Phosphoproteomic Analysis Indicates Phosphorylated Proteins in Response to Postharvest Blueberries Fruit Softening during Shelf Life

Postharvest blueberry fruit is prone to softening. Protein phosphorylation is an important post-translational modification that was involved in fruit softening. However, little is known about protein phosphorylation in postharvest blueberry fruit softening. The firmness, the apparent morphology, and cell structures of blueberry fruit were changed. As the decay rate of postharvest blueberry fruit increased, the soluble solid and titrable acid contents decreased significantly. Phosphoproteomic sequencing results showed that there were 4100 phosphorylated peptides, 5635 phosphorylated sites, and 1437 phosphorylated proteins and showed significant differences on 0 and 8 d. The GO database and KEGG pathway results indicated that these phosphorylated proteins were mainly involved in "biological process", "molecular function", "plant hormone signal transduction", and "metabolic pathways". Besides, a number of phosphorylated proteins were found in cell wall metabolism, plant hormone signaling, primary metabolism, energy metabolism, membrane and transport, ubiquitination-based proteins, and other metabolisms.