Periodic Reporting for period 2 - KleptoSlug (Kleptoplasty: The sea slug that got away with stolen chloroplasts)
Berichtszeitraum: 2022-11-01 bis 2024-04-30
Kleptoplasty is the capacity of a non-photosynthetic host to retain functional chloroplasts from algal sources. In animals, it was first identified in 1965 in the sea slug Elysia atroviridis. Since then, the presence of functional algal chloroplasts was reported in several other species of sacoglossan molluscs, but also in diverse organisms such as dinoflagellates, ciliates and foraminifera, and more recently on another two animals, the flatworms Baicalellia solaris and Pogaina paranygulgus. However, sacoglossan sea slugs remain the only animals in which long-term kleptoplasty has been identified. Animals showing functional chloroplasts for prolonged periods include Elysia viridis, E. crispata, E. timida and E. chlorotica. The later species is reported to maintain functional chloroplasts for almost a year.
The chloroplasts are algae and plants “powerhouses”, providing food and energy to the cells. The machinery required for the functioning of the chloroplast and its repair is dependent not only on the chloroplast but also on the algal/plant nucleus. Yet, these tiny sea slugs can “steal” functional chloroplasts while degrading the algal nucleus. How they do it remains a mystery that KleptoSlug project aims to solve. Unravelling the mechanisms that allow animal cells to host functional isolated chloroplasts is certainly appealing for biotechnological applications, from photosynthetic biomaterials for tissue engineering and regeneration (e.g. local and controllable source of oxygen to circumvent the need for blood perfusion to sustain tissue survival) to the secretion of beneficial secondary metabolites.
To advance our understanding on how chloroplasts are maintained by sea slugs, we are exploring the variability in the capacity for maintaining chloroplasts across Sacoglossa species. Some of the animal-alga associations being studied share the same chloroplast donor alga, others share the same animal species. We then combine different analytical tools, from gene expression to physiological responses, from ‘omics approach to individual imaging, for understanding key-points allowing prolonged maintenance of chloroplasts in those different animal-alga association. Harboring such “powerhouses” does not come without risks for the animal; kleptoplasty in animal cells is in fact a high-risk-high-gain project for the sea slugs. So, we aim at characterizing not only the main benefits of the association but also understand how the sea slugs cope with the high-risks involved in acquiring a foreign organelle.
The chloroplasts are algae and plants “powerhouses”, providing food and energy to the cells. The machinery required for the functioning of the chloroplast and its repair is dependent not only on the chloroplast but also on the algal/plant nucleus. Yet, these tiny sea slugs can “steal” functional chloroplasts while degrading the algal nucleus. How they do it remains a mystery that KleptoSlug project aims to solve. Unravelling the mechanisms that allow animal cells to host functional isolated chloroplasts is certainly appealing for biotechnological applications, from photosynthetic biomaterials for tissue engineering and regeneration (e.g. local and controllable source of oxygen to circumvent the need for blood perfusion to sustain tissue survival) to the secretion of beneficial secondary metabolites.
To advance our understanding on how chloroplasts are maintained by sea slugs, we are exploring the variability in the capacity for maintaining chloroplasts across Sacoglossa species. Some of the animal-alga associations being studied share the same chloroplast donor alga, others share the same animal species. We then combine different analytical tools, from gene expression to physiological responses, from ‘omics approach to individual imaging, for understanding key-points allowing prolonged maintenance of chloroplasts in those different animal-alga association. Harboring such “powerhouses” does not come without risks for the animal; kleptoplasty in animal cells is in fact a high-risk-high-gain project for the sea slugs. So, we aim at characterizing not only the main benefits of the association but also understand how the sea slugs cope with the high-risks involved in acquiring a foreign organelle.
Accurately estimation of chloroplasts’ longevity inside the animal cells is a difficult task. Temperature, light quality and intensity, aeration, water quality, previous life history, are just a few variables that are likely to affect chloroplasts functionality. Therefore, it is of paramount importance to evaluate and compare the performance of chloroplasts, within the species being studied, under controlled conditions. Additionally, control treatments must be implemented and sea slugs under those conditions need to display photosynthetic activity at maximum rates, otherwise the maintenance/culturing conditions may not be acquitted for chloroplasts loss. The first months of the project were spent on improving and expand culturing facilities of Elysia crispata (tropical species) and Elysia timida (Mediterranean species) as well as the maintenance facilities for the local (temperate species) Elysia viridis. While the first two species have a direct development, meaning the sea slug leaves the egg already ready to feed on the macroalgae, the latter species requires a more complex culturing procedure, with a larval phase feeding on microalgae, prior to metamorphose and settlement on the macroalgae.
