The role of lipids in chloroplasts maintenance inside animal cells

• Autor(a) principal: Pereira, João Duarte Gonçalves
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/40999
• topic: Codium tomentosum; Elysia viridis; Kleptoplasty; Lipidome; Marine lipidomic; Photosynthetic activity; Photosynthetic sea slugs; Symbioses

Photosynthetic symbioses in animals is a common phenomenon in marine environments, involving a close relationship between an animal host and photosynthetic organisms, such as algae. However, a few marine heterotrophic organisms have an endosymbiotic relationship with the organelle responsible of photosynthesis. One group of these marine animals are the sea slugs of the Sacoglossa superorder. These sea slugs can retain intracellularly chloroplasts in cells lining the digestive diverticula through a process known as kleptoplasty, keeping them functional for different periods of time. The process that allow the integration of chloroplasts is still unknown, however there are evidence in other symbiotic relationships that lipids can play a role in the maintenance of these organelles. The aim of this work was to study the role of lipids in the maintenance of chloroplasts in the photosynthetic animal Elysia viridis throughout the loss of photosynthetic activity, using lipidomics tools. Individuals of E. viridis previously fed on the macroalga Codium tomentosum were subjected to a starved period to promote the loss of photosynthetic activity. Samples were taken at the start of the experiment (100%) and after reaching approximately 75%, 55%, 35% and < 20% of initial photosynthetic activity. A control group was continuously fed on C. tomentosum until the end of the experiment. Samples were analysed using a lipidomics approach, C18 liquid chromatography, and high-resolution mass spectrometry (C18-LC-HR-MS & MS/MS) and bioinformatics tools. The results showed that the loss of photosynthetic activity was related to alterations in the E. viridis lipidome. A high reduction of glycolipids, exclusive lipids of chloroplasts, was directly related to the degradation of chloroplasts inside the animal tissues, showing an inflection point between 50% and 35% ranges. Sulfoquinovosyl diacylglycerol (SQDG) was the glycolipid class that decreased the slowest through the loss of photosynthetic activity, suggesting that thylakoid membranes were degraded at a lower rate than chloroplast envelope’ membranes. The phospholipids and betaine lipids underwent a steadier decrease through the loss of photosynthetic activity, while sphingolipid maintained stable. On the contrary, sterol lipids incremented across the ranges, potentially due to a protective role of these molecules. These results demonstrated the dynamics of lipids and their relationship with the activity of chloroplasts inside photosynthetic animals. However, further studies are needed to elucidate the relative contribution of starvation alone, from the loss of photosynthetic activity during that period.