Journal Article

Investigating the Regulation of One-carbon Metabolism in <i>Arabidopsis thaliana</i>

Rong Li, Maya Moore and John King

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 3, pages 233-241
Published in print March 2003 | ISSN: 0032-0781
Published online March 2003 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcg029
Investigating the Regulation of One-carbon Metabolism in Arabidopsis thaliana

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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Serine (Ser) biosynthesis in C3 plants can occur via several pathways. One major route involves the tetrahydrofolate (THF)-dependent activities of the glycine decarboxylase complex (GDC, EC 2.1.1.10) and serine hydroxymethyltransferase (SHMT, EC 2.1.2.1) with glycine (Gly) as one-carbon (1-C) source. An alternative THF-dependent pathway involves the C1-THF synthase/SHMT activities with formate as 1-C source. Here, we have investigated aspects of the regulation of these two folate-mediated pathways in Arabidopsis thaliana (L.) Heynh. Columbia using two approaches. Firstly, transgenic plants overexpressing formate dehydrogenase (FDH, EC 1.2.1.2) were used to continue our previous studies on the function of FDH in formate metabolism. The formate pool size was approximately 73 nmol (g FW)–1 in wild type (WT) Arabidopsis plants; three independent transgenic lines had similar-sized pools of formate. Transgenic plants produced more 13CO2 from supplied [13C]formate than did WT plants but were not significantly different from WT plants in their synthesis of Ser. We concluded that FDH has no direct role in the regulation of the above two pathways of Ser synthesis; the breakdown of formate to CO2 by the FDH reaction is the primary and preferred fate of the organic acid in Arabidopsis. The ratio between the GDC/SHMT and C1-THF synthase/SHMT pathways of Ser synthesis from [α-13C]Gly and [13C]formate, respectively, in Arabidopsis shoots was 21 : 1; in roots, 9 : 1. In shoots, therefore, the pathway from formate plays only a small role in Ser synthesis; in the case of roots, results indicated that the 9 : 1 ratio was as a result of greater fluxes of 13C through both pathways together with a relatively higher contribution from the C1-THF synthase/SHMT route than in shoots. We also examined the synthesis of Ser in a GDC-deficient mutant of Arabidopsis (glyD) where the GDC/SHMT pathway was impaired. Compared with WT, glyD plants accumulated 5-fold more Gly than WT after supplying [α-13C]Gly for 24 h; the accumulation of Ser from [α-13C]Gly was reduced by 25% in the same time period. On the other hand, the accumulation of Ser through the C1-THF synthase/SHMT pathway in glyD plants was 2.5-fold greater than that in WT plants. Our experiments confirmed that the GDC/SHMT and C1-THF synthase/SHMT pathways normally operate independently in Arabidopsis plants but that when the primary GDC/SHMT pathway is impaired the alternative C1-THF synthase/SHMT pathway can partially compensate for deficiencies in the synthesis of Ser.

Keywords: Keywords: One-carbon metabolism — Formate dehydrogenase — Glycine decarboxylase complex — Glycine decarboxylase/serine hydroxymethyltransferase pathway — C1-tetrahydrofolate synthase/serine hydroxymethyltransferase pathway — Arabidopsis thaliana (transgenic and mutant).; Abbreviation: D2O, deuterium oxide; FDH, formate dehydrogenase; GC-MS, gas chromatography-mass spectrometry; GDC, glycine decarboxylase complex; Gly, glycine; IC, ion chromatography; NMR, nuclear magnetic resonance; 1-C, one-carbon; Ser, serine; SHMT, serine hydroxymethyltransferase; THF, tetrahydrofolate; WT, wild-type.

Journal Article.  5909 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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