Bacterial endophytome sources, profile and dynamics—a conceptual framework

Currently, it seems inconceivable to dispute the major role of microorganisms in human health or insects with endosymbionts. Although microbial endophytes were discovered long ago, little is known about the roles of plant-associated microorganisms. Some endophytes are horizontally transmitted, whereas others are seed-borne; together, they influence plant health. Beneficial endophytes can promote plant growth and yield by increasing plant resistance to biotic and abiotic stresses. Recently, the tools available to study the phytobiome have much improved, opening doors for a better understanding of the fascinating interactions taking place at the plant level. This review redefines the conceptual framework for “endophyte” and “endophytome,” focusing on the intricate dynamics of bacterial endophytomes. Systematically examining the formation pathways and profiling endophytes allows for a comprehensive exploration of the intricate dynamics governing plant-microbe interactions. Additionally, the assessment of how endophytomes are influenced by both biotic and abiotic factors provides essential insights into the adaptability and resilience of plant-associated microorganisms. Our comprehensive analysis integrates genomic insights with environmental considerations, offering a nuanced perspective on the functional roles of bacterial endophytomes. Therefore, a new, inclusive definition is essential to accurately represent the complexity of interactions within the plant microbiome as well as having the whole picture of associated concepts

Are endophytic bacteria involvedin increasing plant drought tolerance provided by humic and fulvic acids application ?

Positive effects of humic and fulvic acids (HA)-based biostimulants on plant tolerance to drought stress are reported in the literature. Little is known on the mechanisms of action of HA but the regulation of hormonal and redox metabolisms within plants is involved. Based on a plant study model under controlled conditions, the effect of HA in increasing drought stress resistance is assessed and the potential role of bacterial endophytic community in this processis analyzed. Positive impacts of HA on tomato plants grown in hydroponics under osmotic stress were observed on morphological and physiological parameters with an increase of fresh, dry and water weight of aerial and roots parts, plant length and leaf area, as well as a raise of stomatal conductance and total chlorophyll content. The reduction of the malondialdehyde concentration in aerial parts of plants treated with HA reflects a reduction of oxidative stress. The interaction between HA and endophytic bacteria associated to tomato seeds was studied in a second bioassay. Seeds are known to be a major vehicle for PGP bacteria through generations and to maintain a stable community in plants. For this purpose, a sterile culture system in hydroponics was developed. The positive effects of HA were confirmed and the culture in sterile conditions enabled to isolate seed endophytic bacteria, offering new opportunities in studying seed endophytic bacteria–HA interactions

Bacterial endophytome sources, profile and dynamics—a conceptual framework

Currently, it seems inconceivable to dispute the major role of microorganisms in human health or insects with endosymbionts. Although microbial endophytes were discovered long ago, little is known about the roles of plant-associated microorganisms. Some endophytes are horizontally transmitted, whereas others are seed-borne; together, they influence plant health. Beneficial endophytes can promote plant growth and yield by increasing plant resistance to biotic and abiotic stresses. Recently, the tools available to study the phytobiome have much improved, opening doors for a better understanding of the fascinating interactions taking place at the plant level. This review redefines the conceptual framework for “endophyte” and “endophytome,” focusing on the intricate dynamics of bacterial endophytomes. Systematically examining the formation pathways and profiling endophytes allows for a comprehensive exploration of the intricate dynamics governing plant-microbe interactions. Additionally, the assessment of how endophytomes are influenced by both biotic and abiotic factors provides essential insights into the adaptability and resilience of plant-associated microorganisms. Our comprehensive analysis integrates genomic insights with environmental considerations, offering a nuanced perspective on the functional roles of bacterial endophytomes. Therefore, a new, inclusive definition is essential to accurately represent the complexity of interactions within the plant microbiome as well as having the whole picture of associated concepts

Roles of endophytic bacteria against plant stresses

Endophytic microbial communities contribute significantly to plant health. If this is widely accepted, question remains on the mechanisms underlying such interactions. There is a growing interest for endophytic bacteria for diverse practical applications including potential use in agriculture. Unfortunately, because of the lack of knowledge about the endophyte/host-plat interaction, their use is limited. These organisms can be used to improve plant productivity and tolerance against abiotic and biotic stresses. Endophytes can play diverse roles: control of pathogens and stresses through antimicrobial compound production, protection against herbivores, increase of resistance to abiotic stresses, detoxification of organic pollutants in planta and increasing the acquisition of nutrients such as atmospheric nitrogen fixation, phosphate solubilization, phytohormone production, and siderophore production. Although little studied, endophytes are known to be able to spread systemically within the plant and colonize stems and leaves. It is more difficult to specify and measure the various effects of different types of colonization on the plant. This poster aims to present the main known mechanisms involved in increasing plant resistance to biotic and abiotic stresses. Moreover, two thesis topics related to this theme are presented (1) the role of endophytic bacteria is questioned in the increase of osmotic stress tolerance of tomato plants due the addition of humic and fulvic acids; (2) how endophytic microorganisms interfere with phytopathogenic bacteria (Brenneria salicis and Xylella fastidiosa) colonizing the specific niche of the xyle

Are vertically transmitted endophytic bacteria involved in increasing plant drought tolerance provided by humic and fulvic acids application?

Positive effects of humic and fulvic acids (HA)-based biostimulants on plant tolerance to drought stress are reported in the literature. The regulation of hormonal and redox metabolisms within plants is one of the mechanisms involved in the action of HA. The effect of HA in increasing drought stress resistance was assessed on tomato plants grown in hydroponics under osmotic stress. Several morphological and physiological parameters, such as the increase of fresh, dry and water weight of aerial and roots parts, plant length and leaf area, as well as a raise of total chlorophyll content, revealed the positive impacts of HA. The reduction of the malondialdehyde concentration in aerial parts of plants treated with HA reflects a reduction of oxidative stress. We hypothesized that the beneficial effects of HA may be directly or indirectly related to seed endophytic bacteria. Seeds are known to be a major vehicle for PGP bacteria through generations and to maintain a stable community in plants. In order to study their implication, a sterile culture system was developed in hydroponics and the positive effects of HA were confirmed. The culture in sterile conditions enabled to isolate seed endophytic bacteria, to identify the culturable core of vertically transmitted endophytic bacteria and, combined with metagenomics, offers new opportunities in studying seed endophytic bacteria – HA interactions

Implementation of protocols under controlled conditions : study of biostimulants efficacy

Many biostimulants are currently introduced into the agricultural sector. However, their efficacy in the field is sometimes difficult to demonstrate due to manys ources of variability that complicate their accurate evaluation. Within the framework of a project developed by the company Redebel SA, in collaboration with UClouvain and ULg and funded by the Walloon Regionin Belgium, it is attempted to design new efficacy screening methods relying on controlled conditions phenotyping and to evaluate their predictions against trials established in agricultural fields. As part of this study, UCLouvain developed tests to assess the biostimulants behaviour under controlled conditions. Plant responses were evaluated after the application of three representative types of biostimulants (organic, inorganic and microbial) using distinct protocols. Three plant species (maize, wheat and tomato) were tested, using two culture methods (hydroponics and pot culture) and two abiotic limitations (water deficit and limited nitrogen nutrition).Beneficial effects on plant development were observed following the application of biostimulants. However, benefits of biostimulants varied depending on the protocols applied. This highlights the diversity of mechanisms and interactions between biostimulants, plants and their environment and, therefore,the need for further characterization