[en] The L-galactose (Smirnoff-Wheeler) pathway represents the major route to L-ascorbic acid (vitamin C) biosynthesis in higher plants. Arabidopsis thaliana VTC2 and its paralogue VTC5 function as GDP-L-galactose phosphorylases converting GDP-L-galactose to L-galactose-1-P, thus catalyzing the first committed step in the biosynthesis of L-ascorbate. Here we report that the L-galactose pathway of ascorbate biosynthesis described in higher plants is conserved in green algae. The Chlamydomonas reinhardtii genome encodes all the enzymes required for vitamin C biosynthesis via the L-galactose pathway. We have characterized recombinant C. reinhardtii VTC2 as an active GDP-L-galactose phosphorylase. C. reinhardtii cells exposed to oxidative stress show increased VTC2 mRNA and L-ascorbate levels. Genes encoding enzymatic components of the ascorbate-glutathione system (e.g. ascorbate peroxidase, Mn superoxide dismutase, dehydroascorbate reductase) are also up-regulated in response to increased oxidative stress. These results indicate that C. reinhardtii VTC2, like its plant homologs, is a highly regulated enzyme in ascorbate biosynthesis in green algae and that, together with the ascorbate recycling system, the L-galactose pathway represents the major route for providing protective levels of ascorbate in oxidatively stressed algal cells.
Disciplines :
Biochemistry, biophysics & molecular biology
Identifiers :
UNILU:UL-ARTICLE-2012-435
Author, co-author :
Urzica, E. I.
Adler, Lital N.
Page, M. D.
Linster, Carole ; University of Luxembourg > Luxembourg Centre for Systems Biomedicine (LCSB)
Arbing, M. A.
Casero, D.
Pellegrini, M.
Merchant, S. S.
Clarke, S. G.
External co-authors :
yes
Language :
English
Title :
Impact of oxidative stress on ascorbate biosynthesis in Chlamydomonas via regulation of the VTC2 gene encoding a GDP-L-galactose phosphorylase
Publication date :
20 April 2012
Journal title :
Journal of Biological Chemistry
ISSN :
1083-351X
Publisher :
American Society for Biochemistry and Molecular Biology, Baltimore, United States - Maryland