The molecular structure of plant sporopollenin

Abstract

Sporopollenin is a ubiquitous and extremely chemically inert biopolymer that constitutes the outer wall of all land-plant spores and pollen grains1. Sporopollenin protects the vulnerable plant gametes against a wide range of environmental assaults, and is considered a prerequisite for the migration of early plants onto land2. Despite its importance, the chemical structure of plant sporopollenin has remained elusive1. Using a newly developed thioacidolysis degradative method together with state-of-the-art solid-state NMR techniques, we determined the detailed molecular structure of pine sporopollenin. We show that pine sporopollenin is primarily composed of aliphatic-polyketide-derived polyvinyl alcohol units and 7-O-p-coumaroylated C16 aliphatic units, crosslinked through a distinctive dioxane moiety featuring an acetal. Naringenin was also identified as a minor component of pine sporopollenin. This discovery answers the long-standing question about the chemical make-up of plant sporopollenin, laying the foundation for future investigations of sporopollenin biosynthesis and for the design of new biomimetic polymers with desirable inert properties.

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Fig. 1: Pine sporopollenin preparation and degradative analysis by thioacidolysis.
Fig. 2: Structural characterization of pine sporopollenin by whole-polymer derivatization followed by thioacidolysis.
Fig. 3: 13C solid-state NMR spectra of untreated and treated pine sporopollenin for structure determination.
Fig. 4: Structural model of pine sporopollenin highlighting the major units and linkages elucidated through this study.

Data availability

The data that support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

This work was supported by the Pew Scholar Program in the Biomedical Sciences (J.-K.W.) and the Searle Scholars Program (J.-K.W.). The solid-state NMR part of this work (by P.P. and M.H.) was supported by the Center for Lignocellulose Structure and Formation, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award number DE-SC0001090.

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F.-S.L. and J.-K.W. designed the research. F.-S.L. developed thioacidolysis and pretreatment methods for studying sporopollenin, and carried out structural elucidation of all degradative products. P.P. performed SSNMR experiments. J.J. performed electron microscopy imaging. F.-S.L, P.P., M.H. and J.-K.W. interpreted the results and wrote the paper.

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Correspondence to Jing-Ke Weng.

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Supplementary Information

Supplementary Notes 1–3, Supplementary Methods, Supplementary Figures 1–39, Supplementary Tables 1–5, Supplementary NMR data and Supplementary References.

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Li, FS., Phyo, P., Jacobowitz, J. et al. The molecular structure of plant sporopollenin. Nature Plants 5, 41–46 (2019). https://doi.org/10.1038/s41477-018-0330-7

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