Identification of phytochemicals and the associated genes in Eksotika papaya at ripening index 5 using functional genomics

Phytochemicals and the associated genes involved in primary and secondary metabolite pathways at ripening index 5 of Carica papaya var. Eksotika were investigated using GC-MS based metabolomics approach and mRNA pairedend sequencing. A total of 54 metabolites were identified for polar and nonpolar compounds belonging to amino and organic acids, saturated/unsaturated fatty acids, sugars/sugar alcohols, simple phenolics, vitamins and sterols and alkanes. Ascorbic acid (vitamin C), α- and γ-tocopherols (vitamin E) and plant sterols such as stigmasterol, campesterol and β-sitosterol were among the metabolites identified in this study. A total of 48,765 putative unigenes were obtained from mRNA paired-end sequencing of which 59% (28,736) showed significant (E-value ≤10–5) expression to enzymes in the non-redundant (nr) database. Of these, only 4.9% (1,413) were predicted to be potentially involved in the biosynthesis and metabolism of primary and secondary metabolites based on KEGG pathway analysis. These include carotenoids, fruit volatiles including mono- and diterpenoids, stillbenoids, flavonoids, flavones and flavonols, anthocyanins, phenylpropanoids, betalains, isothiocyanates, steroids, saturated and unsaturated fatty acids, sugars and sugar alcohols, brassinosteroids, amino- and organic acids, abscisic acid, laticifers and proteases. GO analysis identified 67 of the unigenes in the molecular function category to be involved in antioxidant activity. By mapping to the KEGG pathway, 29 metabolites were identified to have direct association with several of the predicted papaya unigenes including metabolites belonging to amino and organic acids, sugars, fatty acids and plant sterols