Early Signaling in the Rhizobium-legume Symbiosis - Volume II

Access Volume I by clicking this linkRhizobia are a diverse group of soil bacteria capable of establishing nitrogen-fixing symbioses with legumes through highly coordinated molecular communication. Under favorable environmental and physiological conditions, compatible rhizobial strains colonize the rhizosphere, enter the root through specialized infection programs, and induce the formation of nodules, novel organs in which differentiated endosymbiotic bacteria convert atmospheric nitrogen into ammonia for plant assimilation. This partnership is fundamental for plant productivity and sustainable agriculture, decreasing the need for synthetic nitrogen fertilizers.Over the past two decades, major progress has been made in defining the early events that determine symbiotic compatibility, efficiency, and robustness. The interaction is initiated by plant-derived phenolic compounds in root exudates that shape rhizobial gene expression, including the production of Nod factors and other symbiotic determinants. Nod factor signals are perceived by host receptors, and the resulting symbiotic signaling controls plant developmental pathways that lead to bacterial infection, cortical cell divisions and nodule organogenesis. At the same time, plants must balance symbiotic accommodation with immune surveillance. The outcome depends on how signaling networks intersect across cell types and tissues, and how these networks are tuned by plant genotype, rhizobial genotype, and the surrounding microbiome.Volume II aims to capture and stimulate current advances that are transforming the field. High-resolution approaches such as single-cell and spatial transcriptomics, advanced live imaging, quantitative phenotyping, and multi-omics profiling are revealing how early symbiotic signaling progresses over time, how distinct root cell layers coordinate their responses, and how metabolic and hormonal states influence symbiotic processes. In parallel, expanding knowledge of microbial determinants, including surface polysaccharides and effector proteins translocated into host cells, is refining our understanding of host range, infection strategies, and immune modulation. Emerging concepts also highlight the importance of environmental context, including nutrient status, drought, temperature, soil acidity, and biotic stress, which can reprogram signaling and immunity, thereby altering nodulation outcomes under field-relevant conditions.This Research Topic focuses on the molecular mechanisms governing early rhizobium–legume communication prior to bacterial release into symbiotic cells and the onset of nitrogen fixation. We welcome contributions that provide mechanistic insight into improving symbiotic performance, including integrative studies spanning plant biology and microbiology.Volume II welcomes manuscripts on topics including, but not limited to:• Rhizobial chemotaxis, motility, and rhizosphere colonization in response to root exudates• Biosynthesis, regulation, and diversification of Nod factors and other rhizobial determinants• Plant receptors and early signaling networks, including calcium-based signaling, transcriptional reprogramming, and cell-to-cell coordination• Plant biochemical and physiological responses to microbial cues, including redox dynamics and cell wall remodeling• Rhizobial surface polysaccharides, their perception by host plants, their roles in infection, and their links to symbiotic compatibility• Rhizobial effector proteins, their secretion systems, and their targets in host plants• Control and reconfiguration of plant defense responses during symbiotic initiation• Cross-talk between plant immunity and symbiosis, including mechanisms of immune attenuation and effector-triggered immunity • Roles of phytohormones and peptide signals in early infection and nodule organogenesis• Cytoskeletal and membrane trafficking events during infection thread initiation and progression• Inter-kingdom communication that fine-tunes symbiotic specificity and efficiency, including small molecules, RNAs, and extracellular vesicle–mediated processes• Microbiome composition and community interactions influencing early symbiotic signaling and infection success• Environmental modulation of early symbiosis (nutrients, drought, temperature, salinity, pH, and pathogens) and implications for stress-resilient nitrogen fixation Topic editors: Maria Jose Soto, Christian Staehelin, Jose María Vinardell, Attila Kereszt, Luis Cardenas Source: https://www.frontiersin.org/research-topics/77509/early-signaling-in-the-rhizobium-legume-symbiosis---volume-ii