Principal component analysis and biochemical characterization of protein and starch reveal primary targets for improving sorghum grain

Limited progress has been made on genetic improvement of the digestibility of sorghum grain because of variability among different varieties. In this study, we applied multiple techniques to assess digestibility of grain from 18 sorghum lines to identify major components responsible for variability. We also identified storage proteins and enzymes as potential targets for genetic modification to improve digestibility. Results from principal component analysis revealed that content of amylose and total starch, together with protein digestibility (PD), accounted for 94% of variation in digestibility. Control of amylose content is understood and manageable. Up-regulation of genes associated with starch accumulation is clearly a future target for improving digestibility. To identify proteins that might be targets for future modification, meal from selected lines was digested in vitro with pancreatin in parallel with pepsin and α-amylase. The %PD was influenced by both the nature of the protein matrix and protein body packaging. Owing to its ability to form oligomers, the 20kDa γ-kafirin was more resistant to digestion than counterparts lacking this ability, making it a target for down-regulation. Greater understanding of interactions among the three traits identified by principal component analysis is needed for both waxy and non-waxy varieties.