Proteome Changes in Banana Fruit in Response to High Temperature and Ethylene Treatments

Banana (Musa AAA group) is one of the most consumed fruit in the world due to its eating quality and nutritional value. As a typical climacteric fruit, banana responds to ethylene treatment which stimulates ripening including color, flavour (aroma and taste) and nutritional development. It has also been reported that chlorophyll breakdown and color formation in banana is inhibited by ripening temperatures above 24°C. At these temperatures, chlorophyll degradation is reduced, but the rate of senescence is increased. In order to gain a fundamental understanding of the effect of treatments with high temperature and ethylene, a quantitative proteomic study employing stable isotope dimethyl labeling was conducted. In this study, green (immature), untreated banana fruit were subjected to an ethylene treatment of 10µl/L for 24 hours at 20 C. After ethylene treatment, both treated and untreated fruit were stored at 20 or 30°C for 7 days. Fruit were sampled after 0, 1, 4 and 7 days of storage and color, chlorophyll fluorescence and volatile production were evaluated. Quantitative proteomic analysis was conducted on fruit stored 4 days. In total, 413 common proteins were identified and quantified from two biological replicates. Among them, 91 proteins were found to change significantly in response to high temperature and ethylene treatment. Cluster analysis grouped these 91 proteins into 7 clusters. Ethylene treatment induced 40 proteins that were related to pathogen resistance, cell wall metabolism, ethylene biosynthesis, allergens and ribosomal proteins, while 36 proteins that decreased were associated with fatty acid and lipid metabolism, redox-oxidative response, protein biosynthesis and modifications. Storage at 30°C induced an increase in 32 proteins mainly in clusters 1 and 3, which were in association with pathogenesis related proteins, cysteine synthase and branched amino acids biosynthesis, while decreasing 53 proteins in clusters 2, 4, 5 and 7 that associated with photosynthesis II oxygen evolving protein, photosynthesis I reaction centre, sugar metabolism, redox-oxidative system and fatty acid metabolism. Differences between the effects of ethylene and heat treatments on proteins were also revealed and discussed. Identification and quantification of proteins were linked with quality changes. This study demonstrates that both ethylene and high temperature influence banana fruit ripening and senescence at the proteomic level and reveals that high temperature accelerates banana fruit ripening.