Isolation and characterization of cDNAs encoding β-carotene hydroxylase in Citrus

Citrus (Citrus unshiu Marc.) contains high contents (0.45-5.26 mg%) of beta -cryptoxanthin. cDNA clones (CHX1 and CHX2) encoding beta -carotene hydroxylase (Chx) were isolated from Citrus fruit and leaf cDNA libraries. Sequence analyses indicated that the clones show polymorphism and that cDNA contains an open reading frame encoding 311 amino acids (34 kDa). Phylogenetic dendrogram suggested the evolutionary link among the fruit-producing plants. RNA blot analysis showed that its expression is ubiquitous in three tissues examined - fruits, leaves, and flowers - and that it is detected as a single band. Also, during the development of fruits and leaves, the expression of CHX1 and CHX2 transcripts was consistent in all stages, which indicated that CHX1 and CHX2 genes are not regulated during fruit ripening at the transcriptional level and revealed that their expression varies with plant species, even having the same type of fruit. Our results suggest that the expression of Chx at the transcriptional level does not contribute to the changes of carotenoids biosynthesis in ripening fruit of Citrus. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.