The bacterial consortia promote plant growth and secondary metabolite accumulation in Astragalus mongholicus under drought stress

Functional role of DFR genes in various blue Iris for the regulation of delphinidin synthesis

Flowers belonging to the Iris genus, with a predominant display of blue hues, showcase a variety of blue polymorphisms across different species. This study focused on analyzing the L∗, a∗, and b∗ color values of Iris typhifolia, I. lactea, I. laevigata, and I. sanguinea. Notably, I. lactea exhibited the highest L∗ value, indicating a brighter hue, while I. typhifolia and I. laevigata displayed larger a∗ values, suggesting a shift towards a reddish tone. I. sanguinea, conversely, presented the most profound blue with the lowest b∗ value. Our research delved into understanding the influence of anthocyanin components on these color variations and explored the regulatory role of the dihydroflavonol-4-reductase (DFR) gene. The findings underscore delphinidin as the primary blue pigment, with the additional presence of petunidin in I. typhifolia and I. laevigata introducing a purplish-red hue. Flavonoids were identified as contributors to enhancing the brightness of I. lactea's color. The study elucidates that blue polymorphism predominantly arises from varying proportions of delphinidin pigments, closely linked to substrate selection by Asp type DFRs. Following the expression of different DFR genes from the two blue Iris species, significant substrate selection differences were observed. These findings lay a foundation for future efforts to enhance flower colors in Irises and other related species by offering DFR as a target candidate gene.

Isolation of Bacterial Endophytes Associated with Cinchona ledgeriana Moens. and Their Potential in Plant-growth Promotion, Antifungal and Quinoline Alkaloids Production

For centuries, quinoline alkaloids from the tree bark of Cinchona ledgeriana (C. ledgeriana) have been used in the treatment of malaria. However, unsustainable harvesting and poor growth conditions greatly limit its use as raw materials. Since plant endophytes are known to contribute to the physiology of the host and its metabolism for survival, this study showed the potential of endophytes isolated from C. ledgeriana roots in promoting the germination of Catharathus roseus (C. roseus) seedlings and the biosynthesis of quinoline alkaloid. In this present study, we found that the Enterobacteriaceae family comprised the majority of the bacterial community, with Klebsiella pneumoniae being the most abundant species at the C. ledgeriana roots. Characterization of culturable bacterial endophytes from the C. ledgeriana roots showed that all the isolates displayed plant growth-promoting factors and antifungal activities. Interestingly, chromatographic analyses led to the identification of the quinoline alkaloids producing Achromobacter xylosoxidans (A. xylosoxidans) A1. Moreover, the co-cultures of A. xylosoxidans A1, Cytobacillus solani (C. solani) A3, and Klebsiella aerogenes A6 increased the fresh and dry weight of the C. roseus seedlings. These results suggest that these bacterial endophytes may enhance quinine and quinidine production as well as the growth of the plant host.

Exploring Plant Growth-Promoting Traits of Endophytic Fungi Isolated from Ligusticum chuanxiong Hort and Their Interaction in Plant Growth and Development

Endophytic fungi inhabit various plant tissues and organs without inducing evident disease symptoms. They can contribute positively to the growth of plants, bolster plants resilience to environmental and biological stresses, and facilitate the accumulation of secondary metabolites. These microbial resources possess significant developmental and utilization value in various applications. Hence, this study focused on exploring the plant growth-promoting (PGP) traits of 14 endophytic fungi from Ligusticum chuanxiong Hort (CX) and elucidating the effects and mechanisms that facilitate plant growth. According to PGP activity evaluation, the majority of strains demonstrated the capacity to produce IAA (78.57%), siderophores (50.00%), ammonia (35.71%), potassium solubilization (21.43%), nitrogen fixation (57.14%), and phosphate solubilization (42.86%). Further investigations indicated that the levels of IAA ranged from 13.05 to 301.43 μg/mL, whereas the soluble phosphorus levels ranged from 47.32 to 125.95 μg/mL. In cocultivation assays, it was indicated that Fusarium sp. YMY5, Colletotrichum sp. YMY6, Alternaria sp. ZZ10 and Fusarium sp. ZZ13 had a certain promoting effect on lateral root number and fresh weight of tobacco. Furthermore, ZZ10 and ZZ13 significantly enhanced the germination potential, germination index, and vigor index of tobacco seeds. The subsequent potted trials demonstrated that the four endophytic fungi exhibited an enhancement to growth parameters of tobacco to a certain extent. ZZ10 and ZZ13 treatment had the best promotion effect. Inoculation with YMY5 increased the chlorophyll a and total chlorophyll content. ZZ10 and ZZ13 treatment remarkably increased the net photosynthetic rate, soluble sugars and soluble protein content, catalase and peroxidase activities, and lowered malondialdehyde content in tobacco leaves. In addition, YMY5 remarkably elevated superoxide dismutase activities. ZZ13 upregulated the expression of growth-related gene. Among them, ZZ13 had a better growth-promoting effect. In conclusion, these endophytic fungi possessing multi-trait characteristics and the capacity to enhance plant growth exhibit promising potential as biofertilizers or plant growth regulators.

