Fig. 4: 2D correlation spectra showing intermolecular interactions.

a Overlap of 2D dipolar-gated ¹³C-¹³C correlation spectra measured with a short-mixing time (0.1 s, orange) and a long-mixing time (1.0 s, gray). The latter showed additional signals coming from long-range intermolecular cross-peaks. The basal-A segments of WT and two lignin mutants are included. The spectra were plotted so that the base contour levels of the diagonal peaks are comparable across all panels. Representative spectral regions of lignin-lignin and lignin-polysaccharide cross-peaks are marked. b Key spectral regions of the WT16A sample showing lignin-carbohydrate cross-peaks. Xn^3f: 3-fold xylan; Xn^2f: 2-fold xylan; Ac: acetyl; OMe: lignin methoxy; i: interior cellulose; s: surface cellulose; GA: galacturonic acid; R: rhamnose; CO: carbonyl. For example, the label S1/4-s4 represents the cross-peak observed between the carbon 1 and 4 sites of S-lignin with the carbon 4 of surface cellulose. c Chord diagrams visualizing intermolecular lignin-carbohydrate cross-peaks observed in WT16A, fah1-16A, and ref3-16A. Solid lines and dashed lines represent cross-peaks identified in the short-range and long-range spectra, respectively. Thick lines with arrows indicate unambiguous, site-specific crosslinks, and narrow lines without arrows indicate links from convoluted cross-peaks. Source data are provided as a Source data file.