Proteomic analysis of the effects of gibberellin on increased fruit sink strength in Asian pear (Pyrus pyrifolia)
Gibberellin (GA) is commonly used to improve crop yield and quality in tree fruit production. To better understand the mechanism by which GA increases fruit size at the protein level, fruits from 11-year-old Asian pear cv. ‘Cuiguan’ (Pyrus pyrifolia Nakai) plants were treated with GA (30 mg L−1) on 30 days after anthesis (DAA). Fruits were sampled at the early and middle stages of fruit expansion and the maturation stage for proteomic analysis. Our results revealed that 115 protein spots showed significant differences in abundance between GA-treated and untreated fruits. Among these spots, 60 proteins were successfully identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI–TOF MS). The up-regulated proteins were observed related to primary metabolism, transport, ion channels and stress responses. During the fruit expansion process, the down-regulated proteins were observed related to photorespiration, epigenetics and glycolysis. The greatest protein abundance changes occurred at the early stage of fruit expansion. Seventeen highly abundant proteins that accumulated after GA application and were related to increases in sink strength were further validated by quantitative real time PCR. Increased levels of H2O2, which is associated with advanced cell wall loosening and fruit maturation, were observed after GA application. Microscopic observations of the mesocarp cell wall supported the finding that GA has promoting effects on pear fruit expansion. Increases in the activities of ATPase, Rubisco, serine hydroxymethyltransferases and NAD-dependent formate dehydrogenase were significantly correlated with sugar accumulation. In addition, increased activities of vacuole-associated annexin, the proteasome and adenylate kinase were closely involved in the cell expansion process. Our proteomic results and subsequent validation describes a dynamic protein network supporting the hypothesis that GA application during rapid fruit growth increases both sink size and sink activity, resulting in larger fruit in P. pyrifolia.