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. 2017 Nov 10;5(4):70.
doi: 10.3390/microorganisms5040070.

Transmission of Bacterial Endophytes

Free PMC article

Transmission of Bacterial Endophytes

Anna Carolin Frank et al. Microorganisms. .
Free PMC article


Plants are hosts to complex communities of endophytic bacteria that colonize the interior of both below- and aboveground tissues. Bacteria living inside plant tissues as endophytes can be horizontally acquired from the environment with each new generation, or vertically transmitted from generation to generation via seed. A better understanding of bacterial endophyte transmission routes and modes will benefit studies of plant-endophyte interactions in both agricultural and natural ecosystems. In this review, we provide an overview of the transmission routes that bacteria can take to colonize plants, including vertically via seeds and pollen, and horizontally via soil, atmosphere, and insects. We discuss both well-documented and understudied transmission routes, and identify gaps in our knowledge on how bacteria reach the inside of plants. Where little knowledge is available on endophytes, we draw from studies on bacterial plant pathogens to discuss potential transmission routes. Colonization of roots from soil is the best studied transmission route, and probably the most important, although more studies of transmission to aerial parts and stomatal colonization are needed, as are studies that conclusively confirm vertical transfer. While vertical transfer of bacterial endophytes likely occurs, obligate and strictly vertically transferred symbioses with bacteria are probably unusual in plants. Instead, plants appear to benefit from the ability to respond to a changing environment by acquiring its endophytic microbiome anew with each generation, and over the lifetime of individuals.

Keywords: bacterial endophytes; colonization; dispersion; horizontal; transmission; vertical.

Conflict of interest statement

The authors declare no conflict of interest.


Figure 1
Figure 1
Transmission routes for bacterial endophytes across the life cycle of an apple tree. (A) Vertical transmission via seed; (B) Colonization of the spermosphere, depicted as the grey area surrounding the seed; (C) Colonization of developing reproductive organs via the shoot apical meristem as part of vertical transmission; (D) Colonization of root from soil; (E) Colonization of leaves though stomata after transmission via air; (F) Transmission via sap-feeders; (G) Transmission to flowers via pollinators. Not drawn to scale.

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