Having reached exceptional facilities for breeding sea slugs in a controlled environment, we then tested the shift in algal food sources. Among several combinations tested, the most interesting identified was a common alga as donor of photosynthetically efficient chloroplasts to both highly specialized monophagous and polyphagous sea slugs capable of long-term retention, which opens new experimental routes. From this exhaustive work, it became clear that different algal sources induce drastic changes in kleptoplasty competence. The different animal-alga associations successfully achieved were characterized regarding long-term kleptoplasty, photosynthesis (carbon fixation using the energy of the sun) and photoprotection/photoinhibition (ability for protecting and repairing the chloroplast during light stress) performance. We have discovered that chloroplasts deriving from the same algae but hosted in different animal species do not perform equally inside the different host animal cells. It then became clear as well that the chloroplast source alone does not determine the success of kleptoplasty.
We are now investigating the specificity of each animal-algae combination that makes it successful. The next ongoing steps are the analysis of which genes and lipids are playing a role in maintaining the chloroplast when these are no longer able to be replaced – this approach is paralleled in the different algal-animal associations for elucidating what works and what fails in the different combinations. From these broad overviews, we expect to bring new hypothesis to the field, to be tested by ourselves but also colleagues across the globe.
Having reached exceptional facilities for breeding sea slugs in a controlled environment, we then tested the shift in algal food sources. Among several combinations tested, the most interesting identified was a common alga as donor of photosynthetically efficient chloroplasts to both highly specialized monophagous and polyphagous sea slugs capable of long-term retention, which opens new experimental routes. From this exhaustive work, it became clear that different algal sources induce drastic changes in kleptoplasty competence. The different animal-alga associations successfully achieved were characterized regarding long-term kleptoplasty, photosynthesis (carbon fixation using the energy of the sun) and photoprotection/photoinhibition (ability for protecting and repairing the chloroplast during light stress) performance. We have discovered that chloroplasts deriving from the same algae but hosted in different animal species do not perform equally inside the different host animal cells. It then became clear as well that the chloroplast source alone does not determine the success of kleptoplasty.
We are now investigating the specificity of each animal-algae combination that makes it successful. The next ongoing steps are the analysis of which genes and lipids are playing a role in maintaining the chloroplast when these are no longer able to be replaced – this approach is paralleled in the different algal-animal associations for elucidating what works and what fails in the different combinations. From these broad overviews, we expect to bring new hypothesis to the field, to be tested by ourselves but also colleagues across the globe.
Expected results
1) by mounting a comparative approach between species with variable maintenance of chloroplasts we will advance our insights into strategies and critical biochemical contributions of the animal cells to the chloroplasts.
2) we aim to describe the cellular adaptations to the radical change in the cellular milieu during chloroplast acquisition. In particular, we expect to clarify if damaging byproducts of photosynthesis are linked to different kleptoplastidic abilities or cellular strategies of each animal-algal association.
3) we expect to obtain a comprehensive analysis of which compounds emanate from kleptoplasts and contribute to the metabolism of distinct animal-algae associations and to which extend photosynthesis may contribute to the quality of the offspring, with potential implications for its reproductive success.
4) our findings are not restricted to the sea slugs and kleptoplasty niche of interest; in the frame of characterizing different algal-animal associations, we have encountered peculiarities that come as novel findings in algal physiology field, and we expect to demonstrate how algae from the Bryopsidales order have evolved in a different manner from their green counterparts.
1) by mounting a comparative approach between species with variable maintenance of chloroplasts we will advance our insights into strategies and critical biochemical contributions of the animal cells to the chloroplasts.
2) we aim to describe the cellular adaptations to the radical change in the cellular milieu during chloroplast acquisition. In particular, we expect to clarify if damaging byproducts of photosynthesis are linked to different kleptoplastidic abilities or cellular strategies of each animal-algal association.
3) we expect to obtain a comprehensive analysis of which compounds emanate from kleptoplasts and contribute to the metabolism of distinct animal-algae associations and to which extend photosynthesis may contribute to the quality of the offspring, with potential implications for its reproductive success.
4) our findings are not restricted to the sea slugs and kleptoplasty niche of interest; in the frame of characterizing different algal-animal associations, we have encountered peculiarities that come as novel findings in algal physiology field, and we expect to demonstrate how algae from the Bryopsidales order have evolved in a different manner from their green counterparts.