-accumulating plant, Aucuba japonica

Metallophores are low-molecular-weight compounds capable of chelating heavy metals, which have recently been reported to alleviate heavy metal stress in plants. We isolated two undescribed compounds as Zn-chelating metallophores from the culture broth of the root endophytic Pezicula ericae w12-25, which was collected from a Zn-accumulating plant, Aucuba japonica Thunb. These two compounds were determined to be (3aS,4S,6aR)-3a-hydroxy-3-methylene-4-octyldihydrofuro[3,4-b]furan-2,6(3H,4H)-dione and (3S,3aS,4S,6aR)-3a-hydroxy-3-(hydroxymethyl)-4-octyldihydrofuro[3,4-b]furan-2,6(3H,4H)-dione using spectroscopic methods (HRMS, ¹H and ¹³C NMR, and 2D NMR) and X-ray crystallography, respectively. The two compounds, classified as furofurandiones, were named isoavenaciol and 7-hydroxy-isoavenaciol. After the hydrolysis of the lactone moiety, isoavenaciol would release the carboxyl group to show Zn-chelating activity. Their antifungal activities were confirmed using Cladosporium herbarum (AHU9262).

Oosporein Produced by Root Endophytic Chaetomium cupreum Promotes the Growth of Host Plant, Miscanthus sinensis, under Aluminum Stress at the Appropriate Concentration

Chaetomium cupreum, a root endophyte in Miscanthus sinensis, enhances Al tolerance in M. sinensis by changing aluminum (Al) localization and the production of a siderophore, oosporein, which chelates Al for detoxification. Oosporein has various functions, including insecticidal activity, phytotoxicity, antifungal activity, and a siderophore. In our study, we focused on the detoxification effect of oosporein as a siderophore and on the growth of M. sinensis under Al exposure. In addition, the phytotoxicity of oosporein to M. sinensis was confirmed to compare with those in Lactuca sativa and Oryza sativa as control plants. Under Al stress, oosporein promoted plant growth in M. sinensis seedlings at 10 ppm, which was the same concentration as that detected in M. sinensis roots infected with C. cupreum in our previous study. Oosporein also showed low phytotoxicity to M. sinensis compared with L. sativa at even high concentrations of oosporein. These results suggest that the concentration of oosporein in M. sinensis roots would be maintained at the appropriate concentration to detoxify Al and would promote M. sinensis growth under Al stress, although oosporein would show low phytotoxicity to the natural host plant, M. sinensis, compared with the non-host plant, L. sativa.

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.

Phialocephala fortinii increases aluminum tolerance in Miscanthus sinensis growing in acidic mine soil

Miscanthus sinensis growing in our study mine site contained a high concentration of Al in the adventitious roots. It has a root endophyte, Phialocephala fortinii, in its adventitious roots at a high frequency. The purpose of this study was to elucidate the effects of P. fortinii on Al tolerance mechanisms of M. sinensis and reveal potential underlying mechanisms. In the absence of P. fortinii, M. sinensis produced chlorogenic, citric, and malic acids that could act to alleviate Al toxicity in acidic mine soil. Up on fungal inoculation, the levels of these compounds were reduced, although the growth of seedlings and Mg concentration in the roots were increased. IAA production by the fungus may contribute to enhanced plant growth whereas an increase of Mg uptake could reduce toxicity of reactive oxygen species under Al stress. These actions of P. fortinii could promote growth and survival of M. sinensis in mine sites.

Endophytic Fungi: Biological Control and Induced Resistance to Phytopathogens and Abiotic Stresses

Plant diseases cause losses of approximately 16% globally. Thus, management measures must be implemented to mitigate losses and guarantee food production. In addition to traditional management measures, induced resistance and biological control have gained ground in agriculture due to their enormous potential. Endophytic fungi internally colonize plant tissues and have the potential to act as control agents, such as biological agents or elicitors in the process of induced resistance and in attenuating abiotic stresses. In this review, we list the mode of action of this group of microorganisms which can act in controlling plant diseases and describe several examples in which endophytes were able to reduce the damage caused by pathogens and adverse conditions. This is due to their arsenal of molecules generated during the interaction by which they form a kind of biological shield in the plant. Furthermore, considering that endophytic fungi can be an important tool in managing for biotic and abiotic stresses due to the large amount of biologically active substances produced, bioprospecting this class of microorganisms is tending to increase and generate valuable products for agriculture.

