title: HIGH-LIGHT AND SODIUM CHLORIDE STRESS DIFFERENTIALLY REGULATE THE BIOSYNTHESIS OF ASTAXANTHIN IN CHLORELLA ZOFINGIENSIS (CHLOROPHYCEAE)(1).
abstract: Although light and salt stresses are known to enhance the biosynthesis of astaxanthin in certain green algae, the mechanism of their action remains largely unknown. Here we report the regulation of the genes encoding phytoene desaturase (PDS), carotenoid hydroxylase (CHYb), and carotenoid ketolase (BKT) in the green alga Chlorella zofingiensis Dönz under light or sodium chloride (NaCl) stress. High-light illumination (150 μmol photons · m(-2)  · s(-1) ) up-regulated the transcripts of PDS, CHYb, and BKT and greatly enhanced the biosynthesis of zeaxanthin, canthaxanthin, and astaxanthin. In contrast, sodium chloride stress only up-regulated the transcript of BKT and enhanced the biosynthesis of canthaxanthin and astaxanthin. High-light and NaCl stresses were revealed to result in an increase in the intracellular reactive oxygen species (ROS) level. By applying chemically generated ROS to the algal cells, we determined that (1) O2 specifically up-regulated the CHYb gene, whereas •OH up-regulated the PDS and BKT genes. We suggest that high-light and NaCl stresses may stimulate the generation of different ROS, which in turn trigger the up-regulation of specific carotenogenic genes and the enhanced biosynthesis of carotenoids in C. zofingiensis.
authors.affiliation: School of Biological Sciences, University of Hong Kong, Hong Kong, ChinaBioscience, Goethe University Frankfurt, P.O. Box 111932, D-60054 Frankfurt, GermanySchool of Biological Sciences, University of Hong Kong, Hong Kong, China.
authors.forename: Yantao
authors.initials: Y
authors.lastname: Li
authors.affiliation: School of Biological Sciences, University of Hong Kong, Hong Kong, ChinaBioscience, Goethe University Frankfurt, P.O. Box 111932, D-60054 Frankfurt, GermanySchool of Biological Sciences, University of Hong Kong, Hong Kong, China.
authors.forename: Junchao
authors.initials: J
authors.lastname: Huang
authors.affiliation: School of Biological Sciences, University of Hong Kong, Hong Kong, ChinaBioscience, Goethe University Frankfurt, P.O. Box 111932, D-60054 Frankfurt, GermanySchool of Biological Sciences, University of Hong Kong, Hong Kong, China.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sandmann
authors.affiliation: School of Biological Sciences, University of Hong Kong, Hong Kong, ChinaBioscience, Goethe University Frankfurt, P.O. Box 111932, D-60054 Frankfurt, GermanySchool of Biological Sciences, University of Hong Kong, Hong Kong, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Chen
keywords: Chlorella zofingiensis; NaCl stress; astaxanthin; carotenoid hydroxylase; carotenoid ketolase; high-light stress; reactive oxygen species