The Uniqueness of Tetrahydrofolate Synthesis and One-Carbon Metabolism in Plants

Abstract

In all living organisms a great variety of reactions involve transfer of single carbon units from one molecule to another. These one-carbon (C1) reactions play essential roles in major cellular processes including the synthesis of nucleic acids, protein biosynthesis in the organelles, amino acid metabolism, pantothenate biosynthesis, and the biogenesis of many methylated products. One-carbon transfer reactions are mediated by tetrahydrofolate, a soluble coenzyme (vitamin B9) that is synthesized de novo by plants and microorganisms, and absorbed from the diet by animals. C1 metabolism and tetrahydrofolate synthesis in plants exhibit features that are not found in other organisms. Beyond the unique gene organization and/or biochemical properties of some of these reactions, the most fascinating aspect is the complex subcellular compartmentation of folate synthesis and folate-mediated reactions in the plant cell. Thus, the enzymes involved in the biogenesis of tetrahydrofolate are distributed over the plastids, the cytosol, and the mitochondria. Also, these compartments contain parallel sets of activities required to generate C1-substituted folate coenzymes. This chapter will focus on the most recent advances in knowledge of C1 metabolism in plants with particular emphasize regardir the role of mitochondria and the traffic of folate coenzymes between the different compartments.