Accurate determination of genotypic variance of cell wall characteristics of a Populus trichocarpa pedigree using high-throughput pyrolysis-molecular beam mass spectrometry

Abstract

Background: Pyrolysis-molecular beam mass spectrometry (py-MBMS) analysis of a pedigree of Populus trichocarpa was performed to study the phenotypic plasticity and heritability of lignin content and lignin monomer composition. Instrumental and microspatial environmental variability were observed in the spectral features and corrected to reveal underlying genetic variance of biomass composition.

Results: Lignin-derived ions (including m/z 124, 154, 168, 194, 210 and others) were highly impacted by microspatial environmental variation which demonstrates phenotypic plasticity of lignin composition in Populus trichocarpa biomass. Broad-sense heritability of lignin composition after correcting for microspatial and instrumental variation was determined to be H² = 0.56 based on py-MBMS ions known to derive from lignin. Heritability of lignin monomeric syringyl/guaiacyl ratio (S/G) was H² = 0.81. Broad-sense heritability was also high (up to H² = 0.79) for ions derived from other components of the biomass including phenolics (e.g., salicylates) and C5 sugars (e.g., xylose). Lignin and phenolic ion abundances were primarily driven by maternal effects, and paternal effects were either similar or stronger for the most heritable carbohydrate-derived ions.

Conclusions: We have shown that many biopolymer-derived ions from py-MBMS show substantial phenotypic plasticity in response to microenvironmental variation in plantations. Nevertheless, broad-sense heritability for biomass composition can be quite high after correcting for spatial environmental variation. This work outlines the importance in accounting for instrumental and microspatial environmental variation in biomass composition data for applications in heritability measurements and genomic selection for breeding poplar for renewable fuels and materials.

Keywords: Biomass composition; Heritability; Phenotypic plasticity; Poplar; Pyrolysis-molecular beam mass spectrometry.

Fig. 1

(a) Simple surface from thin plate spline (TPS) analysis for null surface complexity (SC) parameters (ion, such as m/z 38 shown here, or phenotype not impacted by microspatial environment) where environment corresponds to row position and column position (m) in the field and (b) complex surface for SC parameters > 1 indicative of microspatial impacts on the ions (m/z 32 shown here) or phenotype, (c) histogram showing distribution of SC > 1 for ions in MBMS spectra where [ is inclusive of the value and ( is exclusive of the value for the bins in the x-axis as defined in standard mathematical notation, (d) surface complexity and correlation of ion intensities with TPS residuals for corresponding ions

Fig. 2

PCA loadings of thin plate spline (TPS)-predicted ion intensities from py-MBMS spectra of 7 × 7 population of Populus trichocarpa with sources of ions indicated

Fig. 3

PCA loadings of TPS-corrected ions from py-MBMS spectra of 7 × 7 population of P. trichocarpa

Fig. 4

(a) Average spectrum of entire Populus trichocarpa 7 × 7 population after TPS and tray corrections and (b) variance (% of the average) of each ion based on TIC-normalized and corrected spectra. C denotes source as carbohydrate sugar, L: lignin, P: phenolics, S: S-lignin, G: G-lignin, colors correspond with those indicated in Figs. 2 and 3

Fig. 5

(a) PCA of clonal-averaged spectra with maternal/female parent genotype ID indicated (NA indicates maternal parent identity not available) and (b) Ward’s method cluster number indicated

Fig. 6

Histograms of lignin content and S/G ratios for the Populus trichocarpa population for all participants after thin plate spline correction for microspatial variation. [ is inclusive of the value and ( is exclusive of the value for the bins in the x-axis as defined in standard mathematical notation