title: Ascorbate-Deficient vtc2 Mutants in Arabidopsis Do Not Exhibit Decreased Growth.
abstract: In higher plants the L-galactose pathway represents the major route for ascorbate biosynthesis. The first committed step of this pathway is catalyzed by the enzyme GDP-L-galactose phosphorylase and is encoded by two paralogs in Arabidopsis - VITAMIN C2 (VTC2) and VTC5. The first mutant of this enzyme, vtc2-1, isolated via an EMS mutagenesis screen, has approximately 20-30% of wildtype ascorbate levels and has been reported to have decreased growth under standard laboratory conditions. Here, we show that a T-DNA insertion into the VTC2 causes a similar reduction in ascorbate levels, but does not greatly affect plant growth. Subsequent segregation analysis revealed the growth defects of vtc2-1 mutants segregate independently of the vtc2-1 mutation. These observations suggest that it is the presence of an independent cryptic mutation that affects growth of vtc2-1 mutants, and not the 70-80% decrease in ascorbate levels that has been assumed in past studies.
authors.affiliation: School of BioSciences, University of Melbourne, Parkville VIC, Australia.
authors.forename: Benson
authors.initials: B
authors.lastname: Lim
authors.affiliation: Biosciences, College of Life and Environmental Sciences, University of Exeter Exeter, UK.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Smirnoff
authors.affiliation: School of BioSciences, University of Melbourne, Parkville VIC, Australia.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Cobbett
authors.affiliation: School of BioSciences, University of Melbourne, Parkville VIC, Australia.
authors.forename: John F
authors.initials: JF
authors.lastname: Golz
keywords: Arabidopsis; GDP-L-galactose phosphorylase; VTC2; VTC5; ascorbate; vitamin C