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Review
. 2017 Nov 25;5(4):77.
doi: 10.3390/microorganisms5040077.

Bacterial Endophyte Colonization and Distribution within Plants

Shyam L. Kandel  1 , Pierre M. Joubert  1 , Sharon L. Doty  1
Affiliations
Review

Bacterial Endophyte Colonization and Distribution within Plants

Shyam L. Kandel et al. Microorganisms. .

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.

Keywords: Populus endophytes; bacterial endophytes; colonization; microscopy.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Hypothesized colonization cycle of bacterial endophytes in the host plant. (a) Mobilization of seed endophytes in germinating seedlings. (b) Recruitment of alien endophytes from the soil in developing seedlings. (c) Colonization by alien and inherited endophytes. (d) Whole plant colonization by various endophytes. (e) Variation of endophyte communities in the host plant in response to different biotic and abiotic stresses. (f) Vertical transfer of endophytes into seeds.
Figure 2
Figure 2
Maize (hybrid 29B17) roots colonized by WP5gfp visualized under 630× magnification. Image on the left (A,C) were taken with the GFP filter, and images on the right (B,D) were taken without the GFP filter. Groups of WP5gfp cells were observed in the intercellular spaces of cell layers in the longitudinal direction.
Figure 3
Figure 3
Maize (hybrids 14A91 and 29B17) roots were colonized by WP5gfp and visualized under 630× magnification. Image on the left (A,C) were taken with the GFP filter, and images on the right (B,D) were taken without the GFP filter. WP5gfp cells were observed in the middle lamella areas of the transverse wall between two adjacent cells.
Figure 4
Figure 4
Maize (hybrid 29B17) radicle roots were colonized by WP5gfp and visualized under 630× magnification. Images on the left (A,C) were taken with the GFP filter, and images on the right (B,D) were taken without the GFP filter. Microcolonies of WP5gfp were observed along the plant cell wall areas between two adjacent cells.
Figure 5
Figure 5
Maize (hybrid 29B17) leaves were colonized by WP5gfp visualized under 630× magnification. Image on the left (A,C) were taken with the GFP filter, and images on the right (B,D) were taken without the GFP filter. WP5gfp was observed in the intercellular spaces of cell layers and stomatal chambers.
Figure 6
Figure 6
Quantification of CFUs of WP5gfp per gram of tissue in shoots, including leaves and stem, and roots. Errors bars represent standard error of the mean.
Figure 7
Figure 7
Root, and root and shoot biomass of WP5gfp inoculated and mock-inoculated control plants in maize hybrid 29B17. Error bars represent standard error of the mean. Histograms with different letters are statistically different at p < 0.05.
See this image and copyright information in PMC

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