Structure and Interactions of Plant Cell-Wall Polysaccharides by Two- and Three-Dimensional Magic-Angle-Spinning Solid-State NMR

Abstract

The polysaccharide-rich cell walls (CWs) of plants perform essential functions such as maintaining tensile strength and allowing plant growth. Using two- and three-dimensional magic-angle-spinning (MAS) solid-state NMR and uniformly (13)C-labeled Arabidopsis thaliana, we have assigned the resonances of the major polysaccharides in the intact and insoluble primary CW and determined the intermolecular contacts and dynamics of cellulose, hemicelluloses, and pectins. Cellulose microfibrils showed extensive interactions with pectins, while the main hemicellulose, xyloglucan, exhibited few cellulose cross-peaks, suggesting limited entrapment in the microfibrils rather than extensive surface coating. Site-resolved (13)C T(1) and (1)H T(1ρ) relaxation times indicate that the entrapped xyloglucan has motional properties that are intermediate between the rigid cellulose and the dynamic pectins. Xyloglucan absence in a triple knockout mutant caused the polysaccharides to undergo much faster motions than in the wild-type CW. These results suggest that load bearing in plant CWs is accomplished by a single network of all three types of polysaccharides instead of a cellulose-xyloglucan network, thus revising the existing paradigm of CW structure. The extensive pectin-cellulose interaction suggests a central role for pectins in maintaining the structure and function of plant CWs. This study demonstrates the power of multidimensional MAS NMR for molecular level investigation of the structure and dynamics of complex and energy-rich plant materials.

Gradients in Wall Mechanics and Polysaccharides along Growing Inflorescence Stems

“…Three carbonyl peaks are observed at 172, 174, and 176 ppm and can be assigned to GalA methyl ester in homogalacturonan (HG), GalA acetyl, and GalA carboxylate in RG-I and HG, respectively (Wang et al, 2016a). The cellulose intensities in these inflorescence cell walls are much lower than those of seedling cell walls, as seen for the resolved interior cellulose C4 peak at 89 ppm and the C6 peak at 65 ppm (Dick-Pérez et al, 2011). No lignin signals are detected, as evidenced by the absence of the OCH 3 methoxy signal at 56 ppm.…”

“…To fully resolve the matrix polysaccharide signals and compare them between the inflorescence and seedling cell walls, we measured 2D 13 C-13 C DP-based J-INADEQUATE spectra, which correlate the sum chemical shifts of two directly bonded carbons with their individual chemical shifts (Dick-Pérez et al, 2011). The 2D 13 C-13 C J-INADEQUATE spectra were measured using direct 13 C polarization and a short recycle delay of 2 s to preferentially detect the signals of mobile polysaccharides.…”

“…We find that the inflorescence stem also is amenable to mechanical tests, to analysis of wall structure by small-angle neutron scattering (SANS), and to 13 C enrichment, enabling highresolution, multidimensional magic-angle-spinning (MAS) solid-state NMR (SSNMR) spectroscopy to examine wall polysaccharide structures and dynamics along the growth zone, with minimal disruption of cell walls. By enriching cell walls with 13 C and studying them in their hydrated, unextracted state, we previously characterized the chemical linkages, conformations, intermolecular interactions, and nanosecond-tomicrosecond motions of polysaccharides in cell walls from seedlings grown in shaker flasks containing 13 C-enriched Glc (Dick-Pérez et al, 2011;White et al, 2014;Wang et al, 2016b). In this study, we produced 13 C-enriched inflorescences by enclosing plants in an atmosphere supplemented with 13 CO 2 .…”

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…Plant biomass components do not accumulate independently of each other, though their relationships are still an active area of research (Dick-Perez et al, 2011;Tan et al, 2013;Mikkelsen et al, 2015). Biomass component amounts can correlate because they are physically bound to each other through covalent and non-covalent bonds or because they accumulate in the same plant organ or stage of plant development, though a physical interaction may not exist.…”

Structural factors affecting 13C NMR chemical shifts of cellulose: a computational study

“…Since the first two high-resolution solid-state NMR studies of cellulose were published in 1980 (Atalla et al 1980;Earl and VanderHart 1980), solidstate NMR spectroscopy has been an important tool in the study of the 3D architecture of PCWs. Solid-state NMR spectroscopy not only revealed the polymorphic structure of cellulose but also detailed the interactions between cellulose and other macromolecules in intact plant cell walls (Dick-Pérez et al 2011;Earl and VanderHart 1981;Larsson et al 1999;Newman and Hemmingson 1995;Wang and Hong 2016;Wang et al 2016a).…”