changes in carotenoid content and biosynthetic gene expression in juice sacs of four orange varieties citrus sinensis differing in flesh fruit color the contribution of carotenoid composition to the color range of the fruit juice sacs of four orange varieties citrus sinensis differing in flesh color namely shamouti normal orange color sanguinelli blood cultivar purple color cara cara navel pinkreddish and huang pi chen yellowish color was investigated to this end qualitative and quantitative analyses of carotenoid contents were first performed by highperformance liquid chromatography hplc using a c30 column and a photodiode array detector in february at a late developmental fruit stage concomitantly transcript levels of dxs the gene controlling the first step of the mep pathway and six genes involved in betabetaxanthophyll biosynthesis psy pds zds lcyb hyb and zep were determined in august november and february transcript level measurement was carried out by realtime rtpcr on total rna from juice sacs the four orange varieties displayed different carotenoid profiles shamouti and sanguinelli oranges accumulated mainly betabetaxanthophylls as expected in typically colored oranges whereas cara cara navel orange accumulated linear carotenes in addition to cisviolaxanthin huang pi chen fruit flesh orange was characterized by a strong reduction of total carotenoid content whereas gene expression was relatively low and similar in august before color break in all four varieties in november during color break dxs zds hyb and zep expression was higher in cara cara and huang pi chen oranges the betabetaxanthophyll accumulation observed in february in shamouti and sanguinelli oranges was apparently related to the increase of transcript levels of all measured genes ie dxs psy pds zds hyb and zep except lcyb at this time however transcript levels in cara cara were rather similar to those found in sanguinelli although both showed different carotenoid compositions the huang pi chen phenotype correlated with lower expression of dxs and psy genes these results revealed a general pattern of transcript change in juice sacs of citrus fruit characterized by an apparent coordination of dxs and psy expression and a general increase in mrna levels of carotenoid biosynthetic genes these transcript changes correlated well with the betabetaxanthophyll accumulation the normal carotenoid set observed in shamouti and sanguinelli oranges and suggest that the preferential accumulation of linear carotenes in cara cara navel and the practical absence of carotenoids in huang pi chen oranges were not predominantly due to changes in regulation of carotenoid biosynthetic genes at the transcriptional level