Purines enrich root-associated Pseudomonas and improve wild soybean growth under salt stress.

The root-associated microbiota plays an important role in the response to environmental stress. However, the underlying mechanisms controlling the interaction between salt-stressed plants and microbiota are poorly understood. Here, by focusing on a salt-tolerant plant wild soybean (Glycine soja), we demonstrate that highly conserved microbes dominated by Pseudomonas are enriched in the root and rhizosphere microbiota of salt-stressed plant. Two corresponding Pseudomonas isolates are confirmed to enhance the salt tolerance of wild soybean. Shotgun metagenomic and metatranscriptomic sequencing reveal that motility-associated genes, mainly chemotaxis and flagellar assembly, are significantly enriched and expressed in salt-treated samples. We further find that roots of salt stressed plants secreted purines, especially xanthine, which induce motility of the Pseudomonas isolates. Moreover, exogenous application for xanthine to non-stressed plants results in Pseudomonas enrichment, reproducing the microbiota shift in salt-stressed root. Finally, Pseudomonas mutant analysis shows that the motility related gene cheW is required for chemotaxis toward xanthine and for enhancing plant salt tolerance. Our study proposes that wild soybean recruits beneficial Pseudomonas species by exudating key metabolites (i.e., purine) against salt stress.

Ensifer sp. GMS14 enhances soybean salt tolerance for potential application in saline soil reclamation.

Rhizosphere microbiomes play an important role in enhancing plant salt tolerance and are also commonly employed as bio-inoculants in soil remediation processes. Cultivated soybean (Glycine max) is one of the major oilseed crops with moderate salt tolerance. However, the response of rhizosphere microbes me to salt stress in soybean, as well as their potential application in saline soil reclamation, has been rarely reported. In this study, we first investigated the microbial communities of salt-treated and non-salt-treated soybean by 16S rRNA gene amplicon sequencing. Then, the potential mechanism of rhizosphere microbes in enhancing the salt tolerance of soybean was explored based on physiological analyses and transcriptomic sequencing. Our results suggested that Ensifer and Novosphingobium were biomarkers in salt-stressed soybean. One corresponding strain, Ensifer sp. GMS14, showed remarkable growth promoting characteristics. Pot experiments showed that GMS14 significantly improved the growth performance of soybean in saline soils. Strain GMS14 alleviated sodium ions (Na+) toxicity by maintaining low a Na+/K+ ratio and promoted nitrogen (N) and phosphorus (P) uptake by soybean in nutrient-deficient saline soils. Transcriptome analyses indicated that GMS14 improved plant salt tolerance mainly by ameliorating salt stress-mediated oxidative stress. Interestingly, GMS14 was evidenced to specifically suppress hydrogen peroxide (H2O2) production to maintain reactive oxygen species (ROS) homeostasis in plants under salt stress. Field experiments with GMS14 applications showed its great potential in saline soil reclamation, as evidenced by the increased biomass and nodulation capacity of GMS14-inoculated soybean. Overall, our findings provided valuable insights into the mechanisms underlying plant-microbes interactions, and highlighted the importance of microorganisms recruited by salt-stressed plant in the saline soil reclamation.

Effect of planting salt-tolerant legumes on coastal saline soil nutrient availability and microbial communities.

Soil salinization is a serious global environmental problem affecting sustainable development of agriculture. Legumes are excellent candidates for the phytoremediation of saline soils; however, how soil microbes mediate the amelioration of coastal saline ecosystems is unknown. In this study, two salt-tolerant legumes, Glycine soja and Sesbania cannabina were planted in coastal saline soil for three years. Soil nutrient availability and microbiota structure (including bacteria, fungi, and diazotrophs) were compared between the phytoremediated soils and control soil (barren land). Planting legumes reduced soil salinity, and increased total carbon, total nitrogen, and NO3--N contents. Among the soil microbiota, some nitrogen-fixing bacteria (e.g., Azotobacter) were enriched in legumes, which were probably responsible for soil nitrogen accumulation. The complexity of the bacterial, fungal, and diazotrophic networks increased significantly from the control to the phytoremediated soils, suggesting that the soil microbial community formed closer ecological interactions during remediation. Furthermore, the dominant microbial functions were chemoheterotrophy (24.75%) and aerobic chemoheterotrophy (21.97%) involved in the carbon cycle, followed by nitrification (13.68%) and aerobic ammonia oxidation (13.34%) involved in the nitrogen cycle. Overall, our findings suggested that G. soja and S. cannabina legumes were suitable for ameliorating saline soils as they decreased soil salinity and increased soil nutrient content, with microorganisms especially nitrogen-fixing bacteria, playing an important role in this remediation process.

A review of materials, fabrication methods, and strategies used to enhance bone regeneration in engineered bone tissues.

Over the last decade, bone engineered tissues have been developed as alternatives to autografts and allografts to repair and reconstruct bone defects. This article provides a review of the current technologies in bone tissue engineering. Factors used for fabrication of three-dimensional bone scaffolds such as materials, cells, and biomolecular signals, as well as required properties for ideal bone scaffolds, are reviewed. In addition, current fabrication techniques including rapid prototyping are elaborated upon. Finally, this review article further discusses some effective strategies to enhance cell ingrowth in bone engineered tissues; for example, nanotopography, biomimetic materials, embedded growth factors, mineralization, and bioreactors. In doing so, it suggests that there is a possibility to develop bone substitutes that can repair bone defects and promote new bone formation for orthopedic applications.