The application of Fourier transform mid-infrared (FTIR) spectroscopy to identify variation in cell wall composition of Setaria italica ecotypes

Cell wall composition in monocotyledonous grasses has been identified as a key area of research for developing better feedstocks for forage and biofuel production. Setaria viridis and its close domesticated relative Setaria italica have been chosen as suitable monocotyledonous models for plants possessing the C₄ pathway of photosynthesis including sorghum, maize, sugarcane, switchgrass and Miscanthus×giganteus. Accurate partial least squares regression (PLSR) models to predict S. italica stem composition have been generated, based upon Fourier transform mid-infrared (FTIR) spectra and calibrated with wet chemistry determinations of ground S. italica stem material measured using a modified version of the US National Renewable Energy Laboratory (NREL) acid hydrolysis protocol. The models facilitated a high-throughput screening analysis for glucan, xylan, Klason lignin and acid soluble lignin (ASL) in a collection of 183 natural S. italica variants and clustered them into classes, some possessing unique chemotypes. The predictive models provide a highly efficient screening tool for large scale breeding programs aimed at identifying lines or mutants possessing unique cell wall chemotypes. Genes encoding key catalytic enzymes of the lignin biosynthesis pathway exhibit a high level of conservation with matching expression profiles, measured by RT-qPCR, among accessions of S. italica, which closely mirror profiles observed in the different developmental regions of an elongating internode of S. viridis by RNASeq.