Abstract
The plant endosphere contains a diverse group of microbial communities. There is general consensus that these microbial communities make significant contributions to plant health. Both recently adopted genomic approaches and classical microbiology techniques continue to develop the science of plant-microbe interactions. Endophytes are microbial symbionts residing within the plant for the majority of their life cycle without any detrimental impact to the host plant. The use of these natural symbionts offers an opportunity to maximize crop productivity while reducing the environmental impacts of agriculture. Endophytes promote plant growth through nitrogen fixation, phytohormone production, nutrient acquisition, and by conferring tolerance to abiotic and biotic stresses. Colonization by endophytes is crucial for providing these benefits to the host plant. Endophytic colonization refers to the entry, growth and multiplication of endophyte populations within the host plant. Lately, plant microbiome research has gained considerable attention but the mechanism allowing plants to recruit endophytes is largely unknown. This review summarizes currently available knowledge about endophytic colonization by bacteria in various plant species, and specifically discusses the colonization of maize plants by Populus endophytes.
Highlights
The term “endophyte” is derived from the Greek words “endon” meaning within, and “phyton” meaning plant
Bacterial endophytes in several genera such as Azoarcus, Burkholderia, Gluconobacter, Herbaspirillum, Klebsiella, Pantoea, and Rahnella were found in many different plants, facilitating the growth of the host plant in nutrient-poor conditions [10,22,28,29]
Plating studies to determine the number of colony forming units (CFU) of endophytes within the plant in addition to microscopy based techniques used to visualize individual bacterial cells and/or microcolonies, as well as modern genomic sequencing-based approaches are all common techniques used to investigate the colonization of inoculated or indigenous bacterial endophytes in plants
Summary
The term “endophyte” is derived from the Greek words “endon” meaning within, and “phyton” meaning plant. Some bacterial endophytes carry genes necessary for biological nitrogen fixation (BNF), potentially enabling them to convert dinitrogen gas (N2) into usable forms of nitrogen such as ammonium and nitrate within the host plant [24,25]. Bacterial endophytes in several genera such as Azoarcus, Burkholderia, Gluconobacter, Herbaspirillum, Klebsiella, Pantoea, and Rahnella were found in many different plants, facilitating the growth of the host plant in nutrient-poor conditions [10,22,28,29]. Bacterial endophytes can confer resistance or tolerance to the host plant from biotic and abiotic stresses by releasing antimicrobial compounds, producing siderophores, competing for space and nutrients, and modulating the plant resistance response [39,52,53]. The mechanisms used by bacterial endophytes to mitigate abiotic stress remain unclear
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