A comprehensive study on core enzymes involved in starch metabolism in the model nutricereal, foxtail millet (Setaria italica L.)

Starch biosynthesis is an important process in plants as starch serves as a source of carbon and energy. In cereals, starch is the predominant constituent of the grains that provide carbohydrates in food and feed. Given its importance, the biosynthesis and accumulation of starch have been well studied in major cereals. However, in millets, no such study provides insights into the starch biosynthesis and diversity of enzymes involved in this process. In foxtail millet (Setaria italica), we have identified and characterized six classes of enzyme-encoding genes involved in starch metabolism, viz., ADP glucose phosphorylase, starch synthase, starch branching enzyme, starch debranching enzyme, phosphorylase, and disproportionating enzyme. Analysis of gene structure, chromosomal localization, phylogenetic analysis, and study of domain composition were performed to gain insights into the structure and organization of these gene families. Further, expression profiling of these genes in two cultivars contrastingly differing in grain amylose content was performed at different seed development stages. The expression data showed spatiotemporally divergent expression patterns of the genes and pinpointed several candidate genes that could be targeted for further functional characterization to study the starch metabolism in millets as well as to improve starch content through genomics approaches.