Promoting salt tolerance, growth, and phytochemical responses in coriander (Coriandrum sativum L. cv. Balady) via eco-friendly Bacillus subtilis and cobalt

In plant production, evaluation of salt stress protectants concerning their potential to improve growth and productivity under saline stress is critical. Bacillus subtilis (Bs) and cobalt (Co) have been proposed to optimize salt stress tolerance in coriander (Coriandrum sativum L. cv. Balady) plants by influencing some physiological activities. The main aim of this work is to investigate the response of (Bs) and (Co) as eco-safe salt stress protectants to resist the effect of salinity, on growth, seed, and essential oil yield, and the most important biochemical constituents of coriander produced under salt stress condition. Therefore, in a split-plot factorial experiment design in the RCBD (randomized complete block design), four levels of salinity of NaCl irrigation water (SA) were assigned to the main plots; (0.5, 1.5, 4, and 6 dS m-1); and six salt stress protectants (SP) were randomly assigned to the subplots: distilled water; 15 ppm (Co1); 30 ppm (Co2); (Bs); (Co1 + Bs); (Co2 + Bs). The study concluded that increasing SA significantly reduced coriander growth and yield by 42.6%, which could be attributed to ion toxicity, oxidative stress, or decreased vital element content. From the results, we recommend that applying Bs with Co (30 ppm) was critical for significantly improving overall growth parameters. This was determined by the significant reduction in the activity of reactive oxygen species scavenging enzymes: superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) and non-enzyme: proline by 5, 11.3, 14.7, and 13.8% respectively, while increasing ascorbic acid by 8% and preserving vital nutrient levels and enhancing plant osmotic potential to buffer salt stress, seed yield per plant, and essential oil yield increased by 12.6 and 18.8% respectively. The quality of essential oil was indicated by highly significant quantities of vital biological phytochemicals such as linalool, camphor, and protein which increased by 10.3, 3.6, and 9.39% respectively. Additional research is suggested to determine the precise mechanism of action of Bs and Co's dual impact on medicinal and aromatic plant salt stress tolerance.

Linking soil nutrients, microbial community composition, and enzyme activities to saponin content of Paris polyphylla after addition of biochar and organic fertiliser

