Proteomic approach reveals that starch degradation contributes to anthocyanin accumulation in tuberous root of purple sweet potato

Abstract

A comparative proteomic approach was carried out to investigate anthocyanin biosynthesis in the tuberous roots of yellow sweet potato (YSP) and purple sweet potato (PSP) cultivars. More than 800 proteins were reproducibly detected through two-dimensional electrophoresis (2-DE), of which 50 proteins with 39 more and 11 less accumulated in PSP were identified through matrix-assisted laser desorption ionization-time of flight/time of flight mass spectrometry (MALDI-TOF/TOF-MS). Most of the analyzed proteins are annotated to be involved in starch metabolism and glycolysis. The more abundant starch phosphorylase (SP) and phosphoglucomutase (PGM) in PSP promoted the synthesis of precursors for anthocyanin synthesis. The results implied that starch degradation provided abundant substrates for anthocyanin biosynthesis in tuberous roots of PSP. 24kDa vacuolar protein (VP24) is related to anthocyanin transport and accumulation in vacuoles. Vacuole-associated annexin protein, VCaB42, is correlated with tonoplast biogenesis. Synergistic action of the two proteins is probably involved in the microautophagy and the intravacuolar trapping of anthocyanins. Interestingly, both VCaB42 and VP24 were more accumulated in PSP, suggesting that anthocyanins generated in the cytosol were transported into and became stored in the vacuoles of PSP. The present study provides new insights into the mechanism of tuberous root-specific anthocyanin accumulation in PSP.

Biological significance: Sweet potato ranks as the seventh most important crop worldwide. Purple sweet potato, a special sweet potato cultivar, has been extensively investigated because large amounts of anthocyanin accumulate in its tuberous roots. Anthocyanin is well known for its free radical-scavenging activity and beneficial effects on human health. Its biosynthetic pathway has been well characterized in model plants. Although large-scale systematic studies have been performed to identify the proteins present in sweet potato, information on the regulation of anthocyanin synthesis in sweet potato is insufficient. Our proteome study demonstrated that starch degradation may contribute to anthocyanin accumulation in purple sweet potato. To our knowledge, this study is the first to propose that starch degradation may provide precursors of anthocyanin biosynthesis in sweet potato.

Keywords: 2-DE; Anthocyanin accumulation; Differential proteins; Starch degradation; Sweet potato.