Microbial interactions within the rhizosphere are fundamental to plant health, influencing nutrient availability, stress tolerance, and pathogen resistance. Beneficial microbes, such as plant growth-promoting microbes (PGPMs), including bacteria and mycorrhizal fungi, enhance plant resilience through mechanisms like nutrient solubilization, phytohormone production, and pathogen suppression via antimicrobial compounds and siderophores. Root exudates, composed of sugars, organic acids, and secondary metabolites, act as chemoattractants that shape the rhizosphere microbiome by recruiting beneficial microbes. Microbial metabolites can, in turn, modulate plant physiology and exudate profiles, thereby reinforcing mutualistic interactions. Stress conditions alter exudate composition, enabling plants to attract specific microbes that aid in stress mitigation. Given the growing interest in microbiome-based agricultural solutions, this review aims to synthesize recent literature on plant–microbe interactions, with a focus on bidirectional signaling between plants and microbes. A structured literature search was conducted using databases such as PubMed, Scopus, and ScienceDirect to identify key studies on root exudation, microbial functions, and synthetic microbial communities (SynComs). We highlight major findings on how engineered microbiomes can enhance plant growth, resilience, and productivity, particularly under stress conditions. This review also explores how advances in SynCom design can promote sustainable agriculture by reducing reliance on chemical inputs.

Microbial interactions within the rhizosphere are fundamental to plant health, influencing nutrient availability, stress tolerance, and pathogen resistance. Beneficial microbes, such as plant growth-promoting microbes (PGPM) in-cluding bacteria and mycorrhizal fungi, enhance plant resilience through mechanisms like nutrient solubilization, phytohormone production, and pathogen suppression via antimicrobial compounds and siderophores. Root exudates, composed of sugars, organic acids, and secondary metabolites, act as chemoattractants that shape the rhizosphere microbiome by recruiting bene-ficial microbes. Stress conditions alter exudate composition, enabling plants to attract specific microbes that aid in stress mitigation. The dynamic interactions between plants and microbes are central to sustainable agriculture, as they can reduce dependency on chemical fertilizers and pesticides. Advancements in microbiome engineering have led to the development of synthetic microbial communities (SynComs) tailored to enhance plant productivity and disease resistance. Recent studies have highlighted the potential of engineered mi-crobiomes to establish stable, beneficial microbial consortia that support plant growth under diverse environmental conditions. This review will discuss the role of microbial interactions in plant health, the influence of root exudates on microbiome composition, and the emerging potential of SynComs in opti-mizing plant-microbe associations for sustainable agriculture.

Surfactants are widely utilized in agriculture as emulsifying, dispersing, anti-foaming, and wetting agents. In these adjuvant roles, the inherent biological activity of the surfactant is secondary to the active ingredients. Here, the hydrophilic non-ionic surface-active tri-block copolymer Pluronic^® F68 is investigated for direct biological activity in wheat. F68 binds to and inserts into lipid membranes, which may benefit crops under abiotic stress. F68’s interactions with Triticum aestivum (var Juniper) seedlings and a seed-borne Bacillus spp. endophyte are presented. At concentrations below 10 g/L, F68-primed wheat seeds exhibited unchanged emergence. Root-applied fluorescein-F68 (fF68) was internalized in root epidermal cells and concentrated in highly mobile endosomes. The potential benefit of F68 in droughted wheat was examined and contrasted with wheat treated with the osmolyte, glycine betaine (GB). Photosystem II activity of droughted plants dropped significantly below non-droughted controls, and no clear benefit of F68 (or GB) during drought or rehydration was observed. However, F68-treated wheat exhibited increased transpiration values (for watered plants only) and enhanced shoot dry mass (for watered and droughted plants), not observed for GB-treated or untreated plants. The release of seed-borne bacterial endophytes into the spermosphere of germinating seeds was not affected by F68 (for F68-primed seeds as well as F68 applied to roots), and the planktonic growth of a purified Bacillus spp. seed endophyte was not reduced by F68 applied below the critical micelle concentration. These studies demonstrated that F68 entered wheat root cells, concentrated in endosomes involved in transport, significantly promoted shoot growth, and showed no adverse effects to plant-associated bacteria.