The application of organic fertilisers and biochar has become widespread in agroforestry ecosystems to enhance the yield and quality of crops and medicinal plants. However, their specific impact on both the yield and quality of Paris polyphylla (P. polyphylla), along with the underlying mechanisms, remains unclear. In this study, we investigated the distinct effects of organic fertiliser (at concentrations of 5% and 10%) and biochar application (at levels of 2% and 4%) on P. polyphylla saponin content. This content is intricately regulated by available soil nutrients, enzyme activities, and microbial community compositions and activities. Our results clearly demonstrated a significant increase in the saponin content, including total saponin, polyphyllin I (PPI), polyphyllin II (PPII), polyphyllin VI (PPVI), and polyphyllin VII (PPVII), in P. polyphylla following the application of both biochar and organic fertiliser. Moreover, in comparison to the control group, the addition of biochar and organic fertiliser led to a considerable rise in the activity of glycosyltransferase enzyme (GTS) and cycloartenol synthase (CAS) in P. polyphylla. Additionally, it increased soil available potassium (AK) and soil organic matter (SOM) concentration, along with the activity of urease, acid phosphatase, and catalase, although biochar amendment resulted in a decrease in nitrate nitrogen (NO3--N) concentration. Crucially, our findings revealed a positive correlation between total saponin content and the activity of CAS in P. polyphylla, soil AK, SOM concentration, and the activities of urease, acid phosphatase, and catalase. Conversely, there was a negative correlation with NO3--N content. Furthermore, the application of organic fertiliser and biochar significantly influenced microbial community structures and specific microbial taxa. Notably, total saponin content exhibited a positive relationship with the relative abundances of Dehalococcoidia, Saccharomycetes, and Agaricomycetes taxa while showing a negative correlation with the abundance of Verrucomicrobiae. In conclusion, the observed increase in saponin content can be attributed to the modulation of specific microbial taxa in soils, as well as alterations in soil nutrients and enzyme activities resulting from the application of biochar and organic fertiliser. This study identifies a potential mechanism for enhancing saponin content in the artificial cultivation of P. polyphylla.

Exploring the impact of plant growth-promoting bacteria in alleviating stress on Aptenia cordifolia subjected to irrigation with recycled water in multifunctional external green walls

BACKGROUND

Rapid urbanization and population growth exert a substantial impact on the accessibility of drinking water resources, underscoring the imperative for wastewater treatment and the reuse of non-potable water in agriculture. In this context, green walls emerge as a potential solution to augment the purification of unconventional waters, simultaneously contributing to the aesthetic appeal and enjoyment of urban areas. This study aims to optimize water management in green walls by investigating the impact of bacterial strains on the biochemical properties and performance of the ornamental accumulator plant, Aptenia cordifolia, grown with various unconventional water sources. The experiments were designed as split plots based on a completely randomized block design with three replications. The main factor was recycled water with three levels (gray water, wastewater from the Kashfroud region of Mashhad, and urban water (control)). The sub-factor included different bacterial strains at four levels, composed of various bacteria combinations, (B1: Psedoumonas flucrecens + Azosporillum liposferum + Thiobacillus thioparus + Aztobactor chorococcum, B2: Paenibacillus polymyxa + Pseudomonas fildensis + Bacillus subtilis + Achromobacter xylosoxidans + Bacillus licheniform, B3: Pseudomonas putida + Acidithiobacillus ferrooxidans + Bacillus velezensis + Bacillus subtilis + Bacillus methylotrophicus + Mcrobacterium testaceum, and the control level without bacterial application (B0).

RESULT

The findings revealed significant differences at the 5% probability level across all morphophysiological traits, including plant height, the number and length of lateral branches, growth index, and plant coverage. Moreover, superior morphophysiological traits were observed in plants cultivated in substrates inoculated with wastewater irrigation. Substrates inoculated with bacteria exhibited the highest relative water content (RWC) and chlorophyll levels, coupled with the lowest relative saturation deficit (RSD), electrolyte leakage (EL), and carotenoid levels. Furthermore, plant growth-promoting bacteria (PGPB), from a biochemical perspective, were associated with increased carbohydrates, total protein, and anthocyanin. They also contributed to controlling oxidative stress caused by free radicals by enhancing the activity of antioxidant enzymes, such as guaiacol peroxidase (GPX), polyphenol oxidase (PPO), ascorbate peroxidase (APX), and peroxidase (POD), while reducing catalase enzyme (CAT) activity. This led to increased resistance to stress, as evidenced by a decrease in malondialdehyde and proline levels. The study concludes that the MIX B3, being both ecofriendly and economical, represents an effective strategy for mitigating the adverse effects of wastewater on plants.

CONCLUSION

This study showed that plant irrigation using wastewater increases the levels of proline, phenols and oxidative stress. However, the application of plant growth promoting bacteria (PGPB) reduced oxidative damage by increasing antioxidant activity and decreasing proline and phenol levels. These findings show the potential of bacterial treatments to improve plant growth and reduce adverse effects of recycled water irrigation.

