title: Regulation of ascorbate biosynthesis in green algae has evolved to enable rapid stress-induced response via the VTC2 gene encoding GDP-l-galactose phosphorylase.
abstract: Ascorbate (vitamin C) plays essential roles in stress resistance, development, signaling, hormone biosynthesis and regulation of gene expression; however, little is known about its biosynthesis in algae. In order to provide experimental proof for the operation of the Smirnoff-Wheeler pathway described for higher plants and to gain more information on the regulation of ascorbate biosynthesis in Chlamydomonas reinhardtii, we targeted the VTC2 gene encoding GDP-l-galactose phosphorylase using artificial microRNAs. Ascorbate concentrations in VTC2 amiRNA lines were reduced to 10% showing that GDP-l-galactose phosphorylase plays a pivotal role in ascorbate biosynthesis. The VTC2 amiRNA lines also grow more slowly, have lower chlorophyll content, and are more susceptible to stress than the control strains. We also demonstrate that: expression of the VTC2 gene is rapidly induced by H2O2and1O2resulting in a manifold increase in ascorbate content; in contrast to plants, there is no circadian regulation of ascorbate biosynthesis; photosynthesis is not required per se for ascorbate biosynthesis; and Chlamydomonas VTC2 lacks negative feedback regulation by ascorbate in the physiological concentration range. Our work demonstrates that ascorbate biosynthesis is also highly regulated in Chlamydomonas albeit via mechanisms distinct from those previously described in land plants.
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: André
authors.initials: A
authors.lastname: Vidal-Meireles
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476, Potsdam-Golm, Germany.
authors.forename: Juliane
authors.initials: J
authors.lastname: Neupert
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: Laura
authors.initials: L
authors.lastname: Zsigmond
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476, Potsdam-Golm, Germany.
authors.forename: Laise
authors.initials: L
authors.lastname: Rosado-Souza
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Kovács
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: Valéria
authors.initials: V
authors.lastname: Nagy
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: Anikó
authors.initials: A
authors.lastname: Galambos
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476, Potsdam-Golm, Germany.
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: Fernie
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476, Potsdam-Golm, Germany.
authors.forename: Ralph
authors.initials: R
authors.lastname: Bock
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: Szilvia Z
authors.initials: SZ
authors.lastname: Tóth
mesh_terms: D001205:Ascorbic Acid / Q000096:biosynthesis* / Q000494:pharmacology; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics* / Q000528:radiation effects; D002940:Circadian Rhythm / Q000187:drug effects / Q000528:radiation effects; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000528:radiation effects; D006861:Hydrogen Peroxide / Q000633:toxicity; D008027:Light; D055432:Metabolomics; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics* / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects / Q000528:radiation effects
chemical_list: D035683:MicroRNAs; D012333:RNA, Messenger; D006861:Hydrogen Peroxide; D010744:Phosphoric Monoester Hydrolases; D001205:Ascorbic Acid
keywords: 
  Chlamydomonas reinhardtii
  ; 
  VTC2
  ; amiRNA; ascorbate; feed-forward regulation; photosynthesis; reactive oxygen species (ROS)