Surfactants are widely utilized in agriculture as emulsifying, dispersing, anti-foaming, and wetting agents. In these adjuvant roles the inherent biological activity of the surfactant is secondary to the active ingredients. Here, the hydrophilic non-ionic surface-active triblock copolymer, Pluronic® F68, is investigated for direct biological activity in wheat. F68 binds and inserts in lipid membranes, which may benefit crops under abiotic stress. F68 interactions with Triticum aestivum (var Juniper) seedlings and a seed-borne Bacillus spp. endophyte are presented. At concentrations below 10 g/L, F68-primed wheat seeds exhibited unchanged emergence. Root-applied fluoroscein-F68 (fF68) was internalized in root epidermal cells and concentrated in highly mobile endosomes. Potential benefit of F68 in droughted wheat was examined and contrasted with wheat treated with the osmolyte, glycine betaine (GB). Photosystem II activity of droughted plants dropped significantly below non-droughted controls, and no clear benefit of F68 (or GB) during drought or rehydration was observed. However, F68-treated wheat exhibited increased transpiration values (for watered plants only) and enhanced shoot dry mass (for watered and droughted plants), not observed for GB-treated or un-treated plants. Release of seed-borne bacterial endophytes into the spermosphere of germinating seeds was not affected by F68 (for F68-primed seeds as well as F68 applied to roots), and planktonic growth of a purified Bacillus spp. seed endophyte was not reduced by F68 applied below the critical micelle concentration. These studies demonstrated that F68 entered wheat root cells, concentrated in endosomes involved in transport, significantly promoted shoot growth, and showed no adverse effects to root-associated bacteria.

Seed-associated endophytes become active during germination, playing important roles as early colonizers of plant tissues and contributing to plant health while residing in a protective niche. In this study, we characterized a wheat-derived bacterial isolate, JunSE1L, to determine its functional traits and ecological role in the plant microbiome. The isolate was identified as Bacillus atrophaeus based on 16S rRNA analysis. JunSE1L exhibited nutrient-dependent plasticity in colony architecture, forming robust hydrophobic biofilms and pellicles under rich nutrient availability while swarming and forming thin, often dendritic colonies under defined nutrition. JunSE1L produced highly surface-active compounds that lowered the surface tension of water to 30 mN/m and released potent proteolytic and hemolytic compounds, thus equipping JunSE1L for antagonistic interactions, as examined against several fungal pathogens. JunSE1L inhibited Fusarium proliferatum and Mucor hiemalis in live-cell assays, while cell-free supernatant selectively inhibited M. hiemalis. JunSE1L was recovered from multiple plant compartments, including rhizosphere, rhizoplane, and aerial tissues, and was observed to emerge from cut plant tissues, supporting seed-endophyte mobilization upon germination to colonize distal tissues. Seed surface inoculation experiments with JunSE1L showed limited attachment at low cell densities and reduced seedling vigor at higher inoculum levels, indicating that inoculum density and native microbiome interactions influence seedling performance.

Seed-associated endophytes become active during germination, playing important roles as early colonizers of plant tissues, contributing to plant health while residing in a protective niche. In this study, we characterized a wheat-derived bacterial isolate, JunSE1L, to determine its functional traits and ecological role in the plant microbiome. The isolate was identified as Bacillus atrophaeus based on 16S rRNA analysis. JunSE1L exhibited nutrient-dependent plasticity in colony architecture, forming robust hydrophobic biofilms and pellicles under rich nutrient availability, while swarming and forming thin, often dendritic colonies under defined nutrition. JunSE1L produced highly surface-active compounds that lowered the surface tension of water to 30 mN/m and released potent proteolytic and hemolytic compounds, thus equipping JunSE1L for offensive roles, as examined against several fungal pathogens. JunSE1L inhibited Fusarium proliferatum and Mucor hiemalis in live-cell assays, while cell-free supernatant selectively inhibited M. hiemalis. JunSE1L was recovered from multiple plant compartments, including rhizosphere, rhizoplane, and aerial tissues, and was observed to emerge from cut plant tissues, supporting seed-endophyte mobilization upon germination to colonize distal tissues. Seed surface inoculation experiments with JunSE1L showed limited attachment at low cell densities and reduced seedling vigor at higher inoculum levels, supporting agricultural approaches nurturing the existing seed microbiome.