title: Stress-related differential expression of multiple beta-carotene ketolase genes in the unicellular green alga Haematococcus pluvialis.
abstract: The unicellular green alga Haematococcus pluvialis is used as a biological production system for astaxanthin. It accumulates large amounts of this commercially interesting ketocarotenoid under a variety of environmental stresses. Here we report the identification and expression of three different beta-carotene ketolase genes (bkt) that are involved in the biosynthesis of astaxanthin in a single strain of the alga. Bkt1 and bkt2 proved to be the crtO and bkt previously isolated from two different strains of H. pluvialis. Bkt3 is a novel third gene, which shared 95% identical nucleotide sequence with bkt2. Nitrogen deficiency alone could not induce the alga cells to produce astaxanthin in 3 days even though it enhances the expression of the bkt genes to three times of that in normal growing cells within 16 h. High light irradiation (125 micromol m(-2)s(-1)) or 45 mM sodium acetate greatly increased the expression of bkt genes to 18 or 52 times of that in normal growing cells, resulting in an accumulation of substantial astaxanthin (about 6 mg g(-1) dry biomass) in 3 days. It is suggested that the existence of the multiple bkt genes and their strong up-regulation by different stress conditions is one of the reasons that H. pluvialis accumulates large amounts of astaxanthin in an instant response to stress environments.
authors.affiliation: Department of Botany, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China.
authors.forename: Jun-Chao
authors.initials: JC
authors.lastname: Huang
authors.forename: Feng
authors.initials: F
authors.lastname: Chen
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sandmann
mesh_terms: D001483:Base Sequence; D000460:Chlorophyta / Q000201:enzymology* / Q000235:genetics*; D003001:Cloning, Molecular; D005786:Gene Expression Regulation; D005796:Genes; D008969:Molecular Sequence Data; D010105:Oxygenases / Q000235:genetics*; D015854:Up-Regulation; D024341:Xanthophylls / Q000096:biosynthesis
chemical_list: D024341:Xanthophylls; C005948:astaxanthine; D010105:Oxygenases