Evaluation of Immune Responses Induced by Simultaneous Inoculations of Soybean (Glycine max [L.] Merr.) with Soil Bacteria and Rhizobia

Symbiosis vs pathogenesis in plants: Reflections and perspectives

Plant-microbe partnerships constitute a complex and intricately woven network of connections that have evolved over countless centuries, involving both cooperation and antagonism. In various contexts, plants and microorganisms engage in mutually beneficial partnerships that enhance crop health and maintain balance in ecosystems. However, these associations also render plants susceptible to a range of pathogens. Understanding the fundamental molecular mechanisms governing these associations is crucial, given the notable susceptibility of plants to external environmental influences. Based on quorum sensing signals, phytohormone, and volatile organic carbon (VOC) production and others molecules, microorganisms influence plant growth, health, and defense responses. This review explores the multifaceted relationships between plants and their associated microorganisms, encompassing mutualism, commensalism, and antagonism. The molecular mechanisms of symbiotic and pathogenic interactions share similarities but lead to different outcomes. While symbiosis benefits both parties, pathogenesis harms the host. Genetic adaptations optimize these interactions, involving coevolution driving process. Environmental factors influence outcomes, emphasizing the need for understanding and manipulation of microbial communities for beneficial results. Research directions include employing multi-omics techniques, functional studies, investigating environmental factors, understanding evolutionary trajectories, and harnessing knowledge to engineer synthetic microbial consortia for sustainable agriculture and disease management.

Promoting sustainable agriculture by exploiting plant growth-promoting rhizobacteria (PGPR) to improve maize and cowpea crops

Maize and cowpea are among the staple foods most consumed by most of the African population, and are of significant importance in food security, crop diversification, biodiversity preservation, and livelihoods. In order to satisfy the growing demand for agricultural products, fertilizers and pesticides have been extensively used to increase yields and protect plants against pathogens. However, the excessive use of these chemicals has harmful consequences on the environment and also on public health. These include soil acidification, loss of biodiversity, groundwater pollution, reduced soil fertility, contamination of crops by heavy metals, etc. Therefore, essential to find alternatives to promote sustainable agriculture and ensure the food and well-being of the people. Among these alternatives, agricultural techniques that offer sustainable, environmentally friendly solutions that reduce or eliminate the excessive use of agricultural inputs are increasingly attracting the attention of researchers. One such alternative is the use of beneficial soil microorganisms such as plant growth-promoting rhizobacteria (PGPR). PGPR provides a variety of ecological services and can play an essential role as crop yield enhancers and biological control agents. They can promote root development in plants, increasing their capacity to absorb water and nutrients from the soil, increase stress tolerance, reduce disease and promote root development. Previous research has highlighted the benefits of using PGPRs to increase agricultural productivity. A thorough understanding of the mechanisms of action of PGPRs and their exploitation as biofertilizers would present a promising prospect for increasing agricultural production, particularly in maize and cowpea, and for ensuring sustainable and prosperous agriculture, while contributing to food security and reducing the impact of chemical fertilizers and pesticides on the environment. Looking ahead, PGPR research should continue to deepen our understanding of these microorganisms and their impact on crops, with a view to constantly improving sustainable agricultural practices. On the other hand, farmers and agricultural industry players need to be made aware of the benefits of PGPRs and encouraged to adopt them to promote sustainable agricultural practices.

Defense and senescence interplay in legume nodules

Immunity and senescence play a crucial role in the functioning of the legume symbiotic nodules. The miss-regulation of one of these processes compromises the symbiosis leading to death of the endosymbiont and the arrest of the nodule functioning. The relationship between immunity and senescence has been extensively studied in plant organs where a synergistic response can be observed. However, the interplay between immunity and senescence in the symbiotic organ is poorly discussed in the literature and these phenomena are often mixed up. Recent studies revealed that the cooperation between immunity and senescence is not always observed in the nodule, suggesting complex interactions between these two processes within the symbiotic organ. Here, we discuss recent results on the interplay between immunity and senescence in the nodule and the specificities of this relationship during legume-rhizobium symbiosis.

