The Long and Winding Road for Symbiont and Yolk Protein to Host Oocyte.

Takema Fukatsu

doi:10.1128/mbio.02997-20

Abstract

Many insects are intimately associated with microbial symbionts, which are passed to developing oocytes in the maternal body for ensuring vertical transmission to the next generation. Previous studies uncovered that some symbionts utilize preexisting host's molecular and cellular machineries for targeting oocytes. For example, the major yolk protein vitellogenin (Vg) is massively produced in fat body cells, processed and transported to ovaries, and incorporated into developing oocytes via Vg receptor (VgR)-mediated endocytosis, and some symbiotic bacteria were reported to interact with Vg and migrate to oocytes by hitchhiking the VgR-mediated endocytotic mechanism. In a recent study, Mao et al. (mBio 12:e01142-20, 2020, https://doi.org/10.1128/mBio.01142-20) reported that, in some leafhoppers, a considerable proportion of Vg is incorporated into symbiotic bacteria and translocated into oocytes by hitchhiking the symbiont's vertical transmission mechanism, uncovering the host's cooption of the symbiont's oocyte-targeting machineries and highlighting complicated trajectories toward host-symbiont coevolution and integration.

Highlights

Many insects are intimately associated with microbial symbionts, which are passed to developing oocytes in the maternal body for ensuring vertical transmission to the generation
Many insects are either obligatorily or facultatively associated with microbial symbionts, which affect growth, survival, and reproduction of their hosts in a variety of ways. In most cases, such symbionts are maintained in somatic cells and organs of their hosts and are transovarially passed to developing oocytes for ensuring vertical transmission to the generation [1, 2]
The continuous vertical transmission of the symbiont through host generations over evolutionary time facilitates the loss of genes that are not needed for the intrahost life, the depletion of horizontally acquired genes from environmental sources, and the accumulation of deleterious mutations due to strong population bottlenecks, which tend to end up with symbiont genome reduction and uncultivability, thereby skewing the evolutionary trajectories of the symbiotic associations in an idiosyncratic manner [3, 4]

Summary

Introduction

Many insects are intimately associated with microbial symbionts, which are passed to developing oocytes in the maternal body for ensuring vertical transmission to the generation.

Results

Conclusion