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TRANSCRIPTOMIC ANALYSIS OF ETHYLENE-INDUCED TOLERANCE TO NON-CHILLING PEEL PITTING IN CITRUS FRUIT

Non-chilling peel pitting often occurs during postharvest storage in fruit of different citrus cultivars and affects both the inner (albedo) and outer coloured part of the peel (flavedo). Conditioning mature 'Navelate' oranges for 4 days with 10 μl L -1 ethylene reduced the loss of peel integrity during storage at 22°C and 90-95% RH, while peel damage was enhanced by inhibiting ethylene action with 1-methylcyclopropene (1-MCP). To have a general insight of the mechanism underlying the ethylene-induced tolerance of citrus fruit to this disorder, we have evaluated global changes in gene expression occurring in the flavedo and the albedo of 'Navelate' fruit stored under the above mentioned conditions after being treated with ethylene or 1-MCP by using a cDNA microarray containing 12000 unigenes generated by the Spanish 'Citrus Functional Genomics Project'. Gene ontology analysis of differentially expressed genes revealed that ethylene induced the metabolism of amino acid derivatives, including phenylpropanoids, and electron transport in both tissues. Biological processes related to hormone signalling, such as ethylene and jasmonic acid, and to the biosynthesis of aromatic amino acid were also induced in the flavedo, whereas an over-representation of genes involved in the metabolism of sulfur-containing amino acids were found in the albedo. On the other hand, the severe peel damage in the 1-MCP-treated fruit was accompanied by marked changes in the expression of genes related to programmed cell death belonging to the ubiquitination and proteosome pathways, resembling the plant's defence response in an incompatible interaction.