A symbiont's guide to the germline.

Shelbi L. Russell,Laura Chappell,William Sullivan

doi:10.1016/bs.ctdb.2019.04.007

Shelbi L. Russell, Laura Chappell + Show 1 more

Open Access

https://doi.org/10.1016/bs.ctdb.2019.04.007

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Abstract

Microbial symbioses exhibit astounding adaptations, yet all symbionts face the problem of how to reliably associate with host offspring every generation. A common strategy is vertical transmission, in which symbionts are directly transmitted from the female to her offspring. The diversity of symbionts and vertical transmission mechanisms is as expansive as the diversity of eukaryotic host taxa that house them. However, there are several common themes among these mechanisms based on the degree to which symbionts associate with the host germline during transmission. In this review, we detail three distinct vertical transmission strategies, starting with associations that are transmitted from host somatic cells to offspring somatic cells, either due to lacking a germline or avoiding it. A second strategy involves somatically-localized symbionts that migrate into the germline during host development. The third strategy we discuss is one in which the symbiont maintains continuous association with the germline throughout development. Unexpectedly, the vast majority of documented vertically inherited symbionts rely on the second strategy: soma-to-germline migration. Given that not all eukaryotes contain a sequestered germline and instead produce offspring from somatic stem cell lineages, this soma-to-germline migration is discussed in the context of multicellular evolution. Lastly, as recent genomics data have revealed an abundance of horizontal gene transfer events from symbiotic and non-symbiotic bacteria to host genomes, we discuss their impact on eukaryotic host evolution.

Highlights

Microbial symbioses exhibit astounding adaptations, yet all symbionts face the problem of how to reliably associate with host offspring every generation
Vertical transmission through the germline Part 3: continuous germ cell association throughout development Continuous association with the germline presents the most basic form of linkage with host reproduction for symbionts and appears quite important for bacterial taxa such as Wolbachia.While it is likely that other manipulative bacteria such as Rickettsiamay exhibit similar patterns, the data are limited, so we present what is known currently about continuous germline association strategies, starting with the most basic form in unicellular hosts
Our review of the literature reveals that the majority of microbial symbionts across a diversity of host and symbiont taxa are transmitted to the host germline from somatic cells or tissues, making association with the host germline rare for endosymbionts

Summary

Introduction

Microbial symbioses exhibit astounding adaptations, yet all symbionts face the problem of how to reliably associate with host offspring every generation. V. Vertical transmission through the germline Part 3: continuous germ cell association throughout development A.

Results

Conclusion