Transmission of Bacterial Endophytes

Abstract

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.

Long-term warming effects on the microbiome and nitrogen fixation of a common moss species in sub-Arctic tundra

“…While these mite taxa not necessarily feed on bacteria, it illustrates that foodwebs within the bryosphere are affected by warming. Micro- and mesofauna might also act as a source and distribution mechanism of bryophyte-associated bacteria [74]. The candidate genus Xiphinematobacter in our study is for instance likely to be nematode-born [75], but was not affected in relative abundance by warming in our study.…”

Inheritance of seed and rhizosphere microbial communities through plant–soil feedback and soil memory

“…However, recent developments in multi-omics-based analytical techniques suggest that seeds contain plant genotype-specific microorganisms that can be transferred vertically from one generation to the next (Adam et al, 2018;Johnston-Monje et al, 2016;Nelson, 2017;Shade et al, 2017). Microorganisms, mostly fungi and bacteria, enter the seeds through the outer seed coat or pollen granules, or naturally through infiltration of nectarthodes in flowers (Underwood et al, 2007;Frank et al, 2017). However, the mechanisms underlying microbial migration into seeds have only been studied with a limited number of pathogenic bacteria (Donati et al, 2018).…”

Microbial Endophytes that Live within the Seeds of Two Tomato Hybrids Cultivated in Argentina

“…As in the case of other plants, the tomato genome is complemented by a plethora of genes provided by organisms associated both with surfaces as well as intracellular spaces, which is now known as the phytobiome [2][3][4]. The insurmountable amount of genes and proteins provided by these organisms is such that they are considered parts of the plant genomes, since they have a dramatic impact on the quality and production of different crops [5].…”