Proteomic and metabolic profile analysis of low-temperature storage responses in Ipomoea batata Lam. tuberous roots

Abstract

Background: Sweetpotato (Ipomoea batatas L.) is one of the seven major food crops grown worldwide. Cold stress often can cause protein expression pattern and substance contents variations for tuberous roots of sweetpotato during low-temperature storage. Recently, we developed proteometabolic profiles of the fresh sweetpotatoes (cv. Xinxiang) in an attempt to discern the cold stress-responsive mechanism of tuberous root crops during post-harvest storage.

Results: For roots stored under 4 °C condition, the CI index, REC and MDA content in roots were significantly higher than them at control temperature (13 °C). The activities of SOD, CAT, APX, O₂^.- producing rate, proline and especially soluble sugar contents were also significantly increased. Most of the differentially expressed proteins (DEPs) were implicated in pathways related to metabolic pathway, especially phenylpropanoids and followed by starch and sucrose metabolism. L-ascorbate peroxidase 3 and catalase were down-regulated during low temperature storage. α-amylase, sucrose synthase and fructokinase were significantly up-regulated in starch and sucrose metabolism, while β-glucosidase, glucose-1-phosphate adenylyl-transferase and starch synthase were opposite. Furthermore, metabolome profiling revealed that glucosinolate biosynthesis, tropane, piperidine and pyridine alkaloid biosynthesis as well as protein digestion and absorption played a leading role in metabolic pathways of roots. Leucine, tryptophan, tyrosine, isoleucine and valine were all significantly up-regulated in glucosinolate biosynthesis.

Conclusions: Our proteomic and metabolic profile analysis of sweetpotatoes stored at low temperature reveal that the antioxidant enzymes activities, proline and especially soluble sugar content were significantly increased. Most of the DEPs were implicated in phenylpropanoids and followed by starch and sucrose metabolism. The discrepancy between proteomic (L-ascorbate peroxidase 3 and catalase) and biochemical (CAT/APX activity) data may be explained by higher H₂O₂ levels and increased ascorbate redox states, which enhanced the CAT/APX activity indirectly. Glucosinolate biosynthesis played a leading role in metabolic pathways. Leucine, tryptophan, tyrosine, isoleucine and valine were all significantly up-regulated in glucosinolate biosynthesis.

Keywords: Chilling tolerance; Low-temperature storage; Proteometabolomic; Starch metabolism; Sweetpotato.

Fig. 1

Morphological differences in tuber shape and color during storage at 13 °C (a) and 4 °C (b) for 14 d

Fig. 2

Effects of low-temperature storage on relative electrical conductivity (REC) and MDA content in sweetpotato roots for 14 d. a Relative electrical conductivity. b MDA content. Vertical bars represent the mean ± SE. Different letters indicate statistically significant differences (p<0.05) by LSD test

Fig. 3

Effect of low-temperature storage on oxidative stress in terms of SOD (a), CAT (b), APX (c) activities, O₂⁻ producing rate (d), proline content (e) and soluble sugar content (f) such as glucose, fructose, and sucrose in sweetpotatoes for 14 d. Vertical bars represent the mean ± SE. Different letters indicate statistically significant differences (p<0.05) by the LSD test

Fig. 4

Functional classification, subcellular localization and pathway affiliation of proteins. Identified proteins were categorized according to their gene ontology for their biological processes (a), cellular components (b), molecular functions (c), subcellular localizations (d) and association with different metabolic pathways (e)

Fig. 5

Differential multiple of the differentially expressed proteins (DEP) participated in starch and metabolism. P1: Glucose-1-phosphate adenylyltransferase (large subunit); P2: β-xylosidase/α-arabinofuranosidase 2; P3: β-glucosidase 12; P4: Glucose-1-phosphate adenylyltransferase (small subunit); P5: Sucrose synthase 6; P6: Glucan endo-1,3-β-glucosidase 6; P7: 4-α-glucanotransferase; P8: Isoamylase 3; P9: α-amylase; P10: Probable fructokinase 7; P11: Sucrose synthase

Fig. 6

Changes of differentially expressed proteins (DEPs) involved in starch and sucrose metabolism of sweetpotato roots under cold stress. The significantly up-(red) and down-regulated (green) expressed proteins are demonstrated. EC: 3.2.1.1, EC: 2.4.1.13 and EC: 2.7.1.4 proteins (red) were α-amylase, sucrose synthase and fructokinase, respectively. EC: 3.2.1.21, EC: 2.7.7.27 and EC: 2.4.1.21 proteins (green) were β-glucosidase, glucose-1-phosphate adenylyl-transferase and starch synthase, respectively

Fig. 7

Significant fold changes of the metabolites in sweetpotato roots under chilling stress as compared to them under control. Red and blue lines represent up- and down-regulated metabolites, respectively

Fig. 8

The volcano plots and statistics of KEGG pathway enrichment of significantly differential expressed metabolites (DEMs) were demonstrated. In the volcano plots, red, green and black dots represent up-, down-regulated and insignificant changed metabolites, respectively (a). The dimension of dots indicates the amount of the DEMs. The color (P-value) explained the significance of DEM. Rich factor means the ratio of the number of the DEMs to the total number of them detected in the corresponding pathway (b)

Fig. 9

Differential expressed metabolic components in glucosinolate biosynthesis. Red and blue dots represent up-regulated and insignificant changed compounds, respectively