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Serena Flori

Light utilization in microalgae: The marine diatom Phaeodactylum tricornutum and the green algae Chlamydomonas reinhardtii



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Published on 15 September 2016


Thesis presented September 15, 2016

Abstract:
Microalgae have developed distinct approaches to modulate light absorption and utilization by their photosystems in response to environmental stimuli. In this Ph.D Thesis, I characterized different strategies employed by freshwater (Chlamydomonas reinhardtii) and marine algae (Phaeodactylum tricornutum) to optimize their acclimation to the environment. In the first part of this work, I used spectroscopic, biochemical, electron microscopy analysis and 3-dimentional reconstitution to produce a model of the entire cell of the marine diatom Phaeodactylum tricornutum. This model has been used to address the following questions:
i. how is a secondary chloroplast structured to facilitate exchanges with the cytosol via its four membranes envelope barrier ?
ii. how have diatoms shaped their photosynthetic membranes to optimize light absorption and downstream electron flow ? and
iii. how the cellular organelles interact to optimize CO2 assimilation via ATP/NADPH exchanges?
In the second part, I have focused on the regulation of light harvesting and dissipation in C. reinhardtii by studying the role of perception of light color and metabolism on excess light dissipation via the Non-Photochemical Quenching of energy (NPQ). Using biochemical and spectroscopic approaches I found a molecular link between photoreception, photosynthesis and photoprotection in C. reinhardtii via the role of the photoreceptor phototropin on excess absorbed energy dissipation (NPQ) and also demonstrated that besides light, downstream metabolism can also affect this acclimation process.
Overall this Ph.D work reveals the existence and integration of different signal pathways in the regulation of photoprotective responses by microalgae living in the ocean and in the land.


Keywords:
Diatoms, microalgae, photosynthesis, Chlamydomonas

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