Abstract
BackgroundStarch in the lotus seed contains a high proportion of amylose, which endows lotus seed a promising property in the development of hypoglycemic and low-glycemic index functional food. Currently, improving starch content is one of the major goals for seed-lotus breeding. ADP-glucose pyrophosphorylase (AGPase) plays an essential role in regulating starch biosynthesis in plants, but little is known about its characterization in lotus.ResultsWe describe the nutritional compositions of lotus seed among 30 varieties with starch as a major component. Comparative transcriptome analysis showed that AGPase genes were differentially expressed in two varieties (CA and JX) with significant different starch content. Seven putative AGPase genes were identified in the lotus genome (Nelumbo nucifera Gaertn.), which could be grouped into two subfamilies. Selective pressure analysis indicated that purifying selection acted as a vital force in the evolution of AGPase genes. Expression analysis revealed that lotus AGPase genes have varying expression patterns, with NnAGPL2a and NnAGPS1a as the most predominantly expressed, especially in seed and rhizome. NnAGPL2a and NnAGPS1a were co-expressed with a number of starch and sucrose metabolism pathway related genes, and their expressions were accompanied by increased AGPase activity and starch content in lotus seed.ConclusionsSeven AGPase genes were characterized in lotus, with NnAGPL2a and NnAGPS1a, as the key genes involved in starch biosynthesis in lotus seed. These results considerably extend our understanding on lotus AGPase genes and provide theoretical basis for breeding new lotus varieties with high-starch content.
Highlights
Starch in the lotus seed contains a high proportion of amylose, which endows lotus seed a promising property in the development of hypoglycemic and low-glycemic index functional food
Sucrose transported from leaves to storage organs is successively catalyzed by sucrose synthase (SuSy), UDPglucose pyrophosphorylase (UDPase) and phosphoglucomutase (PGM) to produce glucose-6-phosphate, which is transported into amyloplast for starch synthesis, which is catalyzed by PGM, ADP-glucose pyrophosphorylase (AGPase), starch synthase (SS) and starch branching enzyme (SBE) [6]
For seeds collected at 15 days after pollination (DAP), total starch ranged from 12.79– 43.60% with an average of 28.20%, amylose ranged from 5.67–22.58% with an average of 14.41%, amylopectin ranged from 5.68–21.33% with an average of 13.80%, protein ranged from 2.43–8.52% with an average of
Summary
Starch in the lotus seed contains a high proportion of amylose, which endows lotus seed a promising property in the development of hypoglycemic and low-glycemic index functional food. ADP-glucose pyrophosphorylase (AGPase) plays an essential role in regulating starch biosynthesis in plants, but little is known about its characterization in lotus. As a non-structural carbohydrate, starch represents the most significant form of carbohydrate storage in plants. It is composed of two polymers of glucose, amylose and amylopectin, which have different molecular structures, the former is composed of unbranched chains of glucose monomers, while the latter is a branched polysaccharide [4]. The mechanism of starch biosynthesis process has been clarified plant species, such as Arabidopsis, potato, rice and corn [5, 14,15,16]. Little is still known about the mechanism of starch biosynthesis in lotus seed
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