The interplay of symbiont nutrient release and host phagosome maturation in photosymbiosis regulation

Photosymbioses between heterotrophic hosts and phototrophic algal endosymbionts have repeatedly and independently evolved across the tree of life.

The immense productivity of photosymbioses affects global nutrient cycles, yet global warming is disrupting these nutrient-exchange symbioses, destabilizing the ecosystems they support.

Heat stress erodes the metabolic controls underlying the establishment and maintenance of mutualistic carbon recycling in these symbioses.

A link between endosymbiont nutrient release and their intracellular maintenance could thus explain the evolutionary establishment as well as the ecological collapse of photosymbioses in the Anthropocene.

Harnessing recent advances in cell isolation and culture techniques, PhagoPhoRe seeks to understand the processes underlying the establishment, maintenance, and breakdown of the cnidarian-algal symbiosis.

Specifically, I will investigate the idea that the release of photosynthates enables algal endosymbionts to evade phagosomal digestion and autophagic immune responses of the host by mimicking ongoing digestion processes.

In three complementary work packages that combine state-of-the-art single-cell transcriptomics, proteomics, and isotopic imaging techniques, I will: 1) Characterize the role of host phagosome maturation processes in the intracellular establishment and maintenance of algal endosymbionts. 2) Investigate the postulated link between algal nutrient release and host phagosome arrest and immune suppression. 3) Examine the drivers of co-evolution towards obligate metabolic interactions in photosymbioses.

Deciphering the interplay between symbiotic nutrient cycling and host phagosome maturation will be key to understanding the establishment and subsequent breakdown of photosymbioses.

These processes are unlikely restricted to photosymbioses and could reveal fundamental mechanisms enabling the establishment of endosymbioses and, as such, eukaryotic life itself.