title: 5-Formyltetrahydrofolate is an inhibitory but well tolerated metabolite in Arabidopsis leaves.
abstract: 5-Formyltetrahydrofolate (5-CHO-THF) is formed via a second catalytic activity of serine hydroxymethyltransferase (SHMT) and strongly inhibits SHMT and other folate-dependent enzymes in vitro. The only enzyme known to metabolize 5-CHO-THF is 5-CHO-THF cycloligase (5-FCL), which catalyzes its conversion to 5,10-methenyltetrahydrofolate. Because 5-FCL is mitochondrial in plants and mitochondrial SHMT is central to photorespiration, we examined the impact of an insertional mutation in the Arabidopsis 5-FCL gene (At5g13050) under photorespiratory (30 and 370 micromol of CO2 mol(-1)) and non-photorespiratory (3200 micromol of CO2 mol(-1)) conditions. The mutation had only mild visible effects at 370 micromol of CO2 mol(-1), reducing growth rate by approximately 20% and delaying flowering by 1 week. However, the mutation doubled leaf 5-CHO-THF level under all conditions and, under photorespiratory conditions, quadrupled the pool of 10-formyl-/5,10-methenyltetrahydrofolates (which could not be distinguished analytically). At 370 micromol of CO2 mol(-1), the mitochondrial 5-CHO-THF pool was 8-fold larger in the mutant and contained most of the 5-CHO-THF in the leaf. In contrast, the buildup of 10-formyl-/5,10-methenyltetrahydrofolates was extramitochondrial. In photorespiratory conditions, leaf glycine levels were up to 46-fold higher in the mutant than in the wild type. Furthermore, when leaves were supplied with 5-CHO-THF, glycine accumulated in both wild type and mutant. These data establish that 5-CHO-THF can inhibit SHMT in vivo and thereby influence glycine pool size. However, the near-normal growth of the mutant shows that even exceptionally high 5-CHO-THF levels do not much affect fluxes through SHMT or any other folate-dependent reaction, i.e. that 5-CHO-THF is well tolerated in plants.
authors.affiliation: Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611, USA.
authors.forename: Aymeric
authors.initials: A
authors.lastname: Goyer
authors.forename: Eva
authors.initials: E
authors.lastname: Collakova
authors.forename: Rocío
authors.initials: R
authors.lastname: Díaz de la Garza
authors.forename: Eoin P
authors.initials: EP
authors.lastname: Quinlivan
authors.forename: Jerry
authors.initials: J
authors.lastname: Williamson
authors.forename: Jesse F
authors.initials: JF
authors.lastname: Gregory
authors.forename: Yair
authors.initials: Y
authors.lastname: Shachar-Hill
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Hanson
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism*; D019731:Carbon-Nitrogen Ligases / Q000737:chemistry / Q000378:metabolism*; D002384:Catalysis; D004269:DNA, Bacterial / Q000737:chemistry; D035264:Flowers / Q000378:metabolism; D005574:Formate-Tetrahydrofolate Ligase / Q000737:chemistry / Q000235:genetics*; D005575:Formyltetrahydrofolates / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D012696:Glycine Hydroxymethyltransferase / Q000737:chemistry; D006868:Hydrolysis; D002955:Leucovorin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D008956:Models, Chemical; D008957:Models, Genetic; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010641:Phenotype; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism*; D020033:Protein Isoforms; D012313:RNA / Q000737:chemistry; D012694:Serine / Q000737:chemistry; D013696:Temperature; D013763:Tetrahydrofolates / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors
chemical_list: D004269:DNA, Bacterial; D005575:Formyltetrahydrofolates; D020033:Protein Isoforms; C036483:T-DNA; D013763:Tetrahydrofolates; D002245:Carbon Dioxide; C010161:10-formyltetrahydropteroylglutamic acid; D012694:Serine; D012313:RNA; C018092:5,10-methenyltetrahydrofolate; D012696:Glycine Hydroxymethyltransferase; D019731:Carbon-Nitrogen Ligases; C021557:5,10-methenyltetrahydrofolate synthetase; D005574:Formate-Tetrahydrofolate Ligase; D002955:Leucovorin; D005998:Glycine