Cell walls are dynamically O-acetylated in the green seaweed, Ulva compressa

Abstract

We report that cell wall polymers in the chlorophyte algae may be modified by O-acetylation. The importance of cell wall modifications in the green algae is not well understood, although similar modifications play key roles in land plants by modulating the properties of cell wall carbohydrate polymers. Using a combination of biophysical (Fourier-transform infrared and cross-polarisation heteronuclear correlation nuclear magnetic resonance spectroscopy), biochemical (thin-layer chromatography) and molecular approaches (yellow fluorescent protein-tagged transgene localisation), we show that the extractable ulvan fractions of Ulva compressa cell walls contain O-acetyl sidechains, we demonstrate that acetylation is dynamic and decreases reversibly in response to metal-induced stress, we note interactions between acetyl and borate sidechains and we locate two candidate genes that, together, may encode an acetyltransferase. We therefore propose that O-acetylation of ulvan residues is involved in the normal cell wall physiology of at least some chlorophyte algae. To the best of our knowledge, this is the first demonstration of O-acetyl sidechains in green algal cell wall polymers, and of reversible changes in algal cell wall polymer modification in response to stress.

The extracellular matrix of green algae

“…Detailed comparative reviews of the complex sulfated polysaccharides found in other ulvophyte groups, including the Ulotrichales, the giant multinucleate (coenocytic) cells of the siphonous Bryopsidales and Dasycladales, and siphonocladous freshwater Cladophorales, are provided elsewhere ( Fernández et al 2015 ; Arata et al 2017 ; Ciancia et al 2020 ). Recently, pectins have been identified in Ulva ( Holzinger et al 2015 ), and the first identification of O-acetylation of pectin in green algae has been described in Bothwell et al 2022 . These results demonstrate that many CW polymers arose in green algae well before the emergence of land plants.…”