Efficiency of bacteria and bacterial assisted phytoremediation of heavy metals: An update

The aim of this review to address the plant-associated bacteria to enhance the phytoremediation efficiency of the heavy metals from polluted sites and it is also highlighted advances for the application in wastewater treatment. Plant-associated bacteria have potential to encourage the plant growth and resistance under stress conditions. Such bacteria could enhance plant growth by controlling growth hormone, nutrition security, producing siderophore, secondary metabolites, and improving the antioxidant enzymes system. This review also explores the concepts and applications of bacteria assisted phytoremediation, addressing aspects that affect phytoremediation and pathways for restoration. Significant review issues relating to production and application of bacteria for improvement of bioremediation were established and presented for possible future research. Bacteria assisted phytoremediation is cost-effective strategy and metal sequestration mechanism that hold high metal biosorption capacities. This also takes into consideration the current state of technology implementations and proposals for prospective clean-up studies.

Rhizoplane and Rhizosphere Fungal Communities of Geographically Isolated Korean Bellflower (Campanula takesimana Nakai)

Simple Summary

The current study reports fungal diversities in the rhizoplane (RP) and rhizosphere (RS) samples of the geographically isolated Korean bellflower (Campanulatakesimana) obtained from its original habitats of the eastern coast of the Korean Peninsula for the first time. The identification of specific taxa in each site may provide a better understanding of the interaction between the soil fungi and Korean bellflower.

Abstract

Fungal communities in the rhizoplane (RP) and rhizosphere (RS) of geographically isolated C. takesimana habitats in different environments such as oceanic (Seodo, the Dokdo Islands), coastline (Sadong, Ulleungdo Island), and inland (Taeha, Ulleungdo Island) regions were analyzed by MiSeq sequencing. In total, 1279 operational taxonomic units (OTUs) were obtained and they were further classified into 185 genera belonging to five phyla. The total number of fungal taxa in the RP samples was lower than those in the RS samples in all the sampled locations, providing an indication of the existence of a certain level of the selective pressures from the host plant. The richness of the RP in the Dokdo Islands was higher than that of Ulleungdo Island, but the richness of the RS in the Dokdo Islands was lower than that of Ulleungdo Island. These results suggest evidence for strong effects of a harsh geo-climate on the RP and RS fungal diversities in the Dokdo Islands. Additionally, a total of 82 fungal genera were identified in all three RP samples and 63 genera (77%) were uniquely found in each of the geographical regions and 43 genera (52.4%) showed high dependency on the C. takesimana vegetation. It was found that the genus Mortierella was the most dominant taxon in all the samples. The geo-ecological isolation of the Korean bellflower may have caused unique formation of the RP and RS fungal communities in the natural habitats.

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.

Changes in plant function and root mycobiome caused by flood and drought in a riparian tree

Under increasingly harsh climatic conditions, conservation of threatened species requires integrative studies to understand stress tolerance. Riparian Ulmus minor Mill. populations have been massively reduced by Dutch Elm disease (DED). However, resistant genotypes were selected to restore lost populations. To understand the acclimation mechanisms to the succession of abiotic stresses, ramets of five DED-tolerant U. minor genotypes were subjected to flood and subsequently to drought. Physiological and biochemical responses were evaluated together with shifts in root-fungal assemblages. During both stresses, plants exhibited a decline in leaf net photosynthesis and an increase in percentage loss of stem hydraulic conductivity and in leaf and root proline content. Stomatal closure was produced by chemical signals during flood and hydraulic signals during drought. Despite broad similarities in plant response to both stresses, root-mycobiome shifts were markedly different. The five genotypes were similarly tolerant to moderate drought, however, flood tolerance varied between genotypes. In general, flood did not enhance drought susceptibility due to fast flood recovery, nevertheless, different responses to drought after flood were observed between genotypes. Associations were found between some fungal taxonomic groups and plant functional traits varying with flood and drought (e.g. proline, chlorophyll and starch content) indicating that the thriving of certain taxa depends on host responses to abiotic stress.