Abstract
In addition to proteins and/or oils, mature seeds of most legume crops contain important carbohydrate components, including starches and sugars. Starch is also an essential nutritional component of human and animal diets and has various food and non-food industrial applications. Starch is a primary insoluble polymeric carbohydrate produced by higher plants and consists of amylose and amylopectin as a major fraction. Legume seeds are an affordable source of not only protein but also the starch, which has an advantage of being resistant starch compared with cereal, root, and tuber starch. For these reasons, legume seeds form a good source of resistant starch-rich healthy food with a high protein content and can be utilized in various food applications. The genetics and molecular details of starch and other carbohydrate components are well studied in cereal crops but have received little attention in legumes. In order to improve legume starch content, quality, and quantity, it is necessary to understand the genetic and molecular factors regulating carbohydrate metabolism in legume crops. In this review, we assessed the current literature reporting the genetic and molecular basis of legume carbohydrate components, primarily focused on seed starch content. We provided an overview of starch biosynthesis in the heterotrophic organs, the chemical composition of major consumable legumes, the factors influencing starch digestibility, and advances in the genetic, transcriptomic, and metabolomic studies in important legume crops. Further, we discussed breeding and biotechnological approaches for the improvement of the starch composition in major legume crops. The information reviewed in this study will be helpful in facilitating the food and non-food applications of legume starch and provide economic benefits to farmers and industries.
Highlights
Legumes belong to Fabaceae, the third largest and economically important plant family, which has more than 20,000 species including herbs, shrubs, and trees (Doyle, 2003; Gepts et al, 2005; Lewis, 2005; Dash et al, 2016)
This review is focused on legume crops, which have significant potential benefits both for food processing and for human nutrition
Metabolism-related genes, enzymes, and their interaction involved in biological processes in starch and other carbohydrates need a systematic analysis and characterization
Summary
Legumes belong to Fabaceae, the third largest and economically important plant family, which has more than 20,000 species including herbs, shrubs, and trees (Doyle, 2003; Gepts et al, 2005; Lewis, 2005; Dash et al, 2016). The expression of starch biosynthesis genes was continuously increased at the matured seed stage in the adzuki bean, a high starch legume crop, whereas the expression of genes related to fatty acid biosynthesis in the adzuki bean was decreased at the later seed stage (Yang et al, 2015). It is expected, that several starch-metabolizing enzymes might be actively involved in the process of conversion of starch to protein or oil in seeds during seed maturation (Yang et al, 2015). We further analyze the factors influencing the RS content and its genetic variability, and we present the breeding and biotechnological approaches useful for developing legume cultivars with improved seed starch compositions
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