Structural Glycomic Analysis of the Plant Cell Wall

Carbohydrates, also called glycans, are the most abundant biopolymers on Earth. They are essential to all known living organisms from bacteria to humans, but their importance is perhaps most striking in plants. Plants use glycans as their main building material, encasing their cells in a rigid and complex glycan wall that is central to their growth, resistance, and intercellular communication. However, the plant cell wall is also extraordinarily complex, and the molecular-level structure of its many glycan constituents remains poorly understood. This hinders progress in many areas of plant biology, from understanding how the cell wall is formed to uncovering the molecular basis of plant-microbe interactions. The aim of this project is to unravel the structure of plant cell wall glycans and thus provide insight into the molecular diversity underlying the various biological functions of the cell wall. Cell wall glycans consist of sugar units that are linked together via covalent bonds, forming large polysaccharide structures with complex topology and elaborate branching patterns. As studying these large polysaccharides in their entirety is practically unfeasible, they are chopped enzymatically into smaller fragments that can be structurally analyzed. Based on information from analysis of the smaller fragments, the original glycan structures can be puzzled back together. To realize this, we will first build a library of defined plant glycan structures assembled via chemical synthesis and characterize each structure in detail with ion mobility-mass spectrometry (IM-MS). This technique provides information on the mass, size, and shape of the glycans, enabling the determination of their composition, connectivity, and branching. Using this library as a basis, we will expand our study to glycans in the model plant Arabidopsis thaliana, matching new data with structures in the library. When encountering novel glycan species not included in the library, their structure will be determined using an IM-MS-based analytical workflow. This method will then be applied to study Arabidopsis thaliana mutants with cell wall defects, revealing the role of specific genes in the formation of defined structural motifs in the plant cell wall. Through offering molecular-level insight into the main structural building blocks of the cell wall, our project will provide fundamental knowledge that will advance our understanding of cell wall formation, and the structure-function relationships that govern its many roles in plants from development to immunity.