Unlocking the potential of plant growth-promoting rhizobacteria on soil health and the sustainability of agricultural systems

The concept of soil health refers to specific soil properties and the ability to support and sustain crop growth and productivity, while maintaining long-term environmental quality. The key components of healthy soil are high populations of organisms that promote plant growth, such as the plant growth promoting rhizobacteria (PGPR). PGPR plays multiple beneficial and ecological roles in the rhizosphere soil. Among the roles of PGPR in agroecosystems are the nutrient cycling and uptake, inhibition of potential phytopathogens growth, stimulation of plant innate immunity, and direct enhancement of plant growth by producing phytohormones or other metabolites. Other important roles of PGPR are their environmental cleanup capacities (soil bioremediation). In this work, we review recent literature concerning the diverse mechanisms of PGPR in maintaining healthy conditions of agricultural soils, thus reducing (or eliminating) the toxic agrochemicals dependence. In conclusion, this review provides comprehensive knowledge on the current PGPR basic mechanisms and applications as biocontrol agents, plant growth stimulators and soil rhizoremediators, with the final goal of having more agroecological practices for sustainable agriculture.

Effects of continuous cropping of sugar beet (Beta vulgaris L.) on its endophytic and soil bacterial community by high-throughput sequencing

Purpose

As a major sugar crop, sugar beet (Beta vulgaris L.) plays an important role in both sugar industry and feed products. Soil, acts as the substrate for plant growth, provides not only nutrients to plants but also a habitat for soil microorganisms. High soil fertility and good micro-ecological environment are basic requirements for obtaining high-yield and high-sugar sugar beets. This study aimed at exploring the effects of continuous cropping of sugar beet on its endophytic, soil bacterial community structures, and diversity.

Methods

Using high-throughput sequencing technology which is based on Illumina Hiseq 2500 platform, the seeds of sugar beet (sample S), non-continuous cropping sugar beet (sample Bn) with its rhizosphere soil (sample Sr), and planting soil (sample Sn), continuous cropping sugar beet (sample Bc) with its planting soil (sample Sc), were collected as research materials.

Result

The results showed that the bacterial communities and diversity in each sample exhibited different OTU richness; 67.9% and 63.8% of total endophytic OTUs from samples Bc and Bn shared with their planting soil samples Sc and Sn, while sharing 36.4% and 31.8% of total OTUs with their seed sample S. Pseudarthrobacter and Bacillus as the two major groups coexisted among all samples, and other shared groups belonged to Achromobacter, Sphingomonas, Novosphingobium, Terribacillus, Planococcus, Paracoccus, Nesterenkonia, Halomonas, and Nocardioides. Genera, including Pantoea, Pseudomonas, Stenotrophomonas, Weissella, Leuconostoc, and Acinetobacter, were detected in each sugar beet sample but not in their corresponding soil sample. In this study, the bacterial community structures and soil compositions have significantly changed before and after continuous cropping; however, the effects of continuous cropping on endophytic bacteria of sugar beet were not statistically significant.

Conclusion

This study would provide a scientific basis and reference information for in-depth research on correlations between continuous cropping and micro-ecological environment of sugar beet plant.

Genome-wide identification and evolutionary analysis of TGA transcription factors in soybean

The gain of function in genes and gene families is a continuous process and is a key factor in understanding gene and genome evolution in plants. TGACG-Binding (TGA) transcription factors (TFs) have long been known for their essential roles in plant defence in Arabidopsis, but their roles in legume symbiosis are yet to be explored. Here, we identified a total of 25 TGA (named GmTGA1-GmTGA25) genes in soybean. Through phylogenetic analysis, we discovered a clade of GmTGA proteins that appear to be legume-specific. Among them, two GmTGAs were unique by possessing the autophagy sequence in their proteins, while the third one was an orphan gene in soybean. GmTGAs were structurally different from AtTGAs, and their expression patterns also differed with the dominant expression of AtTGAs and GmTGAs in aerial and underground parts, respectively. Moreover, twenty-five GmTGAs showed a strong correlation among the gene expression in roots, nodules, and root hairs. The qRT-PCR analysis results revealed that among 15 tested GmTGAs, six were induced and four were suppressed by rhizobia inoculation, while 11 of these GmTGAs were induced by high nitrate. Our findings suggested the important roles of GmTGAs in symbiotic nodulation and in response to nitrogen availability in soybean.