SeaWall: Understanding environmentally induced cell wall remodelling in the green seaweed Ulva sp.

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Seaweeds such as the worldwide occurring green macroalgae Ulva sp. (Chlorophyta) face harsh environmental conditions in their coastal habitats, yet they produce tremendous biomass accumulations known as “green tides”. The bulk material in these blooms are multi-layered cell walls, which are a polysaccharide-rich matrix that surrounds every cell and constitute up to ~60% of the algal dry matter. Cell walls are the only physical barrier between the sensitive algal protoplast and the environment. This makes them key elements in stress survival, for example, by increasing the water holding capacity of cells or by assisting a controlled shrinkage and expansion during desiccation-rehydration cycles. However, it is largely unknown how the Ulva cell wall composition and architecture respond to external abiotic factors such as water scarcity. This is a fundamental gap in knowledge, because it limits our understanding of how seaweeds cope which stress in coastal habitats and sustain their high ecological significance. To better understand Ulva’s ecological success, we will combine eco-physiological monitoring with state-of-the-art bioimaging and chemical biology tools to investigate how environmental factors shape the composition, remodelling and architecture of the Ulva cell wall. First, we will collect various Ulva thalli from the field and establish stable cultures. Next, we will construct an environmental chamber allowing us to expose Ulva thalli to defined water, temperature, and light stresses typical for coastal habitats. Finally, we will implement imaging and chemical biology tools to visualize and quantify chemical and structural changes of the Ulva cell wall composition due to changing environmental conditions in vivo and in situ. We anticipate that our interdisciplinary approach will allow us to uncover unknown features of seaweed cell wall reorganisation (e.g. enzymatic remodelling of cell wall components), helping us to better understand how seaweeds cope with stress. This will provide crucial information for future seaweed farming efforts that aim to maximize biomass production and provide a foundation for unravelling the molecular basis of cell wall remodelling in seaweeds.