Post Doc
Funcional and Evolutionary Ecology, University of Vienna

Abstract

The mutualism between the giant tubeworm Riftia pachyptila and its endosymbiont Candidatus Endoriftia persephone has been extensively researched over the past 40 years. However, the lack of the host whole information and the closed endosymbiont genome have impeded the full comprehension of the genotype/phenotype interface in Riftia. Compared to theoretical predictions of enlarged and mobile genetic element-rich genomes related to facultative endosymbionts, the complete and closed Endoriftia genome is streamlined with fewer coding sequence regions, insertion-, and prophage-sequences. As previously reported, the endosymbiont contains the necessary gene toolkits to survive both in the free-living and host-associated lifestyles. The Riftia genome presents signs of reductive evolution, with gene family contractions exceeding expansions. Expanded gene families are related to sulphur metabolism, detoxification, anti-oxidative stress, oxygen transport, immune system, and lysosomal digestion, reflecting evolutionary adaptations to the vent environment and endosymbiosis. Gene expression analyses show that the trophosome is marked by intracellular endosomal-mediated digestion of endosymbionts, a scenario which is conserved in other closely-related tubeworms. The Riftia/Endoriftia genomes bridge four decades of physiological research into this mutualistic relationship, whilst simultaneously provide insights into the development, whole organism function, and the evolution of host-symbiont associations."