Batoul Moubarak completed her doctoral thesis, entitled “Understanding the Biochemical Function and Evolutionary Diversification of Galactolipid Synthases” under the joint supervision of Christelle Breton (Professor, University of Grenoble Alpes) and Eric Maréchal (CNRS Research Director, Laboratory of Cellular and Plant Physiology).
Thesis Summary:
“Monogalactosyldiacylglycerol (MGDG), the most abundant lipid in photosynthetic membranes, is synthesized by MGDG synthases that are essential for the biogenesis and function of the photosynthetic apparatus. In the first part of this work, we focused on MGD1 and MGD2, two MGDG synthase isoforms from the plant model Arabidopsis thaliana. At standard conditions, MGD1 synthesizes MGDG by transferring a galactose from UDP-galactose to diacylglycerol (DAG). To address the preference to galactolipids over glucolipids from cyanobacteria to plants, the first part of this PhD project aimed to alter the sugar donor specificity of MGD1 from UDP-galactose to UDP-glucose. In this context, we engineered MGD1 mutants using sequence and structure-based approaches. MGD2 synthesizes MGDG under phosphate deficiency. Whereas MGD1 is a monotopic membrane protein in the inner envelope membrane of the chloroplast, MGD2 localizes to the outer envelope membrane of the chloroplast. MGD2 was found in both soluble and membrane-associated forms, suggesting possible roles outside of plastids. We examined therefore MGD2 at the molecular and activity levels to evaluate potential overlooked function, gained over Angiosperm evolution. In the second part, we extended our study beyond plants to explore MGDs from the snow alga Sanguina nivaloides, a Chlorophyceae capable of photosynthesis under sub-zero conditions. Here, we shed light on characteristics of psychrophilic enzymes in MGDG synthase of S. nivaloides. Finally, we addressed MGD-like genes recently discovered in non-photosynthetic Eugregarinorida parasites, uncovering their features and activities, aiming to understand their unexpected retention and evolutionary significance in these plastid-free organisms.”