Cellulose microfibrils provide the structural scaffold of plant cell walls, but the molecular structure of cellulose in native plant cell walls has been difficult to determine because of the noncrystalline nature of plant cell walls and the significant interactions between cellulose and matrix polysaccharides. We have recently overcome this barrier by enriching entire plants with 13C and conducting two- and three-dimensional high-resolution 13C-13C correlation solid-state NMR experiments. This talk will summarize our key recent discoveries. 1) Cellulose microfibrils of both dicot and grass primary walls contain at least 7 different molecular conformations, as manifested by 7 sets of 13C chemical shifts for the interior crystalline chains and the surface chains. 2) These different conformations are located at different positions of the microfibrils, based on correlation signals between cellulose and matrix polysaccharides and between cellulose and water. 3) Quantitative 13C SSNMR spectra show that the primary-wall cellulose microfibrils contain at least 24 glucan chains. 4) The glucan chains on the surface of the microfibril have distinct exocyclic conformations from that of crystalline bacterial cellulose, as determined using 1H spin diffusion NMR experiments. This gives new molecular structural information about how cellulose microfibrils interact with matrix polysaccharides. 5) Finally, NMR correlation data show that specific types of pectins bind cellulose. Combining solid-state NMR data with viscoelastic and growth measurements, we show that this pectin-cellulose interaction affects wall expansion during plant growth and is thus important for function.

Structural heterogeneity and matrix polysaccharide interactions of cellulose in plant cell walls from multidimensional solid-state NMR

255th National Meeting (2018)

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