Genes Associated with Fruit Colour in Carica papaya: Identification Through Expressed Sequence Tags and Colour Complementation

We have identified candidate genes that are differentially expressed during papaya fruit ripening in 'Tainung' (red-fleshed)and 1B (yellow-fleshed)hybrid varieties. Genes involved in carotenoid production were initially identified by data mining of expressed sequence tags (ESTs). Putative gene function was verified by colour complementation analysis using strains of Escherichia coli engineered to synthesise carotenoids or carotenoid precursors. In all, 1022 ESTs were searched with the BlastX algorithm against existing annotated plant gene databases, identifying seven putative carotenoid and aroma biosynthesis genes. Colour complementation identified papaya cDNA clones with significant homology to three carotenoid pathway genes. Gene expression analysis of these genes in two colour-contrasted papaya cultivars identified cultivar-specific differences in patterns of mRNA accumulation during fruit development. Differential expression of the two carotene desaturase encoding genes, phytoene desaturase and æ-carotene desaturase and a gene encoding the carotene desaturase co-factor 4-hydroxy phenylpyruvate dioxygenase were identified and may be associated with colour phenotype differences in papaya.