Isolation and expression patterns of a cDNA encoding phytoene synthase in Citrus

A cDNA clone (Psy1) encoding phytoene synthase was isolated from the fruit cDNA library ofCitrus (Citrus unshiuMarc.). Sequence analyses and phylogenetic dendrogram revealed that the cDNA contains an open reading frame encoding 437 amino acids (47 kDa), which showed significant similarity to those of phytoene synthases of fruit-producing plants. RNA blot analysis showed that the mRNA is expressed in the edible parts and peels of fruits, leaves, and flowers, as a single transcript. Also, during the ripening of fruits, thePsy1 transcripts were detected in all stages and its expression markedly increased to the maximum level in the latest stage. A similar pattern was also detected in peels. Also, the level ofPsy1 transcripts is changed in the process of leaf development. Our results suggested that Psy1 is an important regulatory enzyme in carotenoid accumulation during fruit ripening. This is the first report to characterize the relationship between the expression ofPsy and fruit development in a woody plant.