Isolation and expression patterns of a zeta-carotene desaturase gene from citrus.

A cDNA clone (Zds) encoding zeta-carotene desaturase (ZDS) was isolated from the Citrus fruit cDNA library. Sequence analyses indicated that the clone contains an open reading frame encoding 570 amino acids. A genomic Southern blot analysis and phylogenic dendrogram indicated that the Zds gene is present as more than two isoforms in the Citrus genome. Sequence analyses revealed that the cDNA showed significant similarity to other dicotyledonous woody plants. An RNA blot analysis showed that the transcripts were expressed in all investigated tissues of Citrus. During the ripening of fruits, the signal of the Zds transcripts was very weak until the break stage, but its expression markedly increased to the maximum level at the last stage. A similar pattern was detected in peels of citrus fruits. Furthermore, the level of Zds transcripts was changed in the process of leaf development. The results suggest that Citrus Zds is one of the important regulatory enzymes in carotenoid accumulation especially in the last stage of fruit ripening.