A neo-functionalized homolog of host transmembrane protein controls localization of bacterial endosymbionts in the trypanosomatid Novymonas esmeraldas

The stability of endosymbiotic associations between eukaryotes and bacteria depends on a reliable mechanism ensuring vertical inheritance of the latter. Here, we demonstrate that a host-encoded protein, located at the interface between the endoplasmic reticulum of the trypanosomatid Novymonas esmeraldas and its endosymbiotic bacterium Ca. Pandoraea novymonadis, regulates such a process. This protein, named TMP18e, is a product of duplication and neo-functionalization of the ubiquitous transmembrane protein 18 (TMEM18). Its expression level is increased at the proliferative stage of the host life cycle correlating with the confinement of bacteria to the nuclear vicinity. This is important for the proper segregation of bacteria into the daughter host cells as evidenced from the TMP18e ablation, which disrupts the nucleus-endosymbiont association and leads to greater variability of bacterial cell numbers, including an elevated proportion of aposymbiotic cells. Thus, we conclude that TMP18e is necessary for the reliable vertical inheritance of endosymbionts. [Display omitted] •TMP18e is neo-functionalized copy of conserved trypanosomatid TMEM18-related protein•It ensures the confinement of bacteria to the nuclear vicinity at proliferative stage•TMP18e is necessary for vertical inheritance of endosymbionts Zakharova et al. demonstrate that a host-encoded protein TMP18e of the trypanosomatid Novymonas esmeraldas regulates the proper segregation of its endosymbiotic bacteria into the daughter cells. The protein regulates the confinement of bacteria to the nuclear vicinity, ensuring their faithful vertical inheritance during cell division.