Proteomic Analysis of Oligosaccharide Metabolism during the Growth and Development of Lycium barbarum Fruit

To explore the metabolic pathways involved in oligosaccharide synthesis during the fruit development of Lycium barbarum, we investigated the differential expression of oligosaccharide synthesis-related proteins at different developmental stages of L. barbarum (S1—young fruit, S2—green fruit, S3—early yellowing, S4—late yellowing, and S5—full fruiting) using isobaric tags for relative and absolute quantitation (iTRAQ). A total of 1799 differentially expressed proteins were identified, 133 of which were found to be associated with oligosaccharide metabolism by Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment. Oligosaccharide accumulation in L. barbarum fruits at the first three stages was mainly dependent on photosynthesis. Changes in the biosynthesis and metabolism of oligosaccharide were mainly related to the gene and protein expression of sucrose synthase (SS), sucrose phosphate synthase (SPS) and hexokinase (HK). At stages S4 and S5, oligosaccharide accumulation was achieved through the metabolism of starch and polysaccharide and the enzymes related to changes in the biosynthesis and metabolism of oligosaccharide included raffinose synthase, β-fructofuranosidase and endoglucanase. The gene expression of 10 oligosaccharide biosynthesis-related enzymes as detected by real-time polymerase chain reaction (PCR) was consistent with the proteomics results. This study provides a theoretical basis for further elucidating the mechanism of oligosaccharide biosynthesis and metabolism during the fruit development of L. barbarum.