Cell wall proteome analysis of banana fruit softening using iTRAQ technology.

Softening is important for quality formation in some climacteric fruits. The molecular mechanism underlying fruit softening is, however, not well understood. In this study, we performed a comparative cell wall proteomics analysis on pre-climacteric (P1) and post-climacteric (P2) banana fruit, corresponding to fruit at the mature green stage and softening ripening stage, respectively, using isobaric tags for relative and absolute quantitation (iTRAQ) technology. A total of 5230 proteins were identified in both sample groups, of which 928 were predicted to be secreted proteins. Of the secreted proteins, 162 were differentially expressed in P2 versus P1. The majority of these proteins had catalytic activity, binding activity, electron carrier activity and antioxidant activity. Compared with P1, P2 had 105 and 57 up- and down-regulated proteins, respectively. GO and KEGG-pathway analysis of these differentially expressed secreted proteins revealed that most were implicated in cell wall metabolism, stress and defense response, signaling, and protein metabolism and modification. Quantitative RT-PCR further validated some key differentially expressed secreted proteins associated with cell wall metabolism, stress and defense response, signaling and protein destination. Our results represent the first cell wall proteome of banana fruit and comprehensive proteomic study of banana fruit softening. SIGNIFICANCE: Softening, which is the consequence of cell wall and turgor modification, is one of the most important factors determining banana fruit quality. The molecular mechanism regulating fruit softening in harvested banana is not currently well understood. In this study, we performed a comparative cell wall proteome analysis for pre-climacteric (P1) and post-climacteric (P2) banana fruit, corresponding to the mature green stage and softening ripening stage, respectively, using iTRAQ technology. We found 162 differentially expressed secreted proteins that were mainly implicated in cell wall metabolism, stress response and defense, signaling, and protein metabolism and modification. We have presented the first cell wall proteome of banana fruit and conducted a comprehensive proteomic study of banana fruit softening that will help to develop strategies to improve the sensorial quality and reduce post-harvest fruit losses.