Polymeric phenylpropanoid derivatives crosslinked by hydroxyl fatty acids form the core structure of rape sporopollenin

Sporopollenin, a critical innovation in the evolution of terrestrial plants, is the core building brick for the outer wall of land-plant spores and pollen. Despite its significance, the basic structure of sporopollenin remains elusive due to its extreme chemical inertness. In this study, we used ethanolamine to completely dissolve rape sporopollenin and successfully identified a total of 22 components, including fatty acids, p-coumaric acid, sterols and polymeric phenylpropanoid derivatives. After that, using NaOH treatment and partial dissolution, alongside Arabidopsis mutants analysis and spectroscopic methods, we determined that polymeric phenylpropanoid derivatives crosslinked by hydroxyl fatty acids serve as the core structure of sporopollenin. The free hydroxyl groups and carboxyl groups of the polymeric phenylpropanoid derivatives can be modified by other fatty acids (C16:0, C18:0 and C18:3) as well as alcohols/phenols (for example, naringenin, β-sitosterol), resulting in a structure that protects pollen from terrestrial stresses. This discovery provides a basis for further exploration of sporopollenin’s role in plant reproduction and evolution.