Carotene hydroxylases catalyze the hydroxylation of a- and β-carotene hydrocarbons into xanthophylls.In red algae,β-carotene is a ubiquitously distributed carotenoid,and hydroxylated carotenoids such as zeaxanthin and lutein are also found.However,no enzyme with carotene hydroxylase activity had been previously identified in red algae.Here,we report the isolation of a gene encoding a cytochrome P450-type carotene hydroxylase（PuCHY1） from Porphyra umbilicalis,a red alga with an ancient origin.Sequence comparisons found PuCHY1 belongs to the CYP97 B subfamily,which has members from different photosynthetic organisms ranging from red algae to land plants.Functional complementation in Escherichia coli suggested that PuCHY1 catalyzed the conversion from β-carotene to zeaxanthin.When we overexpressed PuCHYi in the Arabidopsis thaliana chy2 mutant,pigment analysis showed a significant accumulation of hydroxylated carotenoids,including neoxanthin,violaxanthin,and lutein in the leaves of transgenic plants.These results confirmed a β-hydroxylation activity of PuCHY1,and also suggested a possible ε-hydroxylation function.The pigment profile and gene expression analyses of the algal thallus under high-light stress suggested that P.umbilicalis is unlikely to operate a partial xanthophyll cycle for photoprotection.
Li-En YangXing-Qi HuangYu HangYin-Yin DengQin-Qin LuShan Lu
Carotenoids are important plant pigments for both light harvesting and photooxidation protection. Using the model system of the unicellular green alga Chlamydomonas reinhardtii, we characterized the regulation of gene expression for carotenoid metabolism by quantifying changes in the transcript abundance of dxs, dxr and ipi in the plastidic methylerythritol phosphate pathway and of ggps, psy, pds, Icyb and bchy, directly involved in carotenoid and metabolite treatments. The expression of these metabolism, under different photoperiod, light genes fluctuated with light/dark shifting. Light treatment also promoted the accumulation of transcripts of all these genes. Of the genes studied, dxs, ggps and Icyb displayed the typical circadian pattern by retaining a rhythmic fluctuation of transcript abundance under both constant light and constant dark entrainments. The expression of these genes could also be regulated by metabolic intermediates. For example, ggps was significantly suppressed by a geranylgeranyl pyrophosphate supplement and ipi was upregulated by isopentenyl pyrophosphate. Furthermore, CrOr, a C. reinhardtii homolog of the recently characterized Or gene that accounts for carotenoid accumulation, also showed co-expression with carotenoid biosynthetic genes such as pds and Icyb. Our data suggest a coordinated regulation on carotenoid metabolism in C. reinhardtii at the transcriptional level.
Tian-Hu SunCheng-Qian LiuYuan-Yuan HuiWen-Kai WuZhi-Gang ZhouShan Lu
