Abstract
BackgroundFig fruit are highly perishable at the tree-ripe (TR) stage. Commercial-ripe (CR) fruit, which are harvested before the TR stage for their postharvest transportability and shelf-life advantage, are inferior to TR fruit in size, color and sugar content. The succulent urn-shaped receptacle, serving as the protective structure and edible part of the fruit, determines fruit quality. Quantitative iTRAQ and RNA-Seq were performed to reveal the differential proteomic and transcriptomic traits of the receptacle at the two harvest stages.ResultsWe identified 1226 proteins, of which 84 differentially abundant proteins (DAPs) were recruited by criteria of abundance fold-change (FC) ≥1.3 and p < 0.05 in the TR/CR receptacle proteomic analysis. In addition, 2087 differentially expressed genes (DEGs) were screened by ≥2-fold expression change: 1274 were upregulated and 813 were downregulated in the TR vs. CR transcriptomic analysis. Ficin was the most abundant soluble protein in the fig receptacle. Sucrose synthase, sucrose-phosphate synthase and hexokinase were all actively upregulated at both the protein and transcriptional levels. Endoglucanase, expansin, beta-galactosidase, pectin esterase and aquaporins were upregulated from the CR to TR stage at the protein level. In hormonal synthesis and signaling pathways, high protein and transcriptional levels of aminocyclopropane-1-carboxylate oxidase were identified, together with a few diversely expressed ethylene-response factors, indicating the potential leading role of ethylene in the ripening process of fig receptacle, which has been recently reported as a non-climacteric tissue.ConclusionsWe present the first delineation of intra- and inter-omic changes in the expression of specific proteins and genes of TR vs. CR fig receptacle, providing valuable candidates for further study of fruit-quality formation control and fig cultivar innovation to accommodate market demand.
Highlights
Fig fruit are highly perishable at the tree-ripe (TR) stage
The TR fruit was soft, with 61.9% less firmness compared to CR, while fruit size expanded by about 7% in average transverse diameter, and the average fresh weight increased by 24%
Proteomic and transcriptomic characteristics of the ripening fig receptacle Isobaric tags for relative and absolute quantitation (iTRAQ) proteomic and RNA sequencing (RNA-Seq) transcriptomic analyses were performed on the CR and TR fig receptacle tissues (Additional file 7: Figure S1)
Summary
Fig fruit are highly perishable at the tree-ripe (TR) stage. Commercial-ripe (CR) fruit, which are harvested before the TR stage for their postharvest transportability and shelf-life advantage, are inferior to TR fruit in size, color and sugar content. The development of fig fruit can be divided into three stages; stage III, characterized by the fruit’s rapid increment in size, softening, color change and sugar accumulation, is the main phase of fruit-quality formation, and is much shorter than stages I or II, lasting only. When the figs reach the more advanced ripening level— the tree-ripe (TR) stage, which can be regarded as complete physiological ripeness—the fruit are at their heaviest with highest soluble solids content, soft texture and best flavor. Due to the biological limitations of rapidly declining fruit texture, desiccation and phytopathogen infection [6], fresh figs are usually harvested at the CR stage, before they are fully ripe.
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