| β-Carotene Hydroxylase is a key enzyme in the pathway of carotenoidbiosynthesis in plants, which catalyses the conversion ofβ-carotene to zeaxanthinthroughβ-cryptoxanthin.β-carotene hydroxylase exists broadly in cyanobacteria,bacterium and plant. The genes ofβ-carotene hydroxylase exist in pair in plant but incarotenoid biosynthesize gene cluster in prokaryota.β-carotene hydroxylase is anon-haemachrome di-iron monooxygenase and contains lots of histidine motifs.β-carotene hydroxylase genes of many organisms have been cloned and expressed incyanobacteria, bacterium and plant respectively. Zeaxanthin act as a protective role inplant under stress conditions andβ-cryptoxanthin can inhibit some diseases, such ascancer. Modification ofβ-carotene hydroxylase using the means of biologyengineering will give a new approach for generation of crop plants that will withstandstress caused by excessive sunlight and for mass production ofβ-cryptoxanthin.Four pairs of primers, designed from known sequences ofβ-carotenehydroxylase gene, were used to amplify fragments of the same gene from Citrusreticulate var. kinokuni Hu with the genome DNA as template by PCR. As a result,four fragments ofβ-carotene hydroxylase gene were obtained and then cloned into thepMD18-T vector, in which these fragments were sequenced. Four fragments werecontig into one 2329bps sequence by software. Analysis indicated that theβ-carotenehydroxylase gene contains six introns and seven exons. Its introns are very differentfrom the corresponding introns in Arabidopsis thaliana and its exons code a proteinwhich contains 311 amino acids.β-carotene hydroxylase is conservative amongdifferent species of citrus. Bioinformatics analysis shown thatβ-carotene hydroxylasefrom Citrus reticulate var. kinokuni Hu has many kinds of phosphorylation sites, fivetransmembrane helics and four motifs which construct by ten conservative histidines.
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