Superiority of native soil core microbiomes in supporting plant growth

Native core microbiomes represent a unique opportunity to support food provision and plant-based industries. Yet, these microbiomes are often neglected when developing synthetic communities (SynComs) to support plant health and growth. Here, we study the contribution of native core, native non-core and non-native microorganisms to support plant production. We construct four alternative SynComs based on the excellent growth promoting ability of individual stain and paired non-antagonistic action. One of microbiome based SynCom (SC2) shows a high niche breadth and low average variation degree in-vitro interaction. The promoting-growth effect of SC2 can be transferred to non-sterile environment, attributing to the colonization of native core microorganisms and the improvement of rhizosphere promoting-growth function including nitrogen fixation, IAA production, and dissolved phosphorus. Further, microbial fertilizer based on SC2 and composite carrier (rapeseed cake fertilizer + rice husk carbon) increase the net biomass of plant by 129%. Our results highlight the fundamental importance of native core microorganisms to boost plant production.

Genome-Wide Analysis of the HSF Gene Family Reveals Its Role in Astragalus mongholicus under Different Light Conditions

Astragalus mongholicus is a traditional Chinese medicine (TCM) with important medicinal value and is widely used worldwide. Heat shock (HSF) transcription factors are among the most important transcription factors in plants and are involved in the transcriptional regulation of various stress responses, including drought, salinity, oxidation, osmotic stress, and high light, thereby regulating growth and developmental processes. However, the HFS gene family has not yet been identified in A. mongholicus, and little is known regarding the role of HSF genes in A. mongholicus. This study is based on whole genome analysis of A. mongholicus, identifying a total of 22 AmHSF genes and analyzing their physicochemical properties. Divided into three subgroups based on phylogenetic and gene structural characteristics, including subgroup A (12), subgroup B (9), and subgroup C (1), they are randomly distributed in 8 out of 9 chromosomes of A. mongholicus. In addition, transcriptome data and quantitative real time polymerase chain reaction (qRT-PCR) analyses revealed that AmHSF was differentially transcribed in different tissues, suggesting that AmHSF gene functions may differ. Red and blue light treatment significantly affected the expression of 20 HSF genes in soilless cultivation of A. mongholicus seedlings. AmHSF3, AmHSF3, AmHSF11, AmHSF12, and AmHSF14 were upregulated after red light and blue light treatment, and these genes all had light-corresponding cis-elements, suggesting that AmHSF genes play an important role in the light response of A. mongholicus. Although the responses of soilless-cultivated A. mongholicus seedlings to red and blue light may not represent the mature stage, our results provide fundamental research for future elucidation of the regulatory mechanisms of HSF in the growth and development of A. mongholicus and its response to different light conditions.

Trophic relationships between protists and bacteria and fungi drive the biogeography of rhizosphere soil microbial community and impact plant physiological and ecological functions

Rhizosphere microorganisms play a vital role in enhancing plant health, productivity, and the accumulation of secondary metabolites. Currently, there is a limited understanding of the ecological processes that control the assembly of community. To address the role of microbial interactions in assembly and for functioning of the rhizosphere soil microbiota, we collected rhizosphere soil samples from Anisodus tanguticus on the Tibetan Plateau spanning 1500 kilometers, and sequenced the bacteria, fungi, archaea, and protist communities. We observed a significant but weak distance-decay relationship in the microbial communities of rhizosphere soil. Our comprehensive analysis of spatial, abiotic, and biotic factors showed that trophic relationships between protists and bacteria and fungi predominantly influenced the alpha and beta diversity of bacterial, fungal, and protistan communities, while abiotic factors had a greater impact on archaeal communities, including soil pH, available phosphorus, total phosphorus and mean annual temperature. Importantly, microbial interactions had a more significant influence on Anisodus tanguticus physiological and ecological functions compared to individual microorganisms. Network analyses revealed that bacteria occupy a central position of the co-occurrence network and play a crucial role of connector within this community. The addition of protists increased the stability of bacterial, fungal, and archaeal networks. Overall, our findings indicate that trophic relationships play an important role in assembly and for functioning of the rhizosphere soil microbiota. Bacterial communities serve as a crucial link between different kingdoms of microorganisms in the rhizosphere community. These findings help us to fully harness the beneficial functions of rhizosphere microorganisms for plants and achieve sustainable use of biological resources.

Using Fungi in Artificial Microbial Consortia to Solve Bioremediation Problems

There is currently growing interest in the creation of artificial microbial consortia, especially in the field of developing and applying various bioremediation processes. Heavy metals, dyes, synthetic polymers (microplastics), pesticides, polycyclic aromatic hydrocarbons and pharmaceutical agents are among the pollutants that have been mainly targeted by bioremediation based on various consortia containing fungi (mycelial types and yeasts). Such consortia can be designed both for the treatment of soil and water. This review is aimed at analyzing the recent achievements in the research of the artificial microbial consortia that are useful for environmental and bioremediation technologies, where various fungal cells are applied. The main tendencies in the formation of certain microbial combinations, and preferences in their forms for usage (suspended or immobilized), are evaluated using current publications, and the place of genetically modified cells in artificial consortia with fungi is assessed. The effect of multicomponence of the artificial consortia containing various fungal cells is estimated, as well as the influence of this factor on the functioning efficiency of the consortia and the pollutant removal efficacy. The conclusions of the review can be useful for the development of new mixed microbial biocatalysts and eco-compatible remediation processes that implement fungal cells.

Microbial fortification of pharmacological metabolites in medicinal plants

Medicinal plants are rich in secondary metabolites with beneficial pharmacological effects. The production of plant secondary metabolites is subjected to the influences by environmental factors including the plant-associated microbiome, which is crucial to the host's fitness and survival. As a result, research interests are increasing in exploiting microbial capacities for enhancing plant production of pharmacological metabolites. A growing body of recent research provides accumulating evidence in support of developing microbe-based tools for achieving this objective. This mini review presents brief summaries of recent studies on medicinal plants that demonstrate microbe-augmented production of pharmacological terpenoids, polyphenols, and alkaloids, followed by discussions on some key questions beyond the promising observations. Explicit molecular insights into the underlying mechanisms will enhance microbial applications for metabolic fortification in medicinal plants.

Drought stress modifies the community structure of root-associated microbes that improve Atractylodes lancea growth and medicinal compound accumulation

Atractylodes lancea is an important medicinal plant in traditional Chinese medicine, its rhizome is rich of volatile secondary metabolites with medicinal values and is largely demanded in modern markets. Currently, supply of high-yield, high-quality A. lancea is mainly achieved via cultivation. Certain soil microbes can benefit plant growth, secondary metabolism and induce resistance to environmental stresses. Hence, studies on the effects of soil microbe communities and isolates microorganisms on A. lancea is extremely meaningful for future application of microbes on cultivation. Here we investigated the effects of the inoculation with an entire soil microbial community on the growth, resistance to drought, and accumulation of major medicinal compounds (hinesol, β-eudesmol, atractylon and atractylodin) of A. lancea. We analyzed the interaction between A. lancea and the soil microbes at the phylum and genus levels under drought stress of different severities (inflicted by 0%, 10% and 25% PEG6000 treatments). Our results showed that inoculation with soil microbes promoted the growth, root biomass yield, medicinal compound accumulation, and rendered drought-resistant traits of A. lancea, including relatively high root:shoot ratio and high root water content under drought. Moreover, our results suggested drought stress was more powerful than the selectivity of A. lancea in shaping the root-associated microbial communities; also, the fungal communities had a stronger role than the bacterial communities in protecting A. lancea from drought. Specific microbial clades that might have a role in protecting A. lancea from drought stress were identified: at the genus level, the rhizospheric bacteria Bacillus, Dylla and Actinomadura, and rhizospheric fungi Chaetomium, Acrophialophora, Trichoderma and Thielava, the root endophytic bacteria Burkholderia-Caballeronia-Paraburkholderia, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Dylla and Actinomadura, and the root endophytic fungus Fusarium were closely associated with A. lancea under drought stress. Additionally, we acquired several endophytic Paenibacillus, Paraburkholderia and Fusarium strains and verified they had differential promoting effects on the medicinal compound accumulation in A. lancea root. This study reports the interaction between A. lancea and soil microbe communities under drought stress, and provides insights for improving the outcomes in A. lancea farming via applying microbe inoculation.