Tuning the orchestra: Selective gene regulation and orange fruit quality

Orange fruit quality is highly dependent on time-specific expression of developmental genes in peel tissues, especially those controlling physical structure and synthesis of pigments and aromatic secondary metabolites. Using a custom microarray platform, we examined expression of 366 genes of interest in peel pericarp and endocarp during three developmental stages of Washington Navel orange fruit (Citrus sinensis L. Osbeck). We examined in detail 28 of these genes that showed strong differential expression over time and across tissues. Genes putatively associated with metabolism of flavonoids, carotenoids, aroma compounds, and ascorbic acid were differentially expressed over time in specific tissues, while genes likely associated with disease resistance, photosynthesis, stress responses, and cell wall synthesis were differentially expressed over both tissue and time. Most highly differentially expressed transcripts within peel likely function to modify the cell wall architecture during growth and to develop